An x-ray fluorescence technique for determining a valence state of a sample. An x-ray excitation path is provided for exciting a sample with x-rays; and an x-ray detection path is provided for detecting fluorescence emitted from the sample, and focusing the emitted fluorescence to a focal spot. The detection path may include a monochromating detection optic for focusing the fluorescence; and also may include a detector on which the focal spot is focused. The precise positions of the focal spot are sensed, from which valence states of the sample can be determined; and/or the detection optic can be rocked across certain angles of incidence, to change the Bragg conditions, thereby sensing different valence states within the sample.