MATRIX EFFECTS IN THE DETECTION OF PB AND BA IN SOILS USING LASER-INDUCED BREAKDOWN SPECTROSCOPY

With the use of laser-induced breakdown spectroscopy (LIBS), the effec ts of chemical speciation and matrix composition on ph and Ba measurem ents have been investigated by using sand and soil matrices. A cylindr ical lens was used to focus the laser pulses on the samples because it yielded higher measurement precision than a spherical lens for the ex perimental conditions used here. The detection limits for Pb and Ba sp iked in a sand matrix were 17 and 76 ppm (w/w), respectively. In spike d soil, the detection limits were 57 and 42 ppm (w/w) for Pb and Ba, r espectively. Measurement precision for five replicate measurements was typically 10% RSD or less. Two factors were found to influence emissi ons from Pb and Ba present in sand and soil matrices as crystalline co mpounds: (1) compound speciation, where Ba emission intensities varied in the order carbonate > oxide > sulfate > chloride > nitrate, and wh ere Ph emission intensities varied in the order oxide > carbonate > ch loride > sulfate > nitrate; and (2) the composition of the bulk sample matrix. Emissions from Ba(II) correlated inversely with the plasma el ectron density, which in turn was dependent upon the percent sand in a sand/soil mixture. The analytical results obtained here show that a f ield-screening instrument based on LIBS would be useful for the initia l screening of soils contaminated with Pb and Ba.