Bromothymol blue (also known as bromothymol sulfone phthalein and BTB) is a pH indicator. It is mostly used in applications that require measuring substances that would have a relatively neutral pH (near 7). A common use is for measuring the presence of carbonic acid in a liquid. It is typically sold in solid form as the sodium salt of the acid indicator.
| Bromothymol blue (pH indicator) |
| below pH 6.0 |
|
above pH 7.6 |
| 6.0 |
⇌ |
7.6 |
Bromothymol blue acts as a weak acid in a solution. It can thus be in protonated or deprotonated form, appearing yellow or blue, respectively. It is bright aquamarine by itself, and greenish-blue in a neutral solution. The deprotonation of the neutral form results in a highly conjugated structure, accounting for the difference in color. An intermediate of the deprotonation mechanism is responsible for the greenish color in neutral solution.
| ltem |
| (acid-base indicator) |
| pHVisual transition 6.0()~7.6() |
| Mass absorptivity,L/cm·g ≥52.0 |
| Solubility(in ethanol) |
| Ignition residue,% ≤0.3 |
| |
| |
| ACS,95 % |
| (ACS, Dye content 95 %) |
| Appearance |
| Infrared spectrometry |
| Dye content(HPLC) ≥95% |
| Claroty of solution |
| Visual transition interval pH 6.0(Yellow-Green)-pH 6.7(Green)-pH 7.6 (Blue) |
| Wavelength 419- 425 nm |
| c = 0.02g/L; Me thanol |
| Extinction Coefficient 17,000 |
| Wavelength 326- 332 nm |
| Extinction Coefficient 8,000 |
| Wavelength 279- 285 nm |
| Extinction Coefficient 9,000 |
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