How to control the pH of water after sterilization ? - (Feb/28/2014 )
Dear Forum members,
I want to formulate a parenteral preparation whose pH should be between 10.5 to 11.10;
Here medium is water, the pH of the water adjusted to 11.00 with 0.1N NOH solution, after sterilization the pH decresed to 7.5, why so ?
Without teriziation pH of water is decreasing to 10.5.
Is any alternate is there to maintain the pH (even after sterilization) ?
One possible reason is that dissolved carbon dioxide decreases pH:
CO2 + H2O <--> H2CO3 and then H2CO3 + H2O <--> HCO3- + H3O+
Carbonic acid is a weak acid but might be enough to decrease pH in your unbuffered system. ITo avoid this use a buffer, actually for this alkaline pH, I'm not sure which one.
Another possibility would be pH adjustment after autoclaving (if you did this, you just wrote sterilisation) and then avoid contact to air.
Given that an autoclave system is also pressurized hobglobin suggestion is quite likely correct. The high pressure would drive the carbon dioxide to dissolve into yourbuffer, and you will obtain a sodium hydrogen carbonate solution.
I would suggest that you use a buffer system and filter sterilize your solution.
As for what buffer to you, I am not sure what you will be using the solution for, but there are several options
The table above gives CABS (4-(Cyclohexylamino)-1-butanesulfonic acid ) as an option.
You could also use an amino acid as a buffer.
Lysine, Proline, Cysteine and Tyrosine are within the 10.5 to 11 range.
I've seen many people autoclave their bottles with loose cap, without putting them in autoclave bag. I've personally had problems when dirt got into my bottles specially when the user before me autoclaved dead chicks or eggs and forgot to completely seal the bag. Just be careful with that also.