Determination of Sulfur Amino Acids, Glutathione, and Related Aminothiols in Biological Samples by Gas Chromatography with Flame Photometric Detection

The determination of sulfur amino acids, glutathione (GSH), and related aminothiols has been carried out by isotachophoresis (1 ), amino acid analyzer (AAA) (2 ,3 ), gas chromatography (GC) (4 –8 ), high-performance liquid chromatography (HPLC) (9 –32 ), GC-mass spectrometry (GC-MS) (33 ,34 ), liquid chromatography-mass spectrometry (LC-MS) (35 ), and capillary zone electrophoresis (CZE) (36 –38 ). However, isotachophoresis and AAA methods are nonselective for sulfur amino acids and lack sensitivity. GC methods based on the conversion into trimethylsilyl (4 ,5 ), neopentylidine (6 ), and N-trifluoroacetyl n -butyl ester (7 ) derivatives lack sensitivity, gives a tailing peak and requires anhydrous derivatization conditions. Although GC method based on the preparation of N-heptafluorobutyryl isobutyl or ethyl esters (8 ) is selective and sensitive by flame photometric detection (FPD), this method is not applied to the analysis of biological samples. As the HPLC methods, the ultraviolet (UV) (9 –12 ), and the postcolumn UV derivatization with 4,4′-dithiopyridine (13 ) and 5,5-dithiobis (2-nitrobenzoic acid) (14 ), the precolumn fluorescence derivatization with 4-(aminosulfonyl)- or ammonium-7-fluoro-2,1,3-benzoxadiazole-4-sulfonate (15 ,16 ), methyl 4-(6-methoxynaphthalene-2-yl)-4-oxo-2-butenoate (17 ), N-(1-pyrenyl)maleimide (18 ), monobromobimane (19 –23 ), _o -phthaldialdehyde (24 ,25 ), 9-fluorenylmethyloxycarbonyl chloride (26 ), and 2-chloro-1-methylpyridinium (27 ), and electrochemical detection (28 –32 ) have been reported. Many of these HPLC methods were highly sensitive, but some of these methods lack specificity and require cleanup of the sample to remove the excess reagent and coexisting substances. GC-MS methods based on the conversion into tert -butyldimethylsilyl (33 ) and N(O,S)-propoxycarbonyl propyl ester (34 ) derivatives, and LC-MS method were highly sensitive and specific, but these methods require expensive equipment. Furthermore, CZE methods with electrochemical detection are capable of achieving higher separation efficiency, use less organic solvents, and require small amounts of samples in comparison with HPLC, but these methods are not applied enough to the analysis of biological samples. Current methods for the determination of sulfur amino acids, GSH, and related aminothiols have also been described in detail in refs. 39 –43 .