If you ask about the color change, then it is due to the reaction between the sparying reagent and the compound present on the plate. Most of the times, the concentration of the compound on the plate also affects the intensity of color. So color change is here only a method to identify the different constituent on the basis of its reactivity with the spraying reagent. Same compound may give a different color if you change the spray reagent. If you observe in UV before spraying, you may get an altogether different picture of the plate for those compounds which are only UV sensitive will also be seen.
I would suggest you to carry out a qualitative chemical examination of your extracts before TLC. This would make you sure about the nature of chemical constituents present in the extracts. You will definitely get an idea what type of phytochemicals are supposed to be present in your extracts. Aqueous extracts mainly have carbohydrates, phenolics, tannins, proteins etc. and methanolic extracts being less polar have other constituents of interest like glycosides, alkaloids, terpenooids, steroids etc. Now depending on their presence vide qualitative chemical tests, you can design the TLC experiment. You can choose the perfect solvent combinations depending on the solubility of the phytoconstituents present. Later for spraying you can use sulphuric acid or any other specific reagent like anisaldehyde-Sulphuric acid or vanillin too. Then you will get a variety of colors depending on the reaction with the aldeyde. Concentrated Sulphuric acid will charr the organic compound present on the plate and it will become black or dark brown on heating.
Regards
Please read the book from Eike reich, Anne Schibli, High-Performance Thin Layer Chromatography for the analysis of Medicinal Plants, Theme, 2006, pp. 234-237., I think you can get help from any TLC text-books
If you ask about the color change, then it is due to the reaction between the sparying reagent and the compound present on the plate. Most of the times, the concentration of the compound on the plate also affects the intensity of color. So color change is here only a method to identify the different constituent on the basis of its reactivity with the spraying reagent. Same compound may give a different color if you change the spray reagent. If you observe in UV before spraying, you may get an altogether different picture of the plate for those compounds which are only UV sensitive will also be seen.
I would suggest you to carry out a qualitative chemical examination of your extracts before TLC. This would make you sure about the nature of chemical constituents present in the extracts. You will definitely get an idea what type of phytochemicals are supposed to be present in your extracts. Aqueous extracts mainly have carbohydrates, phenolics, tannins, proteins etc. and methanolic extracts being less polar have other constituents of interest like glycosides, alkaloids, terpenooids, steroids etc. Now depending on their presence vide qualitative chemical tests, you can design the TLC experiment. You can choose the perfect solvent combinations depending on the solubility of the phytoconstituents present. Later for spraying you can use sulphuric acid or any other specific reagent like anisaldehyde-Sulphuric acid or vanillin too. Then you will get a variety of colors depending on the reaction with the aldeyde. Concentrated Sulphuric acid will charr the organic compound present on the plate and it will become black or dark brown on heating.
Regards
10% sulphuric acid used in postchromatographic detection as general reagent for qualitative identification. For any reaction, after spraying with the this reagent the TLC plate is heated. Compounds are charred to give different colour. reagent is not good for quantitative analysis. However, 10% Sulphuric acid in ethanol is used for the detection of polar compounds e.g. carbohydrates
Sulphuric acid is considered an universal chromogenic reagent and normally is used to detect, in general, how many spots (components) you have in your sample. It is supposed all organic compounds are charred if you spray on it. Before you spray with sulphuric acid I recommend you to check your components trough UV 254-366 and iodine. Later you can use other specific reagent for flavonoids , alkaloids, terpenoids and others as Alok indicated. Good luck
thank you so much for all of your explaination and details. And really appreciated with your answers.
Check this interesting link if it is useful to you:
http://www.slideshare.net/rahulbs89/extraction-of-plant-contituents
If colour changes to blue or brown. They may be terpenoid or steroids.
If same plate you evaluate in UV light. Spot with changed colored if give fluroscence then their is more possibility of steroids nucleus.
- Badges
- Science topic
- Similar topics
- Biological Science
- Botany
- Pharmaceutical Botany
- Plant Extracts