Use of tandem mass spectrometry (MS-MS) for aldosterone assay at the nanogram level in complex biological mixtures

Aldosterone in biological samples was measured comparatively by two methods: radioimmunoassay (RIA) and tandem mass spectrometry. The last method is described in this paper. Aldosterone was derivatized as butane boronate cyclic ester. This derivative gives an intense molecular ion under 70-eV electron impact conditions. This ion exhibits an abundant metastable decomposition in the second field free region by loss of formic acid, which can be used for the assay. A linear relationship was observed between the ionic current and the amount of aldosterone from 10 to 200 ng. A good correlation between this new method and the radioimmunological assay is observed. Aldosterone can be readily detected at the nanogram level.