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Effects of Sulfamic Acid to Free Cyanide Test When Added to Sample Containing Nitrate/Nitrite That Is Below 10 mg/L

This is Nayl ReBay , a Corporate Pollution Control Officer of one of Private Companies here in the Philippines. We are currently quantifying the positive interference of Nitrate and Nitrite to Free Cyanide Tests by Ion Selective Electrode in our Industrial Wastewater. The US-EPA 9213 Method says that Nitrate and Nitrite shall only be eliminated when the concentration is more than 10 mg/L...Why so?

Does Nitrate and Nitrite below 10 mg/L in the wastewater do not interfere with the Free Cyanide Test?

If we add 50 mL Sulfamic Acid in 1 Liter sample (as per US-EPA 9213) containing less than 10 mg/L Nitrate and Nitrite, will nitrate and nitrite be eliminated?

We had a sample where we got higher Free Cyanide in the sample with Nitrate/Nitrite Eliminated than with No Elimination with Sulfamic Acid. That is why I am asking these question hoping that someone could kindly answer my queries.

Many thanks.

Nayl ReBay
Pollution Control Officer - Batangas City, Philippines
2007

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Sulfamic acid is a solid. The method says to add it to all samples. It will not hurt.

If memory serves, one adds 2 g. to a 500 ml distillation.

Dave Wichern
Consultant - The Bronx, New York
2007

My understanding is that the sulfamic will oxidize to sulphate and your nitrite will be reduced in the reaction - possibly to nitrogen.

Terry Tomt
- Auburn, Washington
2007