There are three things you can evaluate on your own.
First mix the IPA with water about fifty percent. This mixture should be crystal clear after a second or two. If not, the IPA is contaminated (usually with some type of petroleum distillate).
Second, in a closed container, shake this mixture really hard. The mixture should not support a single bubble. If there is any foam at all, the IPA is contaminated with surfactant.
Third test requires a hydrometer, a glass instrument available from any scientific supply house, with the range centered on 0.8 (the specific gravity of IPA is 0.79). Measure the gravity of the straight IPA. If the gravity is lower than 0.79 the material is not IPA. If the gravity is higher than IPA, the material has been diluted with water. The higher the gravity, the higher the percentage of water.
The dilution of IPA is a common practice and often this is when the IPA is contaminated (a tank or pump used to mix or transfer the dilution containing some other product is usually the cause) although IPA can be contaminated in transport. The less you pay for your IPA, the more likely it is to be both diluted and contaminated.
Diluted alcohol runs just fine, though you need to run more of it. Contaminated alcohol should not be used, and should be returned to the supplier.
