analytical methods are written either in light of a specific laboratory's procedures or in
general terminology. It is unlikely that any given laboratory will follow the method
without incorporating some of their own internal procedures. These minor modifications
should not have any significant impact on the performance of the method. These minor
modifications include items such as:
Other undesirable modifications may be made which increase laboratory throughput or
reduce costs while compromising the performance of the method. Examples of this type of
- variations in the types of glassware used
- variations in the quantities of reagents used for digestions/dissolutions
- variations in instrument manufacturer, and related instrument operation
Major modifications to a referenced method significantly alter the performance and
validation of the method.
- decreasing or excluding the analysis of quality control samples
- extending calibration ranges significantly into non-linear ranges
- decreasing XRD diffraction peak analysis windows or number of peaks analyzed
If a laboratory has modified the reference method, the modifications and the purpose of
the modifications should be examined.
If the performance of the method is not known (e.g., it is a reference method with
major modifications or is a method from an unproven source) it should be thoroughly
validated through the analysis of samples of known results.