Development of quantitative method for determination of γ-glutamyl peptides by capillary electrophoresis tandem mass spectrometry: An efficient approach avoiding matrix effect

• Matrix effects influence the accuracy of γ-glutamyl peptide determination by LC–MS/MS.
• The developed CE-MS/MS method was minimally affected by matrix effects.
• This method was highly selective and sensitive.

Serum γ-glutamyl di- and tripeptides have proven to be useful biomarkers to accurately predict nine different forms of liver disease. Using liquid chromatography–tandem mass spectrometry (LC–MS/MS) with multiple reaction monitoring (MRM), serum and liver samples spiked with γ-glutamyl peptide standards were analyzed to estimate accuracy. Unexpectedly, the recovery rates for several γ-glutamyl peptides in the serum samples were quite low, whereas values for some γ-glutamyl peptides in the liver samples were highly elevated. Most of these peptides were barely retained on the reverse-phase column, resulting in significant ion suppression or enhancement. In contrast, a capillary electrophoresis tandem mass spectrometry (CE-MS/MS) method with MRM was minimally affected by matrix effects. Of the 39 tested compounds, most of γ-glutamyl peptides that did not contain a thiol substituent in its structure gave acceptable recoveries (70–120%), and limits of detection for the analytes were between 3.6 and 800 nmol/l with pressure injection at 5 kPa for 10 s (ca. 10 nl). The CE-MS/MS method provided high resolution and proved to be highly selective and sensitive, its utility being demonstrated by the determination of γ-glutamyl di- and tripeptides in serum and liver samples.