Overview - ISO 6634:1982 (Arsenic in fruits & vegetables)
ISO 6634:1982 specifies a spectrophotometric method for the determination of arsenic content in fruits, vegetables and derived products. The method converts arsenic to arsine (AsH3) by reduction of arsenic(V) to arsenic(III) with tin(II) chloride and nascent hydrogen (platinized zinc). The generated arsine reacts with silver diethyldithiocarbamate to form a red complex whose absorbance is measured at 520 nm.
Key topics and technical requirements
- Scope: Analytical determination of arsenic in fresh, pasty, solid, dehydrated and liquid food matrices.
- Principle: Decomposition → reduction (As(V) → As(III)) → arsine generation → colour development with silver diethyldithiocarbamate → spectrophotometry at 520 nm.
- Reagents required: sulphuric, nitric and (if needed) perchloric acids; platinized zinc; tin(II) chloride; potassium iodide; sodium hydroxide; silver diethyldithiocarbamate reagent; phenolphthalein; arsenic standard solution.
- Apparatus: reaction/conical flask with screw-thread column, vertical column and delivery tube, bubbler (measuring cylinder), spectrophotometer with 10 mm cell, analytical balance and volumetric glassware.
- Sample preparation: typical test portions - 50 ml for liquids; 50–100 g (fresh weight) for pasty/solid samples; homogenization and wet decomposition per ISO 5515 when required.
- Calibration and quantification: calibration curve built using arsenic standard aliquots (examples cited: 5–20 μg As), absorbance measured against silver diethyldithiocarbamate reference; results calculated from calibration graph and expressed per unit mass or volume.
- Quality checks: preliminary reagent reactivity and blank tests; acidity titration of final solution; stated repeatability - difference between two replicate determinations by same analyst should not exceed 10% relative.
Practical applications & users
- Food safety and quality control laboratories testing arsenic in fruits and vegetables.
- Regulatory agencies and public health laboratories performing compliance testing.
- Agricultural product processors and exporters requiring validated arsenic analysis.
- Analytical chemists developing or validating methods for trace metal determinations in food matrices.
Related standards and references
- ISO 5515 - referenced for wet decomposition of organic matter prior to analysis.
- ISO 6634 should be used alongside good laboratory practice, traceable arsenic standards and appropriate safety procedures for handling toxic reagents and generating arsine gas.
Keywords: ISO 6634, arsenic determination, silver diethyldithiocarbamate, spectrophotometric method, fruits and vegetables, arsine generation, platinized zinc, tin(II) chloride, 520 nm, food safety.
