Instrumental Analytics

CZE—Capillary Zone Electrophoresis

2009-05-16T10:00:00.000-07:00

CZE is a relatively new technique involving separations in a coated capillary column filled with buffer under the influence of an electrical field. Samples are drawn into and down the column using electrical charge potential. Migration is controlled by the molecule’s charge and interaction with the wall coating.

Separated components are detected through a fine, drawn-out, transparent area of the column using a variable UV detector or a fluorometer. Still under development, CZE offers great potential as improvements are made in injection techniques and in column coatings to add modified partition, size, ion exchange, and affinity capability. Mass spectrometer interfaces are used to provide a definitive compound identification.

Advantages of CZE include very high resolving power, fairly short run times, and lack of large quantities of solvent to be disposed. Disadvantages include the fact that this is primarily an analytical tool with little capacity for preparative sample recovery and that, again, there is the necessity of working with relatively high-voltage transformers and electrodes. Resolving variables are limited to column coating, applied voltage, buffer character, strength, and
pH.

EP—Electrophoresis

2009-05-16T09:57:00.000-07:00

EP takes advantage of the migration of charged molecules in solution toward electrodes of the opposite polarity. Electrophoresis separating gels are cast in tube or slab form by either polymerizing polyacrylamide support material or casting agarose of controlled pore size in the presence of a buffer to carry an electrical current. Sample is applied to the gel surface, buffer reservoirs and positive and negative electrodes are connected to opposite end of the gel, and electrical current is applied across the gel surface. Because electrical resistance in the media generates heat, the gel surface is usually refrigerated to prevent damage to thermally labile compounds. Compounds migrate within the gel in relation to the relative charge on the molecule and, in size-controlled support matrices, according to their size, charge, and shape.

Two-dimensional GEP, in which separation is made in one direction with buffer and in the second direction with denaturing buffers, has proved a powerful tool for protein and polypeptide separations in proteomics laboratories.

Advantages of electrophoresis include relatively low-priced equipment, solvents, and media, and very high resolving power for charged molecules, especially biological macromolecules. Disadvantages of EP include working with high-voltage power supplies and electrodes in recovering separated components from a polymeric matrix contaminated with buffer, relatively long separation times in many cases, and the effect of heat on labile compounds.

TLC—Thin Layer Chromatography

2009-05-16T09:49:00.000-07:00

TLC separations are carried out on glass, plastic, or aluminum plates coated with thin layers of solid adsorbant held to the plate with an inert binder. Plates are coated with a thick slurry of the solid and binder in a volatile solvent, then allowed to dry before using. Multiple samples and standards are each dissolved in volatile solvent and applied as spots across the solid surface and allowed to evaporate. Separation is achieved by standing the plate in a shallow trough of developing solvent and allowing solvent to be pulled up the plate surface by capillary action. Once solvent has risen a specific distance, the plates are dried and individual compounds are detected by UV visualization or by spraying with a variety of reactive chemicals. Identification is made by calculating relative migration distances and/or by specific reaction with visualizing reagents.

TLC can be used in a preparative mode by streaking the sample across the plate at the application height, nondestructive visualization, and scraping the target band(s) from the plate and extracting them with solvent. Short (3–4 in) TLC strips are an excellent quick and dirty tool for checking reaction mixtures, chromatography fractions, and surveying LC and HPLC solvent/packing material combinations.Two-dimensional TLC, in which each direction is developed with a different solvent, has proven useful for separating complex mixtures of compounds.

Advantages of TLC include very inexpensive equipment and reagents, fairly rapid separations, a wide variety of separating media and visualizing chemicals, and use of solvents and mobile phase modifiers, such as ammonia, not applicable to column separations. Disadvantages include poor resolving power and difficulty in quantitative recovery of separated compounds from the media and binder.

SFC—Supercritical Fluid Chromatography

2009-05-16T09:47:00.000-07:00

SFC is a relatively new technique using a silica-packed column in which the mobile phase is a gas, typically carbon dioxide, which has been converted to a “supercritical” fluid under controlled pressure and temperature. Sample is injected as in a GLC system, carried by the working fluid onto the packed column where separation occurs by either adsorption or partition. The separated components then wash into a high-pressure UV detector flow cell.

At the outlet of the detector, pressure is released and the fluid returns to the gaseous state leaving purified sample as a solid. Doping of carrier gas with small amounts of volatile polar solvents such as methanol can be used to change the polarity of the supercritical fluid and modify the separation.

Advantages of SFC include many of the characteristics of an HPLC separation: high resolving power and fast run times, but with much easier sample recovery. The technique is primarily used as a very gentle method for purifying fragile or heat-labile substances such as flavors, oils and perfume fragrances.

Disadvantages include high equipment cost, the necessity of working with pressurized gases, poor current range of column operating modes and available working fluids, and the difficulty of producing supercritical fluid polarity gradients.

GLC—Gas Liquid Chromatography

2009-05-16T09:45:00.000-07:00

GLC uses a column packed with a solid support coated with a viscous liquid. The volatile sample is injected through a septum into an inert gas stream that evaporated the sample and carries it onto the column. Separation is achieved by differential partition of the sample components between the liquid coating and the continuously replaced gas stream.

Eventually, each compound flushes off the column and into the detector in reverse order to their affinity for the column.The column is placed in a programmable oven and separation can be modified using temperature gradients.

Advantages of the technique include moderate equipment prices, capillary columns for high-resolution, rapid separations, and high-sensitivity detectors and the possibility of direct injection into a mass spectrometer because of the absence of solvents. Disadvantages include the need for volatile samples or derivatives, limited range of column separating modes and eluting variables, the requirement for pressurized carrier gases of high purity, and the inability to run macromolecules.

LC—Traditional Liquid Chromatography

2009-05-16T09:40:00.000-07:00

LC is the predecessor of HPLC. It uses slurry packed glass column filled with large diameter (35–60mm) porous solid material. Materials to be separated are dissolved in solvent and applied directly to the column head.The mobile phase is placed in a reservoir above the column and gravity fed to the column to elute the sample bands. Occasionally, a stirred double-chamber reservoir is used to generate linear solvent gradients and a peristaltic pump is used to feed solvent to the column head. Packing materials generally made of silica gel,
alumina, and agarose are available to allow separation by partition, adsorption, ion exchange, size, and affinity modes.

A useful LC modification is the quick clean-up column. The simplest of this is a capillary pipette plugged with glass wool and partially filled with packing material.The dry packed column is wetted with solvent, sample is applied, and the barrel is filled with eluting solvent. Sample fractions are collected by hand in test tubes. A further modification of this is the sample filtration and extraction columns (SFE). These consist of large pore packing (30–40mm) trapped between filters in a tube or a syringe barrel. They are used with either a syringe to push sample and solvent through the cartridge or a vacuum apparatus to pull solvent and sample through the packed bed into a test tube for collection.

Once the sample is on the bed, it can be washed and then eluted in a step-by step manner with increasingly stronger solvent.These are surprising powerful tools for quick evaluation of the effectiveness of a packing material, sample clean-ups, and broad separations of classes of materials. They are available in almost any type of packing available for HPLC separations: partition, ion exchange, adsorption, and size.

The basic advantages of LC technique are low equipment cost and the variety of separation techniques available.Very large and very small columns can be used, they can be run in a cold room, and cartridge columns are reusable with careful handling and periodic washing. Disadvantages included relatively low resolving power, overnight runs, and walking pneumonia from going in and out of cold rooms.

FPLC—Fast Protein Liquid Chromatography

2009-05-16T09:37:00.000-07:00

FPLC is a close cousin of the HPLC optimized to run biological macromolecules on pressure-fragile agarose or polymeric monobead-based columns. It uses the same basic system components, but with inert fluid surfaces (i.e., Teflon, titanium, and glass), and is designed to operate at no more than 700 psi. Inert surfaces are necessary since many of the resolving buffers contain high concentrations of halide salts that attack and corrode stainless steel surfaces.

Glass columns are available packed with a variety of microporous, highresolution packings: size, partition, ion exchange, and affinity modes. A two-pump solvent gradient controller, injector valve, filter variable detector, and a fraction collector complete the usual system. The primary separation modes are strong anion exchange or size separation rather than reverse-phase partition as in HPLC.

