Determination of the degree of molar substitution of hydroxypropyl cellulose by gas chromatography

Abstract

We have improved the gas chromatography (GC) method with the aid of 1H NMR to determine the degree of molar substitution (MS) of hydroxypropyl cellulose (HPC). This improvement relied on our established dissolution approach for low-substituted HPC, facilitating NMR determination and subsequently expanding the working range of the MS determination from the lower limit of USP specified as 53.4% to 9.3% (MS 0.2). In this method, 2-iodopropane was produced by the reaction of hydroiodic acid with HPC at high-temperature and then measured by GC. 1H NMR was used for the correction of GC method. The MS results via the GC method (MSGC) exhibited a linear correlation with those obtained by the 1H NMR method (MSNMR), with correction equation of MSNMR=1.8026MSGC - 0.2046 (R2 = 0.9979). Method validation results showed that the average recovery and relative standard deviation (RSD) of MS are 103.5% and 0.83%, respectively. Detection limit and quantitation limit were 0.08 and 0.26, respectively. This method is accurate, sensitive with good precision, which is of great value for the production, research and development, and application of HPC, particularly the low-substituted HPC.