Improvement of laser induced breakdown spectroscopy signal for sodium chloride solution

Laser induced breakdown spectroscopy (LIBS) is one of the analytical spectroscopy technique used in determining elemental composition of solid, liquid or gas sample using high energy laser pulse. However, LIBS technique associated with liquid sample often suffers from strong splashing and shockwave, thereby affecting the LIBS experiment repeatability and performance analysis. Therefore, a simple and quick-freeze sample pre-treatment approach using Peltier Thermoelectric Cooler (TEC) to solidify the water is applied to maintain the inherent homogeneity and chemical composition of the initial liquid sample before each LIBS analysis. This approach successfully solidified and maintained the liquid sample at its freezing point throughout the LIBS signal acquisition process. In this work, the qualitative analysis liquid samples and its solidified form, consisting of 0.5, 1.0, 1.5 and 2.0 mol/L sodium chloride (NaCl) were determined under similar experimental conditions by using LIBS. Plasmas were produced by focusing the output of Nd: YAG laser (1064nm, 6 ns and 1 Hz) on the surface of the bulk NaCl solution and its solidified form. LIBS signatures for sodium (Na) and chlorine (Cl) atomic emission lines (589.00 and 499.55 nm, respectively) were collected for estimating sodium and chlorine depositions in NaCl solutions to indicate correlation between their assay and LIBS measurements. For solidified sample, Na and Cl showed improved signal-to-noise ratio and limits of detection (47.8% and 8.8%, respectively) without the difficulties usually associated with liquid samples, demonstrating the benefits of this sample pre-treatment approach