Total Cyanide Analysis
Total Cyanide
The FS3700 measures total cyanide by a UV digestion, gas diffusion technique coupled with amperometric detection in accordance with ASTM Method D7511-12. This non-distillation technique is particularly effective for applications where thiocyanate is present to avoid cyanide loss or positive interference. ASTM D7511-12 is USEPA- approved for analysis of wastewater samples for NPDES compliance reporting. A schematic drawing of the FS3700 highlighting the principal steps of the UV digestion, gas diffusion cyanide analysis technique is presented below.
Learn about the products used in this analysis:
Principle of Operation For total cyanide measurement, a
3
2
Pump
Sample
Gas Diffusion Module
sample is injected into a carrier stream, segmented and acidified. Under acidic conditions the weak acid dissociable cyanide complexes convert to HCN (1) and the strong metal-cyanide complexes are exposed to ultraviolet light in the UV digestion module (2) where they break down and release HCN. The HCN gas from all cyanide species present in the sample diffuses across a hydrophobic membrane into a basic acceptor solution (3), where it converts back to CN - and is carried into the flow cell of an amperomtric detector. Cyanide ions react with a silver electrode and generate current proportional to the cyanide ion concentration (4). WinFlow software displays the detector response in real-time as a peak as the sample passes through the flow cell. The resulting peak height is proportional to cyanide concentration present in the sample.
Waste
1
Waste
UV Digestor
Carrier
4
Valve
Inj. Loop
Acid
Membrane
Air
Detector
Waste
Total Acid 2
Base
Acidification CN - + H +
1 2 3 4
HCN (g)
Ultraviolet Light Digestion Fe(CN) 3 - + H + hv
6 HCN (g) + Fe 3+ (ag)
6
HCN
HCN
HCN
Membrane
CN -
CN -
CN -
Amperometric Detection 2 CN - + Ag
Ag(CN) - + e - at + 0.0 V 2
9
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