Electrode sensitivity

An electrode sensitive to nitrate ions can be prepared by using the salt hexadecyl-(tridodecyl)-ammonium nitrate in the membrane, and a perchlorate... 

Toyoda T, Tsuboya 1, Shen Q (2005) Effect of rutile-type content on nanostructured anatase-type Ti02 electrode sensitized with CdSe quantum dots characterized with photoacoustic and photoelectrochemical current spectroscopies. Mater Sci Eng C 25 853-857... 

Jasinski R, Trachtenberg I, Rice G (1974) A chalcogenide glass electrode sensitive to cupric ions. J Electrochem Soc 121 363-370... 

Suaud-Chagny and Gonon [3] presented a new procedure for protein immobilization adapted to carbon microelectrode characteristics. The principle of this method of immobilization is based on the association of the protein with an inert porous film immobilized around the active tip of the electrode. For this purpose the carbon was coated with an inert, electrochemically obtained protein sheath (bovine serum albumin, BSA) a few micrometers thick. Then the sheath around the fiber was impregnated with lactate dehydrogenase (LDH), which could be immobilized onto the electrode and resulted in an electrode sensitive to pyruvate. 

We saw earlier that the limit of the electrode sensitivity was the ratio of faradiac to non-faradaic currents. The net result of using a microelectrode is to increase this ratio, and thus allow the analyst to analyse solutions of lower concentration - perhaps as low as 10 mol dm . ... 

As stated on p. 28, an analytically ideal sensor would determine the deter-minand both specifically and quantitatively. In potentiometry, this would require an electrode sensitive to one single substance among all the components of the system. 

The determination of fluoride ions has always been difficult, so the discovery of the lanthanum trifluoride electrode by Frant and Ross in 1966 was a great step forward. Until recently, this was the most important sensor in the ISE field, except for the glass electrode sensitive to hydrogen ions. The extraordinary specificity of this electrode made the greatest contribution to its usefulness. The only important interferent is the hydroxide ion. 

The glass electrode for pH measurements has long been a standard laboratory sensor and the subject of several monographs [74, 118, 349]. Consequently, only the basic theory will be given here, though electrodes sensitive to the alkah metal ions and silver will be considered in somewhat greater detail [95]. 

Among potentiometric enzyme sensors, the urea enzyme electrode is the oldest (and the most important). The original version consisted of an enzyme layer immobilized in a polyacrylamide hydrophilic gel and fixed in a nylon netting attached to a Beckman 39137 glass electrode, sensitive to the alkali metal and NHj ions [19, 2A Because of the poor selectivity of this glass electrode, later versions contained a nonactin electrode [20,22] (cf. p. 187) and especially an ammonia gas probe [25] (cf. p. 72). This type of urea electrode is suitable for the determination of urea in blood and serum, at concentrations from 5 to 0.05 mM. Figure 8.2 shows the dependence of the electrode response... 

Kamo, N., Muratsugu, M., Hongoh, R. and Kobatake, Y., (1979) Membrane potential of mitochondria measured with an electrode sensitive to tetraphenyl phosphonium and relationship between proton electrochemical potential and phosphorylation potential in steady state. Journal of Membrane Biology, 49 (2), 105-121. 

Satake et al. reported the use of a coated wire electrode sensitive to procaine and other local anesthetic cations, and their application to potentiometric determination [73]. Electrodes were constructed from a copper wire (0.8 mm diameter), coated with a PVC membrane comprising a mixture of the drug-tetraphenylborate ion-pair, dioctyl phthalate, polyvinyl chloride, and tetrahydrofuran. Potential measurement was made with respect to a Ag-AgCl reference electrode. The electrodes showed linear responses with a Nemstian slope for procaine over the concentration range investigated. The method was used for analyses of the drug in pharmaceutical preparations. 

Particularly promising is the development of nanoporous ceramic semiconductor membranes [692-695], They not only possess all of the advantages of ceramic materials, but they may also be efficient light harvesters having large surface areas which could provide sites for sensitizers [108, 711-714]. Indeed, FeS2 particles, deposited into (and onto) a porous Ti02 electrode, sensitized photoelectron conversion well (Fig. 118) [714]. 

Fig. 26. Dependence of photosensitized current (arb. units) on solution pH at Ti02 (1) and CdS (2) electrodes sensitized by Rhodamin B. [From Watanabe et al. (1976).]...

Umezawa, Y., Umezawa, K., Sato, H. Pure Appl. Chem. 1995, 67, 507 Umezawa, Y., Buhlmann, P., Umezawa, K., Tohda, K., Amemiya, S. Pure Appl. Chem. 2000, 72, 1851 Umezawa, Y. (Ed.) Handbook of Ion-Selective Electrodes Sensitivity Coefficients, CRC Press, Boca Raton, FL, 1990. 

