This International Standard specifies a procedure by which elemental detection limits in X-ray photoelectron spectroscopy (XPS) can be estimated from data for a particular sample in common analytical situations and reported. This document is applicable to homogeneous materials and is not applicable if the depth distribution of elements is inhomogeneous within the information depth of the technique. In many applications, it is used to either confirm or deny the presence of an elemental species at a surface. The XPS detection limit is of great practical importance because the technique is routinely used to measure the concentration of elements which are present in low concentrations at a material surface, and knowledge of the limit of detection provides a statement of confidence when no element can be detected. Furthermore, if a particular detection limit for a specified element is required, it permits the analyst to calculate the acquisition time needed to achieve the required limit of detection. This information is important to plan experimental work, or to assess whether XPS is sensitive enough for the work in a practical timescale.This document provides a straightforward approach to calculating detection limits in XPS from experimental data in common analytical situations. It specifies the minimum requirements for the data, which include XPS measurement of the sample composition, including all detectable elements, and 1 or more XPS spectra taken under the desired operating conditions. The latter spectrum or spectra must include the kinetic energy region where a peak from the specified element is expected, and the kinetic energy region containing a peak from a reference element in the sample. The relative sensitivity factors for all elements present in the sample and the specified element must be known.The standard also provides informative annexes which allow the uncertainty in the calculated detection limit to be determined 1 and describe how the XPS detection limit is defined. Example data and calculations are provided as well as useful conversions. The final annex explains how detection limits calculated in a previous publication 2 are related to those in ISO 19668.The detection limit, X D , for element j is estimated using data from a reference element x, present in the sample and from the background noise at the expected position of a peak from element j. Specifically, the atomic concentration, X x , measured by XPS and the summed intensity (integrated counts) in a peak, A x , of element x are required.Equation 1 describes the relationship.The sensitivity factors for the elemental peaks, S x and S j , are required, and A D is the minimal detectable summed intensity for the peak from element j. In which W j is the full width at half maximum of the peak for element j. If the element is absent, then W j is set equal to W x . The energy step size in the data is ε, and k is the coverage factor, the recommended value being 2.33. The standard deviation of background intensity at the position of peak j is given b...