Determination of total cysteamine in human plasma in the form of its 2-S-quinolinium derivative by high performance liquid chromatography

Cysteamine (mercaptamine) can be determined in plasma by liquid chromatography with ultraviolet detection after precolumn derivatization. The plasma is reduced with sodium borohydride in order to convert disulfides to thiols, and derivatized with 2-chloro-1-methylquinolinium tetrafluoroborate. The 2-S-quinolinium derivative of cysteamine is then separated from other thiols derivatives present in the plasma, and quantitated using high-performance liquid chromatography and then detection at 355 nm. Peaks from the main plasma thiols cysteine, cysteinylglycine, glutathione and homocysteine are also observed and can be measured as needed. The cystamine standards added to the plasma before the reduction step show that the response of the detector is linear within the range studied, from 0.1 to 40 mu mol/L plasma. The imprecisions at the bottom and the top of the calibration range were 11.17 and 0.8% and the inaccuracies 8.64 and 1.50%, respectively, and the lower limit of quantitation was 0.1 nmol cysteamine in 1 ml of plasma.