Positive-ion fast atom bombardment (FAB) mass spectra are reported for a representative series of mono-and bisphosphonium halides derived from triphenylphosphine. The mass spectra of the monoalkyltriphenylphosphonium

The use of laser microprobe mass spectrometry (LMMS) for the structural characterization of thermolabile quaternary phosphonium salts has been evaluated. A comparison has been made between LM mass spectra obtained by direct analysis of "neat" organic salts and the corresponding "matrix-assisted" LM mass spectra. Main limitations of LMMS for the direct analysis of neat organic salts (i.e., no matrix) result from (1) formation of artifact ions that originate from thermal degradation and surface recombination reactions and (2) poor shot-to-shot reproducibility of the spectra. Dilution of the organic salts in a suitable, UV-absorbing matrix (e.g., nicotinic acid) significantly enhances the quality of the LM mass spectra. Improvements are: (1) an increase of the ion yield of preformed cations, (2) reduction or elimination of thermal decomposition and other deleterious surface reactions, and (3) a much better shot-to-shot spectral reproducibility. An interesting analytical feature is that these LM mass spectra, which contain only a few matrix peaks, can be obtained for subnanogram amounts of sample.The results also show that triphenylphosphonium salts with polycyclic aromatic substituents can be used as "molecular thermometers" to probe both the temperatures experienced by the sample molecules during the laser-induced desorption ionization process and the internal energies of the desorbed ion species. In this way, quaternary phosphonium salts can be used for evaluating whether improvements have been achieved by applying different sample treatments. Comparison of four different matrices (i.e., nicotinic acid, ammonium chloride, glycerol, and 3-nitrobenzylalcohol) indicates that the effectiveness of a matrix to reduce thermal degradation and to decrease the internal energies of the ions depends on the UV-absorption characteristics and the volatilization/sublimation temperature of the matrix material.

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The double bond position in long-chain dalkenyl salicylic acids has been determined by collisional activation of ( M -H + 2Lil' and ( M -HI-precursor ions, which were generated by FAB. The pattern of product ions characteristic for charge-remote fragmentations allowed for a straightforward determination of the location of the double bond for the dilithiated precursor ion species, whereas complications from 1 0 s of CO, were experienced for carboxylate anions. The product ion collisionally activated dissociation spectra obtained for both precursor ion species also reveal the formation of stable radical ions, which are likely distonic and point to the involvement of radical processes in charge-remote fragmentation.