Describe in general how chromatography technique can be used to analyses food to identify if it contains any poison? and also Explain the benefits and limitation of the technique used

Since this is not my area of expertise, I searched Google under the key words "chromatography food analysis poison" to get these possible sources:

http://www.google.com/search?client=safari&rls=en&q=chromatography+food+analysis+poison&ie=UTF-8&oe=UTF-8

In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search. Also see http://hanlib.sou.edu/searchtools/.