Description
Thymol Blue Sodium Salt — Dual-Range pH Indicator Dye
Thymol Blue Sodium Salt is the sodium salt form of the classic pH indicator thymol blue, providing superior solubility and handling for laboratory use. This dye is widely used in acid–base titrations, pH indicators, buffer systems, and educational demonstrations, thanks to its clear, vibrant color changes over two pH transition ranges.
Key Attributes & Identity
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CAS Number: 62625-21-2
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Molecular Formula / Weight: C₂₇H₂₉NaO₅S, ~ 488.57 g/mol
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PubChem ID: 23692293 (sodium salt form)
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Appearance / Form: Orange-brown to reddish or greenish powder or crystals
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Melting / Decomposition: Decomposes around 283-285 °C
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Solubility / Solution Behavior: Water-soluble (creating clear colored solutions)
Color Transition Behavior & Optical Features
Thymol Blue has two distinct color-change ranges, making it a versatile indicator:
This dual-range behavior makes thymol blue useful in both strong acid and moderately basic systems. The dye has absorbance peaks in the UV/visible region, typically near ~ 378 nm and ~ 590 nm depending on the ionization state.
Applications & Use Cases
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Acid–Base Titrations & pH assays — Ideal as an endpoint indicator in titrations spanning strong acid or base ranges
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Buffer / Formulation Studies — To monitor pH shifts in multi-component systems
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Education / Demonstrations — Clear, colorful transitions suitable for classroom experiments
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Indicator in Microbiological Media — Occasionally used as a pH indicator dye in media (e.g., in selective agar formulations)
Handling, Preparation & Tips
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Stock Solutions: Dissolve in water or dilute alkaline solution to prepare working concentrations
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Protection: Shield from strong light or UV to avoid photodegradation
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Use Control Blanks: Always run an indicator-only blank to subtract background absorbance
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pH Calibration: Because of its dual transitions, ensure the experiment’s pH range overlaps one of its color-change intervals
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Temperature / Ionic Strength Sensitivity: Color transitions can shift slightly with ionic strength, temperature, or solvent composition — validate under your specific conditions
