K X-ray emission spectra emitted from carbon, aluminum, silicon, phosphorus, titanium, chromium, and manganese compounds were measured, using a compact lab-scale flat crystal X-ray fluorescence spectrometer. The sensitivity of K X-ray transitions line-shape, relative to the atom's chemical speciation, is considered. Spectrometer's optimization concerning high energy resolution takes place for each measured fluorescence transition. The detected changes on the measured X-ray line-shapes allow extracting the chemical speciation of the emitting atom. In-lab high-resolution X-ray emission spectroscopy is shown to be a highly versatile technique for materials chemical characterization. Display omitted •X-ray emission spectroscopy for materials characterization in the laboratory.•Innovative use of a commercial WD-XRF spectrometer for chemical speciation.•Sensitivity of K X-ray fluorescence transitions on the chemical environment.•Crystal spectrometer's energy resolution optimization.