ISO 20289:2025

This document specifies a chemical method for technicians working with total reflection X-ray fluorescence (TXRF) instrumentation to perform measurements of water samples, according to good practices, with a defined degree of accuracy and precision. Target users are identified among laboratories performing routine analysis of large numbers of samples, which also conform with ISO/IEC 17025. This document specifies a method to determine the content of elements dissolved in water (e.g. drinking water, surface water and ground water). This document is also applicable for determining elements in waste waters and eluates, taking into account the specific and additionally occurring interferences. This document does not specify sampling, dilution and pre-concentration methods. Elements determined using the method specified in this document can depend on the X-ray source of the instrument. This document does not specify health, safety or commercial aspects. The determinable concentrations depend on the matrix and the interferences encountered. In drinking water and relatively unpolluted waters, the limit of quantification lies between 0,001 mg/l and 0,01 mg/l for most of the elements. The range of concentrations typically lies between 0,001 mg/l and 10 mg/l, depending on the element and predefined requirements. Annex A reports an example of uncertainty calculation. Annex B provides an example report on validation of the method for TXRF analysis of water performed with instrumentation that has Mo as the X-ray source and uses Ga as the internal calibration standard. Limits of quantification of most elements are affected by blank contamination and depend predominantly on the laboratory air-handling facilities available, on the purity of reagents and the cleanliness of labware.