The extraction and subsequent liquid chromatographic analysis of human plasma samples for cortisol is described. Extraction and chromatography are optimized, resulting in a recovery for cortisol of 96% and a detection limit of 1 microgram cortisol in 100 ml plasma. The application of two chemically modified silicas has been evaluated. The specificity of the method was tested by field desorption - mass spectrometry experiments.
van den Berg, J. H. M., Mol, C. R., Deelder, R. S., & Thijssen, J. H. H. (1977). A quantitative assay of cortisol in human plasma by high performance liquid chromatography using a selective chemically bonded stationary phase. Clinica Chimica Acta, 78, 165-172. https://doi.org/10.1016/0009-8981(77)90303-5