Stopped-flow injection spectrophotometric method for determination of chlorate in soil

A stopped-flow injection (FI) spectrophotometric procedure based on iodometric reaction for the determination of chlorate has been developed. Standard/sample was injected into a stream of potassium iodide solution and then merged with a stream of hydrochloric acid solution to produce triiodide. By stopping the flow while the sample zone is being in a mixing coil, a slow reaction of chlorate with iodide in acidic medium was promoted to proceed with minimal dispersion of the triiodide product zone. When the flow started again, a concentrated product zone was pushed into a flow cell and a signal profile due to light absorption of the product was recorded. Employing a lab-built semi-automatic stopped-FI analyser, the analysis can be performed with higher degree of automation and low chemical consumption. Linear calibration graph in the range of 5-50 mg ClO3 L was obtained, with detection limit of 1.4 mg ClO3 L. Relative standard deviation of 2.2% (30 mg ClO3 L, n=10) and sample throughput of about 20 h were achieved. The system was applied to soil samples and validated by batch spectrophotometric and standard titrimetric methods.