ISO 6703-2:1984

Overview - ISO 6703-2:1984 (Water quality - Easily liberatable cyanide)

ISO 6703-2:1984 specifies procedures for the determination of easily liberatable cyanide in water. The part covers liberation of hydrogen cyanide (HCN) from a sample by acidification and metal-assisted reduction, entrainment by a carrier gas, and absorption into alkaline solution, followed by one of three quantitative analytical methods. It is applicable to natural waters, municipal sewage and industrial effluents and is intended for routine monitoring and process control in water and wastewater treatment.

Key topics and technical requirements

• Scope and limits
  • Applicable to samples with < 50 mg/L easily liberatable cyanide and < 100 mg/L total cyanide; higher concentrations can be measured after dilution.
• Liberation and absorption
  • Liberation of HCN at pH ~4 using zinc (and other reagents) with EDTA; HCN is stripped by air and absorbed into NaOH solution for subsequent analysis.
• Three alternative determination methods
  • Photometric method (pyridine / barbituric acid): sensitive range ~0.002–0.025 mg cyanide (in the absorption solution). Produces a red‑violet dye read by photometer.
  • Titrimetric method using the Tyndall effect: applicable above ~0.005 mg cyanide.
  • Titrimetric method using an indicator: applicable above ~0.05 mg cyanide.
• Reagents and apparatus
  • Specifies analytical-grade reagents (e.g., chloramine‑T, pyridine/barbituric acid reagent), zinc dust, EDTA, tin(II) chloride, buffer solutions, stripping/distillation apparatus and absorption vessels.
• Interferences and limitations
  • Many ions/compounds interfere with liberation or detection (e.g., sulfides, thiosulfate, cyanates, nitrite/nitrate, metal ions and some organics). ISO 6703-2 lists limiting concentrations (Table 1) and gives procedures (e.g., for excluding prussiates) when needed.
• Safety
  • Explicit warnings: cyanide toxicity, use fume cupboard, avoid skin/eye contact, use safety pipettes and proper detoxification of wastes.

Applications and users

• Environmental and regulatory laboratories performing routine water quality monitoring.
• Municipal and industrial wastewater testing and process control (cyanide destruction verification).
• Consultants and QA/QC teams validating cyanide-removal in treatment plants.
• Research groups working on cyanide speciation and environmental fate.

Related standards

• ISO 6703-1: Determination of total cyanide
• ISO 6703-3: Determination of cyanogen chloride
• ISO 6703-4: Diffusion method for low-level cyanide These parts together provide a comprehensive framework for cyanide analysis in water.

Keywords: ISO 6703-2, water quality, cyanide determination, easily liberatable cyanide, photometric pyridine barbituric acid, titrimetric Tyndall effect, wastewater testing, environmental monitoring.