Identification and Separation

Mechanical comminution of the sample is performed because the composition of polymers frequently shows inhomogeneities despite good processing. Furthermore, some tests (e.g., monomer content and H20 content) depend on the sample. 

Products are comminuted with cutting tools such as shears, knives, or razor blades. Drilling, milling, etc. are also suitable. A smaller particle diameter can also be obtained by grinding precooled samples in mills. Depending on the elasticity characteristics of the sample, either dry ice or liquid nitrogen can be effectively used. 

After comminution, samples must be conditioned over phosphorus pentoxide at room temperature in a desiccator. In all mechanical loads and also in low temperature treatment, decomposition processes which may affect polymoleallarity and sample composition must be accounted for. Since the analytical result may be affected, attention must be paid to the reproducibility and uniformity of the comminution processes. 

Plasticizers can be separated by extraction with diethyl ether. Stabilizers based on pure organic or organo-metallic compounds may only be partially separated. Extraction time depends on particle size and on the amount of plasticizer in the sample. 

For the quantitative determination of the mass of plasticizer about 1 to 2 g of the comminuted sample are weighed and extracted with anhydrous diethyl ether in a Soxhlet apparatus. After distilling off the ether and drying the extract at 105°C to constant weight, the amount of ether soluble components is calculated from the difference in weight of the extraction flask before and after the extraction. Preparative separation of the plasticizer before identification of the polymer is performed in an analogous manner. 

Many of the procedures already outlined for the preparation of halo-genated sugars involve the production of two or more isomers. Occasionally, the information required can be obtained from the reaction without isolation of the products. The direction of epoxide cleavage has been initially determined by periodate oxidation, before separation of the products. Similarly, the mixtures obtained by halogenation and halomethoxylation have been investigated by nuclear magnetic resonance, to find the nature of the products prior to isolation. -  

However, in most cases, separation of the products is important it may be achieved by several means. Under favorable conditions, one of the isomers, or a derivative, may crystallize spontaneously, and, by fractional recrystallization from suitable solvents, the isomers may be separated. Methods that are more effective are, however, available. Several cleavage 

3-deoxy-/3-L-xyIopyranoside and methyl 2-bromo-2-deoxy-j3-L-arabinopy-ranoside. The latter forms an isopropylidene acetal, and this can be separated from the methyl L-xyloside derivative. Similarly, in the hexose series, 4,6-0-benzylidene rings are readily formed, and use of benzylidene ring-formation led to the separation of the isomers now known to be methyl 4-chloro-4-deoxy-a-n-glucopyranoside and methyl 2-chloro-2-deoxy-a-D-idopyranoside, which were formed by the action of hydrogen chloride on a mixture of methyl 3,4-anhydro-a-D-galactopyranoside and methyl 2,3-anhydro- -D-gulopyranoside. -  

Identification of the halogenated products may be achieved both by chemical and by physical methods. Bromodeoxy, chlorodeoxy, and deoxy-iodo sugars may be reduced to the deoxy sugars, which are now well characterized. 

An alternative, or supplementary, approach is provided by oxidation with lead tetraacetate or, preferably, periodate, and possibly by identification of the products. Caution must, however, be observed in using this method, as Buchanan has shown that the compound previously designated as methyl 3-chloro-3-deoxy-a-D-gulopyranoside consumes periodic acid extremely slowly (seven days) and is, in fact, methyl 4-chloro-4-deoxy-a-D-glucopyranoside. The products of epoxide cleavage are usually completely defined by these procedures, because irans addition can be assumed, although considerable care must be exercised when there is a possibility of epoxide migration.  

During extraction processes, many undesirable compounds are also released from the sample matrix these must be removed to obtain quantitative results from certain 

Recent advances in circuit miniaturization and column technology, the development of microprocessors and new concepts in instrument design have allowed sensitive measurement at the parts per billion and parts per trillion levels for many toxicants. This increased sensitivity has focused public attention on the extent of environmental pollution, because many toxic materials present in minute quantities could not be detected until technological advances reached the present state of the art. At present, most pollutants are identified and quantified by chromatography, spectroscopy, and bioassays. 

Once the toxicant has been extracted and separated from extraneous materials, the actual identification procedure can begin, although it should be remembered that the purification procedures are themselves often used in identification (e.g., peak position 

When a sample is injected, the injector port is at a temperature sufficient to vaporize the sample components. Based on the solubility and volatility of these components with respect to the stationary phase, the components separate and are swept through the column by the carrier gas to a detector, which responds to the concentration of each component. The detector might not respond to all components. The electronic signal produced as the component passes through the detector is amplified by the electrometer, and the resulting signal is sent to a recorder, computer, or electronic data-collecting device for quantitation. 

Column Technology. Increased sensitivity and component resolution have resulted from advances in solid-state electronics and column and detector technologies. In the field of column technology, the capillary column has revolutionized toxicant detection in complex samples. This column generally is made of fused silica 5 to 60 m in length with a very narrow inner diameter (0.23-0.75 mm) to which a thin layer (e.g., 1.0 11 in) of polymer is bonded. The polymer acts as the immobile or stationary phase. The carrier gas flows through the column at flow rates of 1 to 2 ml/min. 

