The logic of orthogonal techniques and measuring different critical attributes.
Every method has a scope
A method is designed for a particular analytical attribute and reportable range. Selectivity adequate for one question may not be adequate for another. Sound evaluation starts with purpose, not with how advanced the instrument sounds.
Orthogonal evidence
Two techniques are usefully orthogonal when they rely on different physicochemical principles. Agreement can increase confidence, while disagreement can reveal interference or a faulty assumption. The second method should add information, not merely another graph.
A risk-based strategy
Test selection should connect to attributes critical for the research purpose and to the risk of a wrong conclusion. Documentation explains why each method was selected and what uncertainty remains after measurement.