CHARGED DROPLET FORMATION IN SONIC SPRAY

The reasons why sonic spray ionization can readily produce multiply-ch arged ions when a high voltage is applied to the source housing have b een investigated by using aerosol techniques. Charged droplets were pr oduced by sonic spray from a trifluoroacetic acid solution in triethyl ene glycol/ethanol. These droplets were analyzed with a differential m obility analyzer to obtain their mobilities, and also analyzed with an aerodynamic particle size spectrometer to obtain their diameters. By combining these results, the charge numbers of the droplets have been determined. The results show that some droplets have charge numbers cl ose to the Rayleigh limit and that the abundance of these droplets inc reases as the voltage applied to the source housing increases. A quali tative explanation is given for the formation of multiply-charged ions . (C) 1998 Elsevier Science B.V. All rights reserved.