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Tile use of benzenesulphonyl chloride or of p-toluenesulphonyl chloride in the separation and identification of amines is described in Section IV,100. 

Rubinson, J. E. Neyer-Hilvert, J. Integration of GG-MS Instrumentation into the Undergraduate Laboratory Separation and Identification of Eatty Acids in Gommercial Eats and Oils, /. Chem. Educ. 1997, 74, 1106-1108. 

The coupled methods, GC/MS and LC/MS, form very powerful combinations for simultaneous separation and identification of components of mixtures. Hence, these techniques have been used in such widely disparate enterprises as looking for evidence of life forms on Mars and for testing racehorses or athletes for the presence of banned drugs. 

Ben2enesulfonate compounds yield very iasoluble salts which have been used for separation and identification of amino acids (89). Similarly, phosphotungstic acid forms iasoluble salts with basic amino acids such as lysiae, arginine, and cysteiae. 

Table 1 fists the most significant of the hyphenated instmments that were commercially available as of 1990. The instmments and methods discussed in detail herein all have both separation and identification capability. 

HPLC systems coupled to mass spectrometers (LC-MS) are extremely important methods for the separation and identification of substances. If not for the costs involved in LC-MS, these systems would be more commonly found in research laboratories. 

Arid .—Make a solution (if not already dissolved) and test with litmus. If the liquid is acid, a fiee (UvVf is probably present. If the liquid is neutral and a metal has been found, a metallic salt is probably present. If the liquid is alkaline, it may be the alkaline salt of a phenol or an alkaline cyanide, both of which are hydiolysed in solution. The separation and identification ot the acid is not a eiy simple niattei. If the acid is an aromatK ... 

Definitive identification of lysine as the modified active-site residue has come from radioisotope-labeling studies. NaBH4 reduction of the aldolase Schiff base intermediate formed from C-labeled dihydroxyacetone-P yields an enzyme covalently labeled with C. Acid hydrolysis of the inactivated enzyme liberates a novel C-labeled amino acid, N -dihydroxypropyl-L-lysine. This is the product anticipated from reduction of the Schiff base formed between a lysine residue and the C-labeled dihydroxy-acetone-P. (The phosphate group is lost during acid hydrolysis of the inactivated enzyme.) The use of C labeling in a case such as this facilitates the separation and identification of the telltale amino acid. 

In the laboratory you will most likely carry out one or more experiments involving the separation and identification of cations present in an "unknown" solution. A scheme of analysis for 21 different cations is shown in Table A. As you can see, the general approach is to take out each group (I, II, III, IV) in succession, using selective precipitation. 

Qualitative analysis involves the separation and identification of ions by selective precipitation, complex formation, and the control of pH. 

Marutoiu C, Sarbu C, Vlassa M, et al. 1986. A new separation and identification method of some organophosphorus pesticide by means of temperature programming gradient thin-layer chromatography. Analysis 14 95-98. 

Marutoiu C, Vlassa M, Sarbu C, et al. 1987. Separation and identification of organophosphorus pesticides in water by HPTE. J High Resolution Chromatog Chromatog Comm 19 465-466. 

Coutselinis A, Kentarchou P, Boukis D. 1976. Separation and identification of the insecticide "endosulfan" from biological materials. Forensic Sci 8 251-254. 

KHACHiK F BEECHER G R and GOLi M B (1992) Separation and identification of carotenoids and their oxidation products in the extracts of human plasma. Anal Chem. 64(18) 2111-22. 

ZEEB D J, NELSON B c, ALBERT K and DALLUGE J J (2000) Separation and identification of twelve catechins in tea using liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry , Chem, 72, 5020-26. 

Khachik, F. and Beecher, G.R., Separation and identification of carotenoids and carotenol fatty acid esters in some squash products by liquid chromatography. 1. Quantification of carotenoids and related esters by HPLC, J. Agric. Food Chem., 36, 929, 1988. 

Pati, S. et al.. Simultaneous separation and identification of oligomeric procyanidins and anthocyanin-derived pigments in raw red wine by HPLC-UV-ESI-MS, J. Mass Spectrom., 41, 861, 2006. 

M.E. Lacey, Z. J. Tan, A. G. Webb, J. V. Sweedler 2001, (Union of capillary high-performance liquid chromatography and microcoil nuclear magnetic resonance spectroscopy applied to the separation and identification of terpenoids), J. Chromatogr. A 922(1-2), 139. 

Li, J., Kelly, J.F., Chernushevich, I., Harrison, D.J., and Thibault P., Separation and identification of peptides from gel-isolated membrane proteins using a microfabricated device for combined capillary electrophoresis/nanoelectro-spray mass spectrometry, Anal. Chem. 72, 599, 2000. 

Pereira, A., Pereira, M, M., Free amino acids in green coffee from Huambo (Angola). Separation and identification by electrophoresis and thin layer chromatography, Coll. Sc 1. Int. Cafe, 8, 545, 1977. (CA92 196460s)... 

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