Dear Giuseppina,

For triterpenes:

Add carefully 5 mL of acetic anhydride and 5 mL of concentrated sulfuric acid into 50 mL absolute ethanol, while cooling in ice.Heat at 100 C for 5-10 minutes.

 https://books.google.ps/books?id=fBCDK_Tgh10C&pg=PA528&lpg=PA528&dq=preparation+of+a+fresh+Liebermann+burchard+reagent+for+triterpenes&source=bl&ots=5kl1a3MWSk&sig=rr65S5jRiz_ygCoRG--np-qLyyg&hl=en&sa=X&ved=0ahUKEwjYiv79u9zJAhUm_HIKHX-OCGkQ6AEIHzAB#v=onepage&q&f=false

For cholestrol

In the preparation of the Liebermann-Burchard reagent, the following

reagents are necessary: (1) glacial acetic acid, AR; (2) acetic

anhydride, AR; (3) sulfuric acid, AR; and (4) cholesterol.* It is very

important that all glassware for the preparation of this reagent be

chemically clean and dry, or poor reagent quality will result (brown

color).

Cool acetic anhydride and concentrated sulfuric acid in ice water or

in the freezer compartment. To a 500-ml amber glass bottle fitted with

a polyseal cap, add 220 ml of cold acetic anhydride and 200 ml of glacial

aietic acid (room temperature). Mix by inversion and add 30 ml of

coid concentrated sulfuric acid. The reagent is ready for immediate

use and is stable for more than 6 months when stored at 4#{176} in the

dark. When stored at room temperature, the reagent shows signs

(darkening) of deterioration after 1-2 weeks.

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.536.1278&rep=rep1&type=pdf

For carotene

Liebermann-Burchard reagent, using 10 cc. of chloroform solution, 2 cc. of acetic anhydride and 0.2 cc. concentrated sulphuric acid.

http://ebm.sagepub.com/content/31/7/804.abstract

Hoping this will be helpful,

Rafik

Dear Giuseppina,

For triterpenes:

Add carefully 5 mL of acetic anhydride and 5 mL of concentrated sulfuric acid into 50 mL absolute ethanol, while cooling in ice.Heat at 100 C for 5-10 minutes.

 https://books.google.ps/books?id=fBCDK_Tgh10C&pg=PA528&lpg=PA528&dq=preparation+of+a+fresh+Liebermann+burchard+reagent+for+triterpenes&source=bl&ots=5kl1a3MWSk&sig=rr65S5jRiz_ygCoRG--np-qLyyg&hl=en&sa=X&ved=0ahUKEwjYiv79u9zJAhUm_HIKHX-OCGkQ6AEIHzAB#v=onepage&q&f=false

For cholestrol

In the preparation of the Liebermann-Burchard reagent, the following

reagents are necessary: (1) glacial acetic acid, AR; (2) acetic

anhydride, AR; (3) sulfuric acid, AR; and (4) cholesterol.* It is very

important that all glassware for the preparation of this reagent be

chemically clean and dry, or poor reagent quality will result (brown

color).

Cool acetic anhydride and concentrated sulfuric acid in ice water or

in the freezer compartment. To a 500-ml amber glass bottle fitted with

a polyseal cap, add 220 ml of cold acetic anhydride and 200 ml of glacial

aietic acid (room temperature). Mix by inversion and add 30 ml of

coid concentrated sulfuric acid. The reagent is ready for immediate

use and is stable for more than 6 months when stored at 4#{176} in the

dark. When stored at room temperature, the reagent shows signs

(darkening) of deterioration after 1-2 weeks.

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.536.1278&rep=rep1&type=pdf

For carotene

Liebermann-Burchard reagent, using 10 cc. of chloroform solution, 2 cc. of acetic anhydride and 0.2 cc. concentrated sulphuric acid.

http://ebm.sagepub.com/content/31/7/804.abstract

Hoping this will be helpful,

Rafik

hello thank you for your answer. 

However i have 2 concerns: one is that I don't have TLC immediately avalaible; the second is that the original color of the triterpenes extract is red/brown. Once I add the LB testing solution, I obtain a brown/reddish solution that doesn't change in time. I decolorised some ml of this these triterpenes and added the LB with final color grey/bluish. What color is the positive results for triterpenes, exactly?