Cromolyn sodium is an important drug for asthma management. The United States Pharmacopoeia (USP) monograph for cromolyn sodium describes an assay for oxalate based on absorbance after performing a chemical reaction. This method is cumbersome and tedious. The USP has initiated an effort to modernize existing monographs across all compendia. In response to this effort, this study describes an alternative method for oxalate determination using ion chromatography (IC). The assay proposed here is automated, fast, and uses an aqueous mobile phase (eluent). Hence, IC offers a significant improvement to the existing assay described in the USP. Moreover, using a Reagent- Free Ion Chromatography (RFIC™) system with electrolytically generated hydroxide eluent simplifies the method and enhances reproducibility.<br/>The method proposed uses a Thermo Scientific™ Dionex™ IonPac™ AS20 anion-exchange column, and suppressed conductivity detection to determine oxalate in cromolyn sodium in 5.5 min. The Thermo Scientific™ Dionex™ ADRS™ 500 2 mm Anion Dynamically Regenerated Suppressor produces regenerant ions necessary for eluent suppression and allows continuous operation with minimum maintenance. Separation of oxalate was achieved under isocratic elution conditions. Figure 1 shows separation of oxalate from two common anions, sulfate and phosphate. In order to achieve good separation from these common anions, the eluent concentration could be no greater than 30 mM. The method proposed here was validated following the guidelines outlined in USP General Chapter &lt;1225&gt;, Validation of Compendial Procedures. This method is a candidate to replace the existing assay for oxalate in the cromolyn sodium USP monograph, and thereby modernize the monograph.

Fast and automated method for determination of oxalate in cromolyn sodium

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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