Development and validation of a laser-induced breakdown spectroscopic method for ultra-trace determination of Cu, Mn, Cd and Pb metals in aqueous droplets after drying

Abstract

Keywords:Laser-induced breakdown spectroscopy Liquid droplet analysis Oxidized silicon wafer substrate (Si þ SiO 2 ) a b s t r a c tThe present study reports a fast and accurate methodology for laser-induced breakdown spectroscopic, LIBS, analysis of aqueous samples for environmental monitoring purposes. This methodology has two important attributes: one is the use of a 300 nm oxide coated silicon wafer substrate (Siþ SiO 2 ) for the first time for manual injection of 0.5 microliter aqueous metal solutions, and two is the use of high energy laser pulses focused outside the minimum focus position of a plano convex lens at which relatively large laser beam spot covers the entire droplet area for plasma formation. Optimization of instrumental LIBS parameters like detector delay time, gate width and laser energy has been performed to maximize atomic emission signal of target analytes; Cu, Mn, Cd and Pb. Under the optimal conditions, calibration curves were constructed and enhancements in the LIBS emission signal were obtained compared to the results of similar studies given in the literature. The analytical capability of the LIBS technique in liquid analysis has been improved. Absolute detection limits of 1.3 pg Cu, 3.3 pg Mn, 79 pg Cd and 48 pg Pb in 0.5 microliter volume of droplets were obtained from single shot analysis of five sequential droplets. The applicability of the proposed methodology to real water samples was tested on the Certified Reference Material, Trace Metals in Drinking Water, CRM-TMDW and on ICP multi-element standard samples. The accuracy of the method was found at a level of minimum 92% with relative standard deviations of at most 20%. Results suggest that 300 nm oxide coated silicon wafer has an excellent potential to be used as a substrate for direct analysis of contaminants in water supplies by LIBS and further research, development and engineering will increase the performance and applicability of the methodology.

Electrospray deposition followed by laser-induced breakdown spectroscopy (ESD-LIBS): a new method for trace elemental analysis of aqueous samples

“…[10][11][12][13] With the aim to overcome the limitation of LIBS analysis of liquids, different strategies involving the use of sample preparation procedures have been investigated by many authors. Among them, it can be cited the absorption or drying of the sample on a solid matrix, [14][15][16][17][18] the application of solid phase extraction (SPE) procedures, 19,20 or the use of modern microextraction procedures in both Liquid-Liquid Microextraction (LLME) [21][22][23][24] and Solid Phase Microextraction (SPME) 25,26 modalities, among others. In general, the use of these sample preparation procedures prior LIBS detection leads to a substantial improvement in the analytical performance of the method, by decreasing the limits of detection at the low µg L -1 level.…”

Graphene thin film microextraction and nanoparticle enhancement for fast LIBS metal trace analysis in liquids

“…For example, some works propose to perform the LIBS measurement directly on the surface of the liquid sample, to generate an aerosol or a liquid jet to increase the performance of the technique [2]. On the other hand, some authors propose to convert the liquid matrix into a solid in order to eliminate many of the issues [5][6][7][8].…”

“…Aras and co-workers [5] investigated a method for the detection of ultra-trace of heavy metals in aqueous droplets using LIBS. In their work, they coupled the enhancing effects of SENLIBS, using Ni, Mn-alloy, Zn and Si substrates, with a liquid-liquid extraction to pre-concentrate the analytes before drying sample droplets onto the substrates.…”

Investigating silicon wafer based substrates for dried-droplet analysis by Laser-Induced Breakdown Spectroscopy

“…Dried-droplet analysis [21] is another alternative strategy in liquids analysis by LIBS. The methodology consisted of loading, drying and analyzing steps.…”

“…For the last few years in our group, we are developing methods and investigating the performance and capabilities of laser-induced breakdown spectroscopy for dried-droplet analysis by using non-metallic substrates. We have previously shown [21] that, 300 nm oxide-coated silicon wafer (Si + SiO 2 ) has an excellent potential to be used as a substrate for dried-droplet analysis. With high energy laser pulses focused on the sample surface, outside the minimum focal point condition, Cu (I) signal at 324.75 nm indicated more than 7 times enhancement in S/N compared to the one obtained at the minimum focus condition experiments.…”