ISO 20950-1:2018

INTERNATIONAL ISO
STANDARD 20950-1
First edition
2018-05
Water quality — Determination of
available weak and dissociable (WAD)
cyanide —
Part 1:
Method using ligand exchange, flow
injection analysis (FIA), gas-diffusion
and amperometric detection
Qualité de l'eau — Détermination du cyanure à acide faible
dissociable (WAD) disponible —
Partie 1: Méthode par échange de ligand, analyse par injection en flux
(FIA), diffusion gazeuse et détection ampérométrique
Reference number
©
ISO 2018
© ISO 2018
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ii © ISO 2018 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Interferences . 2
4.1 Interferences by oxidizing agents . 2
4.2 Interferences by sulfide . 2
5 Principle . 2
6 Reagents . 3
7 Apparatus . 7
8 Sampling and sample preparation . 7
8.1 General . 7
8.2 Oxidizing agents . 7
8.3 Sulfide removal . 8
8.4 Preservation . 8
9 Procedure. 8
9.1 Flow system set up . 8
9.2 Reagent blank measurement . 9
9.3 Checking the suitability of the flow injection system . 9
9.3.1 Cyanide electrode stabilization . 9
9.3.2 Performance verification of the system . 9
9.4 Calibration . 9
9.5 Sample measurement .10
9.5.1 General.10
9.5.2 Manual ligand addition options .10
9.5.3 Automated ligand addition .11
9.5.4 Cyanide measurement.11
10 Calculations.11
11 Expression of results .11
12 Test report .11
Annex A (informative) Examples of flow injection systems .13
Annex B (normative) Determination of the real cyanide concentration in the potassium
cyanide solution (6.5.1) or potassium tetracyanozincate solution (6.6.1) .15
Annex C (informative) Performance data .16
Bibliography .17
Foreword
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This document was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee SC 2,
Physical, chemical and biochemical methods.
iv © ISO 2018 – All rights reserved

Introduction
Methods using flow analysis automate wet chemical procedures are particularly suitable for the
determination of many analytes in water in large sample series at a high analysis frequency.
Analyses can be performed by flow injection analysis (FIA) using the feature of an automatic dosage
of the sample into a flow system (manifold) where the analytes in the sample react with the reagent
solutions on their way through the manifold. The sample preparation can be integrated into the
manifold. The reaction product is measured by a flow detector (e.g. amperometer).
INTERNATIONAL STANDARD ISO 20950-1:2018(E)
Water quality — Determination of available weak and
dissociable (WAD) cyanide —
Part 1:
Method using ligand exchange, flow injection analysis
(FIA), gas-diffusion and amperometric detection
WARNING — Persons using this document should be familiar with normal laboratory practice.
This document does not purport to address all of the safety problems, if any, associated with its
use. It is the responsibility of the user to establish appropriate safety and health practices.
IMPORTANT — It is absolutely essential that tests conducted in accordance with this document
be carried out by suitably qualified staff.
1 Scope
This document specifies operationally defined methods for the determination of available WAD
cyanide in various types of water such as drinking, ground, and surface, waters, and metallurgical
processing tailings reclaim, heap leach barren, mill slurry tailings and leaching solutions, with cyanide
concentrations from 5 µg/l to 2 000 mg/l expressed as cyanide ions in the undiluted sample. The range
of application can be changed by varying the operation conditions, e.g. by using a different injection
volume, thicker membrane, detector response, etc.
NOTE ISO 2080:2008, 3.105, defines free cyanide. The concentration of available WAD cyanide includes free
cyanide and some of the metals complexed in solution as determined by a specified analytical method but not all
of the metal complexes present in total cyanide (3,191).
In this method, six suitable mass concentration ranges from 5 µg/l to 50 µg/l, from 50 µg/l to 500 µg/l,
from 0,5 mg/l to 5 mg/l, from 5 mg/l to 50 mg/l, from 50 mg/l to 500 mg/l and from 500 mg/l to
2 000 mg/l are described.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 5667-3, Water quality — Sampling — Part 3: Preservation and handling of water samples
ISO 8466-1, Water quality — Calibration and evaluation of analytical methods and estimation of
performance characteristics — Part 1: Statistical evaluation of the linear calibration function
ISO 8466-2, Water quality — Calibration and evaluation of analytical methods and estimation of
performance characteristics — Part 2: Calibration strategy for non-linear second-order calibration
functions
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
available WAD cyanide
sum of HCN, cyanide ions and cyanide bound in the metal-cyano complexes that are dissociated, using
ligand reagents, if necessary, and sulfuric acid into HCN/CN¯ in accordance with this document
4 Interferences
4.1 Interferences by oxidizing agents
Test for the presence of oxidizing agents, which can continue to oxidize the cyanide, leading to low
results.
4.2 Interferences by sulfide
Sulfide will diffuse through the gas diffusion membrane and can be detected in the
...