A Four-Column Parallel Chromatography System for Isocratic or Gradient LC/MS Analyses

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Abstract
A novel approach to parallel liquid chromatography/tandem mass spectrometry (LC/MS/MS) analyses for pharmacokinetic assays and for similar quantitative applications is presented. Modest modifications render a conventional LC/MS system capable of analyzing samples in parallel. These modifications involve the simple incorporation of three valves and four LC columns into a conventional system composed of one binary LC pumping system, one autosampler, and one mass spectrometer. An increase in sample throughput is achieved by staggering injections onto the four columns, allowing the mass spectrometer to continuously analyze the chromatographic window of interest. Using this approach, the optimized run time is slightly greater than the sum of the widths of the desired peaks. This parallel chromatography unit can operate under both gradient and isocratic LC conditions. To demonstrate the utility of the system, atorvastatin, five of its metabolites, and their deuterated internal standards (IS) were analyzed using gradient elution chromatography conditions. The results from a prestudy assay evaluation (PSAE) tray of standards and quality control (QC) samples from extracted spiked human plasma are presented. The relative standard deviation and the accuracy of the QC samples did not exceed 8.1% and 9.6%, respectively, which is well within the acceptance criteria of the pharmaceutical industry. For this particular analysis, the parallel chromatography system decreased the overall run time from 4.5 to 1.65 min and, therefore, increased the overall throughput by a factor of 2.7 in comparison to a conventional LC/MS/MS analytical method.