Hi! Do you want each geometric isomer to also be detected in the analysis? I do not recommend to keep standards in solution for long periods of time for this purpose.

Acetone or ethanol would be a good solvent to dissolve those standards of high purity. The absorption coefficients of each substance in those solvents may be known.

See “Carotenids handbook”.

I am analyzing astaxanthin, which I dissolve in acetone containing B H T to a certain concentration, and the concentration of the solution is determined by its ABS@474nm.

We have confirmed that the solution could be stored for about a month at minus 20°C or lower.

Good luck!

Thank you so much for your valuable feedback Dr Yasuhiro Nishida. the purpose was to dissolve the standards in the best solvent in order to keep them much longer time as the determination period may take quiet long.

Besides, I would like to detect the geometric isomers as well. though this current standard is all trans and the cis forms are not available on the market, I found that some authors have used the illumination method to generate the cis isomers in all trans standards before.

Thanks for the reply. In your case, how about dissolving a certain amount in acetone or dichloromethane, etc., dividing it into small brown vials or ampules, drying them under a stream of nitrogen, and storing them at -80°C with nitrogen or argon sealed in?

If you wish to use it, you can dissolve it in acetone or other solvent, make a constant volume using a volumetric flask, and determine the concentration from its UV/VIS absorbance.

For geometric isomers, I would suggest to obtain the sensitivity coefficient from the ratio of the absorbance of the maximum absorption of geometrical isomers to all-trans. (I am not sure if there is such a paper on zeaxanthin.)

Alternatively, it would be better to use the All-Trans form as a standard for quantification, although this would result in a lower estimate of the quantitative value.

Because the geometric isomers of carotenoids are in thermodynamic equilibrium, so even if you use the pure specific cis-isomer, it will significantly convert to other geometric isomers. Therefore, various problems arise when general analytical validation is performed.

Good luck!

Pure ethanol is best for dissolving lutein and zeaxanthin.

Thank you Prof Maria Stacewicz-Sapuntzakis. I really appreciate your contribution.

Dr Yasuhiro Yasuhiro Nishida . I am really grateful for your time spent to explain all this. I will surely consider your different suggestions.

My pleasure!

Lutein: A(1%,1cm) = 2550@445nm (in EtOH)

Zeaxanthin: E = 2480or2540@450nm (in EtOH), 2340@452nm (in Acetone)

from Carotenoids Vol. 1B:Spectroscopy, ISBN 3-7643-2909-2