Direct quantitative determinations by multiple metastable peak monitoring. 1--Warfarin in plasma

A technique for the direct quantitative determination of plasma warfarin concentrations has been developed using multiple metastable peak monitoring on a double focusing mass spectrometer of normal geometry. The method uses a direct insertion probe and requires no sample purification or derivatization. Deuterated warfarin was added as an internal standard, and the first field free region metastable fragmentations for the loss of an acetyl radical from the molecular ion of both warfarin and internal standard were monitored. These independent daughter ions were focused by a simple combination of linking the magnetic and electric sectors, accelerating voltage switching and selected ion monitoring using standard instrumentation. Results were acquired and processed by normal selected ion monitoring software. Repeated determinations of plasma warfarin concentrations were made with plasma extracts representing approximately 4 microliter of plasma, each sample taking two minutes to process by this technique.