Primary Calibrants and Internal Standards

General principles of calibration of course apply to speciation analysis. This step is often not sufficiently considered, since it is estimated that about 25-30% of erroneous data may be attributed to calibration errors this has been reflected, for example, in the BCR intercomparison on extractable trace elements in soil and sediment [24], where many laboratories were demonstrated to have errors when analysing a common calibrant solution. 

In principle, methods should be validated for each type of matrix and for the extraction agent applied. Matrix effects may affect strongly the calibration (loss of signal, interferences etc.). Standard addition techniques are therefore the only way to control the validity of the detection, but only if the addition is performed with the proper identical form of the compound to be determined it should be noted, however, that by using standard addition procedures, levels of concentration may be reached which are no longer within the linear range of the detector response e.g. for BCD, AAS). It is 

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