Chiang Mai Journal of Science

 A low-cost stopped-flow spectrophotometric system was fabricated in the laboratory for a kinetic study on the reaction of molybdenum blue with arsenate. The influence of the concentration of the reagents on the rate of reaction has been studied. Arsenate and reagent solutions were flowed to mix together in-line, and the mixed zone was stopped at a flow cell where the absorbance at 880nm was continuously recorded. The initial slope of the stopped-flow profile was evaluated as an initial rate of the reaction, and then the order of reaction and rate law equation were derived. The following reaction rate equation: Rate = k[As(V)]2 [Mo]3 [PAT]1 [AA]1[H2SO4]-7 was obtained. This kinetic data could be used to suggest on the influencing of reactants to the reaction rate. The proposed system provided reproducible and accurate kinetic profile, convenient and fast operation, and low chemical consumption. The developed method is a suitable platform for the kinetic study of the reaction.