Preservation of sub-p.p.b. levels of mercury in distilled and natural fresh waters

Several preservatives, containers, etc. have been suggested in relation to the preservation of mercury samples. This paper reports a comparison of sample containers and of preservatives for synthetic and natural low-level (sub-p.p.b.) mercury samples. It is shown that 1% H₂SO₄+ 0.05% K₂Cr₂O₇ is most advantageous with respect to accuracy, precision and practical aspects such as low detection limits and adaptability to the automated cold-vapor atomic absorption technique. Glass is the best container, and is best washed with concentrated nitric acid or chromic acid. Data from a national interiaboratory quality control study on the determination of mercury show that this preservative is satisfactory for the long-term storage of sub-p.p.b. mercury solutions. The presence of mercury as CH₃Hg⁺³ improves preservation efficiency. The method of total errors is used in comparing the methods.