Mary,

Its unlikely that the observed white precipitate has anything to do with the ethanol wipe. The reaction of chlorine dioxide with bacteria or other substances takes place in two steps. During this process disinfection byproducts are formed that will likely remain on the disinfected surfaces. In the first stage the chlorine dioxide molecule accepts an electron and gets reduced. This reaction produces chlorite (ClO3). In the second stage chlorine dioxide accepts 4 electrons and forms chloride (Cl-). On the surfaces of the tissue culture hood some chlorate (ClO3), which is formed during the production of chlorine dioxide, can also be found. Both chlorate and chlorite are oxidizing agents. Chlorine dioxide, chlorate and chlorite can all further react to sodium chloride (NaCl). I suspect that the white precipitate you observed are simply a combination of these post reaction salt residues.

This can be quickly confirmed by performing a surface wipe using a dry dark colored tissue or black cloth without the ethanol. You can also analyze a wipe swab by Ion chromatography to identify and confirm the suspected chlorite, chlorate and chloride residues.

It may also be possible to produce oxidized residues from reaction of the chlorine dioxide with a reactive surface. For example Al2O3 might be formed if the hood surface is aluminum.

Best Regards

Steve

If it remains a little quantity of chlorine dioxide (or chlorites or chlorates), a reaction can happen with ethanol leading to the formation of aldehydes. But these aldehydes have a rather high vapour pressure and are not likely to stay on the surfaces. This white precipitate is probably the result of the reaction of chlorine dioxide with the surfaces or with remaining pollutants: it might simply be NaCl or another chloride.

That should disappear after a careful cleaning of the hood with ethanol (or something else if you do not want to use too much ethanol).

Thank you, Steve and Michel. I appreciate hearing what kind of residue it might be. I did think it could be a salt, but was unsure what type. It does not clean up readily with either water or ethanol. I have washed the hood down 6 or 7 times, alternating between water (sterilized) and ethanol, and I have used dry kimwipes to wipe the powder off as well.

Thanks!