Gas Chromatography-Based Methods

Subramanian [18] has used gas chromatography-mass spectrometry to study the photodecomposition products such as benzaldehyde, a-hydroxyacetophenone, phenyl glycol, a-methoxyacetophenone, and a-henzyloxyacetophenone produced upon UV irradiation of polystyrene peroxide. Diaz and co-workers [19] carried out similar studies on polybenzyl methacrylates and polybenzyl acrylates. 

Thermal Analysis of Polymers, Rapra Review Report No. 95, Rapra Technology Ltd., Shrewsbury, UK, 1997, Vol. 8, No. 11. 

Moore in UV Curing, Science and Technology, Ed., S.R Pappas, Technology Marketing Corporation, Stamford, CT, USA, 1978. 

Rogler, FI. Markert, B. Stapp and E. Zapf, Polymer Preprints, 1988,29, 528. 

Billingham in Encyclopaedia of Polymer Science and Engineering, Ed., J.J. Kroschwitz, Wiley Interscience Publications, New York, NY, USA, 1988, Volnme 2, p.789. 

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Two methods, EPA SW-846 8015 and 8015A, were, in the past, often quoted as the source of gas chromatography-based methods for measurement of the total petroleum hydrocarbons in a sample. However, the original methods were developed for nonhalogenated volatile organic compounds and were designed to measure a short target list of chemical solvents rather than petroleum hydrocarbons. Thus, because there was no universal method for total petroleum hydrocarbons, there were many variations of these methods. Recently, an updated method... 

Huybrechts, T., Dewulf, J., Van Langenhove, H. (2003). State-of-the-art of gas chromatography-based methods for analysis of anthropogenic volatile organic compounds in estuarine waters, illustrated with the river Scheldt as an example. J. Chromatogr. A, 1000(1-2), 283-297. 

Zitko [20] has described a confirmatory method in which the chloroparaffins in sediments are reduced to normal hydrocarbons which are then analysed by gas chromatography. This method lacks sufficient sensitivity for trace (sub-ppm) analysis and the confirmatory method may be difficult to apply. Friedman and Lombardo [21] have described a gas chromatographic method applicable to chloroparaffins that are slightly volatile the method is based on microcoulometric detection and photochemical elimination of chlorinated aromatic compounds that otherwise interfere. 

Nota and Improta [813] determined cyanide in coke oven waste water by gas chromatography. The method is based on treatment of the sample with bromine and direct selective determination of the cyanogen bromide by gas solid chromatography using a BrCN selective electron capture detector. No preliminary treatment of the sample to remove interferences is necessary in this method, and in this sense it has distinct advantages over many of the earlier procedures. Bromine also oxidises thiocyanate to cyanogen bromide. Previous treatment of the sample with aqueous formaldehyde destroys thiocyanate and prevents its interference. 

Carrier gas The mobile phase for gas chromatography. Catalytic method Analytical method for determining the concentration of a catalyst based on measuring the rate of a catalyzed reaction. 

A gas chromatography (GC) method was reported for the trace analysis of I- in processed seaweed by Lin et al. (Lin et al., 2003). The method is based on the derivatization of aqueous iodide extracted from seaweed with 2-(p>entafluorophenoxy)ethyl 2 (pip>eridino) ethanesulfonate in toluene using tetra-n-hexylammonimn bromide as a phase-transfer catalyst. 

Gas phase titration method that has been mentioned in the section, Surface Characterization [69,70] is based on gas chromatography. The method consists of... 

A mixture of cinnamaldehyde, chlorotris (triphenylphosphine) rhodium (and toluene for chromatographic determination) refluxed 15 min. in benzene styrene. Y 77% based on the Rh-complex, determined by gas chromatography. — This method is mild, efficient, and specific. F. e. s. J. Tsuji and K. Ohno, Tetrah. Let. 1965, 3969 steroids s. Y. Shimizu, H. Mitsuhashi, and E. Gaspi, Tetrah. Let. 19(56,4113. 

