Overview
ISO 3705:1976 specifies a silver diethyldithiocarbamate photometric method for the determination of arsenic in sulphur for industrial use. The method applies to sulphur samples with arsenic contents equal to or greater than 0.5 mg/kg and references the general procedures of ISO 2590 (General method for the determination of arsenic). Key laboratory operations include dissolution in carbon tetrachloride, chemical oxidation, and a spectrophotometric measurement of the arsenic-derivative.
Key topics and technical requirements
- Scope: Applicable to industrial sulphur with As ≥ 0.5 mg/kg.
- Sample preparation: Dry laboratory sample (about 80 °C), grind to pass a 630 μm sieve; typical test portion ≈ 5 g.
- Dissolution and oxidation: Dissolve test portion in carbon tetrachloride; oxidize sulphur using bromine and nitric acid. Example reagent additions in the standard: add 20 ml bromine solution, stand 45 min, then add ~25 ml nitric acid dropwise while cooling.
- Removal of excess reagents: Heat in a boiling water bath and evaporate (or sand bath) to eliminate excess bromine, carbon tetrachloride and nitric acid; fume until nitrous compounds are removed and dilute.
- Analysis: Follow ISO 2590 procedures for arsenic determination using the silver diethyldithiocarbamate photometric reaction and calibration graph. For different concentration ranges, prepare volumetric dilutions and take specified aliquots for measurement.
- Reagents and substitutions: The standard replaces hydrochloric acid (ISO 2590 reagent) with sulphuric acid for this method; note and report any other reagent substitutions. Bromine solution composition and nitric acid strength are specified.
- Safety: Operations involve toxic/volatile chemicals (carbon tetrachloride, bromine, nitric acid, pyridine noted in ISO 2590); perform work in a well-ventilated fume cupboard.
- Quality control: Include blank tests and calibration graphs per ISO 2590; report results, method reference, deviations or unusual features.
Applications and users
- Who uses it: Analytical chemists, quality-control laboratories, industrial producers of sulphur and sulphur-containing products, environmental labs monitoring arsenic contamination.
- Practical use: Routine QC of industrial sulphur, verification of supplier specifications, regulatory compliance testing where arsenic content must be quantified above trace levels, and inter-laboratory method standardization.
Related standards
Keywords: ISO 3705, arsenic determination, sulphur for industrial use, silver diethyldithiocarbamate photometric method, spectrophotometric analysis, carbon tetrachloride oxidation, bromine, nitric acid.
Open preview (PDF)Sulphur for industrial use — Determination of arsenic content — Silver diethyldithiocarbamate photometric method
