Determination of serum cortisol by thermospray liquid chromatography/mass spectrometry: Comparison with gas chromatography/mass spectrometry

The determination of serum cortisol by thermospray liquid chromatography/mass spectrometry (LC/MS) has been assessed. The method incorporates stable isotope dilution and innumoadsorption extraction. [M + H] + ions are monitored during LC/MS. The within‐assay reproducibility is satisfactory (coefficient of variation 7% at a concentration of 190 ng ml −1 ), though inferior to that achieved with the (more lengthy) procedure of gas chromatography/mass spectrometry (GC/MS). Satisfactory agreement between LC/MS ( y ) and GC/MS ( x ) data was observed ( y = 0.934 x + 12.4 ng ml −1 ; r = 0.968; n = 14). It is concluded that the generation of precise reference data for the assessment of routine cortisol assays is at present better achieved by GC/MS. LC/MS, however, provides satisfactory quantitative data via a more simple and rapid method.