Determination of Paraquat by Flow Injection-Chemiluminescence

Based on the fact that paraquat could enhance the chemiluminescence intensity of potassium ferricyanate-luminol system in alkaline environment, a method for the determination of paraquat by flow injection-chemiluminescence was proposed, and the luminescence mechanism of the system was discussed. 1.0×10^-3mol·L^-1 potassium ferricyanate standard solution was mixed with paraquat solution through a three-way tube and the mixture was entered into the circulation tank through a 10 cm-mixing tube. Then 2.0×10^-6mol·L^-1 luminol standard solution containing 0.005 mol·L^-1 sodium hydroxide was loaded into the above mixture, and the signal was recorded. It was speculated that potassium ferricyanide catalyzed the oxidation of luminol by dissolved oxygen to produce chemiluminescence under the alkaline condition, and the addition of paraquat increased the concentration level of the excited state of the luminol oxidation product 3-amino-phthalate ion, thus stronger light was emitted. Under the optimal conditions, linear relationships between the mass concentration of paraquat and its corresponding chemiluminescence intensity kept in the ranges of 5.0×10^-4-1.0×10^-2g·L^-1 and 2.0×10^-2-1.0×10^-1g·L^-1, with detection limit of 7.4×10^-5g·L^-1. Paraquat standard solutions were determined 11 times in parallel, and RSD of the determined values were not more than 5.0%. Test for recovery was made on the blank urine sample, giving results in the range of 96.4%-104%.