Methyl Mercury in Water by Distillation, Aqueous Ethylation, Purge and Trap, and CVAFS
This draft performance-based method was developed by EPA's Office of Water to achieve the low limits of detection for methyl mercury in water needed to meet water quality criteria. Mercury background levels in the environment can elevate the amount of methyl mercury detected. In order to meet the low detection limits and eliminate the background contamination, special sampling, handling and analytical procedures are followed.
EPA Method 1669 is referenced as the collection method for Method 1630. Method 1669 is also referred to as the "clean hands/dirty hands" technique. Special collection procedures include eliminating all sources of metal or metal containing materials from sample collection and handling. This involves eliminating gloves that contain talc. In fact it has been shown that samples have been contaminated from the amount of mercury found in a person's breath who had mercury amalgam fillings.
Special sample containers need to be used for collection. These containers should be made of specially cleaned, pretested fluoropolymer with a fluoropolymer lined lid. Most laboratories can supply the bottles needed. Polyethylene bottles should not be used for sample collection. Borosilicate bottles may be used if the analyses are only for mercury or mercury species.
The samples require preservation which is typically done in the field. However, due to the sensitivity of this method it is acceptable to ship the samples to the laboratory unpreserved if there is no head space, the samples are kept at 0-4 °C from the time of collection until preservation, and they are acid preserved within 48 hours of sampling.
The laboratory will need to have the capability to perform the analyses in a Class 100 Clean Room or in a Class 100 Clean Bench. This includes use of a non-metallic hood. The samples are distilled, purged on a carbon trap, desorbed through a pyrolytic decomposition column to convert organic mercury to elemental mercury and then analyzed by CVAFS (cold-vapor atomic fluroescence spectrometry).
(EPA: Office of Water)