Most probably, iodometric determination should be possible in this case. Here chlorine will react with potassium iodide (KI) wherein iodine will be liberated. Liberated iodine could bed determined by titration with thiosulphate.
For further information, I would request you to study a standard text book.
Hello Michael. Our lab works with chlorine and porphyrins, and the concentration is usually determined by HPLC. I am not sure if you want a more rapid, bench method, but I do believe that HPLC is, clearly, good choice.