Thymol Blue

Technical Specifications

Product Description & Scientific Applications

Thymol Blue (thymolsulfonphthalein) is a sulfonephthalein pH-indicator dye used throughout laboratories. Like other sulfonephthaleins, its colour and absorption spectrum shift with pH; its second, alkaline dissociation is followed from the ratio of its absorbances at 435 and 596 nm. The dye's response is reversible, so immobilising it in films and coatings turns chemical changes into a readable colour signal.

Common Scientific Applications

Spectrophotometric pH of natural waters. Added to a water sample, Thymol Blue lets pH be read from an absorbance ratio, the approach used for precise oceanographic work. It is especially useful in surface and shallow waters whose pH can rise above the range of meta-cresol purple — the dye usually used for seawater — extending high-precision spectrophotometric pH measurement upward by about half a pH unit.

Optical gas sensors. Entrapped in a thin film of ethyl cellulose or sol-gel silica, Thymol Blue reports gases that change the film's internal pH. Carbon dioxide dissolving to carbonic acid shifts the dye's protonation, read as a colour change or, in fibre-optic devices, as altered energy transfer from a paired fluorophore — sensors built this way have measured CO₂ in exhaled breath. In a metal-organic framework, paired with a piezoelectric transducer, the dye provides the colour channel of a hybrid sensor reaching the parts-per-billion range for the plant-stress volatile 1-hexanol.

Corrosion-sensing coatings. Sealed into silica capsules or a sol-gel layer and built into a protective coating, Thymol Blue signals incipient corrosion — the hydroxide produced during corrosion raises the local pH, which the dye registers. In one design this same pH rise also releases a stored corrosion inhibitor; in another the dye itself slows the attack, so a single coating both reports corrosion and resists it.

Intelligent pH-indicating materials. Cast into a biopolymer film, Thymol Blue makes a colour-changing freshness label: the volatile amines released by spoiling seafood raise the pH at the film and shift its colour, giving a visible readout of shrimp freshness during cold storage. The dye can also be melt-blended into poly(lactic acid) filament, so 3D-printed parts themselves act as pH sensors.

Inhibitor of mitochondrial anion transport. Beyond its optical uses, Thymol Blue inhibits carrier-mediated anion transport across the mitochondrial membrane. In isolated mitochondria it blocks the exchange of the dicarboxylate anions succinate and malonate, and of the sulfonephthalein dyes tested it was the most potent inhibitor of that exchange.

Shipping Destinations

• EU & UK: Priority delivery, 2–5 business days.
• United States (DDP): 3–7 business days, duties and taxes prepaid.
• EFTA Countries (DDP): 3–7 business days, duties and taxes prepaid.
• Worldwide: 7–14 business days, selected locations.