A mass analyzer based on a rectilinear geometry ion trap (RIT) has been built, and its performance has been characterized. Design concepts for this type of ion trap are delineated with emphasis on the effects of electrode geometry on the calculated electric field. The Mathieu stability region was mapped experimentally. The instrument can be operated using mass-selective instability scans in both the boundary and resonance ejection versions. Comparisons of performance between different versions of the device having different dimensions allowed selection of an optimized geometry with an appropriate distribution of higher-order electric fields. Comparisons made under the same conditions between the performance of a conventional cylindrical ion trap and a RIT of 4 times greater volume show an improvement of 40 times in the signal-to-noise ratio resulting from the higher ion trapping capacity of the RIT. The demonstrated capabilities of the RIT include tandem mass spectrometry, a mass resolution in excess of 1000, and a mass/charge range of 650 Th, all in a simple structure that is only 3.5 cm(3) in internal volume.

Desorption electrospray ionization (DESI) allows the rapid acquisition of highly reproducible mass spectra from intact microorganisms under ambient conditions; application of principal component analysis to the data allows sub-species differentiation.

Acetonitrile vapor and air are useful reagents for the selective detection of nitroaromatic compounds using atmospheric pressure ion/molecule reactions. Reagent ions CH2CN- and CN- generated from acetonitrile, and O-*, OH- and OOH- produced from the oxygen in air, react with vapor-phase and condensed-phase nitroaromatics in the course of atmospheric pressure chemical ionization (APCI) and desorption atmospheric pressure chemical ionization (DAPCI), respectively. The homogeneous and the heterogeneous phase reactions both lead to the formation of the same anionic adducts. These adducts have characteristic fragmentation patterns upon collisional activation, which makes these two reagents valuable for the selective detection of particular nitroaromatics, including explosives present as components of complex mixtures. Complementary information is available from the two reagents because their different chemistry facilitates analyte identification. DAPCI is demonstrated to be a useful ambient detection method for nitroaromatic explosives absorbed on surfaces.

Desorption electrospray ionization mass spectrometry (DESI-MS) of culture of the bacterium Bacillus subtilis as a biofilm growing on agar nutrient gives simple, high quality mass spectra dominated in both the positive and negative ion modes by signals due to the cyclic lipopeptide, Surfactin(C15). This in vivo experiment, performed by direct analysis of untreated microorganism samples under ambient conditions, allows rapid identification of this microorganism and the antibiotics that it produces. The result is suggestive of the capabilities of DESI-MS for in vivo microorganism characterization in general and for monitoring fermentation processes for the production of antibiotics and other biochemicals.