Determination of myo-inositol in biological samples by liquid chromatography–mass spectrometry

Due to the absence of HPLC methods to determine myo-inositol using mass detection and considering its sensitivity and selectivity, a high performance liquid chromatography-mass spectrometry method for the analysis of myo-inositol is described and applied to its direct determination in urine and saliva samples. Successful resolution of myo-inositol and its related substances was achieved with a stationary phase Aminex HPX-87C Column with milli-Q water as mobile phase and 5 mM ammonium acetate added post-column. The detector counted positive ions by monitoring m/z=198, which corresponds to the myo-inositol adduct with ammonium cation. Urine and saliva samples were previously purified by passing through an anion-exchange resin. Concentrations as low as 138 and 461 μg/l in saliva and urine could be respectively quantified. Intra-day R.S.D. ranged from 0.83 to 1.02%, whereas inter-day R.S.D. was between 1.54 and 3.58%.