The procedure is intended for the measurement of less than 25 mg/m3 although it can be successfully applied to concentrations up to 1 000 mg/m3 at 25 °C and 101,3 kPa. Concentrations of less than 1 mg/m3 can be obtained with careful operation. The automatic technique is continuous only in so far as several discrete air samples can be drawn and analysed each hour.