Sub-ppm level high energy resolution fluorescence detected X-ray absorption spectroscopy of selenium in articular cartilage.

The speciation of highly-diluted elements by X-ray absorption spectroscopy in a diverse range of materials is extremely challenging, especially in biological matrices such as articular cartilage. Here we show that using a high energy resolution fluorescence detected X-ray absorption spectroscopy (HERFD-XAS) technique coupled to an array of crystal analyzers, selenium speciation down to 400 ppb (µg kg-1) within articular cartilage can be demonstrated. This is a major advance in the speciation of highly-diluted elements through X-ray absorption spectroscopy and opens new possibilities to study the metabolic role of selenium and other elements in biological samples.