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Standard and Specification
> Synthetic Additives
> Citric Acid
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| 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).
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| [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 |
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