This standard specifies two methods for the determination of certain organic nitrogen and phosphorus compounds in waters by gas chromatography (see Table 1). The methods may be extended to include additional substances, provided the methods are validated for each individual case. Clause 3 describes the liquid/liquid extraction method, which is applicable to samples of drinking waters, ground waters, surface waters and waste waters containing up to 0,05 g/l of suspended solids. In the presence of organic matter, suspended matter and colloids, interferences are more numerous and consequently the detection limits of this method can be higher. NOTE: Because of the very low concentrations normally present in the waters, the problem of contamination is extremely important. The lower the level measured, the more precautions have to observed. Clause 4 describes the liquid/solid extraction method which is applicable to samples of ground water, surface water and drinking water containing mass concentrations of about = 0,05 µ/l. Interferences occurring with the examination of some types of surface water can prevent the application of this method. Detection limits are given for information in annex A. NOTE When applying this standard, the guide on analytical quality control for water analysis (see ISO/TR 13530) should be followed.