A simplified method for the determination of total homocysteine in plasma by electrospray tandem mass spectrometry.

Hyperhomocysteinemia is a risk factor for different diseases. Several methods have been developed to analyze homocysteine and the immunometric ones, although expensive, they are in widespread use. A rapid LC-MS/MS method for homocysteine assay has been developed for the application of large clinical chemistry routines. Selected reaction monitoring was performed through the transitions m/z 136.0→90.1 for homocysteine and m/z 140.0→94.0 for the internal standard. ESI was used to generate [H+] adduct ions. Chromatographic isocratic separation was achieved using a strong cation exchange column. The mobile phase was methanol/water (20:80  v/v, containing 0.1% formic acid and 1.5  mmol/L ammonium formate in the water phase) at a flow rate of 0.250  mL/min (35°C). Samples treatment consisted in the reduction with DTT and deproteinization with methanol. Recovery, linearity, LOD, LOQ and total imprecision were evaluated to validate the method. Homocysteine values on 100 serum samples were compared with those obtained by HPLC and immunometric methods. The method is robust, selective and precise in the whole range of values studied. Moreover, low reagent cost and easiness of sample treatment make this method useful, not only for research, but also for routine work.