Table 6.
Acidity constants of Methylene blue at λmax = 665 nm in numerous solutions of 50% cosolvents at room temperature ~25 °C,ionic strength 0.5 MKCl
| 50%Cosolvent | Method 1 | Method 2 | Method 3 | Average pKa | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| pka1 | pka2 | pKa1 | pKa2 | pKa1 | pKa2 | pKa1 | pKa2 | ε | Ref. | |
| H2O | - | - | - | - | - | - | 3.80 | - | - | [45] |
| - | - | - | - | - | - | - | 2.61 | 11.2 | - | [46] |
| DiX | 3.60 | 11.7 | 3.71 | 11.41 | 3.57 | - | 3.63 ± 0.07 | 11.56 ± 0.21 | 40.36 | This work |
| PrOH | 2.50 | 10.7 | 2.55 | 10.84 | - | - | 2.52 ± 0.03 | 10.78 ± 0.11 | 47.40 | - |
| MeOH | 2.45 | 11.5 | 2.72 | 11.53 | - | - | 2.58 ± 0.19 | 11.52 ± 0.09 | 60.80 | - |
Where: Method 1: half-curve height method, Method 2: limiting absorption modified method and Method 3: Colleter method, ε: relative permittivity