If not, how to preserve marine water samples for Chl a test for longer duration when refrigeration is not possible?
Never tried it but it is not a good idea. Better to put them in the freezer. It is not the effect of temperature on the pigments that is the immediate problem. The big problem with Chlorophyll in organic solvent is that chlorophylases are not denatured in organic solvents and so continue to work. Chlorophylases are nevertheless denatured easily by 60 oC treatment. That is OK for ethanol or methanol but no good for acetone. Chlorophylases are not soluble in organic solvents so you can get rid of them by filtration or the centrifuge.
No, you have to use a freezer, freezing is part of the digestion, that means the water inside the cloroplast will distroy them and the chlorophyll will become available for solvent, nevertheless 90 % ethanol is better working than acetone (method of Nusch).
Gunter - I tend to agree with you. There is also the problem that acetone is a really lousy extractant for chlorophylls. Hot ethanol or methanol is a better idea and has the bonus that the heat will get rid of the chlorophyllases.
I do not recommend 90% ethanol. First reason of course is that the equations I developed for ethanol were for 100% ethanol. The more serious reason is that chlorophylls easily form micelles in organic solvents which are miscible with water. You will get a false low reading.
Raymund, the German Standard Methods (DEV L 16) use ethanol (90 %)....
I think, it's working
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