Detection of amino acids and peptides separated by GLC

The detection of samples in the gas phase through katharometry, electron capture, etc. is well developed and reliable. The linking of a gas chromatograph with a mass spectrometer is increasingly found to be useful in research studies, to identify the components of mixtures whose quantitation has been accomplished by other means. Thermospray techniques that have entered into routine use in mass spectrometry (Section 4.11), have made the CZE MS and various HPLC MS combinations particularly useful. 

Sufficient volatility for GLC analysis is found for A-acylated esters of amino acids and peptides. Their preparation requires a two-step derivatisation protocol and therefore introduces a potential source of error. There is also anxiety about the impurities that may be introduced in this way. However, this applies to any derivatisation protocol and experienced users of the GLC technique can obtain impressive reproducibility of results, sufficient to match the reliability of the classical Moore and Stein procedure. Flexibility because of the additional range of detectors available for GLC can be useful, e.g. highly sensitive electron-capture detectors for halogenated analytes or amino acids and peptides derivatised with halogen-containing groups. 

Estimation of enantiomer ratios is conveniently accomplished using diastereoisomer-forming derivatisation protocols or through separations of enantiomer mixtures over chiral stationary phases. Commercially available chiral coatings for this purpose, such as Chirasil-Val, have been used in the field of amino-acid fossil dating (Section 1.11), exploiting the better resolution of capillary GLC, whereby a thermally stable liquid coats the surface of a narrow tube. 

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