FPLC advantages include excellent performance and lifetimes for the monobead columns, inert construction against the very high salt concentrations often used in protein chromatography, capability to run all columns types traditionally selected by protein chemist, availability of smart automated injection and solvent selection valves, and very simple system programming. Disadvantages include lack of capability to run high-pressure reverse phase columns, lack of a variable detector designed for the system, and lack of a true
autosampler. HPLC components have been adapted to solve the first two problems, but have proved to be poor compromises.The automated valves can partially compensate for the lack of an autosampler.

Barbiturate Detection using Thin-layer Chromatography

2009-02-11T01:24:00.000-08:00

Chemicals
1. Chloroform mixture 9:1 (v/v)
2. HgSO4 spray
suspend, with mixing 5 gr HgO in 100 ml H2O
Add while mixing 20 ml H2SO4
Cool dilute to 250 ml H2O

3. Diphenylcarbazone spray
dssolve 5 gr in 50 ml ChCl2 store in dark bottle

4. Fluorescein spray
to 500 ml H2O add 20 gr NaOH and 20 gr sodium fluoroscein

5. KMNO4 spray
0.1% aqueous solution

6. Standards barbiturate acids
10 mg/100 ml (w/v) in CHCl2

7.Silica gel"G"
According to Stahl

Equipment
1. satndard apparatus for coating glass plates with a 250-u layer of silica gel "G"
2. rectangular jars, 8 1/2 x 4 x 8 1/2 inch with ground glass cover
3. spray bottles
4. Tuberculin syringes with size 24 1/4 inch needles
5. Mineralite ultraviolet hand lamp with 254mu filter

Method
Plates (20 x 20 cm.) were coated with Silica gel G using standard thin-layer chromatography technics. These coated plates were dried in a ventilated oven for 20 mm. at 100 celcius.The dried plates were then stored at room temperature for subsequent use. Prior to an analysis, lines 1/2 inch a part were ruled on the plate, forming a series of parallel columns for concurrent analyses of many samples.

Two drops of a chloroform solution of each sample were applied at a point 1 in. from the bottom of the plate in the center of a column. The spots were air dried and then the plate was placed in the rectangular jar containing 110 ml. of the 9:1 chloroform-acetone mixture. The mixture should beplaced in the jar at the beginning of the preparation for this analysis to insure saturating the jar with the mixture’s vapor. This jar can be reused and its solvent mixture need not be changed for 2 days.

In this solvent system, the solvent front will rise 10-12 cm. in 45-60 mm. The plate is then removed and the solvent front marked immediately.

Then the plate is air dried at room temperature. When dry, the plate is sprayed first with the HgSO4, allowed to dry partially, and then sprayed again with the diphenylcarbazone. In each instance the size, position, and color intensity of each spot is noted. An excess of the diphenylcarbazone is used. The overall colored background resulting slowly disappears and purple or violet spots remain to allow accurate determination of their respective Rf values.

A second identification system that has proved effective consists of an initial spray with alkaline fluorescein. When viewed under 254 m light the barbiturates give a purple spot against a yellow-green background.

After completing this observation, the plate may then be sprayed with the KMnO4). All unsaturated substituted barbiturates yield yellow spots against a purple background. The same
KMnO4 spray can be used without the fluorescein to give similar data.

Since 12-14 columns can easily be ruled on one plate, the same sampie and suitable standards can be applied to consecutive columns, and then a second or third series can be placed on the next group of columns on the same plate. Several different sprays can then be used on one
plate by suitably masking all but one series of columns for each spray.
On each plate, known barbiturates, singly and in mixtures, should be run.

Sample Preparation
Samples for analysis are isolated by direct CHC13 extraction at pH 7. Blood and tissue samples require no p11 adjustment, but urine, stomach content, and drugs should be made alkaline or dissolved in NaOH. The alkaline solution should be filtered and a 3-5 ml. sample taken. These are then made mildly acid with dilute mineral acid and extracted with 50 ml. CHC13.

A filtered 40-ml. aliquot of the chloroform is then evaporated to dryness under forced air and mild heat. The residue is dissolved in 0.5 ml CHCL2, and portions of this solution are applied to the plate along with suitable standards and mixtures there of.

Solvent Delivery in HPLC Instrumentation

2009-02-01T05:42:00.000-08:00

Each contemporary hplc instrument consists of a pump for solvent delivery, an injector device for sample introduction, column(s) for sample separation, detector(s) for visualization of the separated components (solutes), and a computer for system control and data acquisition and reduction, as depicted in Figure 1. Precise temperature control of columns and some other parts of a chromatographic system becomes an important prerequisite for a successful separation.

Solvent Delivery
The function of the solvent delivery system is to deliver the mobile phase (eluent) through the chromatograph, accurately and reproducibly. The most popular are reciprocating-piston pumps, usually with two pump heads containing two sets of moving parts: the check valves and seal-piston assembly. For analytical chromatography, such pumps can deliver liquid at a flow
rate from 100 μL/min up to 10 mL/min. Microscale capillary chromatography needs syringe (positive displacement) pumps with capability to produce a flow rate as low as 1 μL/min, while preparative chromatography utilizes flow rates up to 50 mL/min. Gradient pumping system is capable of delivering more than one solvent during an analysis with variable mobile phase composition. The blending of the solvents can occur in one of two ways: high pressure mixing or low pressure mixing. In the former case the solvents are mixing on the injector side, while in
the latter case the mixing takes place at atmospheric pressure and a single high pressure solvent delivery system is used to pump the mixture.

Accurate and reproducible eluent flow rate and composition are important prerequisites for successful separation and detection. This is achieved in contemporary “intelligent” pumps through completely independent, digitally controlled piston drives. The sophisticated, software-driven mechanism produces pulse-free eluent delivery, compensates for changes in eluent viscosity, and automatically purges any gaseous mobile phase, thereby enhancing performance for both isocratic and gradient applications (2). The quality of solvents affects the accuracy of flow and baseline noise. On-line solvent filtering and degassing become the
necessary elements of any commercial hplc system.

CHROMATOGRAPHY, HPLC : an Intorduction

2009-01-29T23:00:00.000-08:00

High performance liquid chromatography (hplc) is a powerful tool for characterization
of synthetic and natural polymers by separating individual fractions by molecular weight, chemical composition, functional groups, etc. It is also used for isolation and purification of biopolymers and analysis of additives in complex polymer formulations. As in any chromatographic technique, separation occurs due to thermodynamic partitioning between the sample components in the mobile and stationary phases. In hplc, this process takes place in solution inside a chromatographic column packed with inorganic (usually, silica-based) or organic (synthetic resin, such as polystyrene–divinyl benzene and acrylic-based) porous
particles, capable of resisting the high pressure created by a moving liquid (mobile
phase) mechanically pumped through the column. Depending on application, isocratic (constant mobile phase composition) or gradient (variable composition) modes of separation can be employed, which significantly extends the capabilities of the technique.

Column liquid chromatography has been used for more than 60 years for analytical
and preparative separations of polymers. Baker–Williams Fractionation, introduced in the mid-1950s, employed both temperature and solvent gradients to separate polymer fractions according to solubility through multiple precipitation– redissolution steps. This technique has been significantly improved in the last two decades and is still used for fractionation of synthetic copolymers and polymer blends under the term high performance precipitation liquid chromatography (hpplc). Dramatic changes in instrumentation and column preparation for liquid chromatography in 1970s, as well as better understanding of the mechanisms of separation, had a dramatic impact on polymer separation approaches.

Thus, a new technique Chromatography, SEC (a.k.a. gel-permeation chromatography
for organic solutions or gel-filtration chromatography for aqueous mobile phases) emerged at that time as a premier method for molecular weight distribution (MWD) determination of synthetic and natural polymers. Since the early 1970s, sec as well as traditional types of hplc (reversed-phase, ion-exchange, hydrophobic-interaction, and affinity chromatography) have been widely used for analysis of proteins and other biopolymers. For two decades, normal- and reversedphase chromatography have attracted significant interest as methods of separation of synthetic copolymers and polymer blends by chemical composition. Twodimensional hplc techniques (also called chromatographic cross-fractionation)
have been used for most complete polymer characterization in recent years. Thus,
consequently coupling two different modes of chromatographic separation can result in determination of both molecular weight and chemical composition distributions of synthetic copolymers.

Treatment of cancer

2009-01-26T17:32:00.000-08:00

*Surgery: large tumor can be removed surgically with lasting benefit if it has not metastasised.

