Determination of cortisol in human saliva using liquid chromatography–electrospray tandem mass spectrometry

The aim of this work was to develop a method for determination of cortisol in saliva by liquid chromatography–tandem mass spectrometry (LC–MS–MS). Saliva was sampled on Salivette tubes. These were centrifuged, deuterium-labeled cortisol was added as internal standard and the proteins precipitated by acetonitrile. The supernatant was evaporated, dissolved in methanol acidified with acetic acid and analyzed by LC–MS–MS. The with-in run precision, tested by pooling saliva samples from volunteers and then analyzing these in a single run, was found to be 7% at 0.7 μg l−1. The between-run precision was tested by analysis of the same samples at different days and found to be 11% at 2.5 μg l−1. The limit of quantification was 0.5 μg l−1. The method was applied for analysis of saliva samples from three volunteers during their last week before vacation and the first and second week on vacation. In addition, the method was compared to analysis by an immunological method. The values from the immunological method were 2.7 times higher than the LC–MS–MS results.