Development of spray deposition/MALDI-TOFMS and its application to the rapid screening of hydrolysis products derived from nitrogen mustards.

A novel method for preparing samples for use in MALDI-TOFMS (matrix-assisted laser desorption ionization time-of-flight mass spectrometry) is described. Seven hydrolysis products derived from nitrogen mustards and CHCA (alpha-cyano-4-hydroxycinnamic acid) were selected as model compounds and the matrix, respectively. A capillary atomizer was used for evaporative and spray deposition of the sample/matrix solution, leading to the formation of a freestanding film that coated and accumulated on the MALDI substrate (i.e., sample plate). Compared to the traditional method for MALDI, which involves the production of dried droplets, the surface roughness was reduced, resulting in the accumulation of the sample-doped matrix on the sample plate. This resulted in an increase in the limit of detection of 1 - 2 orders of magnitude. In order to compare the structures of the sample-doped matrices obtained by the traditional dried droplet method versus the spray deposition method (developed in this study), the matrices were examined by SEM (scanning electron microscopy). The design of the capillary atomizer and details of the experimental conditions are reported. The application of this method to the above seven degradation products was successful, suggesting that it has great potential for use as a routine monitoring tool.