*Radiation therapy: it is superior to surgery since it effectively destroys a tumor and at the same time causes only minimal damage to the surrounding normal tissue.

*Chemotherapy (Antineoplastic, Cytotoxic, Anticancer, and Antitumor drugs): chemotherapy is not so much limited by metastasis. The requirements for successful antineoplastic drugs in chemotherapy are not yet fully realized because the differences between cancer and normal cells are small. The most common side effects are nausea, hair loss, increased susceptibility to infection and many others.

Mechanism of Cancer Formation

2009-01-26T17:31:00.001-08:00

Altered Gene Expression (Mutation) The function of proto-oncogenes is to control
cell growth. It is generally believed that most human malignancies result from incorrect protooncogene expression.
Abnormal expression of proto-oncogenes can give protein product which may be aberrant oncogene.

Thus, two fundamentally different genetic mechanisms exist consisting of:
(1) enhanced or aberrant oncogene expression or
(2) decreased activity of tumor suppressor Gene (anti-oncogenes).

Normal cells express these genes in such a fashion that the cell populations are
maintained while tumor cells do not.

AntiCancer Drug - Antineoplastic Drugs

2009-01-26T17:26:00.000-08:00

The medical term for cancer or tumor is neoplasm, which means a relatively autonomous
growth of tissue. There are different types of neoplasm and unfortunately there is no system for their nomenclature. Some tumors are named after the individual who first described the condition, such as Hodgkin’s disease. Some are named according to the tissue or origin, for example:
1) a cancer that arises from connective tissues is called a sarcoma, that from epithilium is called carcinoma and that from fibrous tissue is called fibroma;
2) a cancer of the blood involving the abnormal increase of leukocytes is called leukemia.

A lot of contributing factors have been postulated but none of them is the exact
etiologic factor:
- Genetic factors (mutation and changed gene expression).
- Viral factor (human T-lymphotropic virus type I (HTLV-I) has been proved to cause a form of leukemia).

3) Physical factors (long-term exposure to chemicals and/ or irradiation).
4) Hormonal factor.

Analysis of pain management drugs, specifically fentanyl, in hair: Application to forensic specimens

2009-01-23T19:45:00.000-08:00

By: C. Moore, L. Marinetti, C. Coulter, K. Crompton
Available online at www.sciencedirect.com

Abstract
This article discusses the immunoassay screening of pain management drugs, and the mass spectrometric confirmation of fentanyl in human hair. Hair specimens were screened for fentanyl, opiates (including oxycodone), tramadol, propoxyphene, carisoprodol, methadone, and benzodiazepines and any positive results were confirmed using gas chromatography or liquid chromatography with mass spectral detection.

The specific focus of the work was the determination of fentanyl in hair, since autopsy specimens were also available for comparison with hair concentrations. Using two-dimensional gas chromatography with electron impact mass spectrometric detection, fentanyl was confirmed in four of nine hair specimens collected at autopsy. The accuracy of the assay at 10 pg/mg was 95.17% and the inter-day and intra-day precision was 5.04 and 13.24%, respectively (n = 5). The assay was linear over the range 5–200 pg/mg with a correlation of r2 > 0.99. The equation of the calibration curve forced through the origin was y = 0.0053x and the limit of quantitation of the assay was 5 pg/mg. The fentanyl concentrations detected were
12, 17, 490, and 1930 pg/mg and the results were compared with toxicology from routine post-mortem analysis. The screening of pain management drugs in hair is useful in cases where other matrices may not be available, and in routine testing of hair for abused drugs.

# 2007 Elsevier Ireland Ltd. All rights reserved.
Keywords: Hair; Pain management drugs; Two-dimensional gas chromatography

1. Introduction
The testing of biological matrices other than blood or urine is becoming popular in programs intended for the monitoring of medical professionals who may be abusing drugs. Hair provides a longer window of detection than either blood or urine, and is
less invasive to collect. Pain management drugs are increasingly being included in standard drug test profiles, since they are readily available to medical personnel, but their presence and concentration in hair specimens has not been widely
reported. In addition, in some circumstances, post-mortem specimens may not be available, and hair, due to its resistance to decay could be the only sample available for testing. Our research involved developing a screening assay for pain drugs, often related to opioids, in hair as well as comparing results from autopsy specimens with hair results, with specific focus on fentanyl.

Hadidi et al. reported a case of the detection of tramadol in hair [1], while others have reported on the determination of oxycodone, hydrocodone, methadone and benzodiazepines [2–5]. Fentanyl is a synthetic opioid with similar properties to
morphine yet up to 200 times more potent. It was introduced into medical practice as an intravenous anesthetic under the trade name of Sublimaze1. Currently a Schedule II prescription drug, fentanyl is a powerful narcotic analgesic intended for the
treatment of severe pain, and has been associated with a number of overdose accidents and deaths. In June 2006, the Substance Abuse and Mental Health Service Administration (SAMHSA) under the auspices of the Department of Health and Human
Services issued a warning that fentanyl was being combined with heroin and cocaine in street drug specimens in a number of urban areas in the USA. The doses given therapeutically are much lower, with the minimum lethal dose reported to be only
250 mg. In high dose it causes severe respiratory depression and possible coma. The concentration of fentanyl in hair is extremely low when taken therapeutically or even abusively, and to date has been analyzed using immunoassay [6] or
tandem mass spectrometry [7,8]. Stout et al. determined that fentanyl was detectable in the hair of animals subjected to chronic dosing at concentrations ranging from 25 to 50 pg/mg; and that three different extraction procedures utilizing methanol, dilute acid and phosphate buffer were equally effective in extracting fentanyl from the hair matrix. Therefore, phosphate buffer was used for the extraction of
drugs for immunoassay screening.

Since our group had successfully applied two-dimensional chromatography to the analysis of the marijuana metabolite, 11-nor-delta-9-tetrahydrocannabinol-9-carboxylic acid in hair, in order to reduce background effects and improve sensitivity [10], we approached this confirmatory assay in a similar manner, using two-dimensional gas chromatography with pulsed injection and single quadrupole mass spectrometric detection to determine fentanyl concentrations in hair. This is
the first report of single quadrupole GC/MS identification of fentanyl in hair. The procedure was applied to hair specimens taken from autopsy cases where toxicology results were also available.

How to perform instant fire

2009-01-20T00:59:00.000-08:00

Potassium chlorate and ordinary table sugar are combined. When a drop of sulfuric acid is added, a reaction is catalyzed which produces heat, an amazing bright/tall purple flame, and a lot of smoke.

Difficulty: Easy
Time Required: minutes
Here's How:

1. Mix equal parts potassium chlorate and table sugar (sucrose) in a small glass jar or test tube. Choose a container you don't value, as the demonstration will probably cause it to shatter.
2. Place the mixture in a fume hood and equip lab safety gear (which you should be wearing anyway). To initiate the reaction, carefully add a drop or two of sulfuric acid to the powdered mixture. The mixture will burst into into a tall purple flame, accompanied by heat and a lot of smoke.
3. How it works: potassium chlorate (KClO3) is a powerful oxidizer, used in matches and fireworks. Sucrose is an easy-to-oxidize energy source. When sulfuric acid is introduced, potassium chlorate decomposes to produce oxygen:

2KClO3(s) + heat —> 2KCl(s) + 3O2(g)

The sugar burns in the presence of oxygen. The flame is purple from the heating of the potassium (similar to a flame test).

Tips:

1. Perform this demonstration in a fume hood, as a considerable quantity of smoke will be produced. Alternatively, perform this demonstration outdoors.
2. Granulated table sugar is preferable to powdered sugar which is in turn preferable to reagent grade sucrose. The powdered sugar is capable of smothering the fire, while the granules of the reagent-grade sucrose may be too large to support a good reaction.
3. Follow proper safety precautions. Do not store the potassium chlorate and sugar mixture, as it can react spontaneously. Use care when removing the potassium chlorate from its container, to avoid sparking, which can ignite the container. Wear the usual protective gear when performing this reaction (goggles, lab coat, etc.).
4. The 'Dancing Gummi Bear' is a variation on this demonstration. Here, a small quantity of potassium chlorate is carefully heated in a large test tube, clamped to a ring stand over a flame, until it has melted. A Gummi Bear candy is added to the container, resulting in a vigorous reaction. The bear dances amidst bright purple flames.

