Sciencemadness Discussion Board

Testing for alkaloids in unknown plants

alchemizt - 28-2-2022 at 06:42

I'm trying to come up with a way to rapidly screen/test for the presence if alkalods in various plants with unknown phytochemical compositions. I have dragendorffs reagent and marquis reagent for spot tests and TLC. What I'm wondering is how to prepare the plants for these tests. A soxhlet extraction takes too much time for screening plants like this. How would you go about testing a range of unknown plants for alkaloids like this?

wg48temp9 - 28-2-2022 at 09:18

Quote: Originally posted by alchemizt  
I'm trying to come up with a way to rapidly screen/test for the presence if alkaloids in various plants with unknown phytochemical compositions. I have dragendorffs reagent and marquis reagent for spot tests and TLC. What I'm wondering is how to prepare the plants for these tests. A soxhlet extraction takes too much time for screening plants like this. How would you go about testing a range of unknown plants for alkaloids like this?


I would think you would need to concentrate and purify an extract from your plants. Can you try your TLC plates with a crude extract (presumably very dilute and contaminated by lots of non-alkaloids) from a plant that you know contains an alkaloid to see if your reagents work under those conditions.

I am sorry I don't know which suitable extraction solvent could be used. It probably depends on which alkaloid your try to detect.

unionised - 28-2-2022 at 09:43

The classic answer is to grind the plant with water and bicarbonate of soda (to convert any alkaloids to the free base) extract them with chloroform- which will dissolve alkaloids. Any fat or oil will also dissolve in the organic phase.
Then take the chloroform and shake it with dilute acid, so that any alkaloid is now in solution as the salt in the water layer. The oils will remain in the chloroform and can be discarded (for recycling by distillation).

Finally add bicarbonate to that again and extract into chloroform again.
That will mean all the alkaloids are in the chloroform solution (but without any fats / oils this time) ready for spotting onto a TLC plate.

A hundred years ago, anything that didn't make it through that process wouldn't have been called an alkaloid.
On the other hand, it will exclude some interesting materials like N oxides.

draculic acid69 - 7-3-2022 at 03:57

Dragenrorff reagent doesn't work for all alkaloids. Just some of them.