In general, surface waters are analyzed for total metals and groundwaters for dissolved metals. Drinking waters must be analyzed for total metals. In some situations, e.g. environmental modelling, background studies, it may be beneficial to analyze for both total and dissolved metals.
When testing for dissolved metals at routine Regulatory levels, it is recommended to field filter the sample through a proven clean 0.45 μm filter prior to preservation with acid.
If the sample is not filtered, then some particulate matter may be dissolved by the acid preservative. This would result in high bias for dissolved metals. Unfiltered, preserved samples are unsuitable for filtration at the laboratory.
For ultratrace analysis, our experience has shown that it is extremely difficult to field filter without introducing contamination. For that reason, we recommend either the use of a specially designed Bureau Veritas Laboratory field filtration kit, or filtration in the lab under clean room conditions. Although it is possible that some analytes may dissolve or precipitate between sampling and lab filtration / preservation, these changes are small compared to the issues associated with field filtration.
Transport the sample to the lab asap to minimize any changes.