Dual metastable peak monitoring: Application to the analysis of oestradiol-17β 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‐17β 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]+.→[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.