A hydrogel-based solidification method for the direct analysis of liquid samples by laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a simple, fast, and direct technique for the elemental analysis of various samples. However, the practical application of this method in direct liquid analysis is limited due to its inherent disadvantages including surface ripples and extinction of emitted intensity. Applicable treatments of liquids always involve complicated procedures or additional instruments, which is disadvantageous to its analytical performance. In this study, we proposed a novel method for the LIBS analysis of liquid samples via a hydrogel-based solidification technique. In this new method, aqueous solution is directly poured into sodium polyacrylate resins. Owing to the high hydroscopicity of sodium polyacrylate resins, the resins quickly form a hydrogel and immediately solidify the liquid samples. After this, the LIBS analysis is directly performed. To estimate the analytical performance of this proposed method, calibration curves were established and limits of detection for Al, Cu, and Cr were obtained. The limits of detection (LODs) for the emission lines of Al(i) 308.21 nm, Cu(i) 324.75 nm, and Cr(i) 425.43 nm were 0.460 μg mL-1, 4.69 μg mL-1, and 4.44 μg mL-1, respectively. According to the obtained results, this proposed method demonstrates its better analytical performance in terms of LODs at the ppm level and requires shorter processing time as compared to other analytical methods based on the LIBS technique for liquid sample analysis. Especially, the short pretreatment of samples and simple auxiliary equipment make this hydrogel-based solidification method bring LIBS out of the laboratory for the direct analysis of environmental liquid samples. The feasibility and potential of this novel method have also been discussed for special analytical applications in slurry samples. © 2017 The Royal Society of Chemistry.