Determination of mercury in mosses by novel cold vapor generation atmospheric pressure glow microdischarge optical emission spectrometry after multivariate optimization

Abstract

A novel atmospheric pressure glow microdischarge system coupled with chemical vapor generation was applied to the optical emission spectrometry determination of Hg in samples of mosses (Pleurozium schreberi) from parks and surrounding forests of Wroclaw (Poland). The design of experiment (DOE) was used to optimize the operating parameters of the microdischarge system combined with a reaction/separation unit used for chemical vapor generation. Seven experimental factors were examined, i.e., concentrations of NaBH₄ and HCl, the discharge current and flow rates of reagents, the jet-supporting gas, the shielding gas and the liquid cathode solution on the intensity of the Hg I 253.7 nm emission line and the standard deviation of the background in its vicinity. The optimized operating conditions allowed us to obtain a detection limit of 0.066 μg L⁻¹ for Hg, which was close to the predicted value with a fitted model. To separate Hg species from moss samples, a 2-step extraction procedure with a 5.0 mol L⁻¹ HCl solution was carried out instead of complete wet digestion with concentrated HNO₃. To validate the reliability of results, the spike-and-recovery experiment was performed. The obtained results were close to 100% proving the good accuracy of the methodology proposed. The average concentration of Hg in mosses in the urban area of Wroclaw was high (0.37 μg g⁻¹) but no specific source of contamination was found.