Which elements cannot be detected by X-ray photoelectron spectroscopy?

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Moon rock crystals — surface analysis A scanning-electron-microscope photograph of pyroxene and plagioclase crystals (the long and the short crystals, respectively) that grew in a cavity in a fragment of Moon rock gathered during the Apollo 14 mission.

X-ray photoelectron spectroscopy (XPS) is a highly effective technique for the qualitative analysis of elements present on a surface. It is capable of detecting all elements with the exception of hydrogen and helium.1