Effects of structural characteristics of (un)conjugated steroid metabolites in their collision cross section value

In this work, the collision cross section (CCS) value of 103 steroids (including unconjugated metabolites and phase II metabolites conjugated with sulfate and glucuronide groups) was determined by liquid chromatography coupled to traveling wave ion mobility spectrometry (LC-TWIMS). A time of flight (QTOF) mass analyzer was used to perform the analytes determination at high-resolution mass spectrometry. An electrospray ionization source (ESI) was used to generate [M+H](+), [M + NH4](+) and/or [M - H](-) ions. High reproducibility was observed for the CCS determination in both urine and standard solutions, obtaining RSD lower than 0.3% and 0.5% in all cases respectively. CCS determination in matrix was in accordance with the CCS measured in standards solution showing deviations below 2%. In general, CCS values were directly correlated with the ion mass and allowed differentiating between glucuronides, sulfates and free steroids although differences among steroids of the same group were less significant. However, more specific information was obtained for phase II metabolites observing differences in the CCS value of isomeric pairs concerning the conjugation position or the alpha/beta configuration, which could be useful in the structural elucidation of new steroid metabolites in the anti-doping field. Finally, the potential of IMS reducing interferences from the sample matrix was also tested for the analysis of a glucuronide metabolite of bolasterone (5 beta-androstan-7a,17a-dimethyl-3a,17 beta-diol-3-glucuronide) in urine samples.

Automated summary

The collision cross section (CCS) value of 103 steroids was determined by LC-TWIMS. High reproducibility was observed in urine and standard solutions. CCS determination in matrix was in accordance with the CCS measured in standards solution. CCS values were directly correlated with the ion mass and allowed differentiating between glucuronides, sulfates, and free steroids. Specific information was obtained for phase II metabolites, which could be useful in the structural elucidation of new steroid metabolites in the anti-doping field. The potential of IMS reducing interferences from the sample matrix was also tested.