What You Need:

* potassium chlorate
* powdered (confectioners) sugar or table sugar (sucrose)
* sulfuric acid
* small glass jar or test tube

pH

2009-01-18T17:54:00.001-08:00

The strength of acids and bases is measured on a pH (potential of hydrogen) scale:

pH = –log10 [H+]

The hydrogen ion concentration of a normal solution of a strong acid is about 1 gram-ion per litre and that of a typical strong base is 10–14 gram-ion per litre. Because of the vast range of possible concentrations it is convenient to use a logarithmic scale to express the hydrogen ion concentration of a solution. The symbol pH is used to denote the degree of acidity of a solution. Pure water which dissociates slightly to produce 10–7 gram-ions of H+ per litre is taken as the standard of neutrality. Thus water has a pH of 7. Solutions of pH less than 7 are acidic and those greater than 7 are alkali. The pH of a solution can be determined electrically using a hydrogen or glass electrode and reference electrode (e.g. calomel electrode) or by chemical indicators

Aromatic compounds

2009-01-16T21:04:00.000-08:00

Aromatic compounds are benzene and its derivatives and compounds that resemble benzene in their behaviour in a chemistry dominated by ionic substitution. Benzene has the formula C6H6 commonly written as the ring.

In reality all carbon atoms share equally the pool of electrons which constitute the double bonds and benzene resists addition across the double bonds which would otherwise destroy its unique structure and stability. Single or multiple hydrogen atoms can be substituted to form a host of derivatives containing similar functional groups to those above, e.g. saturated and unsaturated aliphatic chains, amino, carboxylic acidic, halogeno, nitro, and sulphonic acid groups.

Benzene and alkylbenzenes possess low polarity with similar physical properties to hydrocarbons. They are insoluble in water but soluble in non-polar solvents such as ether. They are less dense than water (Table 6.1) and boiling points rise with increasing molecular weight (ca 20–30C increment for each carbon atom). Since melting point depends not only on molecular weight but also on molecular shape, the relationship to structure is more complicated. Benzene itself is a colourless liquid boiling at 80C and freezing at 5.4C. It is highly flammable with a flash point of –11C but with a narrow flammable range of 1.4–8%. It is acutely toxic producing narcotic effects comparable to toluene but it also poses chronic effects on bone marrow which may lead to anaemia or even leukaemia. Similar effects are not proven for pure toluene, but in the past commercial toluol was contaminated with benzene.

Aliphatic compounds

2009-01-15T19:31:00.000-08:00

Aliphatic compounds are straight chain or acyclic compounds and are characterized by addition and free-radical chemistry.

Table 3.7 Selected aromatic compounds

Acids

2009-01-15T19:09:00.000-08:00

Acids and bases (see later) are interrelated. Traditionally, acids are compounds which contain hydrogen and which dissociate in water to form hydrogen ions or protons, H+, commonly written as:

Table 3.3 Important common physical properties
Gas
Density
Critical temperature, critical pressure (for liquefaction)
Solubility in water, selected solvents
Odour threshold
Colour
Diffusion coefficient
Liquid
Vapour pressure–temperature relationship
Density; specific gravity
Viscosity
Miscibility with water, selected solvents
Odour
Colour
Coefficient of thermal expansion
Interfacial tension

Liquid
Vapour pressure–temperature relationship
Density; specific gravity
Viscosity
Miscibility with water, selected solvents
Odour
Colour
Coefficient of thermal expansion
Interfacial tension
Solid
Melting point
Density
Odour
Solubility in water, selected solvents
Coefficient of thermal expansion
Hardness/flexibility
Particle size distribution/physical form, e.g. fine powder, flakes, granules, pellets, prills, lumps
Porosity

HX = H+ + X–
Examples include hydrochloric acid, nitric acid, and sulphuric acid. These are strong acids which are almost completely dissociated in water. Weak acids, such as hydrogen sulphide, are poorly dissociated producing low concentrations of hydrogen ions. Acids tend to be corrosive with a sharp, sour taste and turn litmus paper red; they give distinctive colour changes with other indicators. Acids dissolve metals such as copper and liberate hydrogen gas. They also react with carbonates to liberate carbon dioxide:
2HCl + Cu = CuCl2 + H2
2HCl + CaCO3 = CaCl2 + CO2 + H2O
Both acids and alkalis are electrolytes. The latter when fused or dissolved in water conduct an electric current (see page 55). Acids are considered to embrace substances capable of accepting an electron pair.

What is "Biodegradable" meaning on Plastics Terms

2008-11-21T18:19:00.000-08:00

The failure of early ‘biodegradable’ plastics to properly degrade led to the American Society of
Testing and Materials (ASTM) creating definitions on what constitutes ‘biodegradability’. The
ASTM definition, updated in 1994 (ASTM Standard D-5488-84d), has led to the establishment of
labeling terminology for packaging materials.

The ASTM defines ‘biodegradable’ as:

“capable of undergoing decomposition into carbon dioxide, methane, water, inorganic
compounds, or biomass in which the predominant mechanism is the enzymatic action of
microorganisms, that can be measured by standardized tests, in a specified period of time,
reflecting available disposal condition.”

Biodegredation is degradation caused by biological activity, particularly by enzyme action
leading to significant changes in the materials chemical structure. In essence, biodegradable
plastics should break down cleanly, in a defined time period, to simple molecules found in the
environment such as carbon dioxide and water.

Biodegradation rates are highly dependent on the thickness and geometry of the fabricated
articles. While rapid breakdown rates are often quoted these generally apply to thin films.
Thick-walled articles such as plates, food trays and cutlery can take up to a year to biologically
degrade.

INTRODUCTION TO BIODEGRADABLE PLASTICS

2008-11-21T18:17:00.000-08:00

The ‘biodegradability’ of plastics is dependent on the chemical structure of the material and on
the constitution of the final product, not just on the raw materials used for its production. Therefore, biodegradable plastics can be based on natural or synthetic resins.

Natural biodegradable plastics are based primarily on renewable resources (such as starch) and can be either naturally produced or synthesised from renewable resources. Non-renewable synthetic biodegradable plastics are petroleum-based. As any marketable plastic product must meet the performance requirements of its intended function, many natural biodegradable plastics are blended with synthetic polymers to produce plastics which meet these functional requirements.

Many polymers that are claimed to be ‘biodegradable’ are in fact ‘bioerodable’, ‘hydrobiodegradable’ or ‘photo-biodegradable’.

These different polymer classes all come under the broader category of ‘environmentally degradable polymers’. For the purpose of this document the term ‘biodegradable plastics’ shall imply ‘environmentally degradable plastics’. The classes of biodegradable plastics considered, in terms of the degradation mechanism, are:

1) Biodegradable
2) Compostable
3) Hydro-biodegradable
4) Photo-biodegradable
5) Bioerodable

Biodegradable Plastics

2008-11-21T18:11:00.000-08:00

Biodegradable plastics are a new generation of polymers emerging on the Australian market. Biodegradable plastics have an expanding range of potential applications, and driven by the growing use of plastics in packaging and the perception that biodegradable plastics are ‘environmentally friendly’, their use is predicted to increase. However, issues are also emerging
regarding the use of biodegradable plastics and their potential impacts on the environment and
effects on established recycling systems and technologies.

Environment Australia, in consultation with the Plastics and Chemicals Industries Association
(PACIA) has engaged Nolan-ITU, in association with ExcelPlas Australia, to undertake a
national review of biodegradable plastics with the primary aim of identifying and characterising
emerging environmental issues associated with biodegradable plastics to assist industry and the
Commonwealth to develop initiatives to address these issues effectively.

Polymers from Renewable Resources – Polylactide Acid (PLA)

2008-11-21T18:07:00.000-08:00

Polylactide acid is a polymer derived from lactide acid. This means that it can be
fabricated using renewable resources and is also biodegradable.

Polylactide acid has long since been used in the field of medicine in the manufacture of surgical sutures.

