Densitometry is a tool used to quantify analytes in TLC. It relies on the Kubelka-Munk equation. Chapter 12 of this book may help;

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&cad=rja&uact=8&ved=0CEwQFjAF&url=http%3A%2F%2Fwww.researchgate.net%2Fprofile%2FBehnam_Beigzadeh%2Fpublication%2F258559133_High-Performance_Thin-Layer_Chromatography_%2528HPTLC%2529%2Flinks%2F098b63ddb83a47837d28492c.pdf&ei=s2fCVMemDsaxogTYmIG4BQ&usg=AFQjCNH4T0jZTj0ZZEOyZ28cIgzEzvbWtw&sig2=F2KO-gePIEvd7W3gxo3iIg

What exactly do you want to ? actually TLC can be used for different purpose such as quantitative and quantitative monitoring of the progress of organic reactions . 

Dear Rajkoti,

The idea of quantitative TLC is quite simple itself. You have to measure the amount of material in TLC spots. This can be done in several ways.

Old approach is an extraction of the compounds from their spots and then measuring the quantity – e.g. with a spectrophotometer. If compound is not UV- or visible light-absorbing, you can perform some reaction (on TLC plate before extraction, or after the extraction). Then you can compare the quantities. Of course, there are potential problems, e.g. the extraction should be complete, and you should understand that starting compound and the reaction product may have different extinctions. If you are interested in only one component, this is not a problem.

Modern approach is the use of a scanner/analyzer/plate reader, exactly as it is commonly used with electrophoretic gels stained with fluorescent or non-fluorescent dyes. Again, your compound should be either absorbing in UV or visible region, or fluorescent, otherwise you can treat the plate with a suitable reagent to transform your compound into a detectable derivative (as in an old-fashion method above). The choice of visualizing reagent depends on your compound, and it is a separate story. For example, nucleosides or other aromatic compounds can be scanned in UV region; if you want to detect amines, you treat the TLC plate e.g. with fluorescamine, and then detect the fluorescent spots. For scanners, visible working region is more common. If you use some chemical reaction for visualization, you should be sure that it is complete.

Good luck!

Dear Rajkoti, 

We use densitometry technique. But for this you should have CAMAG TLC INSTRUMENT WITH SCANNER.

For reference see chapter 12 of the book as mentioned by David.

For detail of instrument see the CAMAG website

http://www.camag.com/en/tlc_hptlc/products/evaluation_detection/tlc_scanner_4.cfm