Detection of cadmium, lead and zinc in aerosols by laser-induced breakdown spectrometry

Abstract

The repetitive breakdown spark from an Nd: YAG laser was used to generate analytical emission spectra of cadmium, lead and zinc in aerosols. The laser was typically operated at a pulse rate of 10 Hz, with an energy of 100 mJ per pulse and a pulse width of approximately 15 ns. Samples were generated in aerosol form by a nebuliser-heat chamber arrangement. The detection apparatus consisted of a monochromator, photomultiplier tube and boxcar averager. The last component provided amplification, averaging and time resolution. Detection limits for cadmium, lead and zinc in aerosols were 0.019, 0.21 and 0.24 µg g–1, respectively, at a signal to noise ratio of 3. The detection limits for cadmium and zinc were well below the threshold limit value-time weighted average (TLV-TWA) and threshold limit value-short-term exposure limit (TLV-STEL) limits for these two metals. Calibration graphs covering two orders of magnitude were generated. The excitation temperature of the plasma was measured from 20 to 40 µs after plasma initiation using the two-line Boltzman method, and was found to decrease from 6500 K at 20 µs to 5150 K at 40 µs. The effects of chemical form and sodium on the spectroscopic signals were investigated.