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topic 27688

Quantitative analysis of nitric acid in a mixture of nitric and sulfuric acid

A discussion started in 2004 but continuing through 2019


Q. I am working on nitration reaction wherein I need to prepare mixed acid (nitric + sulfuric). I would like to know the standard and a fool proof procedure to analyze the nitric acid in the mixture.



A. Nitin,

I have never found a "fool proof" method for this analysis. I've performed a series of lab tests on bright dip solutions containing high volumes of sulfuric and nitric acids. I've tried combining specific gravity measurements with volumetric titrations, but the most accurate measurement for nitric I could come up with was ± 13 v/v%. All of the analytical laboratories I've contacted about this tell me to use the same procedure:

1. Analyze the solution for total acidity by volumetric titration against Normal sodium hydroxide solution.
2. Analyze the solution for nitrates using either a mass spec or spectrophotometer.
3. Analyze the solution for sulfates using either a mass spec or spectrophotometer.
4. Calculate the respective percentages of NO3 and SO4 by dividing the concentration of NO3 and the concentration of SO4 by the total acidity concentration. Fool proof? Nothing is, but I hope this helps.

randy fowler
Randall Fowler - Fowler Industrial Plating, LLC
Cleveland, Tennessee, USA


A. You could try titrating with ferrous sulphate solution in conc. phosphoric /sulphuric acid medium as usually given in Al bright dip analysis methods.

Geoffrey Whitelaw
Geoffrey Whitelaw
- Port Melbourne, Australia


A. At our lab we analyze spent nitration acid that contains both nitric and sulfuric acids. To quantitate the two we weigh 2 samples, dilute one and titrate it with NaOH. the other we heat on a steam bath for 15 minutes to drive off the nitric then dilute and titrate. The sulfuric is the acid n the heated sample. The nitric is the difference between the two. Repeatability and precision depend on the heating time and temperature employed during sample prep.

Mark Carpenter
- New London, Missouri, USA

January 4, 2013

Q. Hi,
I am a biologist and I don't understand why I have to dilute nitric acid to analyze its impurities in gas or ICP? Thanks.

Dr Igor Roma
- Italy

January 12, 2013

A. Strong oxidising acids can attack organic column packings and polymer connections in the instrument.

geoff smith
Geoff Smith
Hampshire, England

January 15, 2013

A. Dear Igor,

ICP: Nitric acid will not do anything, but the detector is made to measure small quantities, so with concentrated nitric acid you can saturate the detector signal. If you dilute the nitric acid, you might have some small or poor signal, so you can sample some more concentrated nitric acid so you can detect more impurities.

Gaseous Chromatography: Packed columns could be damaged by oxidising agents like nitric acid, as Geoff says. And the sensibility is good enough to measure small quantities of impurities. If you have some small signals, you can concentrate the sample, but NOT OVER the maximum concentration or the lowest pH the instrument can resist.

Hope this could solve your doubt! Regards,

Daniel Montanes
- Canuelas, Buenos Aires, Argentina

January 17, 2013

Thanks for all dear Professor.
Q. I have other 2 questions, please:

1. After microwave digestion of a food or environmental sample, using at start 2 ml nitric acid and H2O2, at the end of this process what is the final concentration of the acid, so I can decide the final volume using water? And what is usually the volume at the end (25 ml) to use for the analysis in gas?

2.What can I download to improve my know-how about gas and microwave digestion?

3. If the sample is to acidify, what can I do to analyze it in gas? Just dilute it?

Thanks for all

Dr Igor Roma [returning]
- Rome, Italy

September 30, 2019

Q. Dear all,

I am also with same request. We are using sulphuric acid and nitric acid in our reaction. After centrifuge we got mixture of Sulphuric acid and nitric acid. I want quantitative analysis for content of sulphuric acid and nitric acid separately.

A Sambasivarao
pharmaceuticals - Telangana, india

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