However, in particular the high cost of the material has prevented it from being used in other spheres. But now latest technological advances have given rise to polylactide acids that are commercially viable and can compete with petrochemical plastics. These polymers are increasingly being used in the manufacture of food packaging. The application areas for PLA are agricultural films, degradable rubbish bags, packaging for hygiene articles, thermoformed trays for fruit and vegetables, cold drink cups and toys. Other articles, such as CDs, telephone packaging, PC and Walkman casings, and overhead transparencies and document folders are shortly to be launched on the market. The starting material for PLA is lactide acid, which is derived from corn by means of biochemical processes. The lactide acid is then polymerized into polylactide acid (PLA). PLA has a glass transition temperature of between 55 and
65° C and a density of 1.25 g /cm3, and is only slightly less transparent than polystyrol or PET. Apart from the fact that PLA is compostable and can be manufactured from renewable
raw materials, it is also excellent for printing on, is highly transparent and has a low density. Moreover, it has great tensile strength, which means that the thickness can be reduced,
thus minimizing both weight and cost.

PLA is biodegraded in an initial step by means of hydyrolytic decomposition, whereby the polymer is degraded into monomers. These are then decomposed biologically by microorganisms. The decomposition process greatly depends on the environmental conditions. In commercial composting facilities, complete decomposition can be achieved within between 30 and 50 days. Polylactide acid has enormous potential and can contribute greatly towards such issues as sustainability and the protection of the climate andnatural resources. We can therefore
assume that we shall increasingly be seeing PLA in the shops and supermarkets in the near future.

Cocaine and Heroin Content Determination with NIR

2008-11-13T00:14:00.000-08:00

The scientific service of the municipal police Zurich has been using NIR technology

as a standard method for street drug analyses for more than ten years. This analytical

technique is primarily used to estimate the drug content in confiscated heroin and cocaine street drugs.

In 1991, the Federal Court of Switzerland decided to change the definition of severe

cases of heroin and cocaine possession. Since that time the possession of more

than 12 g of pure heroin and 18 g of pure cocaine are regarded as severe cases respectively.

In such cases, the penalty is one year of imprisonment, in addition to up to a one million Swiss Frank fine. Because of this federal court decision, the number of court exhibits of street drugs

has increased dramatically. In order to manage the high number of requested analyses, the municipal police of Zurich looked for a quick and reliable method for estimating drug

concentrations.

The first tests with NIR spectroscopy were performed in 1991. Because of the promising results, a routine method was established for the InfraProver FT-NIR system from Bran+Luebbe in 1992. In 1993, the first instrument was bought followed by a second one in 1996.

Until today, the number of samples investigated has increased steadily. Furthermore, a change in consumer behaviour has occurred during the same period. After the disappearance of the „open drug scene“ heroin became the „loser drug“. The number of heroin samples investigated

decreased while the number of cocaine samples increased drastically.

In 2004, more than 400 cocaine and more than 200 heroin analyses were performed.

Generally the drug content of confiscations from “big deals” were higher than those of the drugs sold on the streets

The confiscated street drugs are mixtures of various active, excipient and cutting agents. For

cocaine typical cutting agents are:

• Caffeine

• Lidocain

• Phenacetin

• various sugars (Lactose, Mannitol, Glucose, Dextrose etc..)

For heroin typical cutting agents are:

• Mixtures of Paracetamol, Caffeine and food colours

NIR Method

The first pre-investigation of the confiscated court exhibits is performed using color and immunological tests. Receiving positive results with the pre-investigations, the concentration of cocaine and heroin samples is estimated using NIR spectroscopy. Gas chromatography is used as a classical reference method which, however, takes much more time than NIR. For this reason, the predominant number of all confiscated samples are measured using NIR only. In order to get reliable results, the sample should be homogeneous. If that is not the case, it needs to be ground

in a mortar or mixed.

The NIR spectra of heroin and cocaine court exhibits show various characteristic absorption bands. Therefore, a distinct identification with NIR is possible. However the principal interest was – of course – the quantification using NIR spectroscopy.

The first quantitative NIR calibration for cocaine was developed using court exhibits

with drug concentrations between 31 and 89 %. The spectra were measured using the B+L InfraProver. The SEE (standard error of estimation) was 1.4 % and the SEP (standard error of prediction) was 3.4 % for the cocaine content using 130 spectra in the calibration and 14 spectra

in the validation set.

The first NIR calibration for heroin was developed using spectra for concentrations in a range from 32 to 87 %. The SEE was 1.4 %, the SEP was 2.9 % using 129 spectra in the calibration and 15 spectra in the validation set.

In 2004, the B+L InfraProver spectra were transferred without any problems into the

Buchi NIRCal 4.21 software and new calibrations using the patented Calibration Wizard were calculated.

These calibrations, including B+L Infra- Prover spectra only, were used for NIR measurements with the Büchi NIRFlex N-400 between June and November 2004. For several samples, GC analyses were performed. These samples were used for new calibrations based on NIRFlex N-400 spectra.

The new NIRFlex calibrations clearly show an improved performance. For cocaine samples with a calibration range from 21 to 87%, the SEE is now only 1.5 % and the SEP is also 1.5 % using 107 samples with 536 spectra in the calibration and 34 samples with 171 spectra in the validation

set.

In addition, the regression coefficient increased from 0.9674 for InfraProver to 0.9819 for NIRFlex N-400. The new heroin calibration was calculated using samples in the concentration range between 4 and 78%. The SEE is 0.9 % and the SEP is also 0.9 % using 68 samples

with 340 spectra in the calibration and 21 samples with 105 spectra in the validation set ; the regression coefficient is 0.9958.

It is obvious that the results could be improved considerably using the new calibrations

developed with NIRFlex N-400 and NIRCal 4.21.

The considerable improvements in the quantitative NIR results using the Büchi NIRFlex N-400 and NIRCal 4.21 have different reasons:

Stable and satisfactorily working NIRFlex NR-400

• High-quality optical components for stable measurements

• Better cleaning possibilities of the refer- ence plate at the Büchi NIRFlex N-400 resulting in more reliable spectra.

Efficient chemometric software NIRCal 4.21:

• Fast software – many calculations can be performed in a short time.

• Calibration Wizard for meaningful suggestions for pretreatments and number of calibration factors

• Easy visualization of calibration results

• Good software support

The acceptance of the NIR determination

NIR spectroscopy is regarded as 2: NIR spectra of some court exhibits “extended pre-analysis” by the court. NIR results are rounded to the next 5 % level. If the amount of drug is in the range defined for “severe cases” (18 g pure cocaine ore 12 g pure heroin) the result is verified by gas chromatography automatically. Without NIR spectroscopy the high number of confiscated heroin and cocaine drugs could not be measured with the existing personnel and laboratory status.

In other words – despite the calibrations development NIR spectroscopy is a strong time and cost saving tool.

BÜCHI Labortechnik AG

Postfach

9230 Flawil 1

Schweiz

Tel. +41 71 394 63 63

Fax +41 71 394 65 65

buchi@buchi.com

www.buchi.com

Near Infra Red Spectra List

2008-11-12T04:13:00.000-08:00

MAKING AN NIR ANALYZER WORK FOR YOU

2008-11-12T04:05:00.000-08:00

Keywords: Sample Consideration, NIR analysis, Prediction, Data Procesising, Outlier detection, Building a good calibration model, Validation

Abstract

In recent years, NIR analysis has steadily grown in popularity because of its ability to quickly provide qualitative and quantitative information on many products, especially raw materials. To determine if NIR spectroscopy is a reasonable alternative to more traditional methods, many factors must be considered. These factors include sample characteristics, experiment configuration, and data analysis.

Sample Consideration

The chemical constituents and physical phenomena of interest should have direct or indirect absorbance in the NIR region. Virtually all organic compounds do, particularly those with functional groups like hydroxyl, carboxyl, amine and carbon-hydrogen. A good reference for researching near infrared spectra is The Atlas of Near Infrared Spectra, Bio-Rad Sadtler Division, Philadelphia, Pennsylvania. For calibration samples, the amount of analyte in the sample set should be above the detection limit and have sufficient variability. Some analytes, e.g. water, are detectable at the ppm level. For most analytes, the nominal detection limit is 1% or above.

The analytical chemist must have an accurate independent method for measurement of the properties and must know the level of error in the reference methods. Errors in NIR prediction most often arise from errors in the reference methods, instability of the NIR spectrometer, and/or inappropriate choice of the calibration model method.

The samples used in the development of calibration sets must be representative. All the variations in the future unknown samples should be covered in the "training" calibration sets—for example, sample composition and particle size, homogeneity, and temperature variation at the working environment. As a rule of thumb, the more samples you have for the training set, the more reliable the calibration model.

