Alternative Liquid Chromatographic Method for Determination of the Methoxyl and 2-Hydroxypropoxyl Content in Cellulose Ether Derivatives
Abstract:An alternative liquid chromatographic (LC) method was developed and validated for the simultaneous determination of methoxyl and 2-hydroxypropoxyl substituents in hypromellose and hypromellose acetate succinate. The method uses the hydriodic acid cleavage reaction, catalyzed by adipic acid, of the substituted methoxyl and 2-hydroxypropoxyl groups, which are quantitatively converted to iodomethane and 2-iodopropane. The iodomethane and 2-iodopropane are extracted into xylene, the extract is diluted with methanol, and the analytes are separated and assayed by gradient elution using a reversed-phase C18 column. The method is selective and sensitive and has good linearity with values of 0.999 for R2 and 0.25% for the y-intercept bias from 1.39 to 5.55 mg/mL for iodomethane, and 0.999 for R2 and 0.52% for the y-intercept bias from 0.184 to 0.735 mg/mL for 2-iodopropane. The relative standard precisions for this LC method were found to be ± 2.3% for determining methoxyl at the 23.1% (w/w) level, and ± 3.5% for determining 2-hydroxypropoxyl at the 6.7% (w/w) level. Compared with the current gas chromatographic (GC) compendial (JPE) method, the LC assay method has equal or better precision. It was found that both the standard and sample solutions have limited stability (8 h) after preparation. This limited stability has not been reported previously in the literature and may have an impact on the reported accuracy/precision of the literature data for the GC method. The LC method was proven to be robust with respect to variation in derivatization time and temperature, flow rate, and column temperature. It is well suited for the quality control needed in today's fast-paced pharmaceutical laboratories.
Document Type: Research Article
Affiliations: Groton Laboratories, Pfizer Global Research and Development, Pharmaceutical Sciences, Analytical R/D, Groton, CT 06340
Publication date: 2003-07-01
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- The Journal of AOAC INTERNATIONAL publishes refereed papers and reviews in the fields of chemical, biological and toxicological analytical chemistry for the purpose of showcasing the most precise, accurate and sensitive methods for analysis of foods, food additives, supplements and contaminants, cosmetics, drugs, toxins, hazardous substances, pesticides, feeds, fertilizers and the environment available at that point in time. The scope of the Journal includes unpublished original research describing new analytical methods, techniques and applications; improved approaches to sampling, both in the field and the laboratory; better methods of preparing samples for analysis; collaborative studies substantiating the performance of a given method; statistical techniques for evaluating data. The Journal will also publish other articles of general interest to its audience, e.g., technical communications; cautionary notes; comments on techniques, apparatus, and reagents.
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