Co-Precipitation of Dissolved Metals with Iron
ALS Co-Precipitation Impact Study
ALS recently studied the impact of iron precipitation on the coprecipitation of other metals with a series of high-iron groundwater samples, and found substantial losses of most dissolved metals (in comparison to field filtered metal concentrations), with losses up to 100% in several cases where filtration was delayed (by 6 to 10 days in these somewhat worst-case examples). Arsenic, Lead, and Cadmium were particularly impacted by co-precipitation, in addition to the expected loss of Iron, but most dissolved metals were impacted to some degree. A summary of the ALS study results for Arsenic, Lead, Cadmium, and Iron are shown in Figure 1.
For these 5 samples, Arsenic losses averaged over 80%, lead losses averaged over 95%, and Cadmium losses varied significantly by sample, ranging from zero to 97% loss. The impact on sample results can clearly be seen, with many of the test samples potentially having key metal concentrations underestimated by a factor of 10 to 100 times if correct field filtration techniques were not employed. This study also highlights the necessity of field filtration for the analysis of dissolved ferrous iron.
Recommended Field Filtration Techniques
Field Filtration Blanks are Highly Recommended!
ALS highly recommends the collection of Filtration Blanks whenever field filtration is conducted, as a control of metals background levels that may be contributed by the filtration process. This is the only way to monitor and control against contamination, which is a common problem with many types of filtration media. The laboratory can provide de-ionized water to facilitate the collection of Filtration Blanks.