Experiment Configuration

When using an NIR analyzer, instrument characteristics such as sensitivity, resolution, and signal-tonoise ratio parameters need to be evaluated. The quality of these values is a function of the light source stability, optics throughput, dispersion/filter element accuracy, and detector sensitivity in the instrument.

The choice of accessories is application dependent. For liquid samples, transmission and transflectance modes are commonly employed using fiber optic probes or cuvettes. The optimum path length is sample dependent, usually ranging from 0.1 to 1 cm. The advantage of using a fiber-optic probe is that sample preparation is significantly reduced, and noninvasive or nondestructive measurements are possible. For solid samples, diffuse-reflectance spectra collected by a reflectance probe will provide information for analytes. Diffuse reflectance should be measured without interference from specular reflectance. The setup configuration, such as the angle of incident light and the distance of light illumination/collection ought to be consistent throughout all the measurements, including those taken in developing the calibration set and for predicting the future unknowns.

For solid samples, the sample should be rotated and measurements done on different spots of the sample to average out surface effects and sampling error. A group of spectra may be averaged to increase the signal-to-noise ratio. Random noise is reduced by the factor square root of the number of spectra averaged. For ASD’s NIR spectrometer, it takes 0.1 seconds to acquire one spectrum. Therefore, a 10 second measurement reduces the random noise by a factor of 10.

Data analysis

NIR spectroscopy is an extremely rapid method of measurement, capable of performing an analysis in under a minute. The time-consuming part of NIR work is the data analysis phase, where chemists try to find the correlation between near-infrared spectral characteristics and the property, or properties, of interest as measured by more traditional methods. There are several commercially available software packages for accomplishing this task. Data analysis involves the following steps.

Data preprocessing

When the spectral data plots are presented, first determine if there is any baseline drift or slope in the spectra, which often occurs in diffuse-reflectance measurements. If necessary, baseline subtraction, first derivative and second derivative transformations may be performed to reduce these effects. There is a trade-off though as each successive degree of derivative taken introduces additional noise into the spectral data.

Outlier detection

An outlier is a data point that falls well outside the main population. Outliers result from lab measurement errors, samples from different categories, and instrument error. It is important to check for, and remove, outliers in both the training set and the set of unknowns on which calibration testing will occur (see "validation" and "prediction").

Building a good calibration model

This is one of the most important steps in NIR analysis. Developing a calibration model involves

calculating the regression equation based on the NIR spectra and the known analyte information. The model is then used to predict the future unknowns. Multiple Linear Regression (MLR), Principal Component Regression (PCR) and Partial Least Squares (PLS) are commonly used linear calibration methods, along with Locally Weighted Regression (LWR) for nonlinear models. In developing a calibration model, several parameters are evaluated: factors, loadings, and scores. When choosing the number of factors, one should try to avoid under-fitting, i.e. too few factors, and over-fitting, i.e. too many factors. If an insufficient number of factors are chosen, the prediction is not reliable because useful information has been omitted. If too many factors are chosen, however, more uncertainty is included in the calibration set which results in errors in prediction. Scores are used to check the sample homogeneity and possible clusters, while loadings are used to interpret how the variables are weighted in principal component space.

Validation

The validity of the model must be tested. This is usually done by splitting the sample set into two sets; one set for calibration and the other for validation. If there are not enough samples, “leave-one-out” cross validation can be performed. This means leaving one sample out, using the rest of the samples to build a calibration model and then using the model to predict the one left out. The advantage of doing cross validation is that unlike calibration with a full data set, the sample being predicted is not included in the calibration model. Thus, the model can be tested independently.

Prediction

Finally, the calibration can be used to predict future unknowns, assuming the unknowns are in the same sample population as those used in the calibration set. Whether the unknown is an outlier needs to be tested.

Summary

Applying an NIR analyzer to a particular application requires the development of a reliable calibration model. The most important steps involve a thorough consideration of experimental design and multivariate calibration. Once this is established, one can enjoy the advantages of the NIR analysis. The speed of the analysis will save time and avoid mistakes instantaneously. The speed advantage is so valuable to engineers involved with on-line process monitoring that instruments are routinely installed in or near the process line with feedback loops. With an NIR analyzer such as QualitySpec® Pro spectrometer, samples can be non-invasively analyzed on-the-spot, dramatically reducing costly and time consuming laboratory analysis as well as preventing unnecessary product waste and/or downtime. The low absorptivity in the NIR region allows measurements to be taken on raw materials, in process and finshed product without elaborate sample preparation. In the food, agricultural, pharmaceutical, polymer, cosmetics, environmental, textile, and medical fields, NIR analysis serves a wide range of applications,

with still many unknown applications waiting to be discovered. With the maturity of this technique, more and more people will use NIR analysis for convenience and flexibility.

REFERENCES

Burns D. A. and E. W. Ciurczak (Eds.), Handbook of Near-Infrared Analysis, (Volume 13 in Practical

Spectroscopy Series), Marcel Dekker, Inc., New York, 1992

Hildrum K. I., T. Isaksson, T. Naes and A. Tandberg (Eds.), Near Infra-red Spectroscopy, (Ellis Horwood

Series in Analytical Chemistry), Ellis Horwood, Ltd., England, 1992

Murray I. and I. A. Cowe (Eds.), Making Light Work: Advances in Near Infrared Spectroscopy, 4th

International Conference on Near Infrared Spectroscopy, Aberdeen, Scotland, August 19-23, 1991,

Weinheim, New York, Basel, Cambridge, VCH, 1992

Analytical Spectral Devices, Introduction to NIR Technology

2008-11-12T03:22:00.000-08:00

INTRODUCTION TO NIR

NIR stands for Near Infrared and refers to the region of light immediately adjacent to the visible range, falling between 750 and 3,000 nanometers (nm = nanometers or 1/1000000000 of a meter) in wavelength. Most organic materials have well defined reflectance or transmittance features at these wavelengths.

According to the principles of quantum physics, molecules may only assume discrete energy levels. Similar to the vibrating string of a musical instrument, the vibration of a molecule has a fundamental frequency, or wavelength, as well as a series of overtones. For molecules, the fundamental vibrations involve no change in the center of gravity of the molecule. The spectrum shape for any material is the result of these characteristic fundamentals and overtones. Near-infrared spectra are primarily the result of overtones, whereas there are many fundamentals in the mid and far infrared regions.

Since the molecular structure of most compounds is very complex, the resulting spectra are actually the result of many overlapping peaks and valleys. Generally speaking, persons performing NIR analysis must then identify and characterize specific features in the spectra by means of statistical methods. Chemometrics software is designed to accomplish this task.

The absorption of NIR radiation by organic molecules is due to overtone and combination bands primarily of O-H, C-H, N-H and C=O groups whose fundamental molecular stretching and bending absorb in the mid-IR region. These overtones are anharmonic, i.e., they do not behave in a simple fashion, making NIR spectra complex and not directly interpretable as in other spectral regions. Below is a graph depicting the prominent absorption bands as they relate to the overtone and combination bands of the fundamental vibrations occurring in the Mid IR region.

To understand the types of measurements possible using NIR light, it is useful to understand several general properties of electromagnetic waves, as well as basics of classical molecular and atomic structure. EM radiation, is in the form of waves, and as such, has all the properties of a wave; including wavelength. Figure 1 graph is a typical wave.

Wavelength is a distance between two points. Wavelength is particularly important to our discussion as it is closely connected to energy. Wavelength and energy are readily convertible from one to the other when speaking of EM waves. See figure 2 below

They are related in the following manner:

E = h.c /lambda

E = energy,

h = Planck's constant (6.626 x 10-27),

c = speed of light (2.998 x 1010dm/s),

and l = wavelength.

It is the energy or wavelength that gives a wave its particular properties, and it is the amount of energy an EM wave carries (its wavelength) that determines whether or not a wave (radiation) is harmful. Waves with different wavelengths (energies) act differently. Wavelengths with certain energies will produce the effects associated with an x-ray to microwaves. The general properties of waves of certain energies allow us to classify them across the full EM spectrum.

Another property of light is the manner in which energy is transferred from itself to whatever it may encounter. Light, as well as being a wave, consists of photons. Photons have properties of both waves and particles. For this discussion, we will think of photons as the "carriers" and "transferers" of energy.

