With low level metals analyses, there is an increased risk of sample contamination from extraneous sources. To address this risk, the United States Environmental Protection Agency (USEPA) published Method 1669, “Sampling Ambient Water for Trace Metals at EPA Water Quality Criteria Levels”, referred to as the “Clean Hands/Dirty Hands” sampling technique.
As the nickname implies, “Clean Hands / Dirty Hands” sampling is a two-person task. One team member is identified as “Clean Hands” and the other as “Dirty Hands”, which reflects their roles and tasks associated with the sampling process. In other words the “Clean Hands” team member performs all activities requiring contact with the sample and sample container, sample collection, sample filtration and sample preservation. The “Dirty Hands” team member is responsible for preparing any sampling devices (except the sample container itself), operating machinery, and all other activities that do not involve direct contact with the sample.
 U.S. Environmental Protection Agency, Office of Water Engineering and Analysis Division, Method 1669: Sampling Ambient Water for Trace Metals at EPA Water Quality Criteria Levels, July 1996