Chlorine sensors

Piraud C., Mwarania E., Wylangowski G., Wilkinson J., O Dwyer K., Schiffrin J., An optoelectrochemical thin-film chlorine sensor employing evanescent fields on planar optical waveguides, Anal. Chem. 1992 64 651. 

Ru02 SrClg AgCI Alg03 Fig. 6.41 High-temperature chlorine sensor (adapted from Pelloux et al., 1985)... 

Another opportunity to realize constant activity of the potential determining ion at the reference interface appears when one chooses the solid electrolyte in such a way that the ion of the redox couple is the same as one ion of the major component of the electrolyte. In that case, the change of the activity due to the electrode reaction with the gas can be neglected against the overall constant activity of that ion in the salt. This is the solid-state reference arrangement. An example is the chlorine sensor (Fig. 6.40), in which the reference potential is set up by the constant activity of CP in the solid AgCl electrolyte. This arrangement is equivalent to a reference electrode of the second kind, discussed in Section 6.2.2.1. 

On-wafer membrane deposition and patterning is an important aspect of the fabrication of planar, silicon based (bio)chemical sensors. Three examples are presented in this paper amperometric glucose and free chlorine sensors and a potentiometric ISRET based calcium sensitive device. For the membrane modified ISFET, photolithographic definition of both inner hydrogel-type membrane (polyHEMA) and outer siloxane-based ion sensitive membrane, of total thickness of 80 pm, has been performed. An identical approach has been used for the polyHEMA deposition on the free chlorine sensor. On the other hand, the enzymatic membrane deposition for a glucose electrode has been performed by either a lift-off technique or by an on-chip casting. 

Figure 3. Calibration curve of the chlorine sensor with a 10 im polyHEMA membrane at three different potentials lower 150 mV, middle 50 mV and upper -50 mV vs SCE. (Reproduced with permission from ref. 9. Copyright 1991, IEEE.)...

Figure 4. Chlorine sensor calibration curves at E = 50 mV for two different...

In order to maintain the advantage of the microfabrication approach which is intended for a reproducible production of multiple devices, parallel development of membrane deposition technology is of importance. Using modified on-wafer membrane deposition techniques and commercially available compounds an improvement of the membrane thickness control as well as the membrane adhesion can be achieved. This has been presented here for three electrochemical sensors - an enzymatic glucose electrode, an amperometric free chlorine sensor and a potentiometric Ca + sensitive device based on a membrane modified ISFET. Unfortunately, the on-wafer membrane deposition technique could not yet be applied in the preparation of the glucose sensors for in vivo applications, since this particular application requires relatively thick enzymatic membranes, whilst the lift-off technique is usable only for the patterning of relatively thin membranes. 

Chlorine sensors Online potentiometric and am-perometric chlorine sensors are commonly used to monitor chlorine concentration in process streams. The use of a potentiometric chlorine sensor involves adjustment of solution pH and subsequent reaction with lead iodide (Pbli) to produce iodine. The resulting iodine is detected potentiometrically by an electrode and is related to chlorine concentration. This sensor has been successfully used for continuous monitoring of chlorine levels in water treatment plants. 

The use of an amperometric variation of the chlorine sensor has been reported for monitoring chlorine... 

FIGURE 10.8. Examples of electrochemical gauges (potentiometric sensors) (a) laboratory oxygen sensor (air reference), (b) oxygen minisensor with a solid state internal reference (M-MO), (c) chlorine sensor with a solid state internal reference (Ag-AgCl). 

Very few amperometric gas sensors have been studied so far. A protonic conductor has been used for a Hj amperometric sensor by Miura et al. One may also mention the chlorine sensor proposed by Liu and Weppner, " which is based on 3"-alumina as SIC with an AgCl layer. The electrode reaction is given by... 

The same principle can also be applied to the construction of potentiometric sensors for other gases. Thus, cells with proton-conducting solid electrolytes (water-containing In-doped CaZrOa [540], cf. Section 5.6) are used to measure H activity in aluminium and hence to control the brittleness associated with hydrogen content. It is not necessary that the gas to be detected and the mobile ion refer to the same element. Let us consider a chlorine sensor based on AgCl. AgCl in contact with CI2 gas fixes a defined silver activity and cells of the type... 

Small but environrrientallyjnendly. The Chemical Engineer, March 1993 Huge increases in technology in the past distributed manufacturing in small-scale plants miniaturization of processes domestic methanol plant point-of-sale chlorine simpler and cheaper plants economy of plant manufacture process control and automation start-up and shut-down sensor demand [145],... 

R. Tauler, A.K. Smilde, J.M. Henshaw, L.W. Burgess and B.R. Kowalski, Multicomponent determination of chlorinated hydrocarbons using a reaction-based chemical sensor. 2 Chemical speciation using multivariate curve resolution. Anal. Chem., 66 (1994) 3337-3344. 

In addition, the integration of modem optical technology and electrochemical techniques for sensing applications appears to be a powerful new approach. A new type of optoelectrochemical sensor for chlorine, based on an electrochromic thin-film sensing layer placed on top of a planar waveguide, has demonstrated the applicability of this combined approach. 

Goebel R., Krska R., Kellner R., Katzir A., Development of Protective Polymer-Coatings for Silver-Halide Fibers and Their Application as Threshold Level Sensors for Chlorinated Hydrocarbons in Sea-Water, Fresenius J. Anal. Chem. 1994 348 780-781. 

Tauler R., Smilde A.K., Hemshaw J.M., Burgess L.W., Kowalski B.R., Multicomponent Determination of Chlorinated Hydrocarbons Using a Reaction-based Chemical Sensor. Part 2. Chemical Speciation Using Multivariate Curve Resolution, Anal. Chem. 1994 66 3337-3344. 

Kastner J., Tacke M., Katzir A., Edl-Mizaikoff B., Gobel R. and Kellner R., Optimizing the modulation for evanescent-wave analysis with laser diodes (EWALD) for monitoring chlorinated hydrocarbons in wat, Sensors Actuators B 1997 38 163-170. 

Krska R., Kellner R., Schiessl U., Tacke M. and Katzir, Fiber optic sensor for chlorinated hydrocarbons in water based on infrared fibers and tunable diode lasers, Appl. Phys. Lett., 1993 63 (14), 1868-1871 A. 

Walsh J.E., MacCraith B.D., Meany M., Vos J.G., Regan F., Lancia A., Artjushenko S., Midinfrared fiber sensor for the in-situ detection of chlorinated hydrocarbons, SPIE, 1995 2508 233-242. 

Beyer T., Hahn P., Hartwig S., Konz W., Scharring S., Katzir A., Steiner H., Jakusch M., Kraft M., Mizaikoff B.,, Mini spectrometer with silver halide sensor fiber for in situ detection of chlorinated hydrocarbons, Sensors Actuators B, 2003 90 319 - 323. 

CL sensors based on immobilization of nonenzyme reagents have been extensively studied in recent years. Nakagama et al. [63] developed a CL sensor for monitoring free chlorine in tap water. This sensor consisted of a Pyrex tube, packed with the uranine (fluoresceine disodium) complex immobilized on IRA-93 anion-exchange resin, and a PMT placed close to the Pyrex tube. It was used for monitoring the concentration of free chlorine (as HCIO) in tap water, up to 1 mmol/L, with a detection limit of 2 nmol/L. The coefficient of variation (n =... 

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