Simultaneous and sensitive analysis of Ag(i), Mn(ii), and Cr(iii) in aqueous solution by LIBS combined with dispersive solid phase micro-extraction using nano-graphite as an adsorbent

Abstract

In the present research, dispersive solid phase micro-extraction was combined with laser induced breakdown spectroscopy for the first time to achieve matrix conversion and preconcentration of Ag⁺, Mn²⁺ and Cr³⁺ in liquid samples. Nano-graphite was selected as a novel adsorbent due to its superior adsorption ability, water solubility and lower cost compared with carbon nanotubes and graphene. Sodium diethyldithiocarbamate was used as a complexing reagent to enhance the interaction between nano-graphite and metal ions. After adsorption, the nano-graphite powder was immobilized by mixing with commercial epoxy adhesive before LIBS analysis instead of the traditional tableting method to solve the problem that some carbonaceous materials are difficult to be tableted. Under optimized experimental conditions, the calibration curves were built in the range of 0.1–1.2 mg L⁻¹ and good linearity (R squared better than 0.980 for all of the three target elements) can be obtained. The detection limits of Ag⁺, Mn²⁺ and Cr³⁺ were 16.59 ng mL⁻¹, 10.85 ng mL⁻¹ and 9.51 ng mL⁻¹ respectively. In real sample analyses, the recoveries of three elements at different concentration levels were all in the range of 92.66–105.80% and the relative standard deviations of parallel samples were less than 8.98%.