|
|
|
|
|
|
Calculation Examples pHcalc
|
|
|
|
In the following table, the calibrated measured and guaranteed pH values of SRM-buffers from the NIST internet site are compared with pHcalc Buffer Composer calculations. Please note, that these Buffers are ideally diluted and that the computations may yield a larger difference from measured pH values with higher concentrations and other substances.
|
|
|
|
| Standard buffer |
Molality
[mol/kg] |
guaranteed pH value
(NIST-SRM) |
pHcalc Ver 2.0
pH calculation |
KH2PO3
Na2HPO3 |
0.025
0.025 |
6.863 |
6.879 |
| KH-phthalate |
0.050 |
4.006 |
3.988 |
NaHCO3
Na2CO3 |
0.025
0.025 |
10.001 |
10.005 |
HEPES free acid
Na - HEPESate |
0.025
0.025 |
7.364 |
7.370 |
MOPSO free acid
Na - MOPSOate |
0.025
0.025 |
6.699 |
6.708 |
MOPSO free acid
Na - MOPSOate |
0.04
0.04 |
6.676 |
6.679 |
|
|
|
In the following table, some standard buffers from literature [1] are compared with pHcalc Buffer Composer calculations
|
|
|
| Standard buffer |
Molality
[mol/kg] |
measured
pH [1] |
pHcalc Ver 2.0
pH calculation |
| KH2-Citrate |
0.05 |
3.776 |
3.739 |
TRIS*HCl
TRIS [2] |
0.050
0.01667 |
7.788 |
7.780 |
AcOH
NaOAc |
0.025
0.025 |
4.644 |
4.622 |
|
|
|
[1] Humeres, Quijano & Sierra, J.Braz.Chem.Soc. Vol 1 No3, 1990
[2] The temperature coefficiant of the pK value of Tris(hydroximethyl)aminomethane is in the room temperature range (about 15-25°C) approximately -0.0287 pK/°C: pKa(15°)=8.326, pKa(25°)=8.075,
|
|
|
|
|
|
|
|
