A New Pulsed FAB Control System Coupled with an Array Detector on a Four-Sector Tandem Mass Spectrometer

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A pulsed FAB has been proposed to be a powerful technique for dramatic enhancement in sensitivity and increase in sample lifetimes. Here we developed a new pulsed FAB control system coupled with a photodiode-based array detector on a four-sector tenden mass spectrometer.The trigger pulse initially generated from the array detector control system is transmitted to the data acquisition processor via an optical fiber line, and them, to a function generator. The function generator is designed to provide a set of pulses of various repetitive frequencies and duty cycles. A high voltage power supply combined with the function generator allows a primary ion beam to be accelerated at up to a 6-kV potential with a quick rising and falling time less than 1 millisecond. The pulsing of primary ion beam is synchronized with start-up of the data acquisition on the array detector.When the system was tested on the second MS using a pulsed Xe atom beam, the protonated molecular ion peaks of peptides were obtained with 10 times higher intensity than those by a continuous FAB in the initial ionization event. The detection limits for angiotensin I (m/z 1296.7) and substance P (1347.7) were about 10 femtomoles. This new pulsed FAB control system was further demonstrated to be effective for reducing sample amounts required for MS/MS sequencing of peptides to the subfemtomole order.