ISO 22066:2020 pdf download Water quality — Determination of total cyanide — Method using segmented flow injection, in-line ultraviolet digestion analysis by gas diffusion and amperometric detection
3.1 total cyanide sum of HCN, cyanide ions and cyanide bound in the metal-cyano complexes that are dissociated, using digestion in the presence of ultraviolet (UV) radiation at 312 nm and sulfuric acid into HCN/CN⎺ in accordance with this document
4 Principle In the analytical procedure employed for determination of total cyanide the sample is treated with ultraviolet (UV) radation at 312 nm and sulfuric acid resulting in the release of bound cyanide ion from some metal-cyano complexes. Cyanide is not totally released from the more stable gold and cobalt cyanide complexes. The sample is introduced into a carrier solution of the segmented flow analysis (SFA) system via a valve and confluence downstream with a sulfuric acid solution containing sulfide removal reagent and digested in the presence of UV radiation at 312 nm to measure total cyanide.
The released hydrogen cyanide (HCN) gas diffuses through a hydrophobic gas diffusion membrane into an alkaline acceptor stream where the CN⎺ is captured and sent to an amperometric flow cell detector with a silver-working electrode. In the presence of cyanide, silver electrode surface is oxidized at the applied potential (E app = 0,0 V vs. the reference electrode). The anodic current measured is proportional to the concentration of cyanide in the standard or sample injected. Calibrations and sample data are processed with the instrument’s data acquisition software. The user should be aware that the described method is operationally defined, the analytical protocol of the standard has to be followed strictly to assure comparable results and the actual method conditions used can affect the result obtained. 5 Interferences
5.1 Interferences by oxidizing agents Oxidizing agents react with cyanide causing low results. The presence of oxidizing agents shall be tested and treated, if present, just prior to pH adjustment for cyanide measurement.
5.2 Interferences by sulfide Sulfide will diffuse through the gas diffusion membrane and can be detected in the amperometric flow cell, causing the measurement to be biased high. Oxidized products of sulfide can also rapidly convert CN⎺ to SCN⎺ at a high pH. A two-stage process is specified for sulfide removal. The initial lead carbonate (6.9.4) addition treatment stage and filtration shall be carried out as soon as possible. The sulfide removal and acidification reagent (6.8.14) is specified in this method. Its use will ensure removal of sulfide interference up to 50 mg/l of sulfide. This shall be applied and analysis completed within 24 h of taking the sample (see Clause 8). NOTE In the absence of sulfide in the samples 0,1 mol/l HCl (6.2) as acidification as practiced in the original USEPA method 1677 can also be used.
6 Reagents WARNING — Cyanide solutions and wastes are toxic. Waste containing these substances shall be removed appropriately. Perform work in a fume hood. Avoid contacting cyanides with acids and aeration. Harmful if swallowed and if inhaled, very toxic to aquatic life with long lasting effects. Handle carefully using personal protective equipment and dispose properly. Oxidation of cyanide wastes is commonly used for cyanide waste detoxification. Calcium hypochlorite is suitable at pH 10, using proper ventilation to capture any cyanogen chloride generated.
Use only reagents of recognized analytical grade.
6.1 Water, grade 1, as specified in ISO 3696.
6.2 Sodium hydroxide solution I, acceptor solution, c(NaOH) = 0,1 mol/l.
6.3 Sodium hydroxide solution II, c(NaOH) = 1,0 mol/l.
6.4 Sodium hydroxide solution III, c(NaOH) = 0,01 mol/l.
6.5 Potassium cyanide, KCN.
6.5.1 Potassium cyanide solution, KCN, ρ(CN) = 1 000 mg/l, (see Annex B).
Dissolve (2 503 ± 1) mg of potassium cyanide, KCN, (6.5), in sodium hydroxide solution III (6.4) in a 1 000 ml graduated flask and make up to volume with sodium hydroxide solution III (6.4). Sodium cyanide (1 884 mg) may be substituted for potassium cyanide for stock solution preparation.
This solution is stable for six months at (5 ± 3) °C, if stored in the dark or brown bottles.
Alternatively, a potassium tetracyanozincate (2 380 mg/l) solution (6.6.1) may be used.ISO 22066:2020 pdf download