The following are some commonly used pH indicators that might be suitable for use in colorimetric bioassays for catalysis of redox reactions or other enzyme activities that cause pH changes in a solution.
Common Indicators for Biological Applications
| Common name | Chemical name | pH range (pka) | Color in Acid | Color in Alkaline |
| Bromo-phenol blue | tetrabromophenol-sulphone-phthalein | 3.0-4.6 (4.1) | yellow | blue |
| Methyl yellow | Dimethylamino-azo-benzene | 2.9-4.0 (3.3) | red | yellow |
| Methyl orange | Dimethylamino-benzene sodium sulphonate | 3.1-4.4 (3.7) | red | orange |
| Congo red | Diphenyl-bis-azo-1-naphthylamino-4-sulphonic acid | 3.0-5.0 | blue | red |
| Bromo-cresol green | Tetrabromo-m-cresol-sulphone-phthalein | 3.8-5.4 (4.7) | yellow | blue |
| Methyl red | o-Carboxybenzene-azodimethyl-aniline | 4.2-6.3 (5.0) | red | yellow |
| Chlorophenol red | Dichloro-phenol-sulphone-phthalein | 4.8-6.4 (6.1) | yellow | red |
| 4-Nitrophenol | 4-Nitrophenol | 5.6-7.6 (7.1) | colorless | yellow |
| Bromocresol purple | Dibromo-o-cresol-sulphone-phthalein | 5.2-6.8 (6.1) | yellow | purple |
| Bromo-thymol blue | Dibromo-thymol-sulphone-phthalein | 6.0-7.6 (7.1) | yellow | blue |
| Phenol red | Phenol-sulphone-phthalein | 6.8-8.4 (7.8) | yellow | red |
| Cresol red | 1-Cresolsulphone-phthalein | 7.2-8.8 (8.2) | yellow | red |
| Thymol blue | Thymol-sulphone-phthalein | 8.0-9.6 (8.9) | yellow | blue |
| Phenol-phthalein | Phenolphthalein | 8.3-10.0 (9.6) | colorless | red |
