I'm running out of my preservative for pH meter buffers, Hydrion Color Key Preservative (isopropyl alcohol, polyethylene glycol, methyl p-hydroxy benzoate, thymolsulfonphtalein, water).
It can only be purchased along with a complete bufferset, so I wonder if I can preserve it with something else, without affecting the pH of the buffer?
I think the thymolsulfonphtalein is only there as pH indicator and the PEG (+ IPA) mainly to enhance solubility in water? So that leaves methyl paraben and IPA for preservation?
The cheapest way for me would be adding Germaben II, but I don't know if the formaldehyde releaser and formaldehyde itself affect the pH somehow.
I use pH 4,7 and 10 buffers. pH 10 would be too high for Germaben II, but the shelf life of the pH 10 buffer is already shorter due to CO2 uptake, so I make a fresh batch every 1 to 2 weeks. I would mainly be have to focus on pH 4 and 7, especially pH 4 because I use this as storage solution.
Does anyone know about preservatives for buffer fluids?
Could Germaben II be an idea, or should I make a methyl paraben/IPA/water solution?
Please feel free to share your knowledge!