Detection and quantitation of diazinon and chlorpyrifos : a novel GC

An analytical method was developed for detection and quantitation of diazinon and chlorpyrifos, two widely used pesticides in local water pathway. Solid phase extraction combined with GC/MS detection with selected ion monitoring was employed. In establishing calibration curves for GC/MS analysis, it may be impractical to use isotope-labeled analogs as internal standards for all analytes in a complicated matrix. Compounds may have to be used as internal standards which could cause non-linear effects because of different response of analytes and internal standards. A novel sample introduction method, which could eliminate this negative effect of non-linearity, was proposed. Calibration data were acquired using the traditional constant volume injection method, and a new method: constant mass injection of analytes. Calibration curves by the constant mass injection method show a better linearity and y-intercept. The nonlinear effect observed with data obtained in low concentration ranges using the constant volume injection method was eliminated. The effectiveness of these curves by two methods was also tested. Better accuracy was obtained with the constant mass injection method. This constant mass injection of analytes method could be very useful in quantitative studies of a complicated sample matrix, such as those encountered in the environmental analysis of pesticides, or in the quality control analysis of medical and industrial product. In solid phase extraction, Varian Bondelute SPE C8 cartridge was selected for extraction. With the standard water sample spiked at 500 ng/L for the two analytes, the recovery for diazinon was about 50% and for chlorpyrifos about 60%. With the standard water sample at 1000 ng/L, the recovery for diazinon was about 60% and for chlorpyrifos about 70%. Among three samples from three different sampling sites, diazinon was detected and confirmed. The quantitation of diazinon was done to water sample from the Calaveras River near the Sanguetti Street crossing Stockton, California, with observed concentration 143.2 ng/L