Sulphide sensor

Chen Z, Lu C (2005) Humidity sensors a review of materials and mechanisms. Sensor Lett 3 274-295 Choi MMF, Hawkin P (2003) Development of an optical hydrogen sulphide sensor. Sens Actuators B 90 211-215 Chou J (2000) Hazardous gas monitors a practical guide to selection, operation and apphcation. McGraw-HiU, New York Cleaver KD (2001) The analysis of process gases a review. Accred Qual Assur 6(1) 8-15... 

Silver sulphide exists in two modifications, a-Ag2 S, the cubic form, which is an electronic conductor and is stable above 176°C, and monoclinic/l-AgjS, an ionic conductor, which is stable at lower temperatures [316]. In this latter modification, Ag is almost the only charge carrier [141, 325,428], The good conductivity and negligible solubility of the compact membrane make the Ag2 S ISE one of the most reliable sensors. 

Wall V. I and England R. N. (1979). Zn-Ee spinel-silicate-sulphide reactions as sensors of metamorphic intensive variables and process. Geol Soc. Amer. Abstr. Progr, 11 534. 

Several classical ion-selective electrodes (some of which are commercially available) have been incorporated into continuous systems via suitable flow-cells. In fact, Lima et al. [112] used a tubular homogeneous crystal-membrane (AgjS or AgCl) sensor for the determination of sulphide and chloride in natural and waste waters. However, the search for new active materials providing higher selectivity and/or lower detection limits continues. Thus, Smyth et al [113] tested the suitability of a potentiometric sensor based on calix[4]arene compounds for use in flow injection systems. They found two neutral carriers, viz. methyl-j3-rerr-butylcalix[4]aryl acetate and... 

Kurosawa M, Hiroano T, Nakamura K, Amano Y (1994) Microbial sensor for selective determination of sulphide. Appl Microbol Biotechnol 41 556-559... 

This technique has been recently applied in different studies. One of them evaluated the environmental conditions in the treasure rooms of Reims Cathedral, where silver sensors were exposed during a five-year period [306]. The reduction curves point out that the results strongly depend on whether the coupons were displayed inside or outside a case. Regarding the nature of the products developed on the surface during the exposure, only silver sulphide has been found on the coupons kept inside the showcase, while the additional peak found with coupons exposed outside the case suggests the additional presence of silver chloride (see Fig. 6.4a). Moreover,... 

Traditionally, potentiometric sensors are distinguished by the membrane material. Glass electrodes are very well established especially in the detection of H+. However, fine-tuning of the potentiometric response of this type of membrane is chemically difficult. Solid-state membranes such as silver halides or metal sulphides are also well established for a number of cations and anions [25,26]. Their LOD is ideally a direct function of the solubility product of the materials [27], but it is often limited by dissolution of impurities [28-30]. Polymeric membrane-based ISEs are a group of the most versatile and widespread potentiometric sensors. Their versatility is based on the possibility of chemical tuning because the selectivity is based on the extraction of an ion into a polymer and its complexation with a receptor that can be chemically designed. Most research has been done on polymer-based ISEs and the remainder of this work will focus on this sensor type. 

The main disadvantage of mercury sensors based on bare gold layers is their poor selectivity. This is illustrated in Fig. 12.6 an incubation at 100% humidity (Fig. 12.6a), with saturated vapour of sulphuric acid (Fig. 12.6), volatile sulphides or thiols (10 pg/1 of 1-butanethiol vapour, Fig. 12.6c), or halogens (10 pg/1 of iodine vapour, Fig. 12.6d), results in conductivity changes of the same magnitude as an incubation with 10-20 ng/1 of mercury vapour. This interference with widely spread substances is a serious problem in applications of such sensors for real probes and makes necessary a pre-treatment of probes. 

D. Giovanelli, N.S. Lawrence, S.J. Wilkins, L. Jiang, T.G.J. Jones and R.G. Compton, Anodic stripping voltammetry of sulphide at a nickel film towards the development of a reagentless sensor, Talanta, 61 (2003) 211-220. 

Other early work in this field included the use of tetrakis(p-aminophenyl)-porphyrin (Fig. 7a), which was electrodeposited onto glassy carbon and showed a near-Nernstian response to iodide [76]. Electrodeposited methylthiophene-methylpyrrole copolymer was deposited and shown to give a near-Nernstian response to bromide [77]. Pyrrole-3-boronate (Fig. 7b) could be deposited to give films with a good response and marked selectivity to fluoride [78]. A cobalt aminophthalocyanine could also be electropolymerised to give a good sensor for nitrite [79] or sulphide ion [80]. 

Anion detection at microelectrodes has not been studied widely. Amongst the first was the work of de Beer et al. [ 111 ] who manufactured a nitrite sensor with a tip just a few microns in diameter, which could detect nitrite ions down to 1 pM. This proved to be suitable for profiling the concentrations of nitrite anion within biofilms less than 1-mm thick inside water treatment plants. Other workers have found that use of an interdigitated microelectrode array [ 112] allows measurement of iodide via monitoring of its redox peak down to sub-micromole levels, making it a suitable technique for analysing mineral water. Carbon nanotubes coated onto Pt microdiscs have been utilised to make a nitrite sensor [113,114] with detection levels of 0.1 pM. Sulphide has also been detected at nickel microdiscs (50 pm diameter) [115]. 

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. 

Mozafari, M., Moztarzadeh, F. (2011). Microstructural and Optical Properties of Spherical Lead Sulphide Quantum Dots-based Optical Sensors. Micro Nano Letters, lET, 6(3), 161-164. 

Several types of gas-sensitive MOS devices have been developed since 1975. Already sensors for hydrogen, ammonia, hydrogen sulphide, ethanol vapour, arsine and carbon monoxide have been developed. The devices have the... 

M.S. Attia, H. Zo-elghny, and M.S.A. Abdel-Mottaleb, a new nano-optical sensor thin film cadmium sulphide doped in sol-gel matrix for assessment of alpha-amylase activity in human saliva. Analyst, 139, 793-800, 2014. 

Figure 6. AC (1 kHz) resistivity changes at room temperature for a conducting polypyrrole sensor exposed to eight 15 minute pulses of 0.1% hydrogen sulphide in air over a period of 4 hours.

Cadmium sulphide (CdS) is an II-VI semiconductor material with a direct band gap of 2.42 eV at room temperature with many outstanding physical and chemical properties, which has promising applications in photochemical catalysis, gas sensors, detectors for laser and infrared, solar cells, nonlinear optical materials, luminescence devices and optoelectronic devices [36-39]. CdS also exhibited excellent visible light detecting properties [40]. In the last decades, many techniques have been reported on synthesis of CdS nanoparticles [41-43]. 

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