The study of the speciation of highly-diluted elements by X-ray absorption spectroscopy is experimentally extremely challenging, especially in geochemistry, environmental bio-geochemistry and Earth sciences. Here we present an innovative synchrotron spectroscopy technique, namely high energy resolution fluorescence detected X-ray absorption spectroscopy (HERFD-XAS). Within this approach, measuring the XAS signal in fluorescence mode with a Crystal Analyser Spectrometer (CAS), with a ~1 eV energy resolution, allows to overcome the restrictions on sample concentrations that can be typically conventionaly measured (Proux et al. 2017). On the BM30b beamline (ESRF, Grenoble, France), we developed a CAS in the Johann’s geometry (Llorens et al., 2012). This spectrometer is now on a dedicated beamline (BM16) and opened to regular users since January 2017. The new opportunities brought by this high resolution spectroscopy are i) the possibility to study ultra-diluted elements by filtering with a great efficiency the background photons and ii) to improve the sensitivity of the measurement with the acquisition of better resolved XANES spectra. This is a major technological advance with strong benefits for the study of highly-diluted elements with XAS, and opens new possibilities to explore the speciation of a target chemical element at natural concentration levels, which is critical in the fields of environmental and bio-geochemistry sciences. Llorens et al. (2012) Rev. Sci. Instrum. 83:063104 Proux et al. (2017) J. Environ. Quality (in press).