Automated analysis of oseltamivir and oseltamivir carboxylate in environmental waters by online in-tube solid-phase microextraction coupled with liquid chromatography-tandem mass spectrometry

Abstract

We have developed a simple and sensitive method for the simultaneous determination of the antiviral drug oseltamivir (OS) and its metabolite oseltamivir carboxylate (OSC) in environmental waters by automated online in-tube solid-phase microextraction (SPME) coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS). OS and OSC were separated within 4 min using an ODS-3 column and 1% acetic acid (aq)/methanol (55/45, v/v) as the mobile phase at a flow rate of 0.2 mL min⁻¹. Electrospray ionization conditions in the positive ion mode were optimized for MS/MS detection of OS and OSC. The optimum in-tube SPME conditions were 25 draw/eject cycles of 40 μL of sample at a flow rate of 200 μL min⁻¹ using a CP-Pora PLOT amine capillary column as an extraction device. The extracted compounds were easily desorbed from the capillary by passage of the mobile phase, and no carryover was observed. Using the in-tube SPME LC-MS/MS method, we obtained good linearity of the calibration curve (r ≥ 0.9985) for each compound in the range of 1–500 pg mL⁻¹ using stable isotope-labeled internal standards. The detection limits (S/N = 3) for OS and OSC were 0.078 and 0.16 pg mL⁻¹, respectively. The within-day and between-day precisions (relative standard deviations) were below 7% and 13%, respectively. This method was successfully utilized to analyze OS and OSC in environmental water samples without any other pretreatment or interference peaks, and the recoveries of OS and OSC spiked into river water were each above 91%. OS and OSC were detected at concentrations of several hundred pg mL⁻¹ in these water samples, and their concentrations changed seasonally.