  In this article, we demonstrate the viability of highly monochromatic
full-field X-ray absorption near edge structure based tomography using a
laboratory-scale Johann-type X-ray absorption spectrometer based on a
conventional X-ray tube source. In this proof-of-concept, by using a phantom
embedded with elemental Se, Na$_2$SeO$_3$, and Na$_2$SeO$_4$, we show that the
three-dimensional distributions of Se in different oxidation states can be
mapped and distinguished from the phantom matrix and each other with absorption
edge contrast tomography. The presented method allows for volumetric analyses
of chemical speciation in mm-scale samples using low-brilliance X-ray sources,
and represents a new analytic tool for materials engineering and research in
many fields including biology and chemistry.
