Online solid-phase extraction liquid chromatography–mass spectrometry of hair cortisol using a surrogate analyte

Online SPE LC–MS with 13C3-cortisol as a surrogate analyte was developed, validated and applied for obtaining hair cortisol levels of 114 healthy volunteers. The first 3 cm from a posterior vertex position were analyzed as three individual segments resulting in 310 hair cortisol levels, which were used, after log transformation, to predict a range of values observed in future. The median value of hair cortisol was 4.76 pg/mg. The employed method allowed simple processing, high throughput and may be readily expanded to analyze additional steroid compounds in hair.