Thin-film octadecyl-silica glass coating for automated 96-blade solid-phase microextraction coupled with liquid chromatography–tandem mass spectrometry for analysis of benzodiazepines

A thin-film octadecyl (C18)-silica glass coating was developed as the extraction phase for an automated 96-blade solid-phase microextraction (SPME) system coupled with liquid chromatography–tandem mass spectrometry (LC–MS/MS). Various factors (e.g., sol–gel composition and aging time, coating preparation speed, coating thickness, and drying conditions) affecting the quality of C18-silica glass thin-film coating were studied and optimized. The results showed that the stability and durability of the coating are functions of the coating thickness and drying conditions. Coating thickness is controlled by sol–gel composition, aging time and the withdrawal speed in the dipping method. Automated sample preparation was achieved using a robotic autosampler that enabled simultaneous preparation of 96 samples in a 96-well plate format. Under the optimum SPME conditions the proposed system requires a total of 140 min for preparation of all 96 samples (i.e., 30 min preconditioning, 40 min equilibrium extraction, 40 min desorption and 30 min carry over step). The performance of the C18-silica glass 96-blade SPME system was evaluated for high-throughput analysis of benzodiazepines from phosphate-buffered saline solution (PBS) and human plasma, and the reusability, repeatability, and validity of the system were evaluated. When analysing spiked PBS and human plasma, the inter-blade reproducibility for four benzodiazepines was obtained in the ranges of 4–8% and 9–11% RSD (relative standard deviation), respectively, and intra-blade reproducibility were in the ranges of 3–9% and 8–13% RSD, respectively. The limits of detection and quantitation for plasma analysis were in the ranges of 0.4–0.7 ng/mL and 1.5–2.5 ng/mL for all four analytes.