Column Screening and Development of HILIC and RPLC Methods Coupled to Tandem Mass Spectrometry for the Monitoring of Albumin on Cysteine 34 Exposed to Mustard Agents

Adduction on protein nucleophile sites by mustard agents can be monitored to assess detection of retrospective exposure to these agents. Cysteine 34 (Cys34) on human serum albumin was selected as the target of choice. This work targets di- and tripeptides adducted on Cys34 by sulfur mustard, sesquimustard, and nitrogen mustards separated in hydrophilic liquid chromatography (HILIC) and Reversed-Phase (RP) mode. The effect of several mobile phase additives on the mass spectrometry (MS) and MS/MS signal and on LC retention profile was studied. A mix of ammonium acetate and acetic acid offered satisfactory results in terms of MS sensitivity. Screening of HILIC columns was performed, and ZIC-HILIC stationary phase was selected for HILIC mode, and C₁₈ stationary phase was used for RP analysis. Negative ionization mode leads to a higher S/N ratio compared to positive ionization mode. Adducted tripeptides were selected for the monitoring of mustard agents' exposure, allowing better sensitivity than their dipeptide homologues. The two developed chromatographic methods have similar sensitivities with LOQs ranging from 1.9 to 20.5 ng/mL for the reversed-phase liquid chromatography (RPLC)-ESI-(-)-MS/MS method and from 1.7 to 43.3 ng/mL for the HILIC-ESI-(-)-MS/MS method. The monitoring method should be selected based on the targeted mustard agent, and the remaining method can be a confirmation tool.