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Thymolphthalein (CAS 125-20-2) | High Purity pH Indicator
- Time of issue:Oct . 19, 2025 15:50
(Summary description)Tangshan Moneide Trading Co., Ltd. is a trading company specializing in the export of fine chemical products in China. Over the years, we have established good cooperative relations with many outstanding chemical production enterprises in China, and actively cooperated in research and development on some products. Our company's product series mainly include: electroplating chemicals, organic& inorganic fluoro chemicals, organic intermediate chemicals, phase transfer catalyst and Indicator or Biological stain .
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- Time of issue:2019-12-30 10:55
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If you work around alkalinity testing long enough, you eventually come back to thymolphthalein. To be honest, I did—after a detour through every fluorescent dye and indicator under the sun. It’s the steady, unfussy blue changeover that keeps showing up in real labs, from concrete plants to wastewater basins. And the version coming out of Tangshan, Hebei (2-7-523 Jidong Building Materials, 064000, China) has been getting attention for dependable purity.
Industry chatter shows a quiet shift: more labs standardize on thymolphthalein for high-pH titrations where phenolphthalein can feel a tad too early. Cement QA teams and wastewater operators like the sharper blue endpoint above pH ≈9.3–10.5. Plus, education suppliers keep using it for “disappearing ink” demos—yes, still a hit on open days.
Synonyms: 3,3-bis(4-hydroxy-2-methyl-5-(1-methylethyl)phenyl)-1(3H)-Isobenzofuranone; CAS 125-20-2.
- High-pH titrations: alkalinity in industrial waters. Clear blue endpoint—less ambiguity for operators on shift.
A Northern Europe precast plant swapped from phenolphthalein to thymolphthalein for spot checks on curing tanks. Result: fewer borderline readings, 12% reduction in re-tests over three months, according to their QA notes. Not a randomized trial—but the maintenance crew was relieved.
Custom indicator solutions (0.1–1.0% w/v in ethanol or IPA), low-halogen specs, or tighter heavy-metal limits are feasible. For regulated labs, ask for COA, SDS, and if applicable, ISO 17025 test reports. Many customers say the COA from Moneide includes UV-Vis curves of thymolphthalein, which is useful in audits.
Certifications frequently requested: ISO 9001 QMS, ISO 17025 test-lab data, and where relevant, EU REACH SVHC non-intent, RoHS. Always verify current documentation.
If your workflow needs a confident high-pH cue, thymolphthalein is still one of the easiest wins. Precise, visible, and—when sourced well—remarkably consistent.
thymolphthalein: the reliable blue signal for high-pH analytics (and a few clever tricks)
What’s trending
Technical snapshot
Parameter
Spec (typical)
Method/Notes
Product
thymolphthalein
Indicator grade
Molecular formula
C28H30O4
Molar mass ≈ 430.54 g/mol
Appearance
White to off-white crystalline powder
Visual
Purity (HPLC)
≥ 99.0% (typ.)
HPLC area%
Melting point
≈ 250–253 °C
Capillary, may decompose
Transition range
pH 9.3–10.5 (colorless → blue)
UV-Vis confirmation
λmax (alkaline)
≈ 595–600 nm
NaOH solution
Solubility
Soluble in ethanol; low in water
Indicator solutions 0.1–1% w/v
Shelf life
24–36 months sealed
Cool, dry, light-protected
From raw materials to QC: the process
Where it shines (and why)
- Cement carbonation checks: labs sometimes prefer thymolphthalein when they need a stricter “still-alkaline” signal.
- Education and demos: “disappearing ink” using CO2 from air to nudge pH back—surprisingly crowd-pleasing.
Mini case study
Vendor comparison (abridged)
Vendor
Origin
Purity (typ.)
Lead time
Certs
Customization
Moneide Chem (thymolphthalein)
Hebei, China
≥99.0% HPLC
7–14 days (stock) ≈
ISO 9001; REACH-ready SDS
Custom packs, RM lots
Vendor A (EU)
EU
98–99%
2–3 weeks
ISO 9001/14001
Standard only
Vendor B (US)
US
≥98%
In stock/fast ship
ISO 17034 (selected RMs)
Limited SKUs
Customization and compliance
Test data (typical lot)
Bottom line
Authoritative citations
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