Optimized verification method for detection of an albumin-sulfur mustard adduct at Cys34 using a hybrid quadrupole time-of-flight tandem mass spectrometer after direct plasma proteolysis

- Sulfur mustard is a banned chemical warfare agent alkylating serum albumin.
- Direct plasma proteolysis with pronase yielded HETE-CP as biomarker for SM-exposure.
- A high resolving hybrid mass spectrometer provided excellent selectivity and sensitivity.
- The novel procedure proved applicability to real samples of poisoning.

The vesicant sulfur mustard (SM) is a banned chemical warfare agent that is controlled by the Organisation for the Prohibition of Chemical Weapons (OPCW). Bioanalytical procedures are mandatory for proving an alleged use and incorporation of SM into the body. We herein present the development and application of a novel optimized procedure suitable for qualitative verification analysis of plasma targeting the SM-adduct of human serum albumin (HSA) alkylated at the cysteine34 residue. Diluted human plasma is directly mixed with pronase in an ultrafiltration device (10 kDa cut-off) for proteolysis (4 h, 37 °C). Following ultrafiltration the filtrate is diluted and analyzed by microbore liquid chromatography-electrospray ionization high resolution tandem-mass spectrometry (μLC-ESI HR MS/MS) targeting the alkylated dipeptide hydroxyethylthioethyl-CysPro (HETE-CP). A hybrid quadrupole time-of-flight mass spectrometer provided high mass spectrometric resolution in the MS/MS mode enabling highest selectivity and sensitivity (lower limit of detection corresponding to 9.8 nM SM in plasma). Kinetics of HETE-CP formation from heparin-, citrate-, and EDTA-plasma as well as serum are presented and the influence of different EDTA and pronase concentrations was characterized. The novel procedure was applied to plasma samples provided by the OPCW as well as to patientś plasma derived from real cases of SM-poisoning.