Dual metastable peak monitoring: application to the analysis of oestradiol-17 beta as the bis (tert-butyldimethylsilyl) ether.

A new approach to dual metastable peak monitoring has been developed, based on synchronous switching of the accelerating voltage and electric sector voltage of a double-focusing mass spectrometer. The technique has been applied to the determination of oestradiol-17beta as the bis(tert-butyldimethylsilyl) ether, using the 2H3 analogue as internal standard. The detection limit was approximately 5 pg during monitoring of the [M]+ X----[M-C4H9]+ fragmentation. Analyses of plasma extracts indicated that greater selectivity of detection was achieved during metastable peak monitoring than during high resolution (8000) selected ion monitoring of the parent ion.