Measuring the Astaxanthin content using UV-VIS spectroscopy:

Materials:

1. UV-VIS spectrophotometer
2. Quartz cuvettes
3. Astaxanthin sample
4. Solvent (ethanol)
5. Distilled water
6. Wavelength range: Typically, Astaxanthin absorbs light in the range of 400-550 nm.

Procedure:

1. **Preparation of Astaxanthin Solution**:

   - Weigh an appropriate amount of Astaxanthin sample accurately (usually around 1-10 mg depending on the concentration).
   - Dissolve the Astaxanthin sample in a suitable solvent (ethanol is commonly used) to prepare a stock solution. The concentration should be adjusted to fall within the linear range of the UV-VIS spectrophotometer.

2. **Blank Solution**:

   - Prepare a blank solution using the same solvent (ethanol) without Astaxanthin. This is to calibrate the instrument and account for any absorbance by the solvent.

3. **Baseline Correction**:

   - Place a quartz cuvette containing the blank solution into the spectrophotometer.
   - Adjust the wavelength range to include the absorption maximum of Astaxanthin (around 400-550 nm).
   - Perform a baseline correction by setting the absorbance to zero at the chosen wavelength.

4. **Sample Measurement**:

   - After baseline correction, remove the cuvette containing the blank solution and replace it with a cuvette containing the Astaxanthin solution.
   - Measure the absorbance of the Astaxanthin solution at the same wavelength as the baseline correction.

5. **Data Analysis**:

   - Using the absorbance values obtained from the spectrophotometer, calculate the concentration of Astaxanthin in the sample using Beer-Lambert law:

6. **Validation**:

   - Validate the obtained concentration values by comparing with known standards or by repeating the measurements.

7. **Reporting**:

   - Report the concentration of Astaxanthin in the sample along with any relevant experimental details (solvent used, wavelength of measurement, etc.).