Method: CH was dissolved for 15 seconds into test solutions (ultrapure water, polyethylene glycol (PEG) 200, PEG 400, glycerol, and 50/50 mixtures of each with water) to give a final concentration (w/v) of 2%, which is just above the solubility in pure water (1.85%). pH data was recorded every 60 seconds for 20 minutes using a precision analytical pH meter (Hanna HI4221) fitted with an Orion electrode specifically designed for non-aqueous fluids. The system was calibrated at pH values of 4, 7, 10 and 12, and verified against known buffers at pH 14. Calibration was checked between sample runs using known pH standards. Data sets were analysed using RMANOVA.
Result: Inclusion of either version of PEG into water significantly increased the pH elevation from baseline caused by addition of CH into water alone or PEG alone. Using other solvents increased the maximum pH which could be achieved above the pH 12.40 limit for pure water. The final pH achieved at 20 minutes, which represented the point of stability for all mixtures, was ranked from greatest to least as follows: water/PEG200 13.06, water/PEG400 12.79, PEG200 12.60, water/glycerol 12.49, water 12.40, glycerol 12.32, and PEG400 11.77.
Conclusion: Use of non-aqueous solvents overcomes the common ion effect which restricts the pH to 12.40, and allows higher pH values to be achieved. Of the materials examined, the greatest potential was seen for the polyethylene glycols. Combinations using such materials may have value for eventual clinical application.