General Considerations.This is to verify that the method performance is not

affected by typical changes in normal experiments. Therefore, the variation in

methodconditionsfor robustnessshouldbesmallandreflect typicalday-to-

day variation. Experimental design (e.g., Plackett–Burman screening, factorial

design) is very useful to investigate multiple parameters simultaneously. Critical

parameters are identified during the method development process. Only these

critical method parameters should be investigated for robustness. Common critical

method parameters can be divided into two categories: