Simple and accessible analytical methods for the determination of mercury in soil and coal samples

• New simple and accessible analytical methods are proposed for Hg in soil and coal.
• Proposed methods are successfully validated by analyzing soil and coal CRMs.
• Field-collected soil and coal samples are accurately analyzed by proposed methods.
• Proposed methods are successfully validated by the US EPA Method 7473.

Simple and accessible analytical methods compared to conventional methods such as US EPA Method 7471B and ASTM-D6414 for the determination of mercury (Hg) in soil and coal samples are proposed. The new methods are consisted of fewer steps without the Hg oxidizing step consequently eliminating a step necessary to reduce excess oxidant. In the proposed methods, a Hg extraction is an inexpensive and accessible step utilizing a disposable test tube and a heating block instead of an expensive autoclave vessel and a specially-designed microwave. Also, a common laboratory vacuum filtration was used for the extracts instead of centrifugation. As for the optimal conditions, first, best acids for extracting Hg from soil and coal samples was investigated using certified reference materials (CRMs). Among common laboratory acids (HCl, HNO3, H2SO4, and aqua regia), aqua regia was most effective for the soil CRM whereas HNO3 was for the coal CRM. Next, the optimal heating temperature and time for Hg extraction were evaluated. The most effective Hg extraction was obtained at 120 °C for 30 min for soil CRM and at 70 °C for 90 min for coal CRM. Further tests using selected CRMs showed that all the measured values were within the allowable certification range. Finally, actual soil and coal samples were analyzed using the new methods and the US EPA Method 7473. The relative standard deviation values of 1.71–6.55% for soil and 0.97–12.11% for coal samples were obtained proving that the proposed methods were not only simple and accessible but also accurate.