Ultrasound-enhanced enzymatic hydrolysis of conjugated female steroids as pretreatment for their analysis by LC–MS/MS in urine

Abstract

A fast, selective and sensitive method is here proposed for the analysis of female steroid hormones as conjugated forms (mainly, glucuronides and sulfates). The method has been applied to female urine samples to assess the metabolism of these compounds. The method implements an enzymatic hydrolysis (β-glucuronidase with sulfatase activity) kinetically enhanced by ultrasonic energy in order to generate the free steroid forms. This enables a drastic shortening of the time required for this step as compared with conventional protocols (from 12–18 hours to 30 min). The reaction kinetics of the ultrasound-enhanced hydrolysis was characterized by comparison to that of the conventional protocol. After hydrolysis, the free steroid hormones were isolated and preconcentrated by automated solid-phase extraction and the eluate was subsequently analysed by liquid chromatography–tandem mass spectrometry (LC–MS/MS). The target analytes were confirmed and quantified by multiple reaction monitoring (MRM). The detection and quantification limits were within 0.06–0.8 ng mL⁻¹ and 0.19–2.69 ng mL⁻¹, respectively. The precision of the method, expressed as intra-day and inter-day variability, ranged between 2.1 and 5.2% and between 4.9 and 8.0%, respectively. A complementary study was carried out to assess the storage conditions of urine samples. This study is crucial in those applications involving metabolic processes as the integrity of the sample has to be preserved.