In general you will probably use commercially available calibration buffers, sold either as ready solutions or as tablets to dissolve in deionized water. However, it may be interesting to look at the table of standard solutions that can be used for the electrode calibration. pH given is for 25°C:
| substance(s) | concentration | pH |
|---|---|---|
| hydrochloric acid HCl | 0.1000M | 1.094 |
| potassium trihydrogen oxalate KH3C4O8 | 0.05000m | 1.679 |
| potassium hydrogen phthalate KHC8H4O4 | 0.05000m | 4.005 |
| potassium hydrogen tartrate KHC4H4O6 | saturated in 25°C | 3.557 |
| disodium hydrogen phosphate Na2HPO4 potassium dihydrogen phosphate KH2PO4 | 0.02500m 0.02500m | 6.865 |
| disodium hydrogen phosphate Na2HPO4 potassium dihydrogen phosphate KH2PO4 | 0.03043m 0.008695m | 7.413 |
| disodium tetraborate Na2B4O7 | 0.01000m | 9.180 |
| sodium hydrogen carbonate NaHCO3 sodium carbonate Na2CO3 | 0.02500m 0.02500m | 10.012 |
| calcium hydroxide Ca(OH)2 | saturated in 25°C | 12.45 |
m stands for molality, M for molarity.
Please note that high pH buffers are less stable, as they tend to absorb atmospheric CO2 which lowers their pH. During calibration you should open the bottle only to pour the buffer to the beaker. Never left the bottle open.
It is also important to remember that pH of buffer solutions change with temperature. pH of potassium hydrogen phthalate solution rises to 4.16 at 80°C. Many pH meters doesn't take these changes into account automatically, even if they allow automatic temperature compensation during measurements.
