Overview
ISO 5523:1981 is an international standard specifying a routine method for the determination of sulphur dioxide content in liquid fruit and vegetable products. Developed by ISO Technical Committee ISO/TC 34 on Agricultural food products, this method provides a standardized, iodometric titration procedure to measure both free and bound sulphur dioxide levels. It is widely applicable to various liquid fruit and vegetable derivatives, including juices, concentrates, and beverages, ensuring product safety and quality through reliable chemical analysis.
This standard focuses on the routine iodometric titration of sulphur dioxide at a controlled acidic pH (between 0.7 and 1), followed by blank titrations to distinguish free and bound sulphur dioxide fractions accurately. The method is practical for quality control laboratories in the food and beverage industry requiring consistent sulfur dioxide analysis in compliance with international norms.
Key Topics
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Free Sulphur Dioxide Determination
Direct iodometric titration of the product at pH 0.7–1, using starch as an indicator and iodine as the titrant for quantifying free SO₂.
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Bound Sulphur Dioxide Assessment
This involves rendering the product alkaline to hydrolyze bound sulfur dioxide, releasing it for iodometric titration in acidic medium to assess total and bound fractions.
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Sample Preparation
Includes homogenization of test samples and possible sulphur dioxide removal techniques such as boiling under reflux or treatment with acetaldehyde/propionaldehyde to eliminate interference.
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Use of Standard Solutions and Reagents
Employs analytical-grade reagents such as sodium hydroxide, sulphuric acid, iodine solution, sodium thiosulphate, acetaldehyde or propionaldehyde, and starch solution, adhering to strict purity to ensure accurate results.
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Apparatus Requirements
Specifies laboratory glassware including conical boiling flasks, pipettes, burettes, and distillation apparatus compliant with ISO standards, plus illumination devices to improve titration endpoint detection for colored samples.
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Titration and Calculation Procedures
Details stepwise titration processes with formulas for calculating free, bound, and total sulphur dioxide content expressed in milligrams per litre (mg/L).
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Quality Control Measures
Includes instructions for duplicate determinations, handling products with interfering substances (e.g., ascorbic acid) and options for working in low SO₂ scenarios or with colored liquids.
Applications
ISO 5523:1981 is essential for:
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Food and Beverage Industry Quality Control
Routine sulfur dioxide testing in juices, wines, fruit nectars, and vegetable-based drinks to monitor preservative levels and comply with safety regulations.
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Regulatory Compliance
Ensuring products meet international and national legislation regarding maximum permissible sulfur dioxide concentrations, protecting consumer health.
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Product Development and Research
Supporting R&D laboratories in formulating and improving liquid fruit and vegetable products by accurately tracking sulphur dioxide content throughout processing.
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Trade and Inspection Authorities
Providing reliable, reproducible testing methods for inspection bodies validating sulphur dioxide labeling and quality standards.
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Analytical Laboratories
Serving as a standard reference method for routine chemical analysis of sulphur dioxide, enhancing consistency across labs worldwide.
Related Standards
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ISO 5522: Fruits, vegetables and derived products - Determination of total sulphur dioxide content
A more precise method recommended for detailed analyses or dispute resolution, complementing ISO 5523's routine testing approach.
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ISO 648: Laboratory glassware - One-mark pipettes
Specifies sampling equipment critical for accurate test portion measurements in sulfur dioxide determination.
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ISO 1773: Laboratory glassware - Boiling flasks (narrow-necked)
Defines standardized boiling flask use for reflux and sample preparation steps.
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ISO/R 385: Burettes
Sets requirements for burettes to ensure precise titrant delivery during iodometric analysis.
Keywords: ISO 5523, sulphur dioxide determination, liquid fruit products, vegetable products, iodometric titration, free sulphur dioxide, bound sulphur dioxide, food safety, preservative analysis, quality control, analytical method, beverage industry, sulfur dioxide testing