However, when quats are used incorrectly, their effectiveness is drastically reduced by something called quat binding. Here is a link to a good article that explains this problem and what you can do to be sure it does not happen to you.
WHAT IS QUAT BINDING? HOW DO I PREVENT IT?
Quaternary ammonium chloride (quat) is an active ingredient in disinfectants that are used throughout the cleaning industry. These disinfectants are popular because of their effectiveness against germs, bacteria and viruses; their relatively low toxicity at proper dilution; low odors and; long shelf life.