A miniaturized microplasma excitation source coupled with photochemically induced volatile species generation as a cost-effective tool for in situ mercury pollution analyses †

A new portable miniaturized atmospheric microplasma discharge (μAPD) system coupled with the optical emission spectrometry (OES) detection for the determination of Hg in water samples was developed. The device was built from cheap, easily replaceable, and commercially available parts and was able to work with the photo-induced chemical vapor generation (PCVG). To optimize the photochemical volatile Hg generation process, a wide range of low molecular weight organic compounds (LMWOCs), namely formic, oxalic, acetic, propionic, and malonic acids, in addition to methanol, ethanol, glycerin, ethylene glycol, formaldehyde, and acetaldehyde, were tested to establish their influence on the signal of Hg. To assess the excitation and atomization potential of the newly developed μAPD system and its impact on the analytical performance of this microplasma excitation source, the plasma temperatures and the electron number density were evaluated. The analytical figures of merit were determined for the coupled PCVG-μAPD system. Additionally, the usability of the method was tested in reference to the analysis of selected environmental samples, i.e., tap, well, and river water spiked with Hg. A recovery test was also performed to evaluate the accuracy of the method. The examined analytical system allowed to detect Hg in water at a level lower than 0.33 μg L⁻¹ when operating it at relatively low sample flow rates (2 mL min⁻¹) and Ar supporting and plasma forming gas rates (20 mL min⁻¹). The precision of measurements was better than 5% for formic acid. We believe that the presented system might be an attractive, cheaper alternative to commercial, highly expensive systems, e.g. based on inductively coupled plasma optical emission spectrometry (ICP OES).