To quantify astaxanthin in Haematococcus pluvialis extracts using UV-Vis spectrophotometry (as an alternative to HPLC), you can apply the Beer-Lambert law, which requires the molar extinction coefficient (ε) of astaxanthin in the extraction solvent at a specific wavelength. For acetone, astaxanthin has a strong absorbance peak around 478 nm, with a reported molar extinction coefficient of approximately 140,000 L· mol¹ · cm¹. In ethanol, the peak is slightly shifted to around 474–476 nm, with an ε of approximately 125,000 L· mol¹ · cm¹. To calculate the concentration of astaxanthin, measure the absorbance (A) at the relevant wavelength and apply the formula c = A / (ε × l), where c is the concentration in mol/L, ε is the extinction coefficient in L·mol⁻¹·cm⁻¹, and l is the path length in cm (typically 1 cm). You can then convert the result to mg/L using astaxanthin’s molar mass (~596.84 g/mol). Ensure that your extracts are clear and free of particulate matter to avoid scattering errors, and ideally use a freshly prepared or standardised astaxanthin solution to calibrate your measurements. This method provides a reasonably accurate estimation of astaxanthin content in acetone or ethanol extracts when precise HPLC analysis is not feasible.

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Astaxanthin Quantification

1. Dissolve Sample:Dissolve astaxanthin in a suitable solvent such as acetone or ethanol.

2. Set Wavelength:Use a spectrophotometer set to 478 nm, where astaxanthin shows peak absorbance

3. Blank and Measure:Use the pure solvent as a blank to zero the spectrophotometer.

4. Calculate Concentration (Beer–Lambert Law)