Determination of cortisol in human plasma by capillary gas chromatography-mass spectrometry using [2H5] cortisol as an internal standard

A capillary gas chromatographic-mass spectrometric method for the determination of cortisol in human plasma using cortisol M + 5 as an internal standard is described. For calculation of plasma cortisol, peak areas were measured by selected-ion monitoring of the characteristic fragment ions of the dimethoxime-tri (trimethylsilyl) derivatives of cortisol and cortisol M + 5 (m/z 605 and 610, respectively). The inter- and intra-assay coefficients of variation for plasma sample were 3.07 and 1.77%, respectively. The method needed no complex corrections for contributions and provides a sensitive and reliable technique with good accuracy, precision and reproducibility.