I have a question concerning groundwater analysis. We have been sampling for major ions, including Fe since october 2016. As the AAS was out of operation for the first three months, half of the sampled water was frozen and preserved below zero until the AAS would be operational again and Fe concentration could be determined. Unfortunately the samples that were frozen were anion samples (not acidified). Now, as the samples are being analyzed, the concentrations seem to be below zero, which probably is due to Fe precipitation. Am i correct? The question is, if water samples which have been treated with microwave mineralization prior to AAS analysis, would still be somehow comparable and usable in statistical analysis with the rest of the ion concentrations?
An Fe value less than zero is clearly an artefact, but the problem remains. Once you thaw and subsample for anions why not acidify the solution to dissolve the Fe, measure it and adjust for the volume removed?
Thank you for the answer. Unfortunately the leftovers were thrown away. But then I should ask (sorry if this is a stupid question), if simply acidifying below pH 3.5 would dissolve the ferric iron back into solution? And what is the effect mw. mineralization?
Whilst acidifying to 3.5 might dissolve the iron back into solution it will depend on what else preciptated with it. You may have formed some recalcitrant phases when the precipitation occured However if you try hard enough it should dissolve again eventually.
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