ISO 6703-3:1984

Overview

ISO 6703-3:1984 - "Water quality - Determination of cyanide - Part 3: Determination of cyanogen chloride" specifies an analytical procedure for measuring cyanogen chloride (ClCN) in water. The method is designed for concentrations in the range 0.02 to 15 mg/L and is one part of the ISO 6703 series addressing cyanide forms in water. The standard covers sampling, separation by gas entrainment, chemical trapping, colour development and spectrophotometric measurement.

Key topics and technical requirements

• Scope and range: Applicable for ClCN between 0.02–15 mg/L.
• Principle: Add tin(II) chloride (SnCl2) to sample, free ClCN by air stripping at pH 5.4; trap the gas in an absorbing solution containing pyridine and barbituric acid. ClCN reacts to form glutaconedialdehyde, which condenses with barbituric acid to a violet complex measured at 578 nm by spectrophotometry.
• Calibration and standards: Calibration uses potassium cyanide standards; calibration verification by titration with silver nitrate (AgNO3) is recommended.
• Apparatus: Three-neck distillation flask with air-entrainment setup, fritted absorber, separatory/sampling flasks, flowmeter and a spectrometer with 10 mm cuvettes.
• Sampling: Specific sampling vessels and procedures for different expected concentration ranges are prescribed; samples must be analyzed promptly or refrigerated and kept dark.
• Interferences & limitations: A list of ions/compounds (sulfide, polysulfide, sulfite, thiosulfate, thiocyanate, free chlorine, etc.) can interfere above set limits. Aldehydes (e.g., formaldehyde) can lower apparent cyanide due to cyanohydrin formation. The method is not suitable for interlaboratory proficiency testing because stable ClCN standards cannot be distributed.
• Safety: Emphasizes extreme caution - handle cyanides and reagents (including pyridine) under a fume hood, avoid skin/eye contact, use safety pipettes and detoxify cyanide-containing wastes per regulations.

Applications and users

This standard is intended for:

• Environmental and municipal water quality laboratories
• Industrial wastewater monitoring and compliance testing
• Treatment plant process control where chlorination of cyanide-containing wastes may form ClCN
• Regulatory agencies and consultants assessing cyanide-related risks

ISO 6703-3 provides a validated laboratory procedure for accurate detection of cyanogen chloride in aqueous matrices, useful where separate identification of ClCN (rather than total cyanide) is required.

Related standards

• ISO 6703-1: Determination of total cyanide
• ISO 6703-2: Determination of readily liberated cyanides
• ISO 6703-4: Diffusion-based cyanide determination (pH 6)

Keywords: ISO 6703-3:1984, cyanogen chloride determination, water quality, cyanide analysis, gas stripping, spectrophotometry, analytical method, environmental monitoring.