Vapor and liquid phase detection of cyanide on a microchip

A capillary electrophoresis microchip is used to selectively and sensitively monitor cyanide levels in both vapor (HCN((g))) and aqueous (NaCN in drinking water) phases. Laser-induced fluorescence detection is applied using a violet diode laser to monitor the fluorescent isoindole derivative formed by the reaction of cyanide with 2,3-naphthalenedicarboxaldehyde (NDA) and taurine. Air sampling of hydrogen cyanide is achieved using a miniature impinger (2 mL), giving collection efficiencies as high as 79% for a sampling rate of 1.0 L/min and a 10 s sampling time (relative standard deviation RSD: 2.7% for n = 5). Following the addition of NDA and taurine to either the vapor phase impinger sample or an aqueous drinking water sample, the NDA/cyanide derivative can be detected in just over 40 s on the microchip, giving a detection limit of 0.56 microg/L and a linear dynamic range from 0.56 microg/L-2.4 mg/L. The detection limit for hydrogen cyanide in air was determined to be 2.3 ppb (mole%). On-chip derivatization of cyanide by NDA was successful, although a 50% decrease in signal intensity was observed due to insufficient time for completion of the reaction on the microchip. A number of different interferents were examined, and only iron(II) and chlorine showed any interference due to their capability for masking the presence of cyanide by reacting with free cyanide in solution.     

False Detection of Cyanide Ion in Photographic Processing Waste Solutions Using Standardized Reference Methods

Abstract

Although cyanide compounds are not incorporated in photographic processing solutions, false detection of cyanide ion is often encountered during the determination of total cyanide by various standardized methods such as ISO, ANSI and JIS. Various organic compounds and nitrogen compounds in the processing solutions were examined because of this false detection. The results suggest that hydrogen cyanide is formed by a reaction between these compounds during the distillation process for the separation of total cyanide, even though ISO, ANSI and JIS were used. The results support the following three mechanisms of cyanide formation involved in the process: (1) Hydroxylammonium salts reacts with another ingredient, formaldehyde, to form formaldoxime, which then decomposes to HCN. (2) Hydroxylammonium is oxidized by air to form nitrite ion, which subsequently reacts with organic compounds such as aminocarboxylic acids and aromatic amines (the colour-developing agent) to form HCN. (3) Potassium permanganate oxidizes aromatic amines to form HCN.     

On-line monitoring of cyanide concentration via a gas membrane system in extractive metallurgical processes

The principle of molecular diffusion of gaseous HCN across a tubular microporous hydrophobic PTFE membrane directly immersed in an alkaline solution or in an aqueous mineral suspension has been applied to the design of an on-line sensing system for cyanide. It offers an efficient detection of “available” cyanide and does not require acidification and solution sampling in the reactor. Gaseous HCN diffused through the membrane is dissolved by a sodium hydroxide carder solution which is then submitted to a spectrophotometric analysis by the pyridine-barbituric acid method. The problems related to filtering of sludges are therefore overcome, and many chemical interferences can be eliminated. Complexation reactions of cyanide by metallic cations and the cyanide-consuming properties of sulphide minerals and ores were studied. This method allows the determination of concentrations down to ca. 6 × 10^?7 mol l^?1 HCN + CN^? in the reactor at Ph 10 with a 120-cm membrane tube and a carrier solution flow-rate of 8 cm³ min^?1.     

Removal of Cyanide from Aqueous Solutions by Adsorption on Activated Carbon Prepared from Lignocellulosic By-products

Cyanide is considered one of the most dangerous compounds for the environment. They are discharged by various industries: chemical and metallurgical processes (extraction of gold and silver) and food industries. Adsorption is among the most used processes for elimination of cyanides particularly for the low concentrations. In this work, the cyanide removal is carried out by adsorption onto activated carbons prepared from olive stones and coffee ground. So we can promote this by-product as an inexpensive adsorbent. The prepared activated carbons are characterized by scanning electron micrograph and by determination of the physicochemical properties and specific surface area. All the adsorption experiments were performed in batch mode on synthetic water cyanide (KCN) at pH 10.8–11.0 to avoid volatilization of very toxic HCN. To describe the adsorption kinetics, the kinetic models of pseudo-first-order, pseudo-second-order, and intra-particle diffusion were applied. The experimental equilibrium data for adsorption of free cyanide were analyzed by the Langmuir, Freundlich, and Temkin isotherm models.     

Investigation of NO x precursor compounds and other combustion by-products in the primary combustion zone of a waste-incineration plant using on-line, real-time mass spectrometry and Fourier-transform infrared spectrometry (FTIR)

On-line analysis of trace and bulk gas compounds in the burning chamber of a waste-incineration plant has been performed, with high temporal resolution, by use of a variety of distinctly different measurement techniques. Time-of-flight mass spectrometry was performed with simultaneous use of three ionization techniques—resonance-enhanced multiphoton ionization (REMPI), single-photon ionization (SPI), and electron-impact ionization (EI). Chemical-ionization mass spectrometry (CIMS), Fourier-transform infrared spectrometry (FTIR), and electrochemical methods were also used. Sampling was conducted by means of a newly developed air-cooled stainless steel lance, to cope with the high temperatures and elevated particle concentrations at the sampling location. Nitrogen species were mainly nitrogen monoxide, ammonia, and hydrogen cyanide (HCN), with a small amount (approximately 0.3%) of aromatic nitrogen compounds. NO, NH₃, and HCN are the main contributors to the NO _x -formation process in the postulated fuel–NO reaction scheme dominant at this location. The NO recycling process thereby plays a major role. Changes in plant operating conditions have a noticeable impact only when the air supply is varied. For example, reduction of oxygen leads to an increase in the HCN fraction of the total nitrogen content and a decrease in the NO fraction, and vice versa.     

In situ generation of HCN for mass spectrometric studies

Hydrogen cyanide (HCN) for use in ion preparation can be generated in the gas phase by the neutral-neutral reaction of trimethylsilyl cyanide (Me(3)SiCN) and water in a flowing afterglow mass spectrometer. We demonstrate that the approach can be used to generate a wide range of HCN solvated ions such as F(-)(HCN), Cl(-)(HCN), CN(-)(HCN), PhNO(2)(.-)(HCN), Me(3)SiO(-)(HCN),and PhSiF(4)(-)(HCN), many of which are otherwise difficult to generate. The bond dissociation energy of CN(-)(HCN), generated by using this approach, has been measured by using energy-resolved collision-induced issociation (CID) to be 0.87 +/- 0.07 eV.     

Sorbent-based sampling methods for volatile and semi-volatile organic compounds in air: Part 1: Sorbent-based air monitoring options

Sorbent tubes/traps are widely used in combination with gas chromatographic (GC) analytical methods to monitor the vapour-phase fraction of organic compounds in air. Target compounds range in volatility from acetylene and freons to phthalates and PCBs and include apolar, polar and reactive species. Airborne vapour concentrations will vary depending on the nature of the location, nearby pollution sources, weather conditions, etc. Levels can range from low percent concentrations in stack and vent emissions to low part per trillion (ppt) levels in ultra-clean outdoor locations. Hundreds, even thousands of different compounds may be present in any given atmosphere. GC is commonly used in combination with mass spectrometry (MS) detection especially for environmental monitoring or for screening uncharacterised workplace atmospheres. Given the complexity and variability of organic vapours in air, no one sampling approach suits every monitoring scenario. A variety of different sampling strategies and sorbent media have been developed to address specific applications. Key sorbent-based examples include: active (pumped) sampling onto tubes packed with one or more sorbents held at ambient temperature; diffusive (passive) sampling onto sorbent tubes/cartridges; on-line sampling of air/gas streams into cooled sorbent traps; and transfer of air samples from containers (canisters, Tedlar^® bags, etc.) into cooled sorbent focusing traps. Whichever sampling approach is selected, subsequent analysis almost always involves either solvent extraction or thermal desorption (TD) prior to GC(/MS) analysis. The overall performance of the air monitoring method will depend heavily on appropriate selection of key sampling and analytical parameters. This comprehensive review of air monitoring using sorbent tubes/traps is divided into 2 parts. (1) Sorbent-based air sampling option. (2) Sorbent selection and other aspects of optimizing sorbent-based air monitoring methods. The paper presents current state-of-the-art and recent developments in relevant areas such as sorbent research, sampler design, enhanced approaches to analytical quality assurance and on-tube derivatisation.     

Methodological approach for evaluating operational parameters and the characterization of a popular sorbent for solid-phase extraction by high pressure liquid chromatography

The kinetic and retention properties of a silica-based octadecylsiloxane bonded phase sorbent used in solid-phase extraction (SPE) were determined by high pressure liquid chromatography (HPLC). This sorbent had a high bonded phase density resulting in a material with very low intraparticle porosity. This led to favorable retention and mass transfer properties over the normal sampling flow rate range. Typical cartridges for SPE have a low and variable packing density which is recognized as a significant cause of poor sampling performance and, under some circumstances, results in poor repro-ducibility. The apparent particle size for the sorbent at 55–57 μm is considerably larger than generally indicated in the trade literature but this is not detrimental to its use for SPE since sorbent cartridges are able to function adequately with only a few theoretical plates. Solute size is identified as the primary driving force for sorbent retention under SPE conditions with polar interactions favoring retention in the aqueous mobile phase and a decrease in the breakthrough volume. All parameters required to predict the optimum sampling conditions, breakthrough volume and recovery in SPE can be conveniently obtained from data generated by HPLC. The sampling characteristics of particle-loaded membranes are compared to those of conventional sorbent cartridges and differences in operating characteristics which affect the sampling efficiency for both devices are discussed.     

Direct,On-Site,On-Cartridge Toxicokinetic Sampling Prior to On-Line SPE: A Feasibility Study

A recently developed sample introduction method prior to on-line SPE and liquid chromatography, termed “sorbent sampling” [1], was tested for its applicability in bioanalysis. The proof of principle described in this article demonstrates the applicability of sorbent sampling for a pharmacokinetic (PK) study with carbamazepine in rats. In this experiment two rats were dosed with carbamazepine and at several time intervals plasma samples were taken. Every sample was applied to and stored on a sorbent sample cartridge, while the remaining plasma was collected for processing by a conventional autosampler for comparison purposes. Quantitation was performed with and without the use of internal standard and the performance of the methods was verified. Results obtained with the sorbent sampling technique are comparable to those obtained with a conventional method. Sorbent sampling proved to be suitable for PK studies with a few practical challenges left. Although sorbent sampling is not yet commercially available, this feasibility study indicates that the sorbent sampling technique is a promising new method of sampling for bioanalytical purposes in biopharmaceutical R&D, with significant advantages such as zero sample loss, reduced animal or human sampling volumes (and hence reduction of animal usage), reduced risk of carry-over and fully automated sample preparation and analysis.     

Ab initio studies on hydrogen-bonded clusters. I. Linear and cyclic oligomers of hydrogen cyanide

Large-scale ab initio calculations have been performed on linear and cyclic oligomers of hydrogen cyanide molecules applying basis sets ranging from double-zeta to near-Hartree-Fock quality. Equilibrium geometries of linear (HCN)_n clusters with n = 1 to 5 and of cyclic clusters with n = 3, 4 are reported. For most of the complexes complete vibrational analysis has been carried out. In agreement with recent experimental data the linear HCN trimer was found to be more stable than the cyclic trimer. In case of the tetramer linear and cyclic structures are of comparable stability. The structural changes taking place upon polymerization of linear HCN clusters and the convergence of various stage properties to those of the infinite polymer (HCN)_∞ are discussed in detail. The evolution from vibrational spectra of small oligomers to phonon dispersion curves of the infinite polymer is illustrated too.     

Fullerene(C_(60)) as a Potential Chemical Sensor for Hydrogen Cyanide Detection

To find a novel sensor for the detection and control of toxic hydrogen cyanide(HCN), the geometrical and electronic parameters of HCN adsorption on fullerene C60 were investigated using density functional theory(DFT) calculations by means of B3 LYP functional with 6-31 G* basis set. The calculated density of states(DOSs) shows that the electronic properties of fullerene C60 were very sensitive to the presence of HCN molecule, so that the Eg of C60 was significantly decreased from 2.76 eV in pristine form to 1.81 eV(34.4% change) after the HCN adsorption which would result in electrical conductance increment. The results demonstrated that the C60 may convert the presence of a HCN molecule to an electrical signal for using in HCN-sensor devices through doping, chemical functionalization. Also, based on calculated results, the C60 is expected to be a potential efficient adsorbent as well as a sensor for detecting the presence of toxic HCN.     

MgO脱除HCN的动力学研究

研究了MgO在不同温度下对HCN的脱除作用,并用XRD对反应后固相产物进行分析。研究了温度、MgO质量分数、HCN初始体积分数和停留时间等因素对HCN脱除效率的影响,并求出MgO与HCN反应的动力学参数。结果表明,673 K时,MgO已经开始与HCN发生反应,当温度高于873 K时,HCN中气态"N"已转化到固相产物MgCN₂中;HCN脱除效率随温度、MgO质量分数和停留时间的增加呈线性增加,但随HCN初始体积分数增加呈负幂函数的规律下降;MgO与HCN的反应级数α为0.72,表观活化能E为32.2 kJ/mol。     

Novel chemical sensor for cyanides: boron-doped carbon nanotubes

Boron-doped (B-doped) single-walled (8, 0) carbon nanotubes (SWCNTs) are investigated using density functional theory (DFT) calculations as sensor models to detect the presence of cyanides, such as hydrogen cyanide (HCN) and cyanogen chloride (CNCl). Comparing the results of the intrinsic SWCNTs with HCN and CNCl, we discover that B-doped SWCNTs present a high sensitivity to the gaseous cyanide molecules, which is indicated by optimized geometry and electronic properties of these systems. On the basis of calculated results, we call attention to the fact that B-doped SWCNTs would be potential candidates for the detection of gaseous cyanide molecules. The present results provide guidance to experimental scientists in developing CNT-based chemical sensors.     

Synthesis of Prebiotic Building Blocks by Photochemistry

Ultraviolet(UV) light is a very competent energy source for the synthesis of prebiotic building blocks on early Earth. In aqueous solution, hydrated electron is produced by irradiating ferrocyanide/cuprous cyanide/hydrosulfide by 254 nm UV light. Hydrated electron is a powerful reducing reagent driving the formation of prebiotic building blocks under prebiotically plausible conditions. Here we summarize the photoredox synthesis of prebiotic related building blocks from hydrogen cyanide(HCN) and other prebiotically related molecules. These results indicate biological related building blocks can be generated on the surface of early Earth.     

Application of hydrocyanic acid vapor generation via focused microwave radiation to the preparation of industrial effluent samples prior to free and total cyanide determinations by spectrophotometric flow injection analysis

A sample preparation procedure for the quantitative determination of free and total cyanides in industrial effluents has been developed that involves hydrocyanic acid vapor generation via focused microwave radiation. Hydrocyanic acid vapor was generated from free cyanides using only 5 min of irradiation time (90 W power) and a purge time of 5 min. The HCN generated was absorbed into an accepting NaOH solution using very simple glassware apparatus that was appropriate for the microwave oven cavity. After that, the cyanide concentration was determined within 90 s using a well-known spectrophotometric flow injection analysis system. Total cyanide analysis required 15 min irradiation time (90 W power), as well as chemical conditions such as the presence of EDTA–acetate buffer solution or ascorbic acid, depending on the effluent to be analyzed (petroleum refinery or electroplating effluents, respectively). The detection limit was 0.018 mg CN l⁻¹ (quantification limit of 0.05 mg CN l⁻¹), and the measured RSD was better than 8% for ten independent analyses of effluent samples (1.4 mg l⁻¹ cyanide). The accuracy of the procedure was assessed via analyte spiking (with free and complex cyanides) and by performing an independent sample analysis based on the standard methodology recommended by the APHA for comparison. The sample preparation procedure takes only 10 min for free and 20 min for total cyanide, making this procedure much faster than traditional methodologies (conventional heating and distillation), which are time-consuming (they require at least 1 h). Samples from oil (sour and stripping tower bottom waters) and electroplating effluents were analyzed successfully.     

A new hydrogen cyanide chemiresistor gas sensor based on graphene quantum dots

Graphene quantum dots (GQDs), synthesised via controlled carbonisation of citric acid, were reduced by hydrazine hydrate and then used as hydrogen cyanide (HCN) gas sensors. Checking of the reduction step by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) techniques revealed that most of the oxygen-containing functional groups were removed from the GQDs. It was observed the reduction process is necessary for sensitising of GQDs for HCN gas. The electrical resistance of the reduced GQDs was increased as a result of their exposure to HCN gas. Accepting a p-type semiconducting characteristic for GQD material, the above-mentioned behaviour suggested electron donation from HCN to GQD. The sensor response to HCN gas was reversible, suggesting a reversible adsorption/desorption phenomenon of HCN to the GQDs. The response as well as the recovery time of the sensor was different depending on the HCN concentration tested. The developed sensor showed linear HCN response from 1 to 100 ppm. The detection limit of the sensor was estimated to be 0.6 ppm (S/N). Relative standard deviation f HCN determination by the developed sensor was calculated to be 5.7% (n = 4, [HCN] = 50 ppm). The sensor response was did not vary significantly within 6 months.     

Salts of HCN‐Cyanide Aggregates: [CN(HCN)2]− and [CN(HCN)3]−

Although pure hydrogen cyanide can spontaneously polymerize or even explode, when initiated by small amounts of bases (e.g. CN^?), the reaction of liquid HCN with [WCC]CN (WCC=weakly coordinating cation=Ph₄P, Ph₃PNPPh₃=PNP) was investigated. Depending on the cation, it was possible to extract salts containing the formal dihydrogen tricyanide [CN(HCN)₂]^? and trihydrogen tetracyanide ions [CN(HCN)₃]^? from liquid HCN when a fast crystallization was carried out at low temperatures. X‐ray structure elucidation revealed hydrogen‐bridged linear [CN(HCN)₂]^? and Y‐shaped [CN(HCN)₃]^? molecular ions in the crystal. Both anions can be considered members of highly labile cyanide‐HCN solvates of the type [CN(HCN)_n]^? (n=1, 2, 3 …) as well as formal polypseudohalide ions.     

Pneumatopotentiometric determination of nanogram amounts of cyanide

Hydrogen cyanide is liberated from aqueous samples by reaction with sulphuric acid and transferred by a stream of nitrogen to a silver porous membrane electrode. Some HCN passes through the membrane into an alkaline dicyanoargentate solution; the cyanide ion produced causes a decrease in the equilibrium Ag⁺ concentration and the change of potential is related to the amount of cyanide in the sample. The detection limit is 3.0 ng ml^?1 cyanide in the injected solution; the relative standard deviation is 0.82% for 17 ng of cyanide. Sulphide interferes (as H₂S) but can be removed on a lead acetate column.     

Absorption properties of commercial lead chromates

For the cyanide determination in waste waters containing more than 2.5×10^?6 Mol of CN^?/l a conductometric method has been proposed. The sulphuric acid containing samples were distilled and the obtained HCN was passed into a 5×10^?4 Mol/l AgNO₃ solution, of which the conductivity was measured. The method offers the possibility of a precise observation of the completion of the HCN distillation and also the direct measurement of the cyanide concentration by the change of conductivity. The analysis time is about 40 min.     

An isotopic dilution approach for 1,3-butadiene tailpipe emissions and ambient air monitoring

An isotopic dilution approach for 1,3-butadiene analysis in gaseous samples is presented. The methodology is based on active sampling on sorbent tubes and subsequent analysis by thermal desorption into a gas chromatography/mass spectrometry system. By adding a perdeuterated internal standard onto the sorbent tubes before sampling, and using mass spectrometric detection, the methodology gives high accuracy for this unstable analyte. The method has been used to monitor 1,3-butadiene ambient air concentrations in a residential area in proximity to a heavy-traffic roadway over a one-week period, for comparison with other traffic-related pollutants analysed by standard procedures. It has also been used to determine tailpipe emissions of two vehicles by standard emission testing procedures in a dynamometer. These vehicles were chosen as examples of low- and high-end emission rate vehicles, i.e., an old no-catalytic converter Otto engine and a new direct-injection diesel engine with catalytic converter. Exhaust gas emissions were 0.052 and 35.85 mg/km, reflecting differences in fuel, engine design, age, and presence (or not) of a catalytic abatement system. The ambient air results showed a weekly average concentration of 1,3-butadiene of 0.53 microg/m(3).