·Inosine and internal standard in human plasma were quantitatively analyzed with electrospray ionization positive ion mode and multiple reaction monitoring scan analysis. The ion pairs used for quantitative analysis were m/z 269.1/137.1 (inosine) and m/z 230.2/112.2 (internal standard). The results of method validation included limit of quantification, accuracy, intra-day and inter-day precision, extraction recovery, and stability tests in different conditions.

·The results of method validation showed that the calibration curve of inosine in human plasma exhibited a good linearity (R²>0.999) over the range from 28.5 to 912.0 ng/mL, and quantitative lower limit was 28.5 ng/mL. Accuracy was 96.9%?103.8%, and the relative standard deviations of intra-day and inter-day precision were both less than 10%. The extraction recovery was between 98.9% and 102.3%. In stability tests (samples stored at room temperature for 4 h, 3 freeze-thaw cycles, -70 ℃ for 7 d and 4 ℃ in autosampler for 24 h), the rates of change of inosine in human plasma were less than 15%.

·The established SPE-HPLC-MS/MS method is simple, rapid, sensitive and accurate, and it is suitable for the clinical monitoring of inosine concentration in human plasma.