Ion-selective electrode copper

The potentiometric micro detection of all aminophenol isomers can be done by titration in two-phase chloroform-water medium (100), or by reaction with iodates or periodates, and the back-titration of excess unreacted compound using a silver amalgam and SCE electrode combination (101). Microamounts of 2-aminophenol can be detected by potentiometric titration with cupric ions using a copper-ion-selective electrode the 3- and... 

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).

Buffle, 3., Greter, F.L. and Haerdi, W., 1977. Measurement of complexation properties of humic and fulvic acids in natural waters with lead and copper ion selective electrodes. Anal. Chem., 49 216-222. 

In the early 1970s, Zitko et al. (1973) noted that HAs reduced the activity of the free Cu " ion, as measured by the copper ion-selective electrode, and that this effect was quite well correlated with the observed toxicity of Cu(II) to salmon. Soon thereafter, Pagenkopf et al. (1974) also reported on the effect of complexation on the toxicity of copper to fishes. Sunda and Guillard (1976) demonstrated that the activity of the free Cu " ion in synthetic growth media containing the metal complexing agent TRIS (2-amino-2-hydroxy-methyl-1,3-propanediol) was an excellent... 

The shift in electrode potential caused by the complexing agent is contained in the lecond term of Equation 2.18. In this case, it amounts to a shift of —0.526 V. The important practical consequences of chelation and complexation will be discussed in more detail later. Fdr example, one can determine copper ion by direct potentiometry using a copper-ion-selective electrode, or via a potentiometric titration with EDTA using the electrode as an endpoint detector. 

Application of ion-selective electrodes to determine copper by standard addition method in nickel plating bath was suggested by Frant. Later Hulanicki et al." using a copper ion-selective electrode proposed a method based on multiple standard addition in presence of a copper complexing agent to prevent a harmful influence of chloride ions. In this work a similar method is used to determine copper also in zinc and cobalt baths. 

THE ROLE OF SURFACE PROCESSES IN SIGNAL FORMATION WITH SOLID- STATE ION-SELECTIVE ELECTRODES - CHLORIDE INTERFERENCE ON COPPER ION-SELECTIVE ELECTRODE... 

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. 

Electrochemical Approach in Elucidating the Response Mechanism of Selenide-Based Copper Ion-Selective Electrodes... 

Ion selective electrodes Measurement of the free metal ion is an important goal of metal speciation studies in natural waters, because of the tenet of the free ion activity model, that bioavailability is proportional to the free metal ion concentration. Ion selective electrodes respond to the free metal ion activity. A range of ion selective electrodes are available, but only the copper electrode has sufficient sensitivity for use in measurement at realistic environmental concentrations in natural waters. The correct use of the copper ion selective electrode remains a matter of debate, especially its calibration at the very low free metal ion concentrations using metal ion buffers and the applicability of this procedure to natural samples. 

Olin A, Wallen B (1988) Determination of citrate by potentiometric titration with copper(II) and a copper ion-selective electrode. Anal Chim Acta 151 65-75... 

Figure 4 shows the cahbration plot for a copper ion selective electrode, where a total ionic strength adjustment buffer (TISAB), such as IM NaN03, has been added to each solution so that the response is effectively at constant ionic strength and constant activity coefficient. 

Zirino A, De Marco R, Rivera I, Pejcic B (2002) The influence of diffusion fluxes on the detection limit of the jalpaite copper ion-selective electrode. Electroanalysis 14 493-498... 

Stella, R. and Ganzerli-Valentini, M.T. (1979) Copper ion-selective electrode for determination of inorganic copper species in fresh water. Anal. Chem., 51, 2148—2151. 

De Marco R, Mackey DJ, Zirino A (1997) Response of the jalpaite membrane copper(lI) ion-selective electrode in marine waters. Electroanalysis 9 330-334 Kozicki MN, Mitkova M (2006) Mass transport in chalcogenide electrolyte films - materials and applications. J Non-Cryst Solids 352 567-577... 

