Because of its efficiency, fusion is often the method of choice for preparing a wide range of samples for analysis by x-ray fluorescence (XRF).
To maintain accurate and consistent results, it is prudent to use Drift Monitors for correction of aging x-ray tubes and sample preparation variances.
The monitors are manufactured as stable fortified glass discs that are used to correct for day to day drift in the x-ray output. It is intensities that matter.
These are not intended as primary standards but are normally used for XRF calibration drift. Each type of monitor has element compositions that are appropriate for the mineral type. Trace element intensities are adjusted to be well above background.