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Simple, fast matrix conversion and membrane separation method for ultrasensitive metal detection in aqueous samples by laser-induced breakdown spectroscopy.

A fast, low cost, and sensitive sample pretreatment method was specially developed for laser-induced breakdown spectroscopy (LIBS) based on metal precipitation and membrane separation for simultaneous elemental analysis in liquid samples. The metal elements were reacted with the chelating reagent 2,4,6-trimercapto-1,3,5-triazine (TMT) in the first step and separated by mixed cellulose ester microfiltration membrane subsequently. A specific membrane supporter with smaller aperture than the commercially available needle filter was designed and assembled in the presented research to increase the sensitivity. As a result, the detection limits of Cu, Ag, Mn, and Cr obtained in this research were 2.59 ng·mL(-1), 0.957 ng·mL(-1), 0.958 ng·mL(-1), and 1.29 ng·mL(-1) respectively, which were greatly improved from direct liquid analysis by LIBS. Satisfactory linearity, reproducibility, and accuracy were also obtained in the concentration range of 10-120 ng·mL(-1) for all four elements tested at the optimized experimental conditions. The analytical figures of merits of the proposed method are at an advanced level and are comparable to those reported among other non-LIBS research. In addition, the separation mechanism in this research was initially explored and further varied to be based on metal precipitates adsorption by membrane fibers, rather than a regular size-dependent obstruction.