Low-level Mercury

Sample Containers, Preservation & Holding Time

When DNR revised NR 219, Analytical Test Methods and Procedures to incorporate low-level mercury methods, we inadvertently overlooked the need to update Table F that contains the container, preservation and holding time requirements. After the rules were final, EPA published revision E to method 1631 and updated its requirements for preservation and holding time. DNR will recognize EPA's preservation and holding time requirements for low-level mercury until NR 219 can be revised.

For low-level mercury analyses, there are two choices for sample containers, fluoropolymer (e.g. Teflon ™) or borosilicate glass. It is critical that the container caps seal tightly to avoid passive diffusion of mercury from the atmosphere. Each container should be double-bagged prior to shipment. We recommend that samples be shipped to the laboratory unpreserved and they no longer need to be iced during shipment. Under these conditions, samples must be preserved within 48 hours of sample collection. Method 1631 allows this period to be extended to 28 days if the sample is oxidized in the sample bottle. Bromine chloride or hydrochloric acid are appropriate preservatives.