Stability of Potassium Citrate Liquid Concentrate

[Rudeofus]

Does anyone know whether liquid concentrate of Potassium Citrate can be stored for prolonged periods of time? It is well known that dilute solutions of citrate will catch mold over time, but does this also apply to a 300 g/l concentrate? Would higher concentrations yield a stable liquid? Are there compounds which could be added, which would prevent mold growth yet not interfere with copper red toning? Would a mixture of Copper Sulfate and Potassium Citrate have decent shelf life?

 

[Martin Rickards]

I'd hazard a guess that at that concentration the osmotic pressure would be too high for any fungal growth

 

[Rudeofus]

I'd hazard a guess that at that concentration the osmotic pressure would be too high for any fungal growth

That was my initial guess, too, but then I looked at composition of Citric Acid based stop bath concentrates - these use an additional compound to keep germ growth under control.

 

[Gerald C Koch]

Add a few ml of Listerine to the concentrate. Use the old fashioned stuff that tastes terrible. It contains thymol which is an antibacterial.

 

[Martin Rickards]

Mold is not a bacteria, but a fungus.

 

[Photo Engineer]

I'm trying to get information together on broad spectrum antimicrobials that are relatively harmless to humans and photographic materials.

For now, Thymol will do.

PE

 

[Gerald C Koch]

Mold is not a bacteria, but a fungus.

Mold, bacteria, yeasts, ... are all microorganisms. What kills one usually kills them all. Unless you've done a culture you really don't know what may be growing in a solution.

 

[Rudeofus]

I remember that Thymol barely dissolves in neutral to acidic solutions, its wikipedia entry states 0.9 g/l. Would 0.1 g/l do the trick?

 

[Photo Engineer]

I use a very tiny amount of 10% thymol as a preservative in my emulsions. This is 10% in Ethanol, or 10 g in 100 ml of total solution. It is not very much when 1 - 3 drops are used in 500 ml of emulsion. However, modern biostats are better.

PE

 

[Rudeofus]

However, modern biostats are better.

Can you explain what the advantage of "modern biostats are", especially compared to a compound as simple and widely available as Thymol, added in minuscule amounts like you described? How long does Thymol last in aqueous solution?

 

[Photo Engineer]

Thymol will double the life of a chilled emulsion. A modern biostat can allow one to keep an emulsion for weeks at room temperature. It would be similar for a citrate solution.

PE

 

[Gerald C Koch]

The following is an interesting article of thymol. Being a substituted phenol its solutions should be quite stable. It happens to be also be readily available in Listerine.

https://en.wikipedia.org/wiki/Thymol

During the Middle Ages certain spices like thyme, cloves and black pepper were highly valued because they contained compounds that helped preserve food. Cloves sold for more than gold and spice merchants were the millionaires of their time.

 

[Photo Engineer]

Don't get me started on some of the history of spices. It could take forever.

However, if you open a fresh bag of Ilford paper, the first smell you get from the interior is their biocide. It is Phenol.

PE

 

[falotico]

Don't get me started on some of the history of spices. It could take forever.

However, if you open a fresh bag of Ilford paper, the first smell you get from the interior is their biocide. It is Phenol.

PE

Don't hold back! What is your opinion of cinnamon?

 

[Photo Engineer]

You must get a bottle of pure Cinnamaldehyde to truly appreciate Cinnamon. It is the chemical responsible for the entire Cinnamon experience. It is slush at room temperature and when you open the bottle you feel as if you could eat the whole thing!

Dont even try.

PE

 

[Gerald C Koch]

Another biocide is eugenol the principle constituent of oil of cloves. It was used extensively in dentistry as a cavity liner for fillings to prevent any tooth decay. When mixed with zinc oxide it made a quick setting cement for dental caps and temporary fillings. Cloves are the dried buds of a plant syzygium aromaticum and look like tiny roses. Hence the common name during the Middle Ages the black rose.