Summary

Cyanide is a rapidly acting potentially deadly poison that can exist in numerous chemical complexes. Cyanide can enter the environment as a result of both natural and industrial processes. Methods used for the analysis of cyanide have been developed as an effort to characterize the cyanide ion according to its chemical composition. The chemical composition of cyanide in environmental samples is dependent upon the matrix of the samples and is predominantly a function of pH, temperature, and trace metal content. Cyanide is most deadly as hydrogen cyanide gas and so, therefore, reasons for the monitoring of cyanide forms lie in the potential to generate cyanide gas.

Instrumentation

The FIA Gas Diffusion Method's ability to save you money lies in its unique capability of analyzing for all forms of cyanide without time consuming and costly distillations. Eliminating distillation minimizes interferences producing more reliable results and allowing faster turn around times. The colorimetric method is used in laboratories that are required to determine total cyanide after distillation by EPA 335.4. If distillation is required, but not colorimetry, GD-Amperometry has been proven more accurate than pyridine based reagents.

The low cost of operating the Gas Diffusion - Amperometric FIA instruments allows dischargers to frequently monitor their processes making it possible to quickly detect problems before they can cause serious ecological damage. Routine daily, or even hourly, testing can be realistically implemented so that exact cyanide discharge levels can be accurately known.

Aquatic Free Cyanide

Cyanide is about 1000 times more toxic to aquatic life than it is to humans. For this reason, it is important that free cyanide be measured in fragile aqueous environments. Free Cyanide is defined as the amount of HCN that is liberated from a solution at pH 6.0, and should only measure cyanide present in solution as HCN or as CN-.

Gas-Diffusion Amperometric Flow Injection analyzers accurately measure aquatic free cyanide by ASTM D7237-06.

Simple Cyanide Compounds

Simple Cyanides are the readily soluble salts of cyanide such as sodium, potassium, and calcium and along with free cyanide are the only cyanide complexes likely to be present in Drinking Water.

Gas-Diffusion Amperometric Flow Injection analyzers accurately measure free cyanide in drinking water by OIA1677-DW or ASTM D6888-04. These flow injection methods are the only interference free approved methods for the determination of cyanide in drinking water that do not require time consuming and expensive preliminary distillations.

Gas-Diffusion Amperometric Flow Injection analyzers may also be used to accurately measure simple cyanide in milk, assorted beverages, and food extracts.

Weak and Moderately Strong Metal-Cyanide Complexes

Weak to moderately strong metal-cyanide complexes are compounds that could readily release hydrogen cyanide gas from an acid. Weak Acid Dissociable (WAD), Cyanide Amenable to Chlorination (CATC), and Ligand Exchange methods have been devised in an effort to quantify these complexes.

Gas-Diffusion Amperometric Flow Injection analyzers accurately measure Available Cyanide in wastewater by OIA1677 or ASTM D6888-04, and in ore processing and related metallurgical materials. Gas-diffusion Amperometric flow injection methods are the only interference free approved methods for the determination of available cyanide in wastewater that do not require time consuming and expensive preliminary distillations.

Strong Metal - Cyanide Complexes

Commonly known as "total" cyanide and defined by the USEPA as cyanide ion and complexes converted to hydrogen cyanide gas by reflux distillation in the presence of strong acid and the magnesium ion. Methods for the analysis of "total cyanide" include ferrous and ferric complexes along with all other previously mentioned forms. Thiocyanate or cyanate ions are not included.

Colorimetric post distillation Flow Injection Analyzers precisely measures cyanide in distilled samples according to EPA 335.4. This flow analysis method is currently the only approved method for the determination of total cyanide in wastewater samples.

Years of testing and experiments have demonstrated that distillation and colorimetric methods of cyanide analysis do not accurately yield quantitative, or even qualitative, results in samples with complex matrices. It has been shown that sulfide interferes significantly. Abundant literature references of efforts to minimize sulfide interference have been found to be ineffective. The only accurate way to determine post - distillation total cyanide in sulfide bearing samples is to use Gas-Diffusion Amperometric Flow Injection analyzers according to ASTM D6888-04 without Ligand Exchange Reagents.

Even with post distillation Gas-Diffusion Amperometric Flow Injection Analysis it is not possible to determine total cyanide in complex samples that contain combinations of, or all of, the following ions; thiosulfate, sulfite, nitrate, nitrite, thiocyanate, and peroxide. The US 40CFR mentions that it is not possible to determine cyanide after distillation from samples containing thiosulfate or sulfite. The only method that determines total cyanide in these complex matrices is UV digestion Gas Diffusion Amperometric Flow Injection Analysis. This method uses low temperature, low strength UV technology to selectively disassociate cyanide ions from metal complexes while not allowing the simultaneous destruction or creation of cyanide that is common with high heat distillations. This method accurately determines true total cyanide rapidly and without distillation.

William Lipps
http://www.oico.com
(979) 690-1375 ext. 230
wlipps@oico.com

One Extraction, One Dilution, One Injection, Automation solutions.Segmented Flow, Flow Injection, Discrete Analyzers, TOC Analyzers, Sample Introduction, Gas Chromatography, Gel Permeation, Purge & Trap

Expert Methods Consulting
http://www.williamlipps.com

Classical Wet Chemistry, HPLC, IC, GC, GC/MS, SFA, FIA, Discrete, TOC, TOX, UV-VIS, IR, Osmometry, Petroleum, Proximate Analysis, Extractions, Digestions