How to determine the molecular weight of cellulose using nuclear magnetic resonance method

Nuclear magnetic resonance (NMR) spectroscopy can be used to determine the molecular weight of cellulose, but this process is more complicated because the structure of cellulose is large and complex. The following are the general steps for determining cellulose molecular weight using NMR method:

1. Sample preparation

• Purification of samples : Make sure the cellulose sample is as pure as possible and removes other impurities.

• Dissolved sample : Cellulose is not easily soluble in water, so it is necessary to dissolve with a suitable solvent system, such as sodium dihydrogen phosphate solution (for example, 6% sodium phosphate solution) or other solvent systems.

2. NMR experiment

• Select the right NMR frequency : Use high-field NMR instruments, such as instruments with frequencies of 300 MHz or higher, to obtain a clear spectrum.

• Obtain spectra : Perform a solid or solution NMR experiment, and obtain a ¹³ C-NMR or ¹H-NMR spectrum of cellulose according to the experimental settings. ¹³C-NMR is commonly used in the analysis of cellulose molecular weight because its peak position reflects the changes in different carbon environments in the molecules.

3. Data analysis

• Spectral analysis : By analyzing the NMR spectrum, the main peaks in Especially in the C-NMR spectrum, the C1, C4 and other signals of cellulose can be used to determine the length of the molecular chain.cellulose are identified.

• Molecular weight calculation : Calculate the molecular weight of cellulose by comparing with standard samples of known molecular weight, or using the relationship between signal intensity and molecular weight in the spectrum (such as by measuring the length of cellulose chains).

4. Verification and comparison

• Comparative experimental data : Compare with molecular weight results obtained from other methods such as gel permeation chromatography (GPC) to verify the accuracy of NMR measurement results.

Things to note

• Since cellulose is a highly polymerized polysaccharide, its molecular weight determination may require special sample processing and data analysis techniques.

• The analysis of nuclear magnetic resonance spectrogram requires high professional knowledge and experience, and it is recommended to conduct experiments and data analysis under the guidance of professionals.

This method is more complex, but can provide in-depth information on the molecular structure of cellulose . If conditions permit, more accurate molecular weight data can be obtained in combination with other characterization techniques.