Colorimetric nitrate and phosphate analysis in water samples. EPA and Standard Methods both commonly recommend preservation with sulfuric acid to pH 2 but there is no mention of raising the pH back to 6-8 before analysis. Should this be done? Any citations?
Thanks.
Dear Duane,
In my experience I try to do the measure immediately in the field with a in situ test and then try to acidify the other sampling to carry the sample to the laboratory avoiding any oxygen contact.
Regards,
Romina
Thanks, but if the samples are already acidified, do they need to be neutralized before analysis?
Hi, in my opinion, you do not have to raise the pH again. The role of the acidification is to avoid mineral precipitation of all kinds and to avoid adsorption of elements to the sample bottle; so if you want to analyse exactly nitrate and phosphate, your water has to stay the same as regards to these elements. I hope it helped at least for your thought, regards, L.
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