Quaternary ammonium compounds are nitrogenous organic compounds used as disinfectants in restaurants, hospitals and homes. The basic chemical structure of ammonium is a nitrogen atom with four hydrogen atoms attached around it. Quaternary ammonium is created when each of those four hydrogen atoms are replaced with some combination of four other organic chains or rings. Because of the limitless number of possible combinations, there are many different versions of quaternary ammonium on the market already and new ones are constantly in development. Although some of the variations perform better than others, there are a number of advantages and disadvantages that they have in common.
The widespread availability and relatively low price of quaternary ammonium is one of its biggest advantages. The disinfectant can be purchased in concentrated form to be diluted as needed, in bulk-sized ready to use pre-diluted bottles and even in disposable wipe form.
One of the advantages of quaternary ammonium disinfectants is that they don't damage clothing and carpets the way that bleach does. They are also non-corrosive to metal pipes and other surfaces, another advantage over bleach. Although in its diluted form quaternary ammonium is considered to be safe enough to use without extraordinary precautions like masks, goggles and gloves, INCHEM warns that it can cause burns to the skin and mucous membranes in its non-diluted form.
When quaternary ammonium is mixed with organic matter it loses its effectiveness. This makes it an ineffective disinfectant in situations where blood, urine, fecal matter or soil may be present. For this reason, it is only used on non-critical surfaces like floors and railings in hospitals instead of on critical surfaces such as instruments that may come in contact with broken skin. Hard water is also a concern and should be tested before using a quaternary ammonium as a disinfectant because it loses effectiveness in solution with hard water. Cloths made of cotton or other organic material should not be used to spread the disinfectant because they lower its effectiveness.
Early quaternary ammonium disinfectants were all ineffective at killing gram-negative bacteria like E. coli and Salmonella. This is one reason that scientists have continued to develop and test new versions of quaternary ammonium. Although a 1999 study conducted by the Department of Animal Health found success with N-duopropenide against certain gram-negative organisms, progress has been limited and quaternary ammonium disinfectants should not be relied upon to kill gram-negative bacteria unless specifically certified to do so.