A method for measure the plasma concentration of ibuprofen and pseudoephedrine was established by liquid chromatography-tandem mass spectrometr pseuy (LCMS-MS). The chromatography column is Alltima C18 column (50min×2. 1mm×3μm).The mobile phase consisted of methonal-5 and acetate ammonium. The flow rate is 0.2mL/min. Detection was performed using electrospray ionization (ESI) interface in multiple reactions monitoring (MRM) mode. The assay procedure was shown to produce linear calibration curves over the range 250 to 50000μg/L of ibuprofen,2.5 to 500μg/L of pseudoephedrine in plasma. The limit of detection is 250μg/L of ibuprofen, 2.5μg/L for pseudoephedrine. The extraction recovery of ibuprofen and pseudoephedrine was 50% and 18%, respectively. The linearity of standard curves is in the range of 0. 990-1. 000. Inter- and intra-day precision (RSD%) is all within ±15 % (n = 5) and the accuracy is within 99.3%-103.2% (n=30). The method is sufficiently sensitive, specific, accurate, precise, stable, and fast. Key words: high performance liquid chromatography-tandem mass spectrometry(HPLC-MS/MS); multiple reactions monitoring (MRM); electrospray ionization (ESI).
