Cyanide sensors

The cyanide sensor developed by the authors group is based on the formation of an addition product between cyanide ion and pyridoxal-5-phosphate, and its subsequent retention in the sensor (a fluorimetric flow-cell packed with QAE-Sephadex resin). The eluent is not injected, but merged with a stream of 0.05 M HCl after the reactor that is used both to acidify the complex and elute it after measurement. The calibration graph for the target analyte was linear from 50 ng/mL to 3.0 pg/mL, and the relative standard deviation and sample throughput were 1.4% (for 2 pg CN7mL) and... 

With this sensor, concentrations between 0.1 ppm and 1 ppm of cyanide can be measured with a response time of less than 2 min. The cyanide-sensor shows a stability of some days only. 

Ikebukuro K, Miyata A, Cho SJ, Nomura Y, Chang SM,YamauchiY, Hasebe Y, Uchiyama S, Karube I (1996) Microbial cyanide sensor for monitoring river water. J Biotechnol 48 73-80... 

S. Licht, Developments in photoelectrochemistry light-addressable pho-toelectrochemical cyanide sensors, Colloids Surf. A Physicochem. Eng. Aspects, 134(1-2) (1998) 231-239. 

Ikebukuro K., Honda M., Nakanishi K., Nomura Y., Masuda Y., Yokoyama K., Yamauchi L, and Karube L, Plow-type cyanide sensor using an immobilized microorganism, Electroanalysis, 8, 876-879, 1996. 

Figure 2 Air-gap detectors. (A) Detector with an electrolyte film. 1, detector body 2, sample vessel 3, indicator (pH) electrode 4, electrolyte film 5, reference electrode 6, salt bridge 7, sample 8, stirring bar and 9, seal. (From Ruzicka J and Hansen EH (1974) A new potentiometric gas sensor - the air-gap electrode. Analytica Chimica Acta 69 129-141.) (B) Detector with an electrolyte drop. 1, Conical flask 2, stopper with electrodes 3, indicator electrode (Ag wire) 4, reference electrode (SCE) 5, electrolyte drop 6, sample and 7, stirring bar. (After Fligier J, Czichon P, and Gregorowicz Z (1980) A very simple air-gap cyanide sensor. Analytica Chimica Acta 118 145-148.)...

Taheri, A., Noroozifer, M., and Khorasani-Motlagh, M. (2009) Investigation of a new electrochemical cyanide sensor based on Ag nanoparticles embedded in a three-dimensional sol-gel. J. ElectroanaL Chem., 628 (1-2), 48-54. 

Other usefiil gas sensors include the potentiometric ammonia (64) or hydrogen cyanide probes (65), and amperometric carbon monoxide (66) and nitrogen dioxide (67) devices. The hydrogen cyanide probe is an example of a modem device that relies on changes in the conductivity of electropolymerized film (polyanihne) in the presence of a given gas. 

Cyanide oxidation consists of a reaction with sodium hypochlorite under alkaline conditions in either a batch or continuous system. A complete system includes reactors, sensors, controls, mixers, and... 

Method Cyanide is destroyed by reaction with sodium hypochlorite under alkaline conditions. System component Reaction tanks, a reagent storage and feed system, mixers, sensors, and controls two identical reaction tanks sized as the above-ground cylindrical tank with a retention time of 4 h. Chemical storage consists of covered concrete tanks to store 60 d supply of sodium hypochlorite and 90 d supply of sodium hydroxide. 

The copper flow-through CL sensor comprised an anion-exchange column having luminol and cyanide coimmobilized on the resin, while copper was temporarily retained by electrochemical preconcentration on a Au electrode placed in an anodic stripping voltammetric cell [64], Injection of 0.1 mol/L NaOH through the column eluted the reagents, which then reacted with copper, stripped from the electrode to produce a CL signal. The response was linear in the 0.01-10-pg/L... 

The monitoring of cyanide with microbial sensor is possible in two ways. The first principle is based on the inhibition of respiration of Saccharomyces cervisiae by cyanide [102, 103]. This sensor showed a linear response in the range 0-15 pmol 1 by a response time of approximately 10 min and a stability of 9 days. Another method for the determination of cyanide is enabled by the use of cyanide-degrading microorganisms such as Pseudomonas fluorescens [1041. This bacterium specifically oxidizes cyanide by consuming oxygen ... 

Lee JM, Karube I (1995) A novel microbial sensor for the determination of cyanide. Anal Chim Acta 313 69-74... 

Various fast redox couples such as ferrocene, ferro/ferri cyanide, and ruthenium hexamine have been used as mobile mediators. In order to be electron acceptors their standard potentials must be more positive than that of FADH2/FAD redox couple (E° = 0.05 V, at pH = 7). The requirement of mobility is, however, in conflict with the lifetime of the sensor. Because the mediator is of comparable size to the substrate, it cannot be confined to the electrode proper by, for example, a dialysis membrane. In fact, the only way this type of sensor can operate is in a sample containing a sufficient concentration of the mediator (Cass et al., 1984). Obviously, this requirement makes such sensors suitable only for in vitro applications. 

Nitrate in water may be analyzed by a nitrate selective sensor. Chloride and bicarbonate ions at concentrations about ten times greater than nitrate interfere in this test. Sulfide, cyanide, and halide ions are eliminated by using a buffer solution containing AgS04. The buffer — boric acid at pH 3 — removes bicarbonate. 

Electrochemical techniques anodic stripping voltammetry (ASV) and cathodic stripping voltammetry (CSV) for determining trace elements, and potentiometric sensors for determining dissolved gases (C02, N02, S02, NH3, H2S, HCN, and HF) as well as chloride, fluoride, cyanide, and sulfide. 

Many of the UV-VIS spectrophotometric methods (shown in Tables 12.3 and 12.6) have been automated by using flow analyzers. Thus, nitrite and nitrate,50,82 ammonium,50,83 orthophosphate,50,84,85 silicates,50,86 chloride,50,87 cyanide,50,88 and sulfate50,89 are measured by CFA and FIA. Oxygen is measured by iodometric titration51,90 and electrochemical methods91 (Table 12.7). Other dissolved gasses (Table 12.2) are measured by ISE-based gas sensors. 

An alternative approach, adopted by Albery et al. [59-61], is to determine the mechanism giving rise to the sensor response and to use this information together with the measured data at short times to calculate the final response. This was used for an electrochemical sensor system incorporating cytochrome oxidase where the steady-state responses of the measurement system were insufficiently fast for useful measurement of respiratory inhibitors such as cyanide, hydrogen sulphide, etc. By using mechanistic information, it was possible to successfully calculate the concentration in a test sample by real-time analysis of the sensor signals at short times after exposure to the test sample. The analysis could cope with the gradual loss of enzyme activity commonly found in these biosensor devices. 

Only a few multinuclear cyanide complexes are known to exhibit spin crossover behavior. In all the cases described in Section IV.D, a gradual spin transition is observed, which can be explained by relatively weak intermolecular interactions in the crystal strucmres of these compounds. It is generally known that stronger interactions between individual SCO centers lead to cooperative behavior, abmpt spin transitions, and thermal hysteresis or bistability over a finite temperature range (276). The latter property renders SCO compounds attractive materials for the development of magnetic sensors and memory devices. It is expected that extended... 

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