Simultaneous determination of six analgesics in human plasma using solid-phase extraction and liquid chromatography

Abstract

An analytical method for the simultaneous determination of paracetamol, salicylic acid, metamizol, tramadol, ibuprofen and diclofenac in plasma, using High Performance Liquid Chromatography with a photodiode array detector (HPLC-PDA) was developed. A solid-phase extraction (SPE) using Oasis HLB® cartridges was applied. After conditioning the cartridges with ethyl acetate, methanol and phosphate buffer pH 4, and introducing the plasma sample, the analytes were eluted with ethyl acetate. Then, the eluate was evaporated to dryness, reconstituted in mobile phase, and 30 μL were injected into the chromatograph. The chromatographic separation was performed on an XBridgeTM Shield RP18 column (250x4.6 mm id, 5 μm particle size), and the elution was carried out with a mobile phase consisting of acetonitrile, 5mM phosphate buffer pH 6 and Milli-Q water, at a flow of 1 mL/min, in gradient mode. The response of the detector was linear within the concentration range of 0.1-20 μg/mL in human plasma, with coefficients of correlation higher than 0.997. The limits of detection ranged from 7.3 to 30.1 ng/mL. The coefficients of variation were less than 8%, and the recoveries oscillated between 90.1% for diclofenac and 100.2% for salicylic acid. Finally, the method was applied to 16 plasma samples from subjects poisoned with one o more analgesics.