Design and Evaluation of an Automated Solid-Phase Extraction Method Development System for Use with Biological Fluids

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Abstract
An automated solid-phase extraction method development system, utilizing a Zymate XP robot and a custom-designed solid-phase extraction manifold, has been developed and validated. This system spikes blank liquid matrix, such as plasma, with solutions containing drug, internal standard, and up to three metabolites. Samples are then buffered or diluted with an appropriate reagent. After these samples and corresponding blanks have been prepared, solid-phase cartridges containing selected sorbents are automatically conditioned. Samples are robotically vortexed and transferred to the conditioned cartridges, and analytes are extracted. Validation of this robotic system demonstrated acceptable precision and accuracy for three types of liquid transfer, including metering pump (<6% RSD and RE for ≥2.0 mL dispensation), syringe-based laboratory station (≤2.9% RSD and 0.5% RE for volumes between 0.25 and 1.00 mL), and syringe hands (<3.5% RSD and RE for volumes between 0.10 and 1.00 mL). For two example compounds, the system provided data which effectively distinguished good solid-phase sorbents from marginal ones through precision, recovery, and chromatographic selectivity. Solid-phase extraction of these compounds from human plasma gave precision (2−10% RSD) and extraction efficiency (96 ± 6%) comparable to results obtained from manual extractions (92 ± 11%).