Control samples

Control samples are reference materials with a matrix composition close to that of the analyzed samples, and which elemental mass fractions are close to the expected ones in the unknown samples. They should also be stable over time, and be available in sufficient amount as to be used for years. The control samples should go through the whole measurement procedure.

Samples fulfilling all these requirements are not always available. Therefore there are several choices of control samples:

• Certified Reference Material which elemental mass fractions are known with inaccuracies less than those resulting from the intended analytical method are the ideal choice
  
  
• Test routine sample characterized by alternate analytical methods (in-house material)
  
  
• Reference material, standard solution or in-house material
  
  
• Reference materials, standard solutions or spiked materials
  

Blank samples shall be analyzed for assessment of instrumental blanks or contaminations. Blank samples must be selected or prepared with a matrix similar to that of the unknowns, but with mass fraction of the elements of interest below the detection limits.