No abstract

A negative-ion mode laser spray interface for use in liquid chromatography/mass spectrometry (LC/MS) has been developed and investigated. The laser spray gave sensitivities that were orders of magnitude better than the negative-ion electrospray for all samples investigated with the exception of sugars. Fragment ions, HSO(-4)and SO(-3), were formed from the laser-sprayed aqueous solution of cholesterol 3-sulfate sodium salt. This suggests that structural information may be obtained directly from the laser-spray mass spectra for thermally labile compounds.

The effect of the presence of foreign salts (NaCl, aerosol OT, tetra-n-hexylammonium bromide, and CH3COONH4) on the formation of gaseous ions for electrospray (ES) and laser spray (LS) was studied in the positive and negative modes of operations. The ion signals for amino acids show sudden decrease with the concentration of foreign salts greater than 10(-5) M for both ES and LS. When the surface-active counter ions were added, the signal intensities showed a marked decrease for both ES and LS. This may be due to the enrichment of the surface-active counter ions on the surface of the charged droplets. When CH3COONH4 was added to an aqueous solution of 10(-6) M lysozyme chloride, an increase of the signal intensities for (lysozyme+nH)n+ and a decrease in the values of n were observed. The decrease in n may be due to the salt formation of (lysozyme+nH)n+ with the negative acetate ion leading to the reduction of positive charges.