A commercial WDXRF spectrometer (Bruker S4 Explorer, Karlsruhe,
West Germany) was used for analysis of the different samples.
This instrument is usually equipped with a 1 kW Rh-anode tube
working at a voltage range of 20–50 kV and a current from 50 to
20 mA. It is possible to use primary beam filters (made of Al or Cu)
between the primary radiation and the sample holder to reduce the background continuum and to improve the signal-to-noise ratio.
Energy resolution and efficiency for each analytical line also depend
on the collimator aperture and the analyzer crystal in use.