AC CORONA-DISCHARGE AEROSOL-NEUTRALIZATION DEVICE ADAPTED TO LIQUID-CHROMATOGRAPHY PARTICLE BEAM MASS SPECTROMETRY/

An AC corona-discharge device was inserted upstream of a thermospray v aporizer tip in a liquid chromatography/particle beam mass spectromete r to neutralize static aerosol charging. Response of a test analyte wa s measured with or without discharge initiation. If the solvent contai ned no ammonium acetate buffer, increased analyte signal was associate d with the discharge. However, in the presence of ammonium acetate the benefit of AC discharge neutralization was either not observed or was more subtle. This led to the conclusion that the previously observed ammonium acetate ''carrier'' effect is attributable, at least in part, to neutralization of static electric charges produced spontaneously d uring the solvent nebulization process. In a second experiment, the pa ttern of particles issuing from the system momentum separator was exam ined by aiming the particle beam at a cold target located within a mas s spectrometer ion source. Variations in particle density were observe d depending on (i) whether or not the aerosol had been neutralized and (ii) the proximity of electron-beam-collimating magnets to the partic le beam trajectory. These results are consistent with a hypothesis tha t electrostatic charging occurs spontaneously during the nebulization process in which an aerosol is formed from the high performance liquid chromatography effluent. Such electrostatic charging introduces a fac tor likely to degrade system performance by at least two modes: throug h interactions of the charged aerosol particles (i) with the walls of the aerosol transmission pathway, and, after they are accelerated into a particle beam and introduced into the mass spectrometer, (ii) with the magnets used for electron beam collimation in many mass spectromet er ion sources.