Quantitation of the glutathione in human peripheral blood by matrix-assisted laser desorption ionization time-of-flight mass spectrometry coupled with micro-scale derivatization.

Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been broadly applied to analyze high-molecular-weight compound (such as polymer or proteomic research) but seldom used for low-molecular-weight compound analysis. The objective of this study is the development of a simple analytical method for the determination of the concentration of tripeptide glutathione (GSH) by MALDI-TOF MS. Unfortunately, GSH could not be detected directly by MALDI-TOF MS. Our method is based on the derivatization of GSH with 4-bromomethyl-6,7-dimethoxycoumarin (BrDMC) in acetonitrile using potassium hydroxide (KOH) as a base catalyst. After simple extraction step, the supernatant is spotted on a target plate, mixed with matrix α-cyano-4-hydroxycinnamic acid (CHCA) and then detected by MALDI-TOF MS. Some parameters affecting the derivatization of GSH were investigated, such as the concentration of BrDMC, KOH, different base catalyst, and reaction time, etc. The regression equations of GSH derivative possessed good linearity (r≧0.995) over the range of 1.0-100.0 μM. The relative standard deviation (R.S.D.) and relative error (R.E.) values in intra- and inter-day assays were below 13%, which showed good precision and accuracy. This proposed method was successfully applied to monitor the concentration of GSH in human blood at micro-scale level.