Problems in quantitatively analyzing individual salt aerosol particles using electron energy loss spectroscopy

Polydisperse standard aerosols of NaCl, (NH₄)₂SO₄ and KNO₃ have been generated from their solutions by pneumatic nebulization. These aerosol particles are electron beam sensitive and therefore special precautions are necessary. A methodology is proposed for serially recording electron energy loss spectra (EELS) from sub-micrometer salt particles. The results of quantification are compared with those obtained by parallel electron energy loss spectroscopy (PEELS). Experimental conditions such as the intensity of the primary beam, time of radiation and temperature are responsible for large deviations from the theoretical values. These deviations arise because heavy mass losses occur, especially during the serial spectrum acquisition. The more time consuming serial EELS is therefore at a disadvantage relative to the parallel method. The best results are obtained for NaCl because the halogen loss can be reduced more efficiently than nitrogen and oxygen losses. The results show that nitrogen loss occurs within the first few seconds of the experiment at normal radiation doses. Even at cryogenic temperatures, losses of volatile elements cannot be avoided.