Experience in the use of a 4‐sector instrument and array detector and its application in peptide analysis

A 4‐sector EBEB mass spectrometer, fitted with a liquid secondary‐ion mass spectrometer (Cs + ) ion source and an array detector has been in use at UCSF for the past 18 months. Using this period, calibration procedures have been developed and operating software refined such that the instrument can now be operated in the tandem mass spectrometry (MS/MS) mode using the array on a routine basis and with a high sample throughput. The instrument has been applied successfully to the analysis of a wide range of peptides, up to molecular weights in excess of 2500. The array is usually operated with a mass resolution of about 1500 full width at half maximum (FWHM), and under these conditions a fragment ion dynamic range of 3000:1 is obtainable. Mass assignment is typically reproducible to within 0.1 u.