If one were interested in the total N and P content of a filtered water sample, but it needed to be kept at room temperature for 10 days or so, would they get decent estimates if they performed an acid digestion of the sample, and then standard colorimetric chemical analyses?
I agree with Ewald as regards P. For the nitrogen it will depend on the relative concentrations of the various species present and ,critically, on how much error you are prepared to accept.
If you are interested in tolal N and total P, best methode is do filtrtae the raw samples in thefield and immediate transport to the laboratory and inject into a CHN analyzer which also detect P
Boah! Never heard about a CHN Analyzer which analyzes also P! Tell me where you found it!
Sorry it is not a CHN , TOC Shimadzu machine
TNPC-4110/4110C Online Total Nitrogen/Phosphorus/TOC Analyzers
no harm done Ivan, but you never know what inventions may be possible!
I suggest that you use sulfuric acid (maybe 1+2 water to make the solution more easy to handle). About 1 ml to 100 ml sample will probably give a pH of about 2, which is considered a good level to preserve the sample according to EN ISO 11905 Determination of nitrogen. The same level would work well for total-P. But PO4-P should not be determined on such a sample, since the concentration will increase due to hydrolysis. Also nitrite will be affected.
Our experience is that the sample is very stable
Good luck
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