IMPLEMENTATION OF LIQUID SECONDARY ION MASS-SPECTROMETRY ON QUADRUPOLE MASS SPECTROMETERS - STRATEGY, OPTIMIZATION, AND EVALUATION

A detailed strategy for adding liquid secondary ion mass spectrometry (L-SIMS, similar to fast atom bombardment (FAB)) capability to a quadrupole mass spectrometer equipped with only electron ionization (EI) and chemical ionization (CI) sources is delineated. The complexity of modifications is held to a level whereby any moderately equipped machine shop could complete the work. The manufacturing of specific items to enable the reversible conversion of a Hewlett-Packard HP5985A EI/CI gas chromatography-mass spectrometry instrument to perform L-SIMS was kept to a minimum. The essential fabricated items consist of a source block, a lens assembly, and a sample probe. The rationale behind the construction, and the optimization of the size and placement of each part are described in detail. The new capabilities for L-SIMS experiments are demonstrated for selected biomolecules. Sensitivity evaluations demonstrate that protonated molecules of N6-methyladenosine can be readily detected from as little as two picomoles of analyte.