Another common inorganic crystal electrode uses Ag2S for the membrane. This electrode responds to Ag+ and to S2. If we dope the electrode with CuS, CdS, or PbS, we can prepare electrodes sensitive to Cu2+, Cd2+, or Pb2+, respectively (Table 15-5). 

A pH measurement is usually taken by immersing a glass combination electrode into a solution and reading the pH directly from a meter. At one time, pH measurements required two electrodes, a pH-dependent glass electrode sensitive to H+ ions and a pH-independent calomel reference electrode. The potential difference that develops between the two electrodes is measured as a voltage as defined by Equation 2.2. 

One important application of the Nernst equation is the measurement of pH (and, through pH, acidity constants). The pH of a solution can be measured electrochemically with a device called a pH meter. The technique makes use of a cell in which one electrode is sensitive to the H30+ concentration and the second electrode serves as a reference. An electrode sensitive to the concentration of a particular ion is called an ion-selective electrode. One combination is a hydrogen electrode connected through a salt bridge to a calomel electrode. The reduction half-reaction for the calomel electrode is... 

The election of a reference electrode sensitive to one of the ions of the electrolyte leads to the appearance in Eq. (1.71) of the surface excess of the other. Equation (1.71) is usually named as Lippman s electrocapillary equation. 

Answer. In these methods a glass electrode sensitive to H30+ enables reactions which occur with change in [H30+] or a change in [OH-] to be followed with ease. A pH meter measures pH directly, and a millivoltmeter measures EMFs directly, and these are related to [H30+], e.g. 

Hazemoto et al (1+0) developed an ion-selective electrode sensitive to saccharin, by establishing an ion association between Fe2+-bathophenanthroline chelate and saccharin in nitrobenzene. The electrode developed could measure saccharin ion in presence of other sweetening agents e.g., sucrose, glucose, sodium cyclamate and sorbitol in the concentration range of 10 - - to 10 M. 

The method is based on determining the potential difference between an electrode pair, consisting of a glass electrode sensitive to the difference in the hydrogen ion activity in the sample solution and the internal filling solution, and a reference electrode, which is supposed to have a constant potential independent of the immersing solution. 

Fig. 4.3. Photocurrent action spectra for WO3 electrode sensitized by Dye II in monomeric form...

Fig. 4.4. Photocurrent action spectra for W03 electrode sensitized by thiacarbocyanine dye in monomeric form (dashed line) aggregated by coprecipitation with PD III (solid line). Electrode potential +0.6 V. Electrolyte 0.25 M Na2S04.

Fig. 4.7. Photocurrent action spectra for W03 electrode sensitized by Dye I (dashed line) and Dye I coprecipitated with PD IV (solid line). Spectral distribution of the relative variation in photocurrent Aiph/iph = 1 - iPh(t)/iPh(0), where iph(0) and iph(t) are measured before and after illumination of the positively-biased Dye I PD IV-sensitized W03 electrode (E = 0.6 V) at 550 nm for 10 min. Electrolyte 0.25 M Na2S04.

Fig. 4.9. (a, top) The 8iph/iph vs. v 1 dependence for W03 electrode sensitized by Dye II in monomeric form ( ) partially aggregated by coprecipitation with PD IV (O). The excitation wavelength 560 nm. / = 20 s. The total surface concentration of Dye II 10 8 mol cm 2. Electrolyte 0.25 M Na2S04. (b, bottom) The potential-time programme and corresponding photocurrent-time curves used for x evaluation. Hatched areas indicate the exposure periods. 

The photoelectrochemical activity inherent in thin films of aggregated cyanine dyes permits them to act as the spectral sensitizers of wide bandgap semiconductors [69]. It is seen from Fig. 4.14 that the photoelectrochemical behaviour of semiconductor/dye film heterojunctions fabricated by deposition of 200 nm-thick films of cyanine dyes on the surface of TiC>2 and WO3 electrodes, bears close similarity to that of semiconductor electrodes sensitized by the adsorption of dye aggregates. Thus, both anodic and cathodic photocurrents can be generated under actinic illumination, the efficiency of the photoanodic and photocathodic processes and the potential at which photocurrent changes its direction being dependent on dye and semiconductor substrate [69]. 

Yamamoto et al. developed a direct immunosensor (Y3). The immu-noelectrode was made of titanium wire, on which antigen or antibody was chemically fixed. The electric potential changes when an antigen-antibody reaction occurs. For example, the potential of the electrodes sensitized with anti-hCG antibody shifted to positive polarity when hCG was added. Aizawa et al. also reported a direct immunosensor (Al). The sensitivity is insufficient for clinical use but it is possible that the methods will be improved in the near future. 

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