Dear Mandouh Alsayed Eisa: Perhaps the best way to digest plant samples for determination of chlorine content could stop using HCLO4 and HCl, using larger aliquots of HNO3.

Hi Mandouh Alsayed Eisa: Please go through the following links they will be of great help to you.

http://www.sciencedirect.com/science/article/pii/S0003267006008087

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC438316/

Good Luck

The best answer is in the AOAC manual. 

Aggressive methods of extraction such as dry ashing and conc. acids possibly will result in the loss of chloride. I have found that hot water extraction is the best way in this condition.     

Dear Gamal Mohammad Fahmy,

Can you give me a valid reference for water extraction. Thank you.

You furnish your mail ID I will send you some papers to extract and estimate chlorie content