This HPLC assay with o-phthalaldehyde precolumn derivatization is used to measure the total, oxidized, and protein-bound forms of glutathione in human blood, plasma, and rat tissue. Total glutathione (i.e., sum of reduced, oxidized, and protein-bound fractions) was determined after reduction with dithiothreitol and protein precipitation with perchloric acid (PCA). A preliminary selective blockage of free sulfhydryl groups with N-ethylmaleimide was necessary to evaluate the different oxidized forms. The assay showed high sensitivity (0.05 pmol injected) and good precision (within-day CVs of 5.5% to 6.4%), recovery (101% +/- 4%), and linearity (r0.999). Samples, after PCA acidification, were stable at room temperature and 4 degrees C for 3 days, and at -20 degrees C and -80 degrees C for1 month. The method (involving automated derivatization) not only is very rapid and simple but also allows immediate processing of many different biological samples.