Now that we have discussed light and its properties, it is appropriate to talk about matter. Matter is defined as anything which has mass and takes up space. Matter (pen, paper, ink) is made up of atoms. Atoms are made up of smaller constituents known as neutrons, protons, and electrons. Protons are charged electrically positive, neutrons have no charge, and electrons are negatively charged. This means that protons and electrons are attracted to one another in a similar manner as are magnets of differing polarities. This also means that protons are repelled by other protons, and electrons are repelled by other electrons. These small particles can be arranged in many different ways. The simplest model is shown below

The center area, where the neutrons and protons are located, is referred to as the nucleus. Around the nucleus is the space in which the electrons reside and is knows as an orbital. Orbitals

are distinct areas where an electron can exist. Orbitals also have distinct energies with which they are associated. Continuing addition of protons, neutrons, and electrons would produce

atoms in the numeric sequence listed in the periodic chart of the elements.

Molecules are a group of atoms which have combined together to form a chemical compound. Molecules are simply substances made of several atoms of similar or different elements.

Chemicals made of different types of atoms may have completely different properties than the properties exhibited by the individual atoms of which they are made. The interactions of protons and electrons help to hold the molecules together by producing bonds between the different atoms. Different arrangements of different numbers and kinds of atoms produce different properties and characteristics.

With NIR we will only deal with organic molecules (generally water, H2O, is an exception). This will limit the types of molecules we will observe with NIR, since organic molecules are classified as molecules that contain carbon. Every living thing on earth is made up of thousands upon thousands of different organic molecules. Generally speaking, the interactions of EM waves with matter will simply involve the transfer of energy. The type of interaction we will observe and use is absorption of EM radiation by molecules.

Actually, only a small portion of the molecule is involved in the absorption process — the electrons. As stated before, we know electrons exist in orbitals around the nuclei of atoms. Because of quantum mechanics, scientists now know that electrons can exist only in specified energy states; in other words, specific orbitals. Electrons cannot exist in between energy states (orbitals). This means electrons can only absorb discrete amounts (packages) of energy as the next orbital is a specific amount of energy away.

The photon is absorbed by an electron causing the electron to jump up to a higher energy level. Electrons in differing original orbits will absorb different amounts of energy. Remember that energy and wavelength are closely related (see Equation 1) so if electrons absorb differing energies, this also translates into different wavelengths.

Molecules' atoms are built of electrons, protons, and neutrons in different configurations. Similarly, the electrons, protons, and neutrons in water have different characteristics than those in protein. This also means varying substances absorb different wavelengths of light. This type of absorption is considered an electronic absorption. The absorptions in the NIR are slightly more complicated though they still involve the absorption of energy (light) by electrons.

Remember molecules consist of atoms bonded together. Bonds are produced by atoms sharing and/or giving up electrons to another atom. These bonds actually act similar to little springs (see Figure 4c). As an electron moves about the atom(s), the bonded atom is drawn or repulsed from the atom to which it is bonded, creating a

vibrating motion. Whenever something moves

consistently (vibrates) in time in this manner, it is said to have a frequency (n=frequency). The frequency is the number of times the atom vibrates in a second. The absorptions occurring in the NIR region will therefore be considered vibrational absorptions. These possible absorptions are also quantum mechanical in nature; only

discrete energy amounts can be absorbed. These levels can be roughly calculated using Equation

Equation 2

Where En = the molecule vibrational energy, n = (0,1,2,3 ...), h = Plank's constant, k = the force = thereduced mass.

N is considered a quantum number and can be constant and take on only whole integer values. A

transition where n=1 is known as a fundamental absorption. These fundamental absorptions are about 100 times less energetic in the NIR region and less energetic means longer wavelength. When n is greater than 1, the transition is known as an overtone. By looking at Equation 2, it is evident that as n increases, the energy to be absorbed also increases. This in turn indicates that shorter wavelengths will need to be absorbed. These absorptions generally occur in the NIR region. Equation 2 predicts fairly well the absorptions of two atoms bonded together (called diatomic molecules), but does not take into account all of the surrounding effects for polyatomic (many atom) molecules, such as overlapping absorption bands or hydrogen bonding.

Organic molecules exist in energy states that absorb NIR wavelengths (energies). Metals, such as silver, lead, and most inorganics, cannot absorb NIR light because they have electrons incapable of absorbing NIR wavelengths, therefore there is no interaction to measure. Generally, only organic molecules can absorb wavelengths in the NIR region. It is actually the energy state of a molecule which allows us to perform a measurement with NIR.

Now imagine a sample made up of many, many electrons, protons and neutrons. These particles are arranged into atoms, and further into molecules. The sample can be made of different types of molecules, meaning there can be water molecules, protein molecules and so on. When they take on these arrangements, they also take on different properties such as the ability to absorb different wavelengths of light, therefore, quite a few different energies might be absorbed. When a measurement is performed on this sample, what the instrument is measuring is the number of photons which undergo the absorption process for a particular wavelength. The number of photons absorbed is proportional to the amount of particular type of molecule present in the sample. This statement is more or less Beer's Law which states that “absorption is proportional to concentration.” In principle, that is what is occurring and is the basis for an NIR measurement.

where αλ is the molar absorption coefficient, l is the path length, and c is the analyte concentration. This equation is called the BLB Law and the quantity log(1/Transmittance λ) is called 'absorbance'. Absorbance is a unitless quantity, however, the term absorbance units (AU) is often used to indicate this type of measurement. BLB is valid only for transmittance measurements and much has been written on the mathematics and physics of this law. There is no rigorous derivation of a similar law that relates reflectance to analyte concentration (see Log(1/Reflectance)). Absorbance cannot be measured directly since there is no way to directly count the number of photons as they disappear one-by-one. Therefore, what is being measured is actually transmittance.

Chemometric Models

The single step in NIR analysis requiring the most planning preparation is the assembly of the samples, often called the training set to be used for the development of calibrations. A crucial step in achieving success is ensuring the samples have been analyzed as accurately and precisely as conventional techniques allow. These analyses are termed reference analyses.

In order for any NIR analyzer to make quantitative measurements or qualitative discriminations, the controlling computer must have access to one or more chemometrics models which represent the type of material being tested. The model is a mathematical construct developed using samples of the same product or class of products. The controlling computer applies the model(s) to the target spectrum and returns a model result.

A chemometrics model is developed by collecting spectral readings from a group of samples that display (a) the maximum variability of the characteristic of interest, and (b) non-correlating or random variability in all other characteristics. The same samples are submitted for independent testing to measure the characteristic of interest by a standard analytical method. The spectral data and independent test data are then analyzed using commercially available chemometrics software. The statistical processes used in quantitative spectral analysis include multiple linear regression, classical least squares, inverse least squares, and principal component regression. The statistical processes used in qualitative spectral analysis include K-nearest neighbors, SIMCA and others.

When a sufficient number of samples have been collected and properly analyzed, a mathematical model is constructed that describes the relationship between specific spectral features and the sample characteristic of interest. Thereafter, a chemist or technician may quickly measure that same characteristic in a new target sample by applying the chemometrics model to the spectrum of the target sample. Essentially a calibration is interpreting the information coming from the instrument. If the instrument is taught (calibrated) properly, it will predict the correct amount of parameter in our sample.

Once calibrations are obtained, they are entered into the NIR spectrophotometer. Following the scanning of unknowns, requiring a few seconds per sample, numerous constituents or parameters of interest are simultaneously predicted. In this mode, NIR is a rapid, cost-effective, non-destructive, accurate and efficient analytical method.

Advantages

The biggest advantage of NIR over Mid-IR and Far-IR is little or no sample preparation, and near realtime analysis. Unlike most conventional analytical methods, NIRS is rapid, non-destructive, does not use chemicals, or generate chemical wastes requiring disposal, simultaneously determines numerous constituents or parameters, and can be transported to nearly any environment, or true portable for field work. NIR instrumentation is simple to operate by non-chemists, and operates without fume hoods, drains, or other installations. NIR is not a stand-alone technology. Its accuracy is dependent upon the accuracy of the reference method used for training, however, the data from the NIR method has better reproducibility than the primary method.

Another advantage of NIR over Mid-IR and Far-IR is 'thermal' noise. All internal electronic components are a source of thermal noise in the Mid-IR and Far-IR. However, internal sources of IR are either insignificant to NIR detectors or can be made insignificant by minor shielding.

