Spectroscopic Characterisation of Cationic Quaternary Ammonium Starches

Abstract Near‐infrared, infrared and Raman spectra of native starch and cationic quaternary ammonium starches prepared by different reaction methods were recorded. An interpretation of the spectra is given that takes the structural changes of the starch molecules and the degree of substitution (DS) into consideration. The near‐infrared spectra of the cationic starches showed additional bands compared to native starch at about 6010 cm −1 and 4438 cm −1 , which are assigned to the first overtone of the stretching vibration and to a combination band of the CH 3 groups in the trimethyl ammonium substituent. No significant changes in the infrared spectra of the cationic starches could be observed due to strong absorption bands of OH and H 2 O. By contrast, the Raman spectra of the cationic starches showed characteristic bands of the trimethyl ammonium substituent at about 3030, 970 and 761 cm −1 . Plots of the ratios of intensity of the 761 cm −1 band to an unchanged starch band at 938 cm −1 versus DS gave linear curves which could be used for DS determination. Furthermore, the use of a NIR calibration model for DS determination with a standard error of calibration (SECV) of 0.003 is reported.