A new strategy for MALDI on magnetic sector mass spectrometers with point detectors

We have developed a new strategy to perform matrix-assisted laser desorption/ionization (MALDI) on magnetic sector instruments equipped with nonintegrating point detectors. This approach is based on using liquid matrices to provide very long-lasting analyte ion currents and to overcome the inability of these instruments to simultaneously detect ions over a range of mass-to-charge values. Here, we demonstrate some of the capabilities of MALDI on a magnetic sector for analyzing biological samples. These capabilities include the ability to perform MS/MS experiments, to attain resolutions over 8000 (full width at half-maximum), and to determine relative molecular masses with < 20 ppm error for a single measurement and < 2 ppm error for the average of five measurements. All three of these experiments can be performed on the same 10 pmol sample loading. We also compare the results of MALDI on a magnetic sector instrument with point detection with the reported capabilities of MALDI on time-of-flight-based mass analyzers and with fast atom bombardment on sector-based instruments. This work demonstrates that researchers with magnetic sector-based instruments can perform MALDI experiments with a relatively simple and inexpensive upgrade to their existing equipment.