Ensuring stability in method performance

It is a good laboratory praxis to a have "log-book" documenting the sample preparation (date of preparation, unique sample preparation number, calibration standard / sample description, weight for pressing, etc.) and the spectrum acquisition (date of measurement, spectrum file name, acquisition time, live time, dead time, tube current when applicable).

Also any essential changes (replacement of protective foils, changes in geometry, other high voltage setting, etc.) and problems (instabilities, repair of equipment, etc.) must be noted.

Several parameters shall remain constant during sample's measurements for an established calibration:

• Geometry
  
  
• vacuum conditions (if applicable)
  
  
• thickness and kind of protective foils
  
  

In the case of x-ray tube excitation:

• anode material
  
  
• kind of secondary target
  
  
• high voltage

The sample position must be reproducible and the irradiated area must be in the centre and smaller than the sample area itself. For tube excitation the detector must be electrically insulated from the rest of the spectrometer, because grounding problems will result in deteriorated energy resolution and other spectrum deformations.