Copper ISE

Other than barium, potassium and nitrite ionophores have been incorporated into an optode membrane to detect K+ and N()2 potentiometrically on a plastic disk [767]. In another report, a thin layer of CuS (50-200 nm) was used to construct a copper ISE on a Si-glass chip [768]. 

Htiller, J., Pham, M.T., Howitz, S., Thin layer copper ISE for fluidic microsystem. Sensors Actuators B 2003, 91, 17-20. 

In the complete derivation of usable analytical equation the fact of difference between the surface and bulk concentrations was taken into account. Therefore the final equation, combining the potential of copper ISE with total (bulk) copper concentration was obtained-by using diffusion-layer model principles - in the form ... 

Mercury(II) and silver(I) strongly interfere in every case and copper(II) is an important interferent in sensing lead and cadmium. Copper and lead assays are much more disturbed by the presence of iron(III) than the cadmium assay. A large excess of anions like chloride may interfere with cadmium and lead quantitation but the most notable problem with chloride is found with the copper ISE. The response of these ISEs to complexing agents and complexes of their divalent metal components has been thoroughly studied. The electrode response in the presence of complexes does not always coincide with thermodynamic expectation. 

The copper ISE is important for complexation studies in environmental samples. Potentiometric lead and cadmium electrodes are less popular but the lead electrode has been quite useful for indirect sulfate measurements. The electrodes require frequent recalibration. 

Rg. 4. Electrode potential response for a copper ISE. (a) Against activity (solid line) (b) against concentration (dashed line). 

R, or reagent sensed. A reagent is added, for example, some copperfll) EDTA complex, which is sensed by a copper ISE. Addition of EDTA to a solution containing Ca (or Mg % Ni etc.) ions gives an abmjrt change at the end point where the excess EDTA reduces the concentration of Cu ions. 

In order to use potentiometric methods to study complexometric titrations, an electrode specific to the metal ion may be used (see Topics C3 and C5), for example, a copper ISE to follow the reaction of copper with EDTA. 

Risinger incorporated ion-exchange into the manifold of Fig. 4.14. A in order to improve the determination of copper by using an ISE for the metal ion and a column containing 8-quinolinol immobilized on porous glass for... 

Figure 4.14 — (A) Flow injection system for the preconcentration and determination of copper P peristaltic pumps A 0.5 M HNOj B sample q = 2.5 mL/min) C water (jq = 0.5 mL/min) E 1 M NaNOj/O.l M NaAcO, pH 5.4 q = 0.5 mL/min F 1 M NaAcO/2 x 10 M Cu pH 5.0 (9 = 1.0 mL/min) 3-5 valves ISE copper ion-selective electrode W waste I and II 2 and 3 mL of chelating ion exchanger for purification III 100 fil of chelating ion exchanger for metal ion preconcentration. (B) Scheme of the flow system for the determination of halides A 4 M HAcO/1 M NaCl/0.57 ppm F B 1 M NaOH/0.5 M NaCl C, mixing coil (1 m x 0.5 mm ID PTFE tube) Cj stainless-steel tube (5 cm x 0.5 mm ID) ISE ion-selective electrode R recorder. (Reproduced from [128] and [129] with permission of Elsevier Science Publishers and the Royal Society of Chemistry, respectively).

Figure 8.3 Schematic representation of copper concentrations relevant to freshwater studies and analytical windows of several analytical techniques. ASV, anodic stripping voltammetry CSV, cathodic stripping voltammetry ISE, ion selective electrode SLM, supported liquid membrane SWASV, square wave anodic stripping voltammetry LC50, lethal concentration for 50% of the population [Cu]t, total metal concentration (adapted from Langford and Gutzman, 1992).

There is a little evidence in the literature suggesting that both calculated values of free metal concentration ( 1) and values measured with ISE s ( 8, 9) can be correlated with the biological availability of copper. Additionally, Sunda et (27) have... 

Figure 2. Copper Speciation in Ground Water from Well 3 Computed Using the Complexation Parameters Determined by ISE and CSV. S CuL is Organically Complexed Cu.

This paper gives the illustration of how surface techniques engaged in the interpretation of the electrode signal can help to introduce a new analytical procedure. For this purpose the long discussed case of chloride ion interference on solid-state copper ion-selective electrode (Cu-ISE) will be exploited. However, the same methodology may be applied to any other similar case situations. 

The calibration curves obtained in copper(II) nitrate solutions of pH = 4.8, containing acetic buffer, are shown in Fig,3. (For comparison the calibration curve for a CU2S electrode is also presented). The calibration slopes are near to the expected divalent slope, i.e., 29.6 mV at 25 °C and the basic performance (response time, stability and repeatability of readouts) is similar to that observed with Orion Cu-ISE. Standard potentials observed are close to theoretical values,for graphite contacted membranes standard potential observed is... 

The sulfide ISE is sensitive, reliable, and useful especially in analyses of the atmosphere and waters. The nitrate ISE does not exhibit particularly good analytical properties, but it enables very fast and simple ori-entative determinations of nitrate in, e.g., waters, vegetables, and foodstuffs, which is welcome with regard to public hygiene. ISEs for various inorganic anions have somewhat lost their importance in competition with ion chromatography and those for inorganic cations often cannot compete with spectral methods nevertheless, ISEs for copper(II), lead(II), and cadmium(II) ions are sometimes useful for endpoint detection in complexometric titrations. 

Another example in food analysis is the use of solid state copper and silver electrodes for evaluation of meat freshness. This is due to the change of put-rescine and dimethyl sulfide, the concentration of which changes during meat putrefaction. Such applications indicate the variety of applications of ISEs in food control and analysis. 

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