Enhancement of ion intensity in time-of-flight secondary-ionization mass spectrometry

Enhancement of ion intensity in static secondary-ionization mass spectrometry (SIMS) has been achieved by using a matrix-assisted sample preparation technique. Previous investigations of polymers and biomolecules by SIMS indicated that secondary-ion (SI) yield is dependent on substrate coverage. Recently we discovered a sample preparation technique that enhanced the SI yield of cyclosporin A (CsA) in an allograft patient sample and neat samples of CsA (1202 u) and polystyrene (M w=2650 u). The preparation technique involves deposition of a submonolayer of cocaine hydrochloride (5 µL of a 20-µg/mL MeOH solution) on an etched silver substrate, solvent evaporation, and subsequent deposition of the analyte. This preparation method resulted in ∼300% increase in the SI yield of CsA and polystyrene when deposited from neat solutions. The original discovery was observed when a blood extract that contained CsA was deposited on an etched Ag substrate that had been soaking in a dilute cocaine solution for ∼2 months. In these initial experiments, the SI yield of CsA was enhanced by over 1 order of magnitude.