Highly sensitive and stable analysis of trace arsenic(III) and mercury(II) in water by Low-pulse-energy (15 mJ) laser-induced breakdown spectroscopy assisted by active controllable spark discharge and electrochemical enrichment

Laser-induced breakdown spectroscopy (LIBS) has emerged as promising technology in view of its unique advantages and application in analysis of environmental samples. However, such a method encounters significant challenges in detecting arsenic and mercury, which are prone to volatilization at high pulse energy. Herein, a new approach, low-pulse-energy LIBS supported by active controllable spark discharge and electrochemical enrichment is proposed to overcome the above problems. In this approach, a low pulse energy (15 mJ) instead of high pulse energy (typically 100 mJ) reported in previous work was applied to reducing the volatilization of arsenic and mercury as well as downsizing ablation spot of the sample. The temperature on the samples with pulse energy of 15 mJ, which was simulated with MATLAB, was more than 5 times lower than that of 100 mJ. Active controllable spark discharge makes up for the insufficiency in the content of excited arsenic or mercury plasma resulting from low pulse energy (15 mJ) and especially supplies a stable plasma source. As a result, a high sensitivity of 3.35 counts ppb(-1), low limit of detection of 8.69 ppb and excellent stability (relative standard deviation is lower than 5 %) for arsenic(III) were exhibited. Efficient and fast preconcentration of arsenic(III) is achieved by electrochemical enrichment on the electrode modified using flower-like NiCo2O4-x-NH2 nanosheets with regulable oxygen vacancies. This method provides an opportunity to detect volatile arsenic(III) and mercury(II), as well as heavy metal ions (HMIs) hard to volatilize, such as copper(II). It's an effective new method for detecting HMIs.