Ion-selective electrodes have been used for the potentiometric determination of the total cupric ion content of seawater [284], Down to 2 xg/l cupric copper could be determined by this procedure. 

De Marco [285] evaluated three different types of copper (II) ion-selective electrodes. The copper sulfide electrode was found to be oxidised, whereas the copper selenide and copper sulfide electrodes were found to have chloride ion interference at copper (II) activities exceeding 10 8 M. 

Prior to the introduction of ion-selective electrode techniques, in situ monitoring of free copper (II) in seawater was not possible due to the practical limitations of existing techniques (e.g., ligand competition and bacterial reactions). Ex situ analysis of free copper (II) is prone to experimental error, as the removal of seawater from the ocean can lead to speciation of copper (II). Potentially, a copper (II) ion electrode is capable of rapid in situ monitoring of environmental free copper (II). Unfortunately, copper (II) has not been used widely for the analysis of seawater due to chloride interference that is alleged to render the copper nonfunctional in this matrix [288]. 

Ion-selective electrodes have been used to determine the stability constants for the complexation of copper II ions with soil fulvic acids [4], Two classes of binding sites were found with conditional stability constants of about 1 xf 06 and 8xl03. 

If one wants to understand why such changes occur, one can look at a few of the basic equilibrium properties of such complexes. Figure 1 illustrates the trends which occur when a sample is titrated with copper, monitoring three different parameters. The black dots indicate the relative amount of bound copper as indicated by free copper ions sensed with an ion-selective electrode (Xc of left ordinate). The triangles represent the change of the absorbance of the solution at 465 nm (right ordinate). The curve with the open circles is the relative quenching of the fulvic acid fluorescence (Q of left ordinate). We see that we are able to probe several different types of sites with different types of probes for this multidentate system. 

Elemental composition Cu 64.18%, Cl 35.82%. Copper(I) chloride is dissolved in nitric acid, diluted appropriately and analyzed for copper by AA or ICP techniques or determined nondestructively by X-ray techniques (see Copper). For chloride analysis, a small amount of powdered material is dissolved in water and the aqueous solution titrated against a standard solution of silver nitrate using potassium chromate indicator. Alternatively, chloride ion in aqueous solution may be analyzed by ion chromatography or chloride ion-selective electrode. Although the compound is only sparingly soluble in water, detection limits in these analyses are in low ppm levels, and, therefore, dissolving 100 mg in a liter of water should be adequate to carry out aU analyses. 

Elemental composition Cu 47.26%, Cl 52.74%. Aqueous CuCb maybe analyzed for copper by various instrumental methods (see Copper) and the chloride anion may be analyzed by ion chromatography, chloride ion-selective electrode, or by titration with a standard solution of sdver nitrate. 

Elemental composition Cu 62.58%, F 37.42%. Copper(ll) fluoride acid extract is analyzed for copper by instrumental methods. Powder may be analyzed by tbe x-ray diffraction method. Aqueous solution (in cold water) may be analyzed for fluoride ion using a fluoride ion-selective electrode or by ion chromatography. 

How analytical methods deal with interferences is one of the more ad hoc aspects of method validation. There is a variety of approaches to studying interference, from adding arbitrary amounts of a single interferent in the absence of the analyte to establish the response of the instrument to that species, to multivariate methods in which several interferents are added in a statistical protocol to reveal both main and interaction effects. The first question that needs to be answered is to what extent interferences are expected and how likely they are to affect the measurement. In testing blood for glucose by an enzyme electrode, other electroactive species that may be present are ascorbic acid (vitamin C), uric acid, and paracetamol (if this drug has been taken). However, electroactive metals (e.g., copper and silver) are unlikely to be present in blood in great quantities. Potentiometric membrane electrode sensors (ion selective electrodes), of which the pH electrode is the... 

The extremