Continuous Determination of Free Cyanide by Means of Membrane Diffusion of Gaseous HCN and An Electrode Indicator Technique

Abstract

A continuous measurement system for free cyanide has been developed based on the principle of diffusion across a gas-permeable membrane to affect the separation of hydrogen cyanide from the acidified sample solution. The cyanide absorbed in the alkaline indicator solution is subsequently analyzed by an indirect technique using a silver ion-selective electrode. In the concentration range of 30 to 400 μg CN^?/L, the accuracy and precision of this method is approximately two percent. The detection limit of this system is approximately 0.5 μg CN^?/L.     

A highly selective and sensitive dual-channel chemosensor for cyanide based on sulfahydrazone derivative

A colorimetric and fluorescent cyanide probe bearing naphthol and sulfahydrazone groups has been designed and synthesized. This structurally simple probe displays a rapid response and high selectivity for cyanide in DMSO/EtOH (v/v = 2:8) solution. The addition of CN^? to the sensor p-toluenesulfonyl-2-hydroxy-1-naphthylhydrazone (L3) induced a remarkable color change from pale-yellow to yellow, and green fluorescence changed to yellow. The ¹H NMR titration and DFT calculations suggested that the selective sensing process is based on a nucleophilic addition reaction of cyanide to imine. Test strips based on sensor L3 were fabricated, which could act as a convenient and efficient test kit to detect CN^? for “in-the-field” measurements.     

A Novel Dielectric-Barrier-Discharge Loop Reactor for Cyanide Water Treatment

A novel dielectric-barrier-discharge (DBD) loop reactor was designed for the efficient degradation of cyanide anion (CN^?) in water. The circulation of cyanide water as a falling film through plasma gas discharge zone enhanced gas–liquid mass and energy transfer and induced formation of H₂O₂ which was associated with the efficient destruction of CN^?. It was observed that among different discharge gases, the CN^? degradation rate decreased in the order of Ar > air > H₂/air mixture. Depending on discharge voltage, the treatment time for complete removal of 100 ppm CN^? in this DBD loop reactor is in the range 120–300 min. The dose of Cu²⁺ catalyst in combination with in situ production of H₂O₂ enhanced the destruction of CN^? apparently in this DBD loop reactor. The treatment time for complete degradation of 100 ppm CN^? decreased from 180 min with Ar DBD discharge alone to 40 min with 40 mg/L dose of Cu²⁺ ion in water, making it an efficient means to degrade cyanide water.     

A highly selective chemosensor derived from benzamide hydrazones for the detection of cyanide ion in organic and organic-aqueous media: design,synthesis, sensing and computational studies

ABSTRACT

A new, highly sensitive and selective chemosensing method has been developed for the detection of cyanide ion using benzamide hydrazone receptors (R1-R4). The sensing ability of these compounds towards CN^? in the presence of Br ^?, HSO₄ ^?, Cl^?, OH^?, I^?, F^?, AcO^?, NO₂ ^? and NO₃ ^? in DMF and DMF-Aqueous mixture (DMF:H₂O, 9:1 v/v) was investigated. The binding characteristics of the probe with cyanide ions carried out by ¹ H NMR titrations indicated the deprotonation of N-H group through H-bond interactions between benzamide hydrazones and cyanide ions; it has been theoretically supported by DFT. The binding constant (Ka) and stoichiometry of the host–guest complex formed was calculated by the Benesi–Hildebrand (B–H) plot, and strong interaction of the probe with CN^- ions forming a 1:2 binding stoichiometry has been noted in this study. In a DMF and aqueous medium for CN^? ion, the lower limit of detection (LOD in ppm) is compared to the limit of quantification (LOQ in ppm), which is quite better in terms of sensitivity.     

A Fluorimetric Method for the Determination of Cyanide with Fluorescein and Iodine∗

Abstract

A rapid, simple and sensitive fluorimetric method has been developed for the determination of cyanide with fluorescein as fluorogenic reagent (λ_ex = 494 nm, λ_em = 514 nm) at pH 6.0–7.0. A linear calibration curve was obtained in the range 0.004–2.0 μg CN^?/25 ml. The detection limit is 0.004 μg CN^-/25 ml. The method was successfully applied to the determination of cyanide in waste water.

     

Optical detection of cyanide by palladium(II)-dithiazolopyridine probe at the parts per billion level

Abstract

The ensemble of 2,6-bis(2-chlorophenyl)dithiazolo[4,5-b:5',4'-e]pyridine 1 with Pd²⁺ ions (1?Pd²⁺) was prepared for the detection of cyanide ions (CN^¯) in 50% aqueous methanol. Among the tested metal ions, only Pd²⁺ sensitively induced the red shift of the absorption bands and the complete decrease of fluorescence emission. The detection limit toward Pd²⁺ was 2?ppb. The ensemble 1?Pd²⁺ selectively and rapidly detected a low concentration of cyanide ions by a colorimetric change (40?ppb) as well as a “turn-on” fluorescent response (5?ppb). Job’s plot revealed the complex formation with 1:1 stoichiometry. The binding and replacement mode of 1?Pd²⁺ and CN^¯ were also confirmed by ¹H NMR titrations and IR analysis. In general, a fast and selective recognition of CN^¯ is reported.     

A Fluorometric Method for Cyanogen (C2N2) with No Cyanide Interference

Abstract

A fluorometric method for the analysis of cyanogen (C₂N₂, ethanedinitrile) without cyanide interference is described the procedure is based on the reaction of C₂N₂ with hexamethylenetetramine (HMTA) to produce a fluorophor. the fluorescence yield is linear over a range of 3–4 orders of magnitude. the method is comparable in detection limits to CN^? measurements done electrochemically; in this case >10^?2?<10^?5 M. Many anions and cations were examined for interference; only transition and heavy metal compounds reduced fluorescence. Certain amines may interfere, although all examined reacted much slower than the HMTA.     

Controllable and reversible proton transfer for inorganic cyanide visual sensing based on the deprotonation of azo-phenolic hydroxyl group

ABSTRACT

Methods for optical detection of inorganic cyanide based on the single molecule sensor with high selectivity and sensitivity have attracted increasing interest recently due to the high toxicity of cyanide ions. In this work, a visual sensor (S1) containing both imidazole NH and azo-phenolic OH was synthesised and characterised. The spectral experimental data indicated that protic aqueous solution facilitated enhancing the selectivity of cyanide ions with the nanomolar-level detection limit in semi-aqueous solution. The visual sensing mechanism arising from the deprotonation of azo-phenolic OH and the enhancement of intramolecular charge transfer could be clearly demonstrated by titration experiments of ¹H NMR, HR MS and energy changes between the HOMO?LUMO band gaps. Furthermore, the reversibility and reusability of S1 upon alternating addition of CN^? and H⁺ were studied.     

An Atomic Absorption Analysis Method for Cyanide

Abstract

An atomic absorption analysis procedure for cyanide has been developed. The procedure is based upon the solubilization of copper(II) from a basic copper carbonate in an alkaline medium. The amount of copper complexed by the cyanide ion is determined by atomic absorption and a calibration curve is constructed concurrently. The stoichiometry of the cyanide-copper complex is 3:1, implying formation of the complex ion Cu(CN)^? ₃, with no formation of CuCN observed at the low concentration of cyanide used. The method is used primarily for analyzing low levels of cyanide; the sensitivity of the method extending down to 2.0 × 10^?5 M CN^?. The most likely interference, iron, is considered. Finally, recovery of cyanide from spiked samples is demonstrated.     

Determination of HCN sampled from gasification product gases by headspace gas chromatography with atomic emission detector

Nitrogen-containing fuels produce hydrogen cyanide when the fuel is gasified. The gas is poisonous and produces nitrogen oxides when it is burned. HCN is usually sampled into alkaline solutions and analysed using an ion selective electrode. The method is tedious and the electrode response is temperature-dependent. Samples are not stable and must be analysed immediately, and they contain ions which are poisonous to the electrode. Therefore a new gas chromatographic method was developed. In this new method HCN is released from the alkaline solutions with sulphuric acid in a headspace sampler and analysed by a gas chromatograph connected to an atomic emission detector. Measurements on carbon emission line 193.1 nm gave the limit of detection 0.05 mg CN^–/l in the solution. The calibration curve was linear to 1000 mg CN^–/l and the correlation was 0.997. The relative standard deviation of the calibration was 1.7% at the concentration of 5 mg CN^–/l and 1.0% at 25 mg CN^–/l. The developed headspace method allows automated analysis and it needs less sample preparations than the ion selective electrode method. This paper also reports the effect of sample preparation and storage time on the stability of the samples.     

A simple dual-channel sensor for detecting cyanide in water with high selectivity and sensitivity

Taking advantage of the special nucleophilicity of cyanide, a new simple colorimetric chemosensor has been synthesised. This allows a deprotonation reaction to monitoring the cyanide. With the addition of CN^? to the chemosensor aqueous solution, which could induce a change in the solution colour from yellowish to deep yellow, while no colour change could be observed in the presence of other hackneyed anions, by which CN^? can be distinguished from other anions immediate with the naked eye. At the same time, a fluorescence quenching was implemented upon adding cyanide into the chemosensor aqueous solution. The absorption spectra detection limits of the chemosensor for cyanide was 5.35 × 10^?8 M and the fluorescence spectra detection limit was 2.63 × 10^?8 M. The cyanide test strips based on the chemosensor could serve as a convenient cyanide test kits. Furthermore, the chemosensor was successfully applied to detect cyanide in sprouting potatoes.     

Mimicking a Receptor for Cyanide Ion Based on Ion Imprinting and Its Applications in Potential Transduction

Using the strategy of template polymerization, a presynthesized specific metal‐complexing polymer (poly(methacryloylhistidine‐Ni(II)‐CN^?), Ni‐CN/IP) has been specifically used to recognize cyanide ion. As described previously, nickel(II)‐methacryloylhistidine dihydrate complex monomer was synthesized and reacted with KCN to produce the monomer‐template complex. This monomer‐template complex phase was polymerized in a dispersion medium. After polymerization, the template (CN^?) was removed from the Ni‐CN/IP, producing CN^? ion imprinted metal‐chelate polymer. The synthesized ion imprinted polymer is examined as a novel potential cyanide selective ionophore in polymeric membrane type ion selective electrodes. Membranes formulated with Ni‐CN/IP are shown to exhibit enhanced potentiometric selectivity for cyanide over more lipophilic anions including perchlorate, iodide, and thiocyanate. Addition of lipophilic cationic sites into the organic membranes enhanced the response and selectivity towards CN^? ion, while addition of lipophilic anionic sites deteriorated the response but enhanced the selectivity, indicating that the Ni‐CN/IP particles behaves via the so‐called “mixed‐mode” response mechanism. The fabricated sensors possessed good performance characteristics, in terms of life span, selectivity for CN^? ion over a wide range of other interfering anions, fast response, stability and high reproducibility. Applications for direct determination of cyanide ion in hazardous wastes using the proposed sensors showed good correlation with data obtained using commercial solid state cyanide electrode, with no significant difference in the t‐test values with 95 % confidence level. An F‐test revealed that the standard deviations of the replicate sample measurements obtained by the two methods were not significantly different.     

A novel and synthetically facile coumarin-thiophene-derived Schiff base for selective fluorescent detection of cyanide anions in aqueous solution: Synthesis,anion interactions,theoretical study and DNA-binding properties

A colorimetric and fluorescent chemosensor (chemosensor 2) for the detection of cyanide anions in aqueous solution has been designed and synthesized in high yield. The sensing mechanism of the chemosensor was verified via UV–vis, fluorimetric, and NMR titrations, and was theoretically explained using DFT and TD-DFT calculations. The chemosensor could optically discriminate the presence of fluoride ions over other anions by a color change from yellow to red with an enhancement of pink fluorescence in DMSO. However, it showed strong green fluorescence when CN^? was added to a mixture of DMSO/water (6:4 v/v). Thus, the chemosensor can be employed in selective detecting of CN^? besides other interference anions (F^?, AcO^? and H₂PO₄^?) in aqueous solution. Moreover, 2 can be used to detect CN^? at a concentration as low as 0.32?μM, which is lower than the WHO guideline (2.7?μM) for cyanide. A low quantity of CN^? (1.08?μM) can be detected and quantified using the prepared chemosensor. Moreover, the UV–vis and fluorescence spectroscopy studies of the interactions between 2 and dublex DNA revealed intercalative binding of calf thymus DNA to the chemosensor.     

A Post‐Synthetically Modified MOF for Selective and Sensitive Aqueous‐Phase Detection of Highly Toxic Cyanide Ions

Selective and sensitive detection of toxic cyanide (CN^?) by a post‐synthetically altered metal–organic framework (MOF) has been achieved. A post‐synthetic modification was employed in the MOF to incorporate the specific recognition site with the CN^? ion over all other anions, such as Cl^?, Br^?, and SCN^?. The aqueous‐phase sensing and very low detection limit, the essential prerequisites for an effective sensory material, have been fulfilled by the MOF. Moreover, the present detection level meets the standard set by the World Health Organization (WHO) for the permissible limit of cyanide concentration in drinking water. The utilization of MOF‐based materials as the fluorometric probes for selective and sensitive detection of CN^? ions has not been explored till now.     

Structural,compositional and hardness properties of hydrogenated amorphous carbon nitride thin films synthesized by dense plasma focus device

The hydrogenated amorphous carbon nitride (a‐CN_x:H) thin films were synthesized on the SS‐304 substrates using a dense plasma focus device. The a‐CN_x:H thin films were synthesized using CH₄/N₂ admixture gas and 20 focus deposition shots on substrates placed at different distances from the anode top. X‐ray photoelectron spectroscopy and Raman analysis confirmed different C–N bonding in the a‐CN_x:H thin films. A decrease in the N/C ratio as well as the sp³/sp² ratio with an increase in the substrate distance has been observed. The higher amount of C–N formation for the film synthesized at 10 cm is observed which decreases with increasing distance. The X‐ray photoelectron spectroscopy and Raman analysis affirmed the C ≡ N presence in all the thin films synthesized at different distances. The morphology of the synthesized a‐CN_x:H thin films showed nanoparticles and nanoparticle clusters formation at the surface. The hardness results showed comparatively lower hardness of the a‐CN_x:H thin films due to the presence of C ≡ N. The C–N formation with lower amount of C ≡ N and a higher N/C ratio as well as a higher sp³/sp² ratio for the films synthesized at 10 cm show reasonably higher hardness. Copyright © 2016 John Wiley & Sons, Ltd.     

Kinetics and mechanism of ligand substitution reactions of NiL and Ni2L with cyanide ion (L = hexamethylenediaminetetraacetic acid)

Summary The kinetics and mechanism of reactions of cyanide ion with [NiL] and [Ni₂L] (L = hexamethylenediaminetetraacetic acid) have been studied spectrophotometrically at 25 ±0.1 °C, with pH=11.0±0.02, and I=0.1 M(NaClO₄). In both reactions the final product was [Ni(CN)₄]^2–. The order with respect to [CN^–] was found to be one over a wide range of cyanide ion concentrations for both the systems.In the Ni₂L-CN^– system, however, the reaction becomes zero order with respect to cyanide when [CN^–]<6×10^–4 M.     

Voltammetric evaluation of the electrode material on the oxidation of cyanide catalyzed by copper ions

The cyanide oxidation on vitreous carbon (VC), stainless steel 304 (SS 304) and titanium (Ti) was investigated through a voltammetric study of cyanide solutions also containing copper ions. Results showed that cyanide oxidation occurs by means of a catalytic mechanism involving adsorbed species as CN^–, Cu(CN)₄^3– or Cu(CN)₄^2– depending on the electrode material. It was observed that on VC, the adsorption of Cu(CN)₄^3– controlled the oxidation rate. Instead, for SS 304 and Ti, the adsorption of CN^– controlled the global process. However, in all cases, the adsorption of Cu(CN)₄^3– on the electrode surface was required for the catalytic oxidation of CN^–. Voltammetric experiments for solutions containing cyanide oxidation products, such as cyanogen (CN)₂ and cyanate (CNO^–), confirmed that the adsorbed species mentioned above controlled the catalytic oxidation of CN^– depending on the electrode material. A voltammetric identification of the oxidation products showed that cyanogen, (CN)₂ tended to adosorb on VC, while the formation of cyanate, CNO^– predominated on SS 304.     

Determination of Fluoride,Cyanide, and Thiocyanate Using Horseradish Peroxidase Immobilized on Modified Silica Gel

Abstract

Silica gels modified with different functional groups (amino, epoxy, cycloepoxy, isocyanate, and thiocyanate) were used for the covalent immobilization of horseradish peroxidase (HRP). The catalytic activity and stability of the obtained enzyme preparations were studied using the reaction of o‐dianisidine oxidation with hydrogen peroxide as an indicator. The covalent immobilization of horseradish peroxidase using silica gel modified with thiocyanate groups provided not only the improvement of the enzyme stability, but also the development of the sensitive, rapid, and simple procedures for the determination of fluoride, cyanide, and thiocyanate. Enzymatic determination of inorganic anions is based on their inhibitory effect on the enzyme as the ligands capable to form stable complexes with Fe(III)‐HRP cofactor. The proposed procedures were applied for the determination of F^? in mineral and drinking waters; CN^? and SCN^?—in biological fluids (blood and saliva).     

Catalytic Reduction of CN−, CO,and CO2 by Nitrogenase Cofactors in Lanthanide‐Driven Reactions

Nitrogenase cofactors can be extracted into an organic solvent to catalyze the reduction of cyanide (CN^?), carbon monoxide (CO), and carbon dioxide (CO₂) without using adenosine triphosphate (ATP), when samarium(II) iodide (SmI₂) and 2,6‐lutidinium triflate (Lut‐H) are employed as a reductant and a proton source, respectively. Driven by SmI₂, the cofactors catalytically reduce CN^? or CO to C₁–C₄ hydrocarbons, and CO₂ to CO and C₁–C₃ hydrocarbons. The C? C coupling from CO₂ indicates a unique Fischer–Tropsch‐like reaction with an atypical carbonaceous substrate, whereas the catalytic turnover of CN^?, CO, and CO₂ by isolated cofactors suggests the possibility to develop nitrogenase‐based electrocatalysts for the production of hydrocarbons from these carbon‐containing compounds.     

Catalytic Reduction of CN−, CO,and CO2 by Nitrogenase Cofactors in Lanthanide‐Driven Reactions

Nitrogenase cofactors can be extracted into an organic solvent to catalyze the reduction of cyanide (CN⁻), carbon monoxide (CO), and carbon dioxide (CO₂) without using adenosine triphosphate (ATP), when samarium(II) iodide (SmI₂) and 2,6‐lutidinium triflate (Lut‐H) are employed as a reductant and a proton source, respectively. Driven by SmI₂, the cofactors catalytically reduce CN⁻ or CO to C₁–C₄ hydrocarbons, and CO₂ to CO and C₁–C₃ hydrocarbons. The C C coupling from CO₂ indicates a unique Fischer–Tropsch‐like reaction with an atypical carbonaceous substrate, whereas the catalytic turnover of CN⁻, CO, and CO₂ by isolated cofactors suggests the possibility to develop nitrogenase‐based electrocatalysts for the production of hydrocarbons from these carbon‐containing compounds.