DEFINITION
(2RS)-2-Hydroxybutanedioic acid.
Content: 99.0 per cent to 101.0 per cent (anhydrous substance).
CHARACTERS
Appearance: White or almost white, crystalline powder.
Solubility: Freely soluble in water and in alcohol, sparingly soluble in
acetone.
IDENTIFICATION
A. Melting point: 128°C to 132°C.
B. Infrared absorption spectrophotometry.
TESTS
Solution S: Dissolve 5.00 g in water R and dilute to 25 ml with the same
solvent.
Appearance of solution: Solution S is clear and colourless.
Optical rotation: - 0.10° to + 0.10°, determined on solution S.
Water-insoluble substances: Maximum 0.1 per cent.
Related substances
Liquid chromatography (2.2.29).
Limits: (Please see the original monograph)
impurity A: not more than twice the area of the corresponding peak in the
chromatogram obtained with reference solution (b) (1.0 per cent);
impurity B: not more than 0.25 times the area of the corresponding peak in the
chromatogram obtained with reference solution (b) (0.05 per cent);
any other impurity: for each impurity, not more than 0.5 times the area of the peak
due to impurity B in the chromatogram obtained with reference solution (b) (0.1 per
cent);
total of other impurities: not more than 2.5 times the area of the peak due to
impurity B in the chromatogram obtained with reference solution (b) (0.5 per
cent);
disregard limit: 0.1 times the area of the peak due to impurity B in the
chromatogram obtained with reference solution (b) (0.02 per cent).
Heavy metals: Maximum 20 ppm.
Water: Maximum 2.0 per cent, determined on 1.00 g.
Sulphated ash: Maximum 0.1 per cent, determined on 1.0 g.
ASSAY
Dissolve 0.500 g in 50 ml of carbon dioxide-free water R. Titrate with 1 M sodium
hydroxide determining the end-point potentiometrically. 1 ml of 1 M sodium hydroxide
is equivalent to 67.05 mg of C4H6O5.
IMPURITIES
Specified impurities A, B. (Please see the original monograph)
R' --- COOH --- R
A. R = CO2H, R' = H: (E)-butenedioic acid (fumaric acid),
B. R = H, R' = CO2H: (Z)-butenedioic acid (maleic acid).
Malic Acid contains not less than 99.0 percent and not more than 100.5 percent of C4H6O5.
Identification: Infrared Absorption 197K , on undried specimen.
Residue on ignition: not more than 0.1%.
Water-insoluble substances: Dissolve 25 g in 100 mL of water, filter the
solution through a tared filtering crucible, wash the filter with hot water, and dry
at 100 to constant weight: the increase in weight is not more than 25 mg (0.1%).
Heavy metals: 0.002%.
Fumaric and maleic acids: To pass the test. Not more than 1.0% of fumaric
acid and not more than 0.05% of maleic acid are found.
Organic volatile impurities: meets the requirements.
Assay: Transfer about 2 g of Malic Acid, accurately weighed, to a conical
flask, dissolve in 40 mL of recently boiled and cooled water, add phenolphthalein
TS, and titrate with 1 N sodium hydroxide VS to the first appearance of a faint pink
color that persists for not less than 30 seconds. Each mL of 1 N sodium hydroxide is
equivalent to 67.04 mg of C4H6O5.
DESCRIPTION
Malic Acid occurs as a white or nearly white, crystalline powder or granules having
a strongly acid taste. One gram dissolves in 0.8 mL of water and in 1.4 mL of
alcohol. Its solutions are optically inactive. It melts at about 130°C.
Function: Acidifier; flavoring agent.
REQUIREMENTS
Identification: The infrared absorption spectrum of a neat dispersion of the
sample between two potassium bromide plates exhibits maxima only at the same
wavelengths as those of a similar preparation of USP Malic Acid Reference
Standard.
Assay: Not less than 99.0% and not more than 100.5% of C4H6O5.
Fumaric Acid: Not more than 1.0%.
Lead: Not more than 2 mg/kg.
Maleic Acid: Not more than 0.05%.
Optical (Specific) Rotation [α]25°/D: Between −0.10° and +0.10°.
Residue on Ignition: Not more than 0.1%.
Water-Insoluble Matter: Not more than 0.1%.
