Overview
ISO 5515:1979 specifies a wet decomposition (acid digestion) method for the mineral analysis of fruits, vegetables and derived products. The standard describes heating a measured test portion until all organic matter is decomposed and a clear solution is obtained. Two wet routes are covered: digestion with sulfuric acid and nitric acid (with hydrogen peroxide added in some cases), or digestion using sulfuric and nitric acids with the addition of perchloric acid for more refractory samples. The procedure prepares samples for subsequent determination of minerals (ash-forming elements) by analytical techniques.
Key topics and technical requirements
- Scope and principle: Complete mineralization of organic matter to a clear solution prior to mineral analysis.
- Reagents: Analytical-grade acids - nitric acid, sulfuric acid, optional hydrogen peroxide (30%) and perchloric acid. Acid concentrations and handling are specified.
- Apparatus and materials: Borosilicate or quartz Kjeldahl flask, heating support with controlled heat, glass boiling beads, fume hood and glassware washed with hot nitric acid then distilled water.
- Operational steps:
- Weigh or pipette the test portion (typical 5–10 g or ml) and add specified acid mixtures.
- Heat gradually, maintain boiling cycles, monitor for nitrous fumes and the appearance of white fumes indicating removal of nitric acid.
- Add water at controlled stages, repeat boiling cycles, and dilute to a defined volume (50 or 100 ml) for mineral analysis.
- Use hydrogen peroxide when mineralization stalls; use perchloric acid for samples with high starch or low soluble solids per the standard’s decision rules.
- Completion criteria: Solution becomes colorless (or slightly green/yellow) and white fumes indicate strongly sulfuric, nitrite-free conditions.
- Safety and precautions: Strong warnings for perchloric acid (explosive risk with organics/dehydrating agents), requirements for incombustible, washable exhaust systems, protective equipment, and strict procedures for handling and neutralization.
Applications and users
- Intended for food testing laboratories, agricultural and agro‑food quality control, regulatory authorities, and analytical chemists performing mineral and elemental analysis of fruits, vegetables and derived products.
- Practical for sample preparation prior to ICP, AAS, colorimetric or other mineral assays where organic matrix removal is required.
- Useful in QA/QC of processed fruit/vegetable products, research labs studying nutrient content, and certification/testing bodies.
Related standards
- ISO 5516 - Decomposition by incineration (alternative mineralization method)
- ISO 2173 - Soluble solids / refractometric methods (used to guide digestion choice)
- ISO 1042 - Volumetric glassware specifications
Keywords: ISO 5515:1979, wet method, decomposition of organic matter, acid digestion, fruits and vegetables, mineralization, perchloric acid safety, sample preparation, analytical chemistry.
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