Chromatography Forum

Hello forum:

We analyze nitrate and nitrite by IC. EPA has set a 48 hours hold time for this analysis. Sometimes, in order to meet the hold time samples are acid preserved and results are reported as nitrate-nitrite to pH of less than 2. When we analyze the acidified samples, the baseline on our IC gets elevated and it takes a long time (more than 12 hours) to get back to normal.

Any suggestions?

Thank you very much for your time.

Hi 01310040231,

Is it possible to treat the acidified samples selectively with SPE to remove the ions added to the sample(s) to acidify them? Say with a resin in barium form for sulfate or a resin in silver form for chloride?

Please, see what you think and thank you.

Hi,

Three types of QC samples are routinely collected for metals-in-water studies. The collection of an acidified 24 hour urine sample. The difference between acidic and non-acidic (alkaline) most complete loss in samples preserved.

Thanks
Smith

I'm running the same analysis. Since the detector we are using is measuring conductivity and acidified samples have a conductivity much greater than the baseline of the system, it cannot be used to accurately determine nitrate/nitrite concentration. In addition, use of nitric acid will result in even greater false positives ( had that issue once.) I have circumvented this problem in the past by running preserved samples via SM (standard method) Nitrate / nitrite 4500 using a cadmium column. This method doesn't use conductivity for determination (its colormetric) and therefore you can avoid damaging your system by running an inappropriate matrix.

We simply have samples that are collected as preserved and unpreserved. We run the unpreserved samples on the IC for anion analysis.

I agree with daved.
Acidification preserves samples for metal analysis. But for anion determinations acidification is not useful. especially nitrite will be less stable under acidic conditions.
Samples for anion analysis should kept cool and analyzed as soon as possible.