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topic 3642

Looking for an analytical method for Citric Acid


(1999)

We have recently introduced a new passivation process consisting of 8-10 W% citric acid.(powder). The bath only contains citric acid. We are trying to find an analytical procedure and calculation for this acid. Any help on this would be greatly appreciated.

Thank You.

Jeff Huh
Oakland, California


(1999)

Analysis of citric acid is a simple titration with sodium hydroxide. I don't remember the exact sample size, sodium hydroxide normality, and indicator, but phenolphthalein should do the trick. Make a standard from a known amount of powder in water if you aren't sure of the calculation factor. I'm sure someone reading this has the information handy.

bill vins
Bill Vins
microwave & cable assemblies
Mesa (what a place-a), Arizona 


(1999)

Citric acid:
10 ml sample
phenolphthalein
titrate with 1N NaOH
%by wt =(mls of NaOH X 0.7)/Specific Gravity of solution

Hope this helps.

Steve Kingsley, CEF
Techmetals Inc.
supporting advertiser
Dayton, Ohio

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(2005)

The formula to calculate Citric Acid titrimetric method is:
W (weight en grams)=V of NaOH(ml) x Molarity x Molar Mass x 10-3.
You have to Know the mass of the sample and the Specific Gravity D=m/v) just in case you want to calculate %(v/v).

%(w/v)= W(analite)/w(sample in g)x100

Luis Sarmiento
interamerican University - Arecibo, Puerto Rico


March 18, 2009

%CA=Normality x volume of NaOH x Equivalent weight of CA
Weight of sample (g) x 10

Equivalent weight of Citric acid = Molecular weight of CA
Basicity of CA

= 192 / 8 = 24
NOTE: Basicity of CA = Number of Hydrogen ion present in CA, Which is 8.

OJEDIRAN, OLUSOLA O.
- FOOD TECHNOLOGY DEPARTMENT, UNIVERSITY OF IBADAN, NIGERIA.



July 27, 2012 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I am looking for a way to accurately determine (± 0.1 %) the concentration of Citric Acid in a passivation tank. Can I get an accurate reading with pH or Density or do I need to titrate?

Brad Smith
- Naples, Florida, USA

July 31, 2012

A. pH is a logarithmic scale, so there is no way to get a 0.1% accuracy.
Density will reflect both the acid and any soluble material in it, giving you a false high reading that gets progressively worse with use.
Titrations can be done wrong also. Many people do not use proper mixing and get false answers. It takes the correct indicator or a very good pH probe and meter to get good results. Free iron will react with the hydroxide titrant, so use a weak one with spin bar agitation. There is a possibility that the citrate will form complex ions which can skew the results. Get a good procedure from a good reference or one of the companies in the business.

James Watts
- Navarre, Florida


August 1, 2012

A. Your vendor can't help?

Then, something like this ought to work:

Take a suitable sample (10 ml?) and dilute to about 100 ml with DI water. Adjust the pH to about 9 with sodium hydroxide, then add about 1 g sodium sulfide (best done in a fume hood) to precipitate Fe as FeS. Filter, and wash filter cone well with DI water.

Then, titrate under suitable conditions (that you'll have to figure out) with 0.1 N KMnO4, to a purple endpoint.

You may find more details in the AOAC methods manual. This has methods for foodstuffs, likely several for citric acid.

dave wichern
Dave Wichern
Consultant - The Bronx, New York


August 8, 2012

A. Two things:

First, I forgot to mention that you need to bubble air through the filtrate after the iron precipitation step, to oxidize any excess sulfide ion. Otherwise, you will get a positive error in the titration.

Secondly, another way to go might be to add an excess of 0.1 N ceric ammonium sulfate, some sulfuric acid, and then boil the mixture briefly. After allowing it to cool, you can then back titrate the excess oxidant with standard ferrous ammonium sulfate, using ferroin as indicator. You may then calculate the citric content by simple arithmetic.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

August 13, 2012

A. Brad,
Naturally, all the easy monitoring methods are not highly accurate, though they are generally good enough to keep a bath at the proper concentration for passivation.

pH monitoring is traditional for a standard citric acid bath, titration works as well. Some citric baths are buffered to a higher pH though, which takes away the equivalence between citric concentration and both titration and pH readings.

In this case the general fallback is specific gravity/density, which does assume that the bath is kept well filtered so that the citric acid concentration is the major source of your reading. Other methods that should be viable include refractive index and conductivity.

More complex analytical methods such as those Dave suggest should be fine as long as you have a staff chemist and the necessary equipment on hand.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
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August 23, 2012

A. I was in the library yesterday, and I looked up 'citric acid' in the ASTM stds index. I found ASTM D4608 [link by ed. to spec at TechStreet] and ASTM D3908 [link by ed. to spec at TechStreet] - methods for citric acid in detergents.

One (I forget which) involved titrating a sample with a standard copper solution, using a copper ion selective electrode as the endpoint indicator. I imagine you could also use an chemical indicator, like PAN.

dave wichern
Dave Wichern
Consultant - The Bronx, New York


July 11, 2013 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Thanks to all who replied to my previous query about bacteria growth in a citric acid bath (letter 46618). I've been asked to inquire what is the best method of determining the strength of the citric acid in the bath?
Many thanks
Dave

Dave Foot
- Weymouth, Dorset, UK



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