This International Standard specifies a gas chromatographic method for the determination of the mass concentration of carbon monoxide in ambient air from a variety of sources. The method is free from interference because the appropriate gas chromatographic conditions are used to separate the carbon monoxide from all the other constituents in the air Sample, before the carbon monoxide is measured. lt is intended for the measurement of carbon monoxide at concentrations less than 25 mg/m3 although it tan be successfully applied to concentrations up to 1 000 mg/m3 respectivelyl) at 25 OC and 101,3 kPa. Measurements of carbon monoxideatconcentrations of less than 1 mg/m3 tan be obtained with careful Operation. The automatic technique is continuous only insofar as several discrete air samples tan be drawn and analysed each hour. NOTE - Although this International Standard is written for two ranges, i.e. 0 to 1 mg/m3 and 0 to 25 mg/ms, an intermediate range, e.g. 0 to IO mg/m3, could be utilized to advantage if all the concentrations fall within the expected range and more accuracy is desired. lt is dependent on the error in reading the output trace.