The application of multiple analyte adduct formation in the LC-MS3 analysis of valproic acid in human serum.

LC-MS using electrospray ionisation (negative ion mode) and low-energy collision-induced dissociation tandem mass spectrometric (CID-MS/MS) analysis, together with the multiple analyte adduct formation with the components of the mobile phase, were applied to analyse valproic acid in human serum with LC-MS3. The CID-fragmentation of the precursor analyte adduct [M+2CH3COONa-H]- was applied in the method validation (307.1/225.1/143.0). Chromatographic separation was performed with a Luna 5μm C18 (2) 100A, 150mm×2mm column and the elution with a mobile phase consisting of A (H2O/methanol=95/5, v/v) and B (H2O/methanol=3/97, v/v), both with 10mM ammonium acetate and 0.1% acetic acid. A binary flow pumping mode with a total flow rate of 0.400mL/min was used. The calculated limit of detection/quantification of the method calibrated in the range of 10-200μg/mL was 0.31/1.0μg/mL. The sample preparation based on protein precipitation with 1mL of H2O/methanol solution (3/97, v/v) with 10mM sodium acetate and 100mM acetic acid. On the basis of the experiments performed could be demonstrated, that multiple analyte adduct formation can be applied to generate MS3 quantitation of analytes with problematic fragmentation. The presented new strategy makes the analysis of small drugs, which do not produce any stable product ions at all, on the basis of LC-MS3 possible.