Method to detect and sequence post translationally modified peptides

摘要

A method of detecting and sequencing post translationally modified peptides is disclosed wherein a negative ion precursor scan is performed. A negative ion high resolution MS scan is then performed and then MRM channels in positive ion mode are determined and monitored. A positive ion MS/MS scan is then performed.

主权项

1. A method of detecting post translationally modified peptides using mass spectrometry comprising:
providing a mass spectrometer comprising an ion source, a first mass filter or mass analyser, a collision, fragmentation or reaction device arranged downstream of said first mass filter or mass analyser and a second mass filter or mass analyser arranged downstream of said collision, fragmentation or reaction device; performing a relatively low resolution neutral loss or gain scan wherein a mass to charge ratio transmission window of said first mass filter or mass analyser is scanned whilst a mass to charge ratio transmission window of said second mass filter or mass analyser is scanned in synchronism with said first mass filter or mass analyser and monitoring for first fragment ions of interest having a first mass to charge ratio difference above a threshold; wherein when first fragment ions of interest are detected by reaching the threshold then said method further comprises: (i) performing a relatively high resolution MS scan wherein a mass to charge ratio transmission window of either said first mass filter or mass analyser or said second mass filter or mass analyser is scanned whilst the other mass filter or mass analyser is operated in a non-resolving mode of operation; (ii) determining at least a first Multiple Reaction Monitoring channel corresponding to ions having a first charge state, a second Multiple Reaction Monitoring channel corresponding to ions having a second charge state and a third Multiple Reaction Monitoring channel corresponding to ions having a third charge state; (iii) setting and monitoring at least said first, second and third Multiple Reaction Monitoring channels and determining which Multiple Reaction Monitoring channel results in a highest intensity of observed ions; (iv) determining a mass to charge ratio or charge state of parent ions which correspond with the Multiple Reaction Monitoring channel which resulted in the highest intensity of observed ions; and (v) performing a MS/MS scan wherein a mass to charge ratio transmission window of said first mass filter or mass analyser is set so as to correspond with a mass to charge ratio transmission window at which said first mass filter or mass analyser was set for the Multiple Reaction Monitoring channel which resulted in the highest intensity of observed ions, and wherein a mass to charge ratio transmission window of said second mass filter or mass analyser is scanned to detect post translationally modified peptides.