This is a complex subject, but I'll give you some insights to begin thinking about the problem, A performance qualification is meant to determine the the system meets the requirements you say it does, and achieves the goals you need it to achieve to meet the results you claim.
Example: you have a raw material, you would reject it if the vendor sent you something contaminated, say as much as 1% of a breakdown product, or related chemical. You'll be called upon to determine the the system actually does that: you'll deliberately contaminate some pure standard with a detectable impurity and show that the system can detect it.