Challenges for Detecting Valproic Acid in a Nontargeted Urine Drug Screening Method
Valproic acid (VPA) is a widely prescribed medicine, and acute toxicity is possible. As such, it should be included in any nontargeted urine drug screening method. In many published liquid chromatography–electrospray ionization–mass spectrometry (LC–ESI–MS/MS) methods, VPA is usually measured using a pseudo-multiple reaction monitoring (MRM) transition. We investigate a simple ultra-high-performance liquid chromatography–quadrupole time-of-flight (QTof) approach to detect the presence of VPA with more confidence.Methods:
Three commercially sourced VPA metabolites were characterized and added to a nontargeted high-resolution MS urine drug screening method. All analyses were performed on a Waters Xevo G2-XS LC-QTof in negative electrospray ionization mode. The mass detector was operated in MSE mode, and data were processed with UNIFI software. Sixty-eight patient urine samples, which were previously identified by a well-established gas chromatography–MS method as containing VPA, were analyzed on the Waters Xevo G2-XS LC-QTof, to validate this approach.Results:
VPA metabolite standards were characterized, and their detection data were added to the broad drug screening library. VPA metabolites were readily detectable in the urine of patients taking VPA.Conclusions:
The inclusion of characterized VPA metabolites provides a simple and reliable method enabling the detection of VPA in nontargeted urine drug screening.