Gas chromatography-based separation methods for the identification of bacterial metabolites are well established. The maximum molecular weight of compoimds... 

Analytical and Test Methods. o-Nitrotoluene can be analyzed for purity and isomer content by infrared spectroscopy with an accuracy of about 1%. -Nitrotoluene content can be estimated by the decomposition of the isomeric toluene diazonium chlorides because the ortho and meta isomers decompose more readily than the para isomer. A colorimetric method for determining the content of the various isomers is based on the color which forms when the mononitrotoluenes are dissolved in sulfuric acid (45). From the absorption of the sulfuric acid solution at 436 and 305 nm, the ortho and para isomer content can be deterrnined, and the meta isomer can be obtained by difference. However, this and other colorimetric methods are subject to possible interferences from other aromatic nitro compounds. A titrimetric method, based on the reduction of the nitro group with titanium(III) sulfate or chloride, can be used to determine mononitrotoluenes (32). Chromatographic methods, eg, gas chromatography or high pressure Hquid chromatography, are well suited for the deterrnination of mononitrotoluenes as well as its individual isomers. Freezing points are used commonly as indicators of purity of the various isomers. 

Air Monitoring. The atmosphere in work areas is monitored for worker safety. Volatile amines and related compounds can be detected at low concentrations in the air by a number of methods. Suitable methods include chemical, chromatographic, and spectroscopic techniques. For example, the NIOSH Manual of Analytical Methods has methods based on gas chromatography which are suitable for common aromatic and aHphatic amines as well as ethanolamines (67). Aromatic amines which diazotize readily can also be detected photometrically using a treated paper which changes color (68). Other methods based on infrared spectroscopy (69) and mass spectroscopy (70) have also been reported. 

The actual Russian standards allow presentation of hydrocarbon components of UGC as individual compounds only for C -C hydrocai bons. The rest is described as pseudo-compound C,, although its content may reach 60 % m/m. Apparently, the detailed determination of composition of hydrocarbons C, in UGC allows essentially to raise quality of both its processing and its record. The best method for the determination of heavy hydrocai bons is capillary gas chromatography. Typical approach is based on preliminary sepai ation of UGC samples to gaseous and liquid phases. 

There are two main approaches to its solution. Traditional approach is based on preliminary separation of UGC samples to gaseous and liquid phases and their subsequent analyses [1]. This approach is well-developed and it allows obtaining quite precise results being used properly. However, this method is relatively complicated. Multi-stage procedure is a source of potential errors, then, it makes the analyses quite time consuming. More progressive approach is based on the direct analysis of the pressurized UGC samples. In both cases the determination of heavy hydrocarbons (up to C ) is made by capillary gas chromatography. 

At present moment, no generally feasible method exists for the large-scale production of optically pure products. Although for the separation of virtually every racemic mixture an analytical method is available (gas chromatography, liquid chromatography or capillary electrophoresis), this is not the case for the separation of racemic mixtures on an industrial scale. The most widely applied method for the separation of racemic mixtures is diastereomeric salt crystallization [1]. However, this usually requires many steps, making the process complicated and inducing considerable losses of valuable product. In order to avoid the problems associated with diastereomeric salt crystallization, membrane-based processes may be considered as a viable alternative. 

Ethanol concentration in the fermentation broth is determined by using gas chromatography (HP 5890 series II with HP Chemstation data processing software, Hewlett-Packard, Avondale, PA) with a Poropak Q Column, and a Hewlett-Packard model 3380A integrator. A flame ionisation detector (FID) is used to determine ethanol. The oven temperature is maintained at 180 °C, and the injector and detector temperature are maintained at 240 °C. The sample taken from the fermentation media has to be filtered and any internal standard must be added for analysis based on internal standard methods otherwise, the area under the peak must be compared with known standard samples for calculation based on external standard methods. 

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