Summary of Cyanide and its Methods for Analysis

SummaryWeak and Moderately Strong Metal-Cyanide
Cyanide is a rapidly acting potentially deadly poisonComplexes
that can exist in numerous chemical complexes.Weak to moderately strong metal-cyanide complexes
Cyanide can enter the environment as a result ofare compounds that could readily release hydrogen
both natural and industrial processes. Methods usedcyanide gas from an acid. Weak Acid Dissociable
for the analysis of cyanide have been developed as(WAD), Cyanide Amenable to Chlorination (CATC),
an effort to characterize the cyanide ion according toand Ligand Exchange methods have been devised in
its chemical composition. The chemical composition ofan effort to quantify these complexes.
cyanide in environmental samples is dependent uponGas-Diffusion Amperometric Flow Injection analyzers
the matrix of the samples and is predominantly aaccurately measure Available Cyanide in wastewater
function of pH, temperature, and trace metalby OIA1677 or ASTM D6888-04, and in ore
content. Cyanide is most deadly as hydrogen cyanideprocessing and related metallurgical materials.
gas and so, therefore, reasons for the monitoring ofGas-diffusion Amperometric flow injection methods
cyanide forms lie in the potential to generate cyanideare the only interference free approved methods for
gas.the determination of available cyanide in wastewater
Instrumentationthat do not require time consuming and expensive
The FIA Gas Diffusion Method's ability to save youpreliminary distillations.
money lies in its unique capability of analyzing for allStrong Metal - Cyanide Complexes
forms of cyanide without time consuming and costlyCommonly known as "total" cyanide and defined by
distillations. Eliminating distillation minimizesthe USEPA as cyanide ion and complexes converted
interferences producing more reliable results andto hydrogen cyanide gas by reflux distillation in the
allowing faster turn around times. The colorimetricpresence of strong acid and the magnesium ion.
method is used in laboratories that are required toMethods for the analysis of "total cyanide" include
determine total cyanide after distillation by EPA 335.4.ferrous and ferric complexes along with all other
If distillation is required, but not colorimetry,previously mentioned forms. Thiocyanate or cyanate
GD-Amperometry has been proven more accurateions are not included.
than pyridine based reagents.Colorimetric post distillation Flow Injection Analyzers
The low cost of operating the Gas Diffusion -precisely measures cyanide in distilled samples
Amperometric FIA instruments allows dischargers toaccording to EPA 335.4. This flow analysis method is
frequently monitor their processes making it possiblecurrently the only approved method for the
to quickly detect problems before they can causedetermination of total cyanide in wastewater
serious ecological damage. Routine daily, or evensamples.
hourly, testing can be realistically implemented so thatYears of testing and experiments have
exact cyanide discharge levels can be accuratelydemonstrated that distillation and colorimetric
known.methods of cyanide analysis do not accurately yield
Aquatic Free Cyanidequantitative, or even qualitative, results in samples
Cyanide is about 1000 times more toxic to aquatic lifewith complex matrices. It has been shown that
than it is to humans. For this reason, it is importantsulfide interferes significantly. Abundant literature
that free cyanide be measured in fragile aqueousreferences of efforts to minimize sulfide interference
environments. Free Cyanide is defined as the amounthave been found to be ineffective. The only accurate
of HCN that is liberated from a solution at pH 6.0, andway to determine post - distillation total cyanide in
should only measure cyanide present in solution assulfide bearing samples is to use Gas-Diffusion
HCN or as CN-.Amperometric Flow Injection analyzers according to
Gas-Diffusion Amperometric Flow Injection analyzersASTM D6888-04 without Ligand Exchange Reagents.
accurately measure aquatic free cyanide by ASTMEven with post distillation Gas-Diffusion Amperometric
D7237-06.Flow Injection Analysis it is not possible to determine
Simple Cyanide Compoundstotal cyanide in complex samples that contain
Simple Cyanides are the readily soluble salts ofcombinations of, or all of, the following ions;
cyanide such as sodium, potassium, and calcium andthiosulfate, sulfite, nitrate, nitrite, thiocyanate, and
along with free cyanide are the only cyanideperoxide. The US 40CFR mentions that it is not
complexes likely to be present in Drinking Water.possible to determine cyanide after distillation from
Gas-Diffusion Amperometric Flow Injection analyzerssamples containing thiosulfate or sulfite. The only
accurately measure free cyanide in drinking water bymethod that determines total cyanide in these
OIA1677-DW or ASTM D6888-04. These flowcomplex matrices is UV digestion Gas Diffusion
injection methods are the only interference freeAmperometric Flow Injection Analysis. This method
approved methods for the determination of cyanideuses low temperature, low strength UV technology
in drinking water that do not require time consumingto selectively disassociate cyanide ions from metal
and expensive preliminary distillations.complexes while not allowing the simultaneous
Gas-Diffusion Amperometric Flow Injection analyzersdestruction or creation of cyanide that is common
may also be used to accurately measure simplewith high heat distillations. This method accurately
cyanide in milk, assorted beverages, and fooddetermines true total cyanide rapidly and without
extracts.distillation.