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pK of acids and bases used as an additive for HPLC mobile phases
pKa of acidic buffers at HPLC for mobile phase preparation
| Acidic buffer | Temperature (°C) | pK1 | pK2 | pK3 | |
| ACES 2-[(2-amino-2-oxoethyl)amino]ethan sulfonic acid | 20 | 6.9 | - | - | |
| Acetic acid | 25 | 4.8 | - | - | |
| Boric acid | 20 | 9.1 | 12.7 | 13.8 | |
| CAPS 3-(cyklohexylamino)ethan sulfonic acid | 20 | 10.4 | - | - | |
| Citric acid | 25 | 3.1 | 4.8 | 6.4 | |
| Formic acid | 20 | 3.8 | - | - | |
| Glycine | 25 | 2.3 | 9.6 | - | |
| Glycylglycine | 20 | 8.4 | - | - | |
| HEPES N-2-hydroxyethylpiperazine-N'-2-ethan sulfonic acid | 20 | 7.6 | - | - | |
| Imidazole | 20 | 7.0 | - | - | |
| MES 2-(N-morfolino)ethan sulfonic acid | 20 | 6.2 | - | - | |
| MOPS 3-(N-morfolino)propan sulfonic acid | 20 | 7.2 | - | - | |
| Oxalic acid | 25 | 1.3 | 4.3 | - | |
| Phosphoric acid | 25 | 2.1 | 7.2 | 12.7 | |
| TES 2-[tris(hydroxymethyl)methyl]aminoethane sulfonic acid | 20 | 7.5 | - | - | |
| Trifluoroacetic Acid | 25 | 0.3 | - | - | |
| Tricine N-[tris(hydroxymethyl)methyl]glycine | 20 | 8.2 | - | - | |
| TRIS Tris(hydroxylmethyl) aminomethane | 20 | 8.3 | - | - | |
| pKb of Bases at HPLC for mobile phase preparation | |||||
| Bases | Temperature (°C) | pK1 | pK2 | pK3 | |
| Ammonia | 25 | 9.3 | - | - | |
| Diethylamine | 20 | 11.1 | - | - | |
| Dimethylamine | 25 | 10.7 | - | - | |
| Ethylamine | 20 | 10.8 | - | - | |
| Ethylendiamine | 20 | 10.1 | 7.0 | - | |
| Methylamine | 25 | 10.7 | - | - | |
| Morfoline | 25 | 8.3 | - | - | |
| Triethylamine (TEA) | 18 | 11.0 | - | - | |
| Trimethylamine | 25 | 9.8 | - | - | |
Note: The pH range for which the given buffer is suitable is in the range of pK ± 1. The UV Cutoff of the used buffer must also be taken into consideration (table 2).