Determination of meropenem in endotracheal tubes by in-tube solid phase microextraction coupled to capillary liquid chromatography with diode array detection

Meropenem is a widely used antimicrobial for the treatment of infections associated with the use of invasive medical devices in intensive care unit patients. These treatments are not always effective, in fact, in-vitro studies have demonstrated the difficulty of antimicrobials to penetrate into the biofilm, however in-vivo studies of the effect of these compounds is a trend, mostly because of the complexity of pulmonary samples extracted from ETTs. Therefore, the objective of this study was to evaluate in-tube solid phase microextraction (in-tube SPME) coupled to capillary liquid chromatography (CapLC) with DAD to determine meropenem in ETTs in order to estimate the penetration capability into the biofilm. Firstly, different parameter affecting in-tube SPME, such as processed sample volume, capillary length, flow and capillary coating were studied. The best analytical response was achieved by processing 500 μL of standards/samples at 9 μL/seg with a 60-cm capillary column coated with 35%-diphenyl 65%-polydimethylsiloxane. Under these conditions, the analytical performance of in-tube SPME-CapLC-DAD, using acetonitrile-water in gradient mode as mobile phase, showed satisfactory results for estimation of meropenem in terms of sensitivity (LOD = 3 μg/L) and precision (RSD < 10%). Once the experimental conditions were stablished for in-tube SPME, the extraction of meropenem from the ETTs was studied. Liquid extraction, vortex-assisted liquid extraction (VALE) and ultrasound-extraction (UAE) extraction were tested. The results indicated that meropenem could be quantitatively extracted (91 ± 6%) from ETTs, for its subsequent determination by in-tube SPME-CapLC-DAD using water as extraction solvent and 1 min as extraction time. Finally, samples from ETTs used for critically ill patients with different antimicrobial treatments were analysed with successful results.