Development of an ultra fast online-solid phase extraction (SPE) liquid chromatography electrospray tandem mass spectrometry (LC-ESI-MS/MS) based approach for the determination of drugs in pharmacokinetic studies.

High-throughput analyses of a large number of samples for pharmacokinetic (PK) studies are essential in drug development. Analysis of drug candidates from blood using LC-ESI-MS generally requires separation of the plasma fraction followed by various offline sample preparation procedures. This step is a bottleneck that impedes throughput. In order to overcome this difficulty and accelerate analysis in PK and other studies, we developed an approach allowing the direct analysis of low volumes of whole blood (10 μL) after dilution and centrifugation. Samples were injected in an online-SPE-LC-ESI-MS/MS setup allowing a total run time of only 126 s for a full gradient separation. Analytes were extracted from the matrix within 30 s by turbulent flow chromatography. Subsequently, a full gradient separation was carried out within 1.5 minutes on a 50 × 2.1 mm (1.7 μm) RP-18 column and the analytes were sensitively detected by ESI-MS/MS in SRM mode. The performance of this new ultra fast online SPE-LC-ESI-MS/MS approach was demonstrated by the analysis of diclofenac (DCF), a widely used anti-inflammatory drug. DCF eluted at stable retention times (±0.33%) with narrow peak width (FWHM 3.3 ± 0.15 s). The method displays excellent analytical performance, with a limit of detection of 6 fmol on column, a linear range of over four orders of magnitude and a negligible carry over of 0.12 ± 0.03% for DCF. The PK profile of DCF administered by topical and intraperitoneal routes in rats and by oral route in one human volunteer is investigated using this method. Finally, general applicability of the approach for drugs is demonstrated by analysis of rofecoxib and several inhibitors of the soluble epoxide hydrolase. This new method requires only readily available, off the shelf standard LC instrumentation, and is compliant with the requirements of green analytical chemistry.