Sulfate titration
Endpoint indicator for the titrimetric determination of sulfate and organic sulfur compounds with standardized barium perchlorate — a standard method for atmospheric particulate and water analysis.
product photo —
10 g amber bottle of Thorin indicator powder
10 g amber bottle of Thorin indicator powder
Orange-yellow to red-brown crystalline powder
CAS 3688-92-4 · METAL-ION INDICATOR
Thorin, ACS/AR Grade
CAS 3688-92-4
EC 222-993-1
Synonyms: Thorin I; Aspan; APANS; Thoron; Thoron(ol); Thorin GR; Disodium 1-(2-Arsonophenylazo)-2-naphthol-3,6-disulfonate; 1-(2-Arsonophenylazo)-2-naphthol-3,6-disulfonic acid disodium salt; 1-(2-Arsonophenylazo)-2-hydroxy-3,6-naphthalene-disulfonic acid sodium salt; 2-(2-Hydroxy-3,6-disulfo-1-naphthylazo)benzenearsonic acid disodium salt
Disodium 1-(2-arsonophenylazo)-2-naphthol-3,6-disulfonate — the standard indicator for titrimetric sulfate determination with barium perchlorate, and a colorimetric reagent for thorium, zirconium, and rare-earth metal ions.
- Purity ≥97%
- ·
- λmax 480–490 nm
- ·
- MW 576.30 g/mol
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- Lot-specific COA + SDS
Pricing available on request — contact Sjonni@4MedChem.com. Bulk quotes available for kilogram-scale orders.
Overview
Thorin (also sold as Thorin I or Aspan) is a water-soluble azo-dye indicator that forms intensely colored complexes with polyvalent metal cations. In titrimetric sulfate analysis, a solution of Thorin turns from yellow to pink at the equivalence point when sulfate is titrated with standardized barium perchlorate — a method used to quantify sulfate in atmospheric particulates, water, and industrial process streams.
Thorin is also the classical colorimetric reagent for microgram-level determination of thorium, and is used in the photometric and X-ray fluorescence analysis of zirconium, lanthanides, and other rare-earth elements after preconcentration on Thorin-loaded chelating resins.
Specifications
| CAS Number | 3688-92-4 |
|---|---|
| EC Number | 222-993-1 |
| MDL Number | MFCD00003888 |
| Synonyms | Thorin I, Aspan, APANS, Thoron |
| Chemical Name | Disodium 1-(2-arsonophenylazo)-2-naphthol-3,6-disulfonate |
| Molecular Formula | C16H11AsN2Na2O10S2 |
| Molecular Weight | 576.30 g/mol |
| Appearance | Orange-yellow to red-brown crystalline powder |
| Melting Point | > 300 °C |
| Solubility | Soluble in water (0.5 g / 100 mL) |
| Absorption Maximum | 480–490 nm (H2O / propan-2-ol) |
| Assay (Purity) | ≥ 97.0% |
| Storage | Sealed, dry, protected from light, 2–30 °C |
| UN Number / Transport | UN 1557, Class 6.1, PG III |
Applications
Thorium determination
Classical colorimetric reagent for microgram-level spectrophotometric determination of thorium in ores, monazite sands, and standard reference samples.
Zirconium & rare-earth analysis
Used in the photometric and X-ray fluorescence determination of zirconium and lanthanides, including after preconcentration on Thorin-loaded chelating resins.
General metal-ion indicator
Forms a red complex with magnesium and other polyvalent cations, enabling sensitive detection in complex sample matrices.
Safety & Handling
GHS Signal Word: Danger
- H301 — Toxic if swallowed
- H331 — Toxic if inhaled
- H410 — Very toxic to aquatic life with long-lasting effects
Contains arsenic. Handle with nitrile gloves, safety glasses, and adequate ventilation; avoid dust generation. Store sealed, dry, and protected from light at 2–30 °C. Dispose of as hazardous chemical waste per local regulations. Full precautionary statements are in the SDS.
Documents
Frequently Asked Questions
What is Thorin used for?
Thorin is a metallochromic indicator used in the titrimetric determination of sulfate with barium perchlorate, and as a colorimetric reagent for thorium, zirconium, lanthanides, and other rare-earth and actinide metal ions. Its complex shifts from yellow to pink/red at the titration endpoint.
What is the CAS number for Thorin?
Thorin’s CAS Registry Number is 3688-92-4. It is also listed under EC number 222-993-1 and MDL number MFCD00003888.
What is the chemical formula and molecular weight of Thorin?
Thorin has the molecular formula C16H11AsN2Na2O10S2 and a molecular weight of 576.30 g/mol. Its full chemical name is disodium 1-(2-arsonophenylazo)-2-naphthol-3,6-disulfonate.
Is Thorin hazardous?
Yes. Thorin contains arsenic and is classified as acutely toxic if swallowed or inhaled (H301, H331) and very toxic to aquatic life with long-lasting effects (H410). Handle with gloves, eye protection, and adequate ventilation, and dispose of as hazardous waste.
How should Thorin be stored?
Store Thorin sealed, dry, and protected from light at 2–30 °C. It is stable under these conditions but incompatible with strong oxidizing agents.
What grades and pack sizes does Purity Solvents offer?
Purity Solvents supplies Thorin as ACS/AR-grade indicator powder, ≥97% purity, in 500 g, 1 kg, and 10 kg packs, plus bulk quantities, each shipped with a lot-specific Certificate of Analysis and Safety Data Sheet.