How to determine the molecular weight of cellulose by ultracentrifugation

Determining the molecular weight of using ultracentrifugation cellulose is not a standard method, but the following steps can be tried. The basic idea of ​​this method is to use the settlement behavior of cellulose in the centrifugal field to infer its molecular weight.

1. Prepare samples and solutions

Sample preparation: Dissolve cellulose in a suitable solvent. Commonly used solvents include amino acid salt solutions, ionic liquids or other solvents that can dissolve cellulose. The solubility of cellulose is usually low, so it may be necessary to choose suitable solvents and conditions.

Solution preparation: Dissolve cellulose into a solution of a certain concentration and ensure that the solution is uniform. The complete dissolution of the cellulose can be ensured by ultrasonic treatment or other methods.

2. Ultracentrifugation experiment

Equipment Setup: Use an ultracentrifuge (such as a liquid centrifuge) and select the appropriate rotor and speed as needed. Common speed ranges are hundreds of thousands to millions (centrifugal acceleration).

Centrifugal conditions: Select the appropriate centrifugal conditions (speed, time, etc.). The conditions for centrifugation should be adjusted according to the nature of the sample and the expected molecular weight range. Higher centrifugation rates can cause larger molecules or particles to settle, while lower centrifugation rates are suitable for smaller molecules.

Centrifugation process: Put the sample into the centrifuge tube, and after equilibrating the centrifuge tube, start the centrifugation process. Record centrifugation time and rotation speed.

3. Data analysis

Analyze the settlement data: After centrifugation, remove the centrifuge tube and observe the settlement of the sample. The molecular weight of can be estimated by analyzing the position, thickness, etc. of the settlement belt cellulose . Generally, larger molecules settle in higher regions.

Calculate molecular weight: Based on the data of settlement, use the Stokes-Einstein equation or other related formulas to calculate the molecular weight. This process may require the calculations in combination with cellulose concentration and centrifugal conditions.

4. Correction and Verification

Calibration: Use standard samples of known molecular weight to ensure the accuracy of measurement results.

Verification: Compare with the results of other measurement methods (such as gel permeation chromatography, laser light scattering, etc.) to verify whether the molecular weight determined by ultracentrifugation is accurate.

Things to note

Solubility Issues: The solubility of cellulose is low, and it may be necessary to choose appropriate solvents and methods to ensure that the cellulose is sufficiently dissolved.

Choosing centrifugal conditions: The selection of conditions such as rotation speed, centrifugal time will affect the results and need to be adjusted according to the specific situation.

Data Explanation: The molecular weight calculation of ultracentrifugation involves multiple factors, and data interpretation may require experience and in-depth understanding of the theory.

In general, ultracentrifugation requires high technical requirements and experience to determine the molecular weight of cellulose, and other more direct and common analytical methods are usually used.