Automated in-tube solid-phase microextraction-liquid chromatography-electrospray ionization mass spectrometry for the determination of ranitidine

The technique of automated in-tube solid-phase microextraction (SPME) coupl ed with liquid chromatography-electrospray ionization mass spectrometry (LC -ESI-MS) was evaluated for the determination of ranitidine. In-tube SPME is an extraction technique for organic compounds in aqueous samples, in which analytes are extracted from the sample directly into an open tubular capil lary column by repeated aspirate/dispense steps. In order to optimize the e xtraction of ranitidine, several in-tube SPME parameters such as capillary column stationary phase, extraction pH and number and volume of aspirate/di spense steps were investigated. The optimum extraction conditions for ranit idine from aqueous samples were 10 aspirate/dispense steps of 30 mu l of sa mple in 25 mM Tris-HCl (pH 8.5) with an Omegawax 250 capillary column (60 c mx0.25 mm LD., 0.25 mu m film thickness). The ranitidine extracted on the c apillary column was easily desorbed with methanol, and then transported to the Supelcosil LC-CN column with the mobile phase methanol-2-propanol-5 M a mmonium acetate (50:50:1). The ranitidine eluted from the column was determ ined by ESI-MS in selected ion monitoring mode. In-tube SPME followed by LC -ESI-MS was performed automatically using the HP 1100 autosampler. Each ana lysis required 16 min, and carryover of ranitidine in this system was below 1%. The calibration curve of ranitidine in the range of 5-1000 ng/ml was l inear with a correlation coefficient of 0.9997 (n=24), and a detection limi t at a signal-to-noise ratio of three was ca. 1.4 ng/ml. The within-day and between-day variations in ranitidime analysis were 2.5 and 6.2% (n=5), res pectively. This method was also applied for the analyses of tablet and urin e samples. (C) 1999 Elsevier Science B.V. All rights reserved.