Colorimetric determination of a polymeric quaternary ammonium antimicrobial preservative in an ophthalmic solution
Good, R.M.; Liao, J.C.; Hook, M.J.; Punko, C.L.
Journal - Association of Official Analytical Chemists 70(6): 979-980
1987
ISSN/ISBN: 0004-5756 PMID: 3436913 Document Number: 379
A simple colorimetric method is presented for the determination of Polyquad®, a polymeric quaternary ammonium antimicrobial preservative, in an ophthalmic solution. Polyquad and magnesium are coprecipitated by ion pairing with Ponceau S, a highly colored sulfonate dye, at an acidic pH. The sample is centrifuged and the supernate analyzed spectrophotometrically. The concentration of Polyquad is determined by the decrease in dye concentration. Formulation excipients such as disodium edetate, dextran, and hydroxypropylraethylcellulose did not interfere with the quantitation. The method is specific, accurate, precise, and stability-indicating for the quantitation of 10 ppm Polyquad.
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