Summary for nitric acid analysis Discussion
Nitric acid in mixed acid is the focus of this thread, where the original poster asked for a standard, foolproof way to analyze nitric acid in a nitric/sulfuric mixture used for nitration. Geoff Smith suggested titrating with ferrous sulfate in a concentrated phosphoric/sulfuric acid medium, similar to bright-dip analysis methods. The later discussion drifted into instrument-based analysis: Daniel Montañés noted that ICP can be overwhelmed by concentrated nitric acid and may require dilution, while gas chromatography can be sensitive enough for small impurities but may be damaged by oxidizing agents and must stay within instrument limits. A later commenter asked for separate quantitative analysis of sulfuric and nitric acids after centrifuging a reaction mixture, but no definitive method was given in the excerpt. Overall, the thread points to titration as the practical answer, with caution that analytical technique depends on concentration and equipment compatibility.
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.
NITIN VASANT BHATE
Research Scholar – MUMBAI, MAHARASHTRA, INDIA
2004
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 sulphates 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.
Randall Fowler – Fowler Industrial Plating, LLC
Cleveland, Tennessee, USA
A. You could try titrating with ferrous sulfate
⇦ on
eBay or
Amazon [affil link] solution in conc. phosphoric /sulfuric acid medium as usually given in Al bright dip analysis methods.
Geoffrey Whitelaw
– Port Melbourne, Australia
2004
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
2004
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 4, 2013
A. Strong oxidising acids can attack organic column packings and polymer connections in the instrument.
Geoff Smith
Hampshire, England
January 12, 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 Montañés
– Cañuelas, Buenos Aires, Argentina
January 15, 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
January 17, 2013
Q. Dear all,
I am also with same request. We are using sulfuric acid and nitric acid in our reaction. After centrifuge we got mixture of sulfuric acid and nitric acid. I want quantitative analysis for content of sulfuric acid and nitric acid separately.
A Sambasivarao
pharmaceuticals – Telangana, India
September 30, 2019