With NIR analysis most of the useful features in a spectrum consist of overtones, or combinations of overtones, which are more subtle than the fundamentals found in Mid-IR and Far-IR spectra. However, recent developments in off-the-shelf chemometrics software and powerful PC's have made NIR analysis the practical choice for most applications. Because the absorbances in the NIR region are lower than in neighboring regions and generally obey the Beer/Lambert Law, i.e., absorbance increases linearly with concentration, it is possible to analyze bulk samples without the need for dilution or other elaborate sample preparation. Thus, the results provided by NIR are typically more representative than that provided by other analytical means.

Disadvantage

NIR is not a stand-alone technology. Separate calibrations are required for each constituent or parameter and a portion of unknown samples must periodically be analyzed by the reference method to ensure that calibrations remain reliable. It may be necessary to update calibrations several times during the initial phases of use to incorporate "outlying" samples, until the calibration is acceptable. Despite the intuitive disadvantage of broad and overlapping absorption bands, sophisticated chemometric techniques can extract meaningful information from the complex NIR spectra.

Polyurethane Recycling Gains as Regulatory and Cost Pressures Mount

2008-11-12T01:18:00.000-08:00

Introduction

Polyurethane recycling is an issue that is becoming increasingly important, especially in Europe, where landfill space is dwindling and waste disposal costs are soaring. Growing regulatory pressures to "close the loop" in polyurethane (PUR) product life cycles are additional factors promoting recycling. Many innovative recycling technologies have emerged over

the past decade, and quite a few of them are already being used routinely.

Which particular recycling process is suitable for a particular product depends on the nature of the material, plus a variety of economic and environmental considerations. For example, incinerating PUR wastes for their energy value may be a viable option if many different products are co-mingled and regulations limit their disposal in landfills. But if the wastes are relatively pure, it is often more profitable to break them down into valuable monomeric PUR starting materials.

Impact of regulations

The European Union is gradually implementing stringent new quotas on recycling and energy recovery for materials used in the packaging, automotive, and the electrical and electronics sectors. These quotas affect plastics in general, and polyurethanes in particular. In addition, landfills in most central European countries will be phased out over the next few years.

Recycling regulations are less strict in North America, although, more and more manufacturers who produce and consume plastics in this region are developing voluntary recycling programs. Their aim is to reduce the likelihood of mandatory government quotas and imposed technological solutions, which could be more costly than voluntary programs.

Several trade groups, such as the U.S.-based Alliance for the Polyurethanes Industry (API), and the European Isocyanate Producers Association (ISOPA), have actively promoted PUR recycling initiatives within the industry.

Materials and methods

Common sources of PUR for recycling are post-consumer products such as appliances, automobiles, bedding, carpet cushions and backings, and upholstered furniture. Industrial manufacturing scrap is another important source of recycled PUR.

PUR accounts for about 5% of all plastic waste, according to the Polyurethane Recycle and Recovery Council (PURRC), a unit of API. The extent of recycling varies with the type of product. PUR carpet cushions have a particularly high rate of recycling. In 2002, some 98% of the PUR used to make carpet cushions in the U.S. came from scrap PUR foam, reports

PURRC. Of the total scrap used, about 6% came from post-consumer waste.

Although transportation is a major consumer of PUR, recycling of PUR in this sector has been modest. The high costs of separating the PUR wastes from other components of discarded automobiles have been barriers to recovery and re-use of PUR in motor vehicles. However, automakers around the world are beginning to design vehicles for easy and economical removal of PUR seat cushions for recycling. Reaction injection molded (RIM) parts in autos, found in bumper skins and side protection panels, have been commercially recycled for various applications, both automotive and nonautomotive.

Among the methods used to recycle PUR products are energy recovery processes such as incineration and use of the resulting heat for electric power generation. Another strategy involves mechanical recycling, such as grinding and re-use of PUR wastes as fillers in molded PUR goods. A third method is to chemically break down PUR into its monomeric constituents and then re-use the monomers to make new PUR products.

Energy recovery

When PUR is part of a larger, undifferentiated waste stream - such as municipal solid waste, or ground up post-consumer products made of a variety of combustible materials - incineration and recovery of the thermal energy is often the most satisfactory recycling option. As a fuel, a given amount of PUR has an energy content nearly equal to coal on an equivalent weight basis. Incineration reduces PUR to about 1% of its original volume, thus lessening the burden on

landfills.

PURRC studies have found that PUR can be added to municipal solid waste in amounts up to 20% by weight without increasing levels of undesirable gas emissions or ash. ISOPA reports that PUR can be fed into advanced incinerators linked to thermal energy recovery units and flue-gas cleaning equipment. Such combination units are said to be capable of providing up to 10% of electricity requirements of local communities. PUR wastes have also been used as fuel for

domestic heating and cement kilns

Mechanical recycling

Grinding PUR wastes into powders and then re-using these powders in various ways constitute the mechanical recycling approach. Wastes for this process can come from factory trim and scrap, as well as post-consumer products. The powdered PUR is available as filler in production of PUR foams or elastomers. When used as fillers, the powders are usually first added to the polyol component in a PUR production process. Molded PUR products, such as auto seat

cushions, can contain up to 20% regrind without any deterioration in properties or performance.

Mechanical recyclers grind PUR into powders with various milling and knife-cutting processes. To be used as fillers, PUR particles should be less than 200 microns in size, and preferably under 100 microns. Shredded PUR foam wastes can be rebonded using heat, pressure and an adhesive binder. Rebonding is commonly used to make vibration sound dampening mats, flooring, sports mats, cushioning and carpet underlay. In a similar process, known as adhesive pressing, PUR granules are coated with a binder and cured under heat and pressure. Contoured products are made from adhesive pressing; they include automotive floor mats and tire covers.

RIM and reinforced-RIM parts can also be ground into small particles, which can be molded under high pressure and heat to form solid parts for the auto industry. These compression-molded solid parts - such as pump and motor housings, and catalytic converter shields - can contain up to 100% RIM regrind.

Chemical recycling

Depolymerization of PUR into its chemical constituents, known as chemolysis, is best practiced when the starting PUR wastes are of known and uniform chemical composition. PUR products made from the recovered monomers are usually of the same chemical type as the original products and offer the same performance. According to PURRC, chemolysis yields polyols that can replace up to 90% of the polyols in semi-rigid foams, creating a foam with a recycled content of 30%. Similar results have been reported with rigid foams, the organization adds.

Chemolysis exists in the following variants:

Hydrolysis, where PUR wastes react with water under heat and pressure, producing polyether polyols and diamines (the hydrolysis products of the original diisocyanates). These components can be separated, purified and re-used.

Glycolysis, in which PUR foam reacts with diols at elevated temperatures (above 200° C) in the presence of a catalyst. The high molecular weight polyurethane chain, and its many cross-linkages, are cleaved by this process to form lower molecular weight polyols and other liquid products. After purification, the polyol recyclate can be used to make various goods such as rigid foams, flexible foams and shoe soles. Much of the work in glycolysis has been done in Europe.

Glycolysis is most useful for recycling production waste rather than post-consumer waste.

Aminolysis, in which the PUR foam is reacted under heat and pressure with amines such as dibutylamine, ethanolamine, lactams or lactam adducts. Aminolysis is still in the research stage.

Also included in the chemical recycling category is pyrolysis, in which mixtures of PUR and other plastic wastes are heated in the absence of oxygen. The resulting products are various gases and oils that can be used as fuels and chemical feedstocks. Hydrogenation is a further treatment, in which the pyrolysis products are reacted with hydrogen to produce even purer gases and oils. Economic issues, such as the high cost of hydrogen, occasionally rule out hydrogenation. Briquetted waste PUR can be used as an iron ore reducing agent, another process that that harnesses the chemical properties of PUR.

Conclusion

Technologies for recycling polyurethane wastes have been under development for more than a decade, but the recycling issue has recently become more urgent. Reasons for this include the closing of landfill sites, rising waste disposal fees, and government regulations that mandate quotas for recycled plastics. The main technologies for PUR recycling are energy recovery, mechanical recycling and chemical recycling. Which of these methods is suitable depends on the

product being recycled, the location, local energy costs, and intended end-use markets. Much of the PUR recycled today is industrial scrap. The lack of a collection, sorting and processing infrastructure has hindered recycling of post-consumer PUR wastes to some extent, although industry is addressing this issue through the efforts of various trade groups.

Source:

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