Overview

Cyanides form simple salts with alkali earth cations and ionic complexes of varying strengths with numerous metal cations; the stability of these compounds is dependent on the cation and on the pH. Cyanide forms complexes with gold, mercury, cobalt and iron that are very stable even under mildly acidic conditions. Metal cyanide complexes also form salt-type compounds with alkali or heavy-metal cations, such as potassium ferrocyanide (K₄[Fe(CN)₆]) or copper ferrocyanide (Cu₂[Fe(CN)₆]). Cyanides can be present in soil both as cyanide ions and as complex cyanides. Determination of cyanides can be carried out under different conditions. When using mild acidic conditions (for example, pH = 4), only so-called "easily liberatable cyanides" (also known as "weak-acid dissiciable cyanides") are measured. Under strong acidic conditions (for example, pH = 1), all cyanides (both easily liberatable and complex cyanides) can be determined, these are called "total cyanides". A number of studies in soil samples have demonstrated that it is impossible to obtain reliable results for easily liberatable cyanide (ELC) using a manual ELC cyanide extraction/reflux method. Consequently, this revised standard does not include an ELC method. This International Standard is applicable to as-received (field-moist) samples and specifies two different procedures for the liberation of cyanide from the soil: - direct liberation of hydrogen cyanide using orthophosphoric acid (normative); - extraction with sodium hydroxide solution and subsequent liberation using orthophosphoric acid (informative, see Annex B). The liberated cyanide is determined either by a photometric method or a titrimetric method using an indicator. The method is applicable to all types of soil. Under the conditions specified in this International Standard, the lower limit of application is 0,5 mg/kg of total cyanide for photometric determination and 10 mg/kg for titrimetric determination (with regard to a field-moist sample). Using the alkaline extraction followed by liberation using phosphoric acid, the lower limit of application is 1 mg/kg of total cyanide (expressed on the as-received basis) for photometric determination and 30 mg/kg for titrimetric determination. The committee responsible for this standard is NA 119-01-02-02 UA "Chemische und physikalische Verfahren" ("Chemical and physical processes") at DIN.

Document: references other documents

Document: referenced in other documents

Responsible national committee

NA 119-01-02-02-04 AK - Elementary analysis  

Responsible international committee

ISO/TC 190/SC 3/WG 1 - Inorganic analysis