Chlorophenols are by-products of the drinking water purification process and are also widely used as wood preservatives, herbicides and pesticides. In this study, the derivatization and extraction happened in the headspace vials during the vial thermostatting step. The derivatization reaction is affected by temperature and time, therefore the thermostat time and oven temperature of the headspace sampler were investigated for optimum derivitization/extraction conditions.