Take samples of 100 ml to 200 ml beaker, add 1 ml of concentrated hydrochloric acid,  heat the beaker to concentrate the solution to make its volume less than 50 ml slightly. Cool the beaker then shift the solution to 100 ml volumetric flask, use high pure water to dilute the solution to the scale, then move the solution to the original 20ml beaker. Add 10% hydroxylamine hydrochloride solution of 2 ml, shake it well and let it be static for 5 min, add 10 ml of acetic acid,-ammonia solution, after shaking, add 2ml  zinc reagent solution, then  shake it again, test the sample.