A few days ago I asked a question about persulfate contamination and how it might interfere with a total nitrogen determination.
We are doing a persulfate digestion of river water samples and oxidizing all organic nitrogen to NO3.
All of our blanks and background show extremely high levels of nitrates.
The glassware washing procedure is to wash with phosphate-free detergent, rinse, soak in concentrated acid (not trace-metal grade), and rinse with reverse-osmosis water followed by 18-megaohm water from our Millipore system.
My question is, could detergent residues survive this process and linger to interfere with our nitrogen determination?
Anyone else have this problem?
With increasing desperation,
Kevin
Your RO water may have nitrate salts in it. You should be able to just clean with 10% HCl followed by 3x with the millipore.
You are correct, we did find nitrate salts in our RO water. The Milli-Q water has been free of nitrates.
However we did trace the problem to our potassium persulfate, apparently there have been several labs reporting the same problem with the same reagent.
Thank you for taking the time to answer.
Kevin
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