Rapid Determination Of Degree Of Substitution Of Carboxymethyl Cellulose By Spectral Methods

Because of limitations, there is no suitable method can be use as a online rapid detection of degree of substitution (DS) of carboxymethyl cellulose (CMC) for industry currently. Therefore, Fourier Transform Infrared Spectroscopy (FTIR) and Ultraviolet Spectrometry (UV) methods are presented to determine DS of CMC rapidly and accurately in this paper. Three methods have been studied, including FTIR external reference method, FTIR internal reference method and UV analysis method.In study of FTIR analysis methods,we propose the symmetric stretching vibration absorption at 1420cm-1 attributed to -COO- of CMC and the stretching vibration absorption at 1735cm-1 attributed to -COOH of CMC-H as the marker bands for DS analysis. And influences of different baselines and methods (including peak height and peak area) on the absorbance measurements of marker bands are discussed. In FTIR external method, characteristic absorption at 2060cm-1 of KSCN is used as the standard band, and calibration curves of A1420/A2060 vs. DS/C(KSCN) and A1735/A2060 vs. DS/C(KSCN) are created respectively. In FTIR internal reference method, symmetric stretching vibration absorption attributed to -CH2 of CMC is used as the standard band, and calibration curves of A1420/A2925 vs. DS and A1735/A2925 vs. DS are created respectively. DS values of CMCs are determined by these calibration curves and the results are compared with those got by national standard method, which shows that: absorbance measured by peak height is more accurate than that by peak area; marker band 1735cm-1 is more accurate than marker band 1420cm-1; and they have high accuracy in determination of DS used commonly (0.70~1.20) of CMCs for industry. In DS determination of CMC, both these two methods need little sample, few preliminary steps (even no preliminary step), simple operation sequences and have considerably high accuracy. Therefore, they are suitable to use as online rapid detections of DS of CMC for industry.In study of UV analysis method, CMC and Cu (â…¡) ions form a complex of CMC-Cu (â…¡) which has characteristic absorption in UV area (242.0nm). By the analysis of relationship between UV absorption (A) of CMC-Cu (â…¡) complex and volume (V) of copper sulfate solution and their interaction mechanism, we determine the reaction end point between carboxymethyl groups and Cu (â…¡) ions in UV analysis based on Lambert-Beer's law, and then DS of CMC is calculated. DS values of CMCs with high DS are determined by the UV analysis method and the results are compared with those got by national standard method, which confirms that the UV analysis method has high accuracy (relative deviation 1.7%~3.5%). In DS determination of CMC with high DS, the UV analysis method needs no preliminary step, simple operation sequences and it's sensitive and precise. Therefore, it's suitable to use as a online rapid detection of DS of CMC with high DS for industry.