Preliminary Study on Possibility Cl Detection in Soil by Means of The Unique Sub-target in a Transversely Excited Atmospheric Pressure (TEA) Carbon Dioxide (CO2) Laser Induced Breakdown Spectroscopy

Abstract

A preliminary study on Cl detection in soil sample using LIBS has been carried out. The soil sample was mixed with silicon grease to allow attachment to the surface of a nickel plate acting as a sub-target. The laser used in this work is a TEA CO2 laser that operates at wavelength of 10.6μm with energy and pulse duration of 2.5 J and 200 ns, respectively. The laser beam was focused onto the sample using a zinc selenium lens (f = 200 mm) under air and helium surrounding gas at atmospheric pressure. The emission spectrum from the generated plasma was detected using an optical multichannel analyser (OMA)system consisting of a 0.32-m-focal length spectrograph with a grating of 1200 graves/mm and a 1024-channel photodiode detector array with a micro-channel plate intensifier. Soil sample used in this work is a standard soil sample mixed with NaCl solution at various concentrations. The results show that many emission lines due to salts such as Ca, Mg, Na and K can be detected clearly. Nevertheless, Cl emission line cannot be detected in soil sample, although the sample has been intentionally mixed with Cl, even when Cl content reaching 1000 ppm. It is therefore necessary to develop a new approach to allow LIBS techniques for detecting Cl in soil samples.