Wavelength and size dependence in single particle laser aerosol mass spectra

The impact of particle size and desorption/ionization laser wavelength on ion signal in single particle laser mass spectrometry was investigated. Individual particles of α-cyano hydroxy-cinnamic acid, dihydroxy benzoic acid, and nitroguanadine were sized, tracked, and desorbed/ionized by 266 or 355 nm laser light, and the resulting mass spectra were analyzed. Sodium ion signal and total ion signal were determined. Sodium ion is a measure of desorption efficiency, while total ion signal is sensitive to both desorption and ionization. The sodium ion signal was found to be independent of wavelength, above a minimum laser energy which varied by compound. The total ion signal was found to be higher for 266 nm desorption/ionization laser mass spectra in most cases. The sodium ion and total ion signals were found to be linear with particle size, regardless of laser energy or wavelength. Both sodium ion and total ion signals were also found to vary roughly linearly with laser energy, showing a much weaker dependance on laser energy than predicted by MALDI results. These results suggest that the absorbance spectrum of the compound does not predict desorption and ionization efficiency, above some minimum laser energy.