My opinion:
Don't test for cleanliness / purity in production. Instead, validate a number of uses after which the IPA is discarded (preferably recycled). If practical, use only once and that's it. Make sure that your supplier guarantees the required cleanliness / purity in the first place.
Lab methods will vary depending on your concerns - checking for particulate matter is not the same as checking chemical purity.
Cheers,
Ronen.