5. Conclusion

External validation of an analytical method is only necessary when it is to be used by different laboratories. In this article, three classic external validation methods are presented:

• interlaboratory analyses, to estimate the precision of a standardized method;

• proficiency testing, to verify a laboratory’s ability to quantify an analyte;

• certification of reference materials, to create reference standards that can be linked to the international system of units in chemistry and biology.

The common point for all these studies is to involve a set of laboratories. This is a major administrative and logistical burden. However, it is essential. It also explains why certain structures specialize in organizing interlaboratory comparisons. For example,...