Determination of cyanide, thiocyanate, cyanate, hexavalent chromium, and metal cyanide complexes in various mixtures by ion chromatography with conductivity detection

Abstract

The first aim of this study was to develop a selective, sensitive and reliable method for direct simultaneous determination of cyanate, thiocyanate and hexavalent chromium by ion chromatography with conductivity detection. The other target was to successfully determine cyanides by utilizing same chromatographic system. Yet, since cyanides can not be detected by the direct method, free cyanide ions were converted into cyanate with chloramine-T at alkaline pH. In addition, strongly complexed metal cyanides were converted into cyanate by using photo-oxidation following chloramine-T. Total cyanate ion obtained from developed methods were analysed with IC. The chromatographic separations on anion exchange column were accomplished by optimized multi-step gradient eluent program using NaOH as the eluent. Proposed method was applied for the simultaneous determination of cyanide and hexavalent chromium in electroplating bath solutions and in industrial wastewater. Cyanide and hexavalent chromium could be measured in the linear dynamic ranges of 0.6 -961.5 µmol L‾ 1 and of 0.9 -118.5 µmol L‾ 1 , respectively. The limit of detection and limit of quantification of cyanide were 0.18 and 0.61 µmol L‾ 1 , and these values for chromium(VI) were 0.26 and 0.86 µmol L‾ 1 , respectively. GRAPHICAL ABSTRACTDownloaded by [University of Cincinnati Libraries] at 06:50 31 May 2016 2 INTRODUCTİONCyanide ion (CNˉ) and hexavalent chromium (Cr(VI)), which are highly toxic compounds, are extensively used in electroplating industry. Since cyanide compounds can form stable complexes with metals in a wide spectrum, they are used in mining, metallurgy, manufacture, photography, etc. The complexes of zinc, nickel, copper and cadmium metals with cyanide can be ionized in acidic medium and they are known as weak acid dissociable (WAD) species. In addition to free cyanide, WAD species, metal cyanide and strongly complexed metal cyanides, thiocyanate, cyanogen chloride, and cyanate show very distinct differences in terms of toxicity, reactivity, and effect on the environment. The ionization constants of metallocyanides have significant differences with oxidation state, pH, temperature, and photodegredation playing as important factors. [1] The toxicity of metallocyanides exhibits diversity according to their stabilization constants. The concentration of cyanate gradually increases with time as the cyanide concentration decreases in environment due to oxidation of cyanide. [2] The most harmful cyanide species to the environment are shown to be free and WAD cyanides. [3] Inhalation of hydrocyanic acid (prussic acid (HCN)) or digestion of cyanide salts causes fast-appearing symptoms. HCN vapors are formed by mixing the salts with acids or in the stomach following oral ingestion. The lethal dose is probably 100 mg for hydrocyanic acid while it is 300 mg for potassium cyanide. [4] Furthermore, according to US EPA, the maximum contaminant level for cyanide in drinking water is 0.2 mg Lˉ1. [5] Downloaded by [University of Cincinnati Libraries] at 06:50 31 Ma...

Headspace gas chromatography-mass spectrometry method for the determination of total cyanide concentration in water and postmortem blood samples

“…Therefore, simple cyanide salts and WAD cyanide complexes are the most hazardous compounds, whereas strong acid dissociable (SAD) cyanide complexes like hexacyanoferrate(II,III) are the less toxic species. To degrade the metal-cyanide bonds of the SAD complexes, a process needs more heavier conditions such as UV radiation, higher temperatures, and strong acids 5,7,11 .…”

“…Many methods have been developed for the determination of the cyanide species in different types of samples including ion chromatography 6,7 , capillary electrophoresis (CE) 12,13 , headspace gas chromatography (HS-GC) 14 , GC-Mass Spectrometry (MS) [15][16][17][18] , electrochemicalsensors8 , [19][20][21] , Headspace(HS)-single-drop microextraction (SDME)-NanoDrop® microspectrophotometry (ND) 11 , HS-GC-ato-O n L i n e F i r s t mic emission detector (AED) 22 , HS-GC-electron capture detector(ECD) 23 , HS-GC-ECD/photoionization detection (PID) 24 , HS-GC-Nitrogen-phosphorus detector (HS-GC-NPD) [25][26][27][28][29][30] , HS-solid-phase microextraction (HS-SPME)-NPD 31 , HS-SPME-CE 32 , HS-GC-MS 9,15,33,34 , HS-SPME-GC-MS 35 .…”

Recent Advances in Electrochemical Monitoring of Chromium

“…A coupling between HPLC analysis and UV technique along with the use of solid-phase extraction were utilized for the separation and speciation of Cr(III) and Cr(VI) in aqueous medium [ 15 ]. Suppressed conductivity and its combination with ion chromatography were employed for Cr(VI) measurement [ 16 , 17 ]. Solid-phase spectrophotometry technique was proposed for the preconcentration of chromium on a solid matrix, aided by 4-(2-benzothiazolylazo)2,20-biphenyldiol as a complexing agent followed by the measurement of the absorbance of the formed complex in the solid phase.…”

Ionic liquids as mobile phase additives for determination of thiocyanate and iodide by liquid chromatography

“…Therefore, the determination of thiocyanate and iodide in food is of great significance to human health. At present, the analytical methods of thiocyanate include spectrophotometry , MS , IC . The detection methods of iodide include IC , MS , and HPLC etc.…”