Rapid extraction of isoproturon and diuron from granular activated carbon

This paper describes the development of a rapid extraction method for the recovery of the herbicides isoproturon and diuron from spiked granular activated carbon using supercritical carbon dioxide modified with high proportions of various organic solvents. Recovery of the herbicides increased with increasing extraction temperature, decreasing extraction pressure and increasing proportion of liquid solvent in the CO2 stream. Highest recoveries were achieved when liquid solvent alone was pumped through the extraction cell at high temperature (140 °C) indicating that the liquid solvent facilitates the extraction. Extraction efficiency of isoproturon and diuron from spiked GAC (0.5 mg g−1) was 75% (rsd 4%) and 41% (rsd 8%) respectively after only 5 minutes extraction with 20 mL dichloromethane:methanol (93:7). Increasing the extraction time led to the thermal degradation of the herbicides and consequently did not have a perceptible effect on their recovery. This very rapid extraction method has great potential as a screening technique for the routine monitoring of organic micro-pollutant concentrations in GAC filters. Such information may be used to optimise GAC regeneration time and to reduce the risk of pollutant breakthrough into drinking water supplies.