Effects of flow rate on high-throughput quantitative analysis of protein-precipitated plasma using liquid chromatography/tandem mass spectrometry

The effects of flow rate and column length on analyte response (peak area and height), total cycle time, column backpressure, and elution volume are presented. Rapid chromatographic separations and tandem mass spectrometric (MS/MS) detection are applied to the supernatant of protein-precipitated plasma standards containing four compounds from a drug discovery screen. The plasma samples were injected onto three C-18 columns (2 x 10,2.1 x 30 and 2.1 x 50 mm) at flow rates of 0.25, 0.50, 1.00 and 1.50 mL/min. The plasma samples were detected using a Sciex API 3000 tandem mass spectrometer operated in the Turbo Ionspray mode. A post-column split was used to maintain a flow rate of 0.25 mL/min into the mass spectrometer source to avoid differences in nebulization efficiency. The data show that diluted protein-precipitated plasma supernatants show average matrix effects (i.e. suppression) of 60.0% (2 x 10 mm), 89.3% (2 x 30 mm), and 76.7% (2 x 50 mm) of expected response at 10 ng/mL. Average matrix effects of 70.2% (2 x 10 mm), 88.9% (2 x 30 mm), and 81.2% (2 x 50 mm) of expected response at 1000 ng/mL plasma. The data also show if peak widths remain relatively constant, analytes are less sensitive as flow rates are increased. These data are consistent with the concentration-dependent relationship of ionspray in the range of flow rates studied. The data show that, while analyte response decreased proportionately to increases in flow rate, the analysis cycle times did not decrease proportionately.