Overview
ISO 5282:1982 defines a laboratory procedure for the determination of sulphur in aromatic hydrocarbons that boil below 200 °C. The method combines the Pitt–Ruprecht reduction (reduction to nickel sulphide using Raney nickel) with methylene‑blue spectrophotometry to quantify hydrogen sulphide after absorption. It is directly applicable for sulphur concentrations from 0.1 mg/kg to 30 mg/kg; higher concentrations can be analysed after suitable dilution.
Key practical features:
- Reduction of sulphur compounds to nickel sulphide with Raney nickel.
- Stripping of generated hydrogen sulphide in an HCl medium and absorption in alkaline zinc acetate solution.
- Formation of methylene blue using N,N-dimethyl-p-phenylenediamine sulphate and iron(III) ammonium sulphate.
- Spectrophotometric measurement of the blue complex at 667 nm (20 mm path length cells).
Key Topics
- Scope and applicability: Aromatic hydrocarbons with boiling point <200 °C; direct range 0.1–30 mg/kg. Samples with higher sulphur require dilution prior to analysis.
- Limitations: Alkylsulphones, arylsulphonic acids and arylsulphonates give incomplete sulphur recovery and may bias results.
- Reagents and apparatus: Uses analytical‑grade reagents (Raney nickel, zinc acetate, hydrochloric acid, N,N‑dimethyl‑p‑phenylenediamine sulphate, iron(III) ammonium sulphate) and a spectrophotometer set at 667 nm. PVC or other sulphur‑free tubing must be used for gas lines; rubber tubing is not acceptable.
- Quality control: Includes blank tests, calibration graph preparation from standard sulphur solutions, and routine checks of Raney nickel reducing power.
Applications
This ISO method is intended for quality control, compliance testing and process monitoring where accurate low‑level sulphur measurement in aromatic solvents, fuels or feedstocks is required. Typical applications include:
- Petrochemical laboratory QC for aromatic solvents and intermediates.
- Incoming raw material inspection where sulphur content impacts downstream processing or catalyst life.
- R&D and method comparison when developing or validating alternative sulphur analysis techniques.
Practical benefits: the method yields a sensitive, colorimetric determination with established calibration procedures and documented precision data in the standard.
Related Standards
- ISO 1995 - referenced for sampling of aromatic hydrocarbons (see ISO 5282 reference section).
- Annex in ISO 5282 provides the procedure for preparing sulphur‑free toluene used in blank and calibration tests.
For laboratory implementation, follow the standard’s procedural steps for sample handling, reduction, absorption, colour development and spectrophotometric measurement to ensure repeatability and inter‑laboratory comparability.