BS 6068-2.17:1986

National foreword
Method
0. Introduction
1. Scope and field of application
2. Definition
Subsection one: Liberation and absorption of hydrogen
cyanide
3. Principle
4. Reagents
5. Apparatus
6. Sampling and samples
7. Procedure
Subsection two: Determination of cyanide ions - Photo-
metric method with pyridine/barbituric acid
8. Applicability
9. Principle
10. Reagents
11. Apparatus
12. Procedure
13. Expression of results
14. Precision
15. Test report
Subsection three: Determination of cyanide ions - Titri-
metric method using the Tyndall effect
16. Applicability
17. Principle and reactions
18. Reagents
19. Apparatus
20. Procedure
21. Expression of results
22. Precision
23. Test report
Subsection four: Determination of cyanide ions - Titri-
metric method using an indicator
24. Applicability
25. Principle
26. Reagents
27. Apparatus
28. Procedure
29. Expression of results
30. Test report
Tables
1. Interferences
2. Precision data (photometric method)
3. Precision data (titrimetric method)
Figures
1. Apparatus for separation of hydrogen cyanide by
    stripping
2. Apparatus for determination of cyanide ions using
    Tyndall effect
Bibliography

Three methods for concentrations of up to 100 mg/l in water: a photometric method with pyridine/barbituric acid, a titrimetric method using the Tyndall effect and a titrimetric method using an indicator.

This Section of this British Standard specifies three methods for the determination of total cyanide (see clause 2) in water.

The methods are applicable to water containing less than 100 mg of cyanide per litre, but higher concentrations may be determined by suitable dilution of the sample.

The methods and corresponding ranges of cyanide contents for which they are suitable are as follows:

• Photometric method with pyridine/barbituric acid: applicable when the absorption solution contains 0,002 to 0,025 mg of cyanide, corresponding to 0,02 to 0,25 mg/l in a 100 ml aliquot portion of the undiluted sample;
• Titrimetric method using the Tyndall effect: applicable when the absorption solution contains > 0,005 mg of cyanide, corresponding to > 0,05 mg/l in a 100 ml aliquot portion of the undiluted sample;
• Titrimetric method using an indicator, applicable when the absorption solution contains > 0,05 mg of cyanide, corresponding to > 0,5 mg/l in a 100 ml aliquot portion of the undiluted sample.

A large number of ions and compounds interfere with the determination. These are listed in the Table 1, together with the concentrations below which they do not interfere (the list is not exhaustive). If present singly or in combination, up to the limiting concentrations, they do not interfere with the separation of hydrogen cyanide. The presence of aldehydes, e.g. formaldehyde, causes low cyanide values because of the formation of cyanohydrin.

If any of the limiting concentrations of the interferences is likely to be exceeded, the sample shall be diluted with distilled water before stabilization (see clause 6).

Other interference may arise from the presence of fatty acids, which will distil and form soaps during titration of alkaline solution, and from the presence of elementary sulfur.