Gas chromatographic separation and detection

Some additional remarks on operational conditions may be useful to maintain column integrity when determining extremely low concentrations ot e.g., CBs in seawater at concentrations as low as 0.1-2pg/L. 

New capillary columns have to be conditioned to remove residual traces of solvent and lower relative molecular mass fractions of the liquid phase. Carrier gas should flow at room temperature for some time to remove oxygen the column is then eiqiosed to moderate temperatures (80-100 °C) for some hours before the temperature is increased to a value that must be a compromise between minimum time required to achieve a stable baseline and maximum column life time. The normal temperature is the maximum temperature required for the analysis. To avoid destruction of the column at higher temperatures, a sufficient flow of carrier gas through the column should be maintained. During conditioning, the column should be left disconnected from the ECD so as to minimize detector contamination. 

Older columns may have to be subjected to higher temperatures periodically to remove carrier gas impurities that have accumulated. The ECD may remain connected to the column provided that it is kept at an elevated temperature (300-320 °C). 

The carrier gas must be of high purity (Ha, at least 99.999 %). Impurities can saturate molecular sieve traps, gas lines and other materials and, if not removed, result in bleeding at higher temperatures which causes baseline instability and shortens the life of the column. 

22A2 Single colunm and multi-dimensiiMial dironiatojpraphy 

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Concise The general analytical procedure for the determination of PCBs in full-fat milk includes four main steps extraction from the matrix, preconcentration and cleanup, gas chromatographic separation, and detection. (From Llompart et ah, 2001) (1 sentence, 28 words)... 

J. W. F. Davidson, F. J. Dicarlo, and E. F. Szabo, Gas chromatographic separation and detection of pentaerythritol nitrates and other organic nitrate esters, J. Chromatogr., 57 345 (1971). 

The methods using hydride generation and AAS as final determination were, however, in considerable difficulty with this complicated matrix, due to unknown interferences either at the derivatisation step or in AAS detection, or determination limits that were too low. As observed by the participants, the laboratories using gas chromatographic separation and detection either by FPD or MS tended to agree which would confirm that these methods would be more suited to the determination of TBT in this particular material. 

The hydrogenation method is promising [194] as alkoxy groups are spUt off in a flow-type reactor which reduces considerably the duration of the analysis. The saturated hydrocarbons formed on hydrogenation are suitable for both gas chromatographic separation and detection. 

Perry developed a technique for the recovery of zinc dialkyidithiophosphates from a thin-layer chromatogram and for the pyrolysis of the resulting separated compounds and for the gas chromatographic separation and detection of the olefinic fractions thus formed. 

For determination of Pb(C2H5)4 and other tetraalkyllead compounds in air by a diffusion technique employing an ICl-coated annular denuder, see [520] see also [442]. For determination of gaseous lead in exhaust gas by microwave-induced air-plasma emission spectrometry, see [532]. Methods for determination of Pb(C2H5)4 in hazardous waste incinerator flue gas were developed, based on gas chromatographic separation and detection by flame ionization or mass spectrometry [565]. 

Figure 27-5 Diagram of C.H.N.S elemental analyzer that uses gas chromatographic separation and thermal conductivity detection. [Adapted from E. Pella, Elemental Organic Analysis. 2. State of the Art, Am. Lab, August 1990, p. 28.]...

Purge-and-trap techniques in which volatile analytes are evolved from blood or urine in a gas stream and collected on a trap for subsequent chromatographic analysis have been developed. Such a technique employing gas chromatographic separation and Fourier transform infrared detection has been described for a number of volatile organic compounds in blood.6... 

The peak area A obtained after chromatographic separation and detection is proportional to the analyte concentration in the gas phase ... 

For measuring at low concentrations, the derivatisation of the extracted organotin compound with sodium tetraethylborate is an established procedure to make a more sensitive gas chromatographic analysis possible. Derivatisation can be combined with the extraction as prescribed in the German method but can also be carried out after the extraction. Selective detection is possible using GC-MS. For organo-metallic compounds atomic emission or atomic absorption detection is not only very sensitive, but very selective. The steps necessary for the chromatographic separation and detection are described in ISO/CD 17353 (2001). Application of this well-described method for soil samples does not mean that the difficulties with the extraction have been overcome. 

The successful application of the CFD method in combination with subsequent gas chromatographic separation and the use of an BCD has resulted in the extensive development of this technique. However, other CFD methods aimed at obtaining derivatives that can be selectively detected by other selective detectors (e.g., sodium thermionic, flame photometric) have not been developed adequately, despite their obvious promise. It seems that the high selectivity of the method should be used for the elaboration of selective methods of functional group analysis in order to identify compounds at the picogram level. This is especially pertinent to the analysis of microsamples on capillary columns. 

Tenax (2,6-diphenyl- -phenylenoxid) has been used by several authors. " " " Tenax is thermally very stable (320°C), but has a relatively low enrichment capacity. " It is recommended for the analysis of compounds with more than six C atoms. It has also been proved suitable for compounds of lower molecular weights. Tangerman " enriched H2S, COS, CS2, thiols, sulfides, and disulfides from air at — 196°C on Tenax. After gas chromatographic separation, he detected the compounds by flame photometric detector (FPD) in the lower ng/1 range. 

In GCMS, chemical derivatization of the sample molecule often improves peak symmetry, volatility and thermal stability for gas chromatographic separations and can afford improved selectivity and detection limits for mass spectral... 

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