ISO 18857-1:2005 specifies a method for the determination of 4-nonylphenol (mixture of isomers) and 4-(1,1,3,3-tetramethylbutyl)phenol in non-filtered samples of drinking water, ground water and surface water. The method is applicable in a concentration range from 0,005 micrograms per litre to 0,2 micrograms per litre for 4-(1,1,3,3-tetramethylbutyl)phenol and from 0,02 micrograms per litre to 0,2 micrograms per litre for 4-nonylphenol (mixture of isomers). Depending on the matrix, the method is also applicable to waste water containing the analyzed compounds in the concentration range from 0,1 micrograms per litre to 50 micrograms per litre. Higher concentrations can be measured after appropriate dilution of the sample.