Limit of maleic acid
Mobile phase
Prepare 0.005 N sulfuric acid that has been suitably filtered and degassed.
Standard preparation
Using
Mobile phase as the solvent, prepare a solution containing an accurately known concentration of about 0.001 mg of
USP Maleic Acid RS per mL.
Test preparation
Transfer about 100 mg of Fumaric Acid, accurately weighed, to a 100-mL volumetric flask, dissolve in Mobile phase, dilute with Mobile phase to volume, and mix.
Chromatographic system
(see
Chromatography 621)The liquid chromatograph is equipped with a 210-nm detector and a 4.6-mm × 22-cm column that contains packing L17. The flow rate is about 0.3 mL per minute. Chromatograph the
Resolution solution, and record the peak responses: the resolution,
R, of the maleic acid and fumaric acid peaks is not less than 2.5, and the relative standard deviation of the maleic acid peak for replicate injections is not more than 2.0%.
Procedure
Separately inject equal volumes (about 5 µL) of the
Standard preparation and the
Test preparation into the chromatograph, record the chromatograms, and measure the peak responses. The relative retention times are about 0.5 for maleic acid and 1.0 for fumaric acid. Calculate the quantity, in mg, of maleic acid in the total weight of Fumaric Acid taken by the formula:
100C(rU / rS),
in which
C is the concentration, in mg per mL, of
USP Maleic Acid RS in the
Standard preparation, and
rU and
rS are the responses of the maleic acid peaks obtained from the
Test preparation and the
Standard preparation, respectively. Not more than 0.1% of maleic acid is found.
Assay
Transfer about 1 g of Fumaric Acid, accurately weighed, to a conical flask, add 50 mL of methanol, and warm gently on a steam bath to effect solution. Cool, add
phenolphthalein TS, and titrate with 0.5 N sodium hydroxide VS to the first appearance of a pink color that persists for not less than 30 seconds. Perform a blank titration, and make any necessary correction. Each mL of 0.5 N sodium hydroxide is equivalent to 29.02 mg of C
4H
4O
4.