QUANTITATIVE DETERMINATION OF METHOXY AND HYDROXYETHOXY GROUPS IN HYDROXYETHYL METHYL CELLULOSE BY FTIR SPECTROSCOPY WITH CALIBRATION USING 13C NMR DATA

A method for the quantitative determination of methoxy and hydroxyethoxy groups in hydroxyethyl methyl cellulose (HEMC) by FTIR spectroscopy with calibration using 13C NMR data was developed. Nine commercial HEMC samples were studied. Linear regression relationships between the relative intensities of the 1373 cm–1 (CH3 deformation) and 1312 cm–1 (CH2CH2OH deformation) bands and the substituent content were established. The best results were obtained with normalization to the 949 cm–1 band (pyranose ring skeletal vibrations): for methoxy groups R2 = 0.9515, RMSE = 0.284 %; for hydroxyethoxy groups R2 = 0.825, RMSE = 0.98 %. Validation on three independent samples showed deviations from the reference 13C NMR values not exceeding 1.8 % for methoxy and 0.7% for hydroxyethoxy groups, which is acceptable for screening tasks. The proposed rapid method can be used for incoming raw material control.