Anhydrous Citric Acid

Citric Acid

 

(Ph Eur monograph 0455)

 

C6H8O7    192.1      77-92-9

 

Ph Eur


 

 

Definition

 

Anhydrous citric acid contains not less than 99.5 per cent and not more than the equivalent of 101.0 per cent of 2-hydroxypropane-1,2,3-tricarboxylic acid, calculated with reference to the anhydrous substance.

 

Characters

 

A white, crystalline powder, colourless crystals or granules, very soluble in water, freely soluble in alcohol, sparingly soluble in ether. It melts at about 153C with decomposition.

 

Identification

 

First identification

 

B, E.

 

Second identification

 

A, C, D, E.

 

A.    Dissolve 1 g in 10 ml of water  R. The solution is strongly acidic (2.2.4).

 

B.    Examine by infrared absorption spectrophotometry (2.2.24), comparing with the spectrum obtained with anhydrous citric acid CRS after drying both the substance being examined and the reference substance at 100C to 105C for 24 h.

 

C.    Add about 5 mg to a mixture of 1 ml of acetic anhydride R and 3 ml of pyridine R. A red colour develops.

 

D.    Dissolve 0.5 g in 5 ml of water  R, neutralise using 1M sodium hydroxide (about 7 ml), add 10 ml of calcium chloride solution R and heat to boiling. A white precipitate is formed.

 

E.    It complies with the test for water (see Tests).

 

Tests

 

Appearance of solution

 

Dissolve 2.0 g in water  R and dilute to 10 ml with the same solvent. The solution is clear  (2.2.1) and not more intensely coloured than reference solution Y7, BY7 or GY7 (2.2.2, Method II).

 

Readily carbonisable substances

 

To 1.0 g in a cleaned test tube add 10 ml of sulphuric acid R and immediately heat the mixture in a water-bath at 90C 1C for 60 min. Immediately cool rapidly. The solution is not more intensely coloured than a mixture of 1 ml of red primary solution and 9 ml of yellow primary solution (2.2.2, Method I).

 

Oxalic acid

 

Dissolve 0.80 g in 4 ml of water  R. Add 3 ml of hydrochloric acid R and 1 g of zinc R in granules. Boil for 1 min. Allow to stand for 2 min. Transfer the supernatant liquid to a test-tube containing 0.25 ml of a 10 g/l solution of phenylhydrazine hydrochloride R and heat to boiling. Cool rapidly, transfer to a graduated cylinder and add an equal volume of hydrochloric acid R and 0.25 ml of a 50 g/l solution of potassium ferricyanide R. Shake and allow to stand for 30 min. Any pink colour in the solution is not more intense than that in a standard prepared at the same time in the same manner using 4 ml of a 0.1 g/l solution of oxalic acid R (350 ppm, calculated as anhydrous oxalic acid).

 

Aluminium (2.4.17)

 

If intended for use in the manufacture of dialysis solutions, it complies with the test for aluminium. Dissolve 20 g in 100 ml of water  R and add 10 ml of acetate buffer solution pH 6.0 R. The solution complies with the limit test for aluminium (0.2 ppm). Use as the reference solution a mixture of 2 ml of aluminium standard solution (2 ppm Al) R, 10 ml of acetate buffer solution pH 6.0 R and 98 ml of water  R. To prepare the blank use a mixture of 10 ml of acetate buffer solution pH 6.0 R and 100 ml of water  R.

 

Sulphates (2.4.13)

 

Dissolve 1.0 g in distilled water  R and dilute to 15 ml with the same solvent. The solution complies with the limit test for sulphates (150 ppm).

 

Heavy metals (2.4.8)

 

Dissolve 5.0 g in several portions in 39 ml of dilute sodium hydroxide solution R and dilute to 50 ml with distilled water  R. 12 ml complies with limit test A for heavy metals (10 ppm). Prepare the standard using lead standard solution (1 ppm Pb) R.

 

Water (2.5.12)

 

Not more than 1.0 per cent, determined on 2.000 g by the semi-micro determination of water.

 

Sulphated ash (2.4.14)

 

Not more than 0.1 per cent, determined on 1.0 g.

 

Bacterial endotoxins (2.6.14)

 

Less than 0.5 IU/mg, if intended for use in the manufacture of parenteral dosage forms without a further appropriate procedure for the removal of bacterial endotoxins.

 

Assay

 

Dissolve 0.550 g in 50 ml of water  R. Titrate with 1M sodium hydroxide, using 0.5 ml of phenolphthalein solution R as indicator.

 

1 ml of 1M sodium hydroxide is equivalent to 64.03 mg of C6H8O7.

 

Labelling

 

The label states:

 

where applicable, that the substance is free from bacterial endotoxins,

 

where applicable, that the substance is intended for use in the manufacture of dialysis solutions.

 

 

 


Ph Eur