Hi Mandira,

there are a number of dedicated enzymatic assay kits. You can find a lot of them on internet. They are usually very reliable, since used for clinical chemistry. Though, you probably need to assay separately the two acids.

Another good method is potentiometric titration. Metrohm has develped an application for titrating citric and oxalic acid mixtures http://partners.metrohm.com/GetDocument?action=get_dms_document&docid=696176

For a less quantitative, inexpensive method, you can check Thin Layer Chromatography. If you find a good eluting system, you can stain the acids using bromocresol green

Best wishes

Dear Mandira,

You may try these sites:

http://www.ihc-platform.net/sancho.pdf

http://www.usp.org/sites/default/files/usp_pdf/EN/USPNF/revisions/updated_anhydrous_citric_acid.pdf

http://www.knauer.net/fileadmin/user_upload/produkte/files/Dokumente/application_notes/vcl0001n_citrate_and_oxalate_in_urin.pdf

http://www.clinchem.org/content/16/7/547.full.pdf

https://www.google.com.eg/search?biw=1366&bih=627&q=estimation+of+oxalic+acid+by+titration&revid=14952262&sa=X&ei=ueAbVM63EOSe7Aast4DoCw&ved=0CIYBENUCKAE

http://www.jbc.org/content/154/1/207.full.pdf

Good luck

Hanem

Dear Mandira,

You may try this

http://staff.du.edu.eg/upfilestaff/355/researches/3355_1396614280__SOME.FACT.S.CITR.pdf

Also

Citric acid determinations:

Pyridine-acetic anhydride method:

Citric acid estimation was carried out colorimetrically with pyridine-acetic anhydride method according to (Marier and Boulet, 1958) as follows:

Reagents:

- Reagent-grade acetic anhydride and pyridine.

- Anhydrous citric acid.

Procedure:

To a test tube, 1 mL of culture filtrate (containing from 25 to 200 mg of citric acid), or citric acid standard, or water (for the reagent blank) was added, followed by 1.30 mL of pyridine, and swirl the briskly. After similar additions have been made to all tubes in a series, add 5.70 mL of acetic anhydride, swirl the tube again, and immediately place it in the constant-temperature water bath at 32°C. Color development was completed after 30 min., and the color was stable for at least another 30 min., either in the 32°C bath or in air at a temperature of 22-29°C. The color intensity was read at 420 mm with the blank set at 100% transmission and the citric acid content of the samples were estimate by eference to the standards.

Determination of citric acid using the reference titration method:

Citric acid was determined using the reference titration method according to (Rugsaseel et al., 1995a) as follows:

50 mL of the samples of fermented molasses was titrated with 0.5 N NaOH to end point. To know the end point the fermented molasses was titrated until pH 8.1 (the iso-electric point) because it was impossible to use an indicator in the dark molasses medium. The resulting citric acid was calculated as grams per 100 mL as follow:

mL NaOH x N x 6.4

                                   = g citric acid per 100 mL

mL sample

REFERENCES

Marier, J. R. and M. Boulet (1958). Direct determination of citric acid in milk with improved pyridine acetic anhydride method. J. Dairy Sci. 41 1683-1692.

Rugsaseel, R., S. Morikawa, K. Kirimura and S. Usami (1995a). Stimulation of citric acid production in Aspergillus niger by addition of viscous substances in shake culture. Appl. Microbiol. Biotechnol. 42: 839-843.

El-Kady, Sh. M. (2003). Studies on the microbial production of citric acid. MSc. Theses, Agric. Microbiol. Fac. of Agric. Mansoura Univ, Mansoura, Egypt.

Sherif Sir, can you provide me the full text of citric acid estimation using titration method by Rugsaseel et al., 1995a