Introduction
The need for unambiguous data to support milestone transition and compound selection for drug discovery and development has fueled an unrelenting desire for instruments with higher sensitivity. Consequently sensitivity enhancement has been a critical attribute in each evolution of modern LC-MS instrumentation.
To address this need, Waters has focused on integrating and optimizing both the inlet and the MS detector. The ionKey/MS System integrates the separation into the source of the Xevo® G2-XS Mass Spectrometer, yielding a single integrated platform. The iKey™ is a microfluidic separation device that combines a traditional column, column oven, and electrospray emitter into one, and is integrated into the source of the mass spectrometer.To address this need, Waters has focused on integrating and optimizing both the inlet and the MS detector. The ionKey/MS System integrates the separation into the source of the Xevo® G2-XS Mass Spectrometer, yielding a single integrated platform. The iKey™ is a microfluidic separation device that combines a traditional column, column oven, and electrospray emitter into one, and is integrated into the source of the mass spectrometer. Through enhanced ionization efficiency and reduced matrix interference, ionKey/MS produces signal enhancements for small molecule analysis, compared to analytical scale LC. The Xevo G2-XS Q-Tof™ delivers enhanced mass resolution and sensitivity compared to its predecessor. This enhanced sensitivity is realized through a collision cell design that improves ion focusing and reduces losses in ion transfer through the cell. In addition to new hardware, innovative software and acquisition methods were also introduced to enable simple Tof-MRM modes of operation targeted for routine bioanalytical work.Here, a variety of drugs in human plasma were analyzed using several configurations of the ionKey/MS System with the Xevo G2-XS Q-Tof. In the first series of experiments, the linearity and limits of quantitation (LOQ) were determined using direct injection and under Tof-MRM mode of operation. In the second set of experiments, a trap valve manager was configured to load samples onto the trap column for initial injection and wash, before being switched into the LC stream for compound elution, thus significantly increasing the injectable sample volume. Trapping using either single pump or dual pump configuration is described. The advantages of using trap-and-elute for optimum peak shape and higher sample volume is discussed.
Sample description
Human plasma was prepared by protein precipitation with the addition of acetonitrile (ACN) using a volume ratio of 3:1. The solution was centrifuged at 13000 relative centrifugal force (RCF) and the supernatant was transferred to a new vial and further diluted 1:4 with water. The final %ACN in sample was approximately 19%. Test compounds (propranolol, verapamil, buspirone, and clopidogrel) were combined in a 100 ng/mL solution in diluted human plasma as previously described. The mixture was then serially diluted using diluted human plasma from a range of 100 ng/mL to <1 pg/mL.
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