Rapid screening of anabolic steroids in horse urine with ultra-high-performance liquid chromatography/tandem mass spectrometry after chemical derivatisation

Abstract

Liquid chromatography/mass spectrometry (LC/MS) has been successfully applied to the detection of anabolic steroids in biological samples. However, the sensitive detection of saturated hydroxysteroids, such as androstanediols, by electrospray ionisation (ESI) is difficult because of their poor ability to ionise. In view of this, chemical derivatisation has been used to enhance the detection sensitivity of hydroxysteroids by LC/MS. This paper describes the development of a sensitive ultra-high-performance liquid chromatography/tandem mass spectrometry (UHPLC/MS/MS) method for the screening of anabolic steroids in horse urine by incorporating a chemical derivatisation step, using picolinic acid as the derivatisation reagent. The method involved solid-phase extraction (SPE) of both free and conjugated anabolic steroids in horse urine using a polymer-based SPE cartridge (Abs Elut Nexus). The conjugated steroids in the eluate were hydrolysed by methanolysis and the resulting extract was further cleaned up by liquid-liquid extraction. The resulting free steroids in the extract were derivatised with picolinic acid to form the corresponding picolinoyl esters and analysed by UHPLC/MS/MS in the positive ESI mode with selected-reaction-monitoring. Separation of the targeted steroids was performed on a C18 UHPLC column. The instrument turnaround time was 10.5min inclusive of post-run equilibration. A total of thirty-three anabolic steroids (including 17β-estradiol, 5(10)-estrene-3β,17α-diol, 5α-estrane-3β,17α-diol, 17α-ethyl-5α-estran-3α,17β-diol, 17α-methyl-5α-androstan-3,17β-diols, androstanediols, nandrolone and testosterone) spiked in negative horse urine at the QC levels (ranging from 0.75 to 30ng/mL) could be consistently detected. The intra-day and inter-day precisions (% RSD) for the peak area ratios were around 7–51% and around 1–72%, respectively. The intra-day and inter-day precisions (% RSD) for the relative retention times were both less than 1% for all analytes, except the inter-day precision for boldione at 1.2%. The extraction recoveries for all targets were not less than 48%. With exceptional separation achieved by the UHPLC system, matrix interferences were minimal at the expected retention times of the selected transitions. As detection was performed with an UHPLC system coupled to a fast-scanning triple quadrupole mass spectrometer, the method could easily be expanded to accommodate additional steroid targets. This method has been validated for recovery and precision, and could be used regularly for doping control testing of anabolic steroids in horse urine samples.