The determination of sulphoxide in degraded phenothiazine formulations by difference spectrophotometry
Davidson, A.G.
Journal of Pharmacy and Pharmacology 30(7): 410-414
1978
ISSN/ISBN: 0022-3573 PMID: 27605 Document Number: 132566
A method is described for the assay of phenothiazine sulfoxides which may be formed in phenothiazine formulations during storage under unfavorable conditions. The assay is based upon the measurement of difference absorbance of the sulfoxide solution in 0.2 M HCl relative to an equimolar solution reduced with Zn dust. A solvent extraction procedure avoids interference from coloring agents and colored photolytic breakdown products of the phenothiazines. The assay is specific in the presence of intact drug, sulfone and co-formulated drugs for the formulations examined and is sensitive to 0.5% of the total phenothiazine present as sulfoxide. Many aqueous formulations stored in partially filled containers have been shown to contain up to 31.5% of the total phenothiazine as sulfoxide.