This European Standard specifies two methods for the determination of mercury. For the method described in Clause 4, tin(II) chloride is used as the reducing agent. For the method given in Clause 5, sodium borohydride serves as the reducing agent. The choice of method depends on the equipment available and the matrix (see Clause 3). Both methods are suitable for the determination of mercury in water, for example in drinking, ground, surface and waste waters, in a concentration range from 0,1 µg/l to 10 µg/l. Higher concentrations can be determined if the water sample is diluted. Lower concentrations in the range of 0,001 µg/l to 5 µg/l can be determined if special mercury analysers with an optimised instrument are used or if atomic fluorescence spectrometry is applied (see EN 13506 or ISO 17852).