Overview
ISO 2164:1975 defines a standardized laboratory method for the determination of glycosidic hydrocyanic acid (HCN) in pulses (leguminous grains). The procedure measures HCN released after enzymatic or acid hydrolysis of cyanogenic glycosides by steam distillation of the liberated acid followed by volumetric analysis. Results are reported as milligrams of HCN per kilogram of sample. An annex describes an alternative mercurimetric back‑titration method.
Key topics and technical requirements
- Scope: Quantification of glycosidic hydrocyanic acid in pulses; method may be adapted if sulphides or other interfering sulphur compounds are present.
- Hydrolysis options:
- Enzymatic hydrolysis (preferred): uses crushed sweet almonds as enzyme source, incubated at controlled temperature.
- Acid hydrolysis: alternative procedure described in the standard.
- Distillation: Steam distillation of liberated HCN; distillate collected into defined receiving solutions depending on titration method.
- Titration methods:
- Direct titration: titrate distillate in an ammoniacal medium with 0.01 N silver nitrate in presence of potassium iodide; end point indicated by permanent turbidity from silver iodide.
- Back titration: collect distillate in 0.02 N silver nitrate, then titrate excess AgNO3 with 0.02 N ammonium thiocyanate in dilute nitric acid with Fe(III) indicator (brown‑red end point).
- Annex (mercurimetric): optional back titration replacing AgNO3 with 0.02 N mercury(II) nitrate when sulphur compounds are absent.
- Quality controls: blank tests, duplicate determinations, use of analytical‑grade reagents and distilled water, and specific apparatus (grinding mill, sieves, steam‑distillation apparatus, incubator).
- Interference handling: presence of sulphides causes black precipitate with silver; the standard prescribes procedure modifications (e.g., use of lead nitrate) or use of direct titration only.
Applications and users
ISO 2164:1975 is intended for:
- Food safety and quality control laboratories testing pulses for cyanide content (HCN).
- Agricultural and cereal/pulse processors ensuring raw material safety.
- Regulatory bodies and inspection laboratories validating compliance and assessing toxicological risk.
- Research and breeding programs monitoring cyanogenic glycoside levels in varieties and processing studies.
Practical uses include evaluating raw material safety, guiding processing/ detoxification steps, and supporting product labeling and regulatory compliance.
Related standards
- ISO/R 951 - Pulses: sampling
- ISO 2170 - Cereals and pulses: sampling of milled products
Keywords: ISO 2164:1975, pulses, glycosidic hydrocyanic acid, HCN determination, steam distillation, silver nitrate titration, ammonium thiocyanate, mercurimetric method, food safety.