Sensitive determination of diquat by a kinetic method using the stopped-flow mixing technique

A simple, sensitive, selective, fast and inexpensive assay for the determin ation of diquat is proposed. The method is based on the reduction of the he rbicide to a strongly fluorescent monocation radical with sodium dithionite . The initial rate of this reaction is directly proportional to the diquat concentration. The stopped-flow mixing technique was used because the kinet ic data can be obtained in only 7 s, meaning that the method can be automat ed. The calibration graph is linear over the range 5-500 ng ml(-1) and the precision (RSD) is close to 1.2%. The applicability of the method was demon strated by determining the herbicide in different kinds of samples.