Experimental Bias Involved in the Collection of Gaseous Elemental Mercury by the Gold Amalgam Method

Abstract

The analytical bias involved in the application of the gold (Au) amalgamation method for gaseous elemental mercury (Hg) analysis was investigated as a function of three major parameters such as the total sampling volume, concentration levels of Hg samples, and differences in the tube sampler used for replicate sampling. Gaseous standards of Hg were prepared at five different concentration levels (S1–S5, ranging from the highest 876 ng m⁻³(S1) to the lowest 16.6 ng m⁻³ (S5) by mixing Hg vapor and ultrapure N₂ gas at varying ratios. Each standard gas type was then analyzed by the Au amalgam method by adjusting sampling volumes to a large degree (0.1, 0.5, 1, 5, and 10 L). All of experiments were basically conducted to obtain five replicate analyses using five individual tubes at a given sampling volume. An ancillary experiment was also performed to obtain replicate data using a single tube for comparison against those data sets obtained using multiple tube applications. The overall results are evaluated in terms of recovery rate for each standard and of reproducibility, (e.g., relative standard error values: RSE in %). Maximum recovery of most Hg standard types was generally attained at the highest sampling volume, that is, 10 L selected for this study. It is found that analytical uncertainties tend to decrease with an increase both in total sampling volume and in concentration levels of the Hg standard. Based on this comparative analysis for the gold amalgamation method, it is concluded that the quality of the Hg analysis is sensitively affected by the combined effects of the major variables investigated in this study.