Chlorophosphonazo Ⅲ can be reacted with chitosan (CTS) to form an electrochemically in-active complex in the buffer of (CH2)6N4 (PH = 5,0), Chlorophosphonazo Ⅲ has a well-defined second order derivative polar graphic wave at -0. 158V (SCE). Adding CTS into the chlorophosphonazo Ⅲ solution resulted in the decrease of the peak current without the change of the peak potential. The decrease is proportional to CTS concentration from 2.5 to 30 mg/L. The limit of the dtection is 0.5 mg/L, with the correlation coefficient of 0. ...