Poly(N-vinylcarbazole-co-divinylbenzene) monolith microextraction coupled to liquid chromatography–high resolution Orbitrap mass spectrometry to analyse benzodiazepines in beer and urine

A poly( N -vinylcarbazole- co -divinylbenzene) (NVC/DVB) monolithic column was successfully prepared in a silanized capillary for microextraction of six benzodiazepines (BZPs) in complex samples. The polymerization was optimized primarily by changing the ratio of porogen content. The optimized polymer monolith had a homogeneous and continuous column bed, good permeability and mechanical stability. Poly(NVC/DVB) had good affinity to BZPs because of its through-pore structure and strong π-π stacking interactions derived from the rich benzene functional groups in the polymer. Potential factors that affect the extraction efficiency were studied in detail. In the optimized method, 3   mL of sample (pH 2) was extracted with the polymer monolithic column and eluted with 80   μL of methanol, and the eluent was analysed with ultra-high-performance liquid chromatography and quadrupole high resolution Orbitrap mass spectrometry (UHPLC/Q-Orbitrap MS). Under these conditions, the developed method gave the linear range of 0.005–0.5   ng/mL for most of the six BZPs, whereas 0.05–0.5   ng/mL for nitrazepam, 0.01–0.5   ng/mL for lorazepam, respectively, with coefficients of determination (R 2 )   ≥   0.9991. The detection limits (LODs) were 1.08–6.04   ng/L, and the quantification limits (LOQs) were 3.60–20.1   ng/L. The method repeatability was investigated in terms of intra- and inter-day precision, which were indicated by relative standard deviations (RSDs) of ≤8.3% and ≤9.9%, respectively. Finally, the proposed method was successfully applied to detect BZPs in beer and human urine samples. The percentages of extraction recovery were 80.4–94.2% for beer and 79.6–95.2% for urine.