Influences on detectability of heavy metals in soils by laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a rapid remote measurement method for determination of levels of metals in the environment. A major factor in the acceptance of this technique involves the detection limits under both laboratory and field operations. Research on limits of detection of heavy metals in different types of soils under various conditions using LIBS has been carried out. Pulses from a Nd:YAG laser operating at 150 mJ at λ=1.06 μm are focused on sample surfaces to produce laser sparks (plasmas). Atomic emissions from the plasmas are recorded using an optical multichannel analyzer after delays of a few microseconds when interference from broadband emissions is reduced. Research has been performed on the detection limits of As, Cd, Cr, Hg, Pb, and Zn in soil matrices. Results are reported on the detectability of Cr in sand samples. The LIBS method described is well-suited to monitoring of subsurface soils using this technique installed in a cone penetrometer. Conditions that would be encountered by a cone penetrometer-based LIBS system are simulated by compressing soil samples and then allowing them to relax for specific intervals before LIBS analysis. Results are presented of the dependence of LIBS measurements on the relaxation time after soil sample compression. This data is important to understand how to implement field-deployable LIBS systems