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Standard Solution Appendix
Name
Content
Definition
Description
Identification
Purity
Assay
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A. Synthetic Additives
B. Natural Additives
C. Mixture Additives
Standard and Specification > Synthetic Additives > Citric Acid
16. Citric Acid  
Chemical Formula C6H8O7 
Molecular Weight 192.13  
Definition Citric Acid occurs as crystals (mono hydrated) called citric acid (crystal) or as anhydrous material called citric acid (anhydrous). 
[Compositional Specifications of Citric Acid]
Content Citric Acid should contain not less than 99.5% of citric acid (C6H8O7=192.13).  
Description Citric Acid occurs as colorless, transparent crystals. granules. or lumps, or as a white powder. It is odorless and has a strongly acid taste. 
Identification (1) An aqueous solution of Citric Acid (1→10) is acidic.

(2) Citric Acid shows the reaction of citrate salt in Identification. 
Purity (1) Sulfate : When 0.5 g of Citric Acid is tested for sulfates, its content should not be more than the amount that corresponds to 0.5 ml of 0.01 N sulfuric acid.
(2) Oxalate : When 1 g of Citric Acid is dissolved in 10 ml of water, where 2 ml of calcium chloride solution is added, it should not be turn turbid.

(3) Arsenic : When 0.25 g of Citric Acid is dissolved in 5 ml of water, which is tested for arsenic, its content should not be more than 4ppm.

(4) Heavy metals : 2 g of Citric Acid is tested by (2) Purity for [Guar Gum] (Not more than 10ppm).

(5) Calcium : 1 g of Citric Acid is dissolved in 10 ml of water, which is neutralized with ammonia solution. When 1 ml of ammonium oxalate solution is added, it should not be turn turbid.

(6) Readily sulfurizable substances : When 0.5 g of Citric Acid is dissolved in 5 ml of sulfuric acid by heating, the color of the solution should not be deeper than that of the color standard solution K.

(7) Polynuclear aromatic hydrocarbon : 25 g of Citric Acid is dissolved in 30 ml of water by heating at approximately 50°. After cooling, the solution is extracted 3 times with 20 ml each of n-hexane (UV absorption spectrophotometry grade). It is centrifuged at 2,500~3,000 rpm for approximately 10minutes and concentrated to 1~2 ml by evaporating n-hexane out. After cooling, n-hexane (UV absorption spectrophotometry grade) is added to the concentrate to bring the total volume to 10 ml, Test Solution. Absorption of Test Solution is measured at 260~350 nm with 1 cm path length. The difference in absorbance (compared to reference solution) should not be more than 0.05 in this range. In this case, a reference solution is prepared by following the same procedure with 30 ml of water instead of the sample solution.

(8) Isocitric acid : 0.5 g of Citric Acid is heated at 105° for 3 hours and cooled, which is dissolved in 10 ml of acetone, Test Solution. Using 0.005 ml of the test solution, it is tested by the Method 1 in Paper Chromatography. Only one spot should be observed. For the filter paper, a No.2 filter paper for chromatography is used. When the developing solvent front reaches approximately 25 cm, it is dried in air. Bromophenol blue solution is sprayed upon the paper. A reference solution is not used for this test. N-butyl alcohol, formic acid, and water (8:3:2) are mixed and set-aside. TS for citric acid. The supernatant is used as a developing solvent. 
Residue on Ignition When thermogravimetric analysis is done with 2 g of Citric Acid, the residue should not be more than 0.1%. 
Water Content Citric Acid is tested by the direct titration method in water content determination (Karl-Fischer Method). The water content should not be more than 0.5% for citric acid (anhydrous) and 8.8% for citric acid (crystal) 
Assay Approximately 1.5 g of Citric Acid is accurately weighed and dissolved in water (total volume = 250 ml), 25 ml of which is then titrated with 0.1 N sodium hydroxide solution (indicator : 2~3 drops of phenolphthalein solution).

             0.1 N sodium hydroxide 1 ml = 6.404 mg C6H8O7