Determination of aldosterone in serum by liquid chromatography–tandem mass spectrometry

Measurement of serum aldosterone is clinically important in the diagnosis of hypertension. While isotope dilution gas chromatography–mass spectrometry (ID-GC–MS) provides reliable results, it requires derivatization and is lengthy and time-consuming. Detection by liquid chromatography–mass spectrometry (LC–MS) is a potentially superior method. The analysis utilizes 0.5 mL of serum. The samples were extracted with dichloromethane–ether. The extract was evaporated to dryness and aldosterone was analyzed by LC–MS/MS operating in the negative mode ESI after separation on a reversed-phase column. Aldosterone was also measured by RIA. The calibration curves for analysis of serum aldosterone exhibited consistent linearity and reproducibility in the range of 60–3000 pmol/L. Interassay CVs were 4.3–7.5% at aldosterone concentrations of 97–993 pmol/L. The lower limit of quantitation (LOQ) was 30 pmol/L (signal to noise ratio = 10). The mean recovery of the analyte added to serum ranged from 95 to 102%. The regression equation by LC–MS/MS (x) and RIA (y) method was: y = 1.33x + 185 (r = 0.95; n = 124). Sensitivity and specificity of the LC–MS/MS method for serum aldosterone offer advantages over GC–MS by eliminating derivatization. The novel method is rapid, reliable and simple to perform with a routine LC–MS/MS spectrometer. The sensitivity is adequate for patient samples. Aldosterone concentrations reported by nonextraction RIA were consistently higher than those produced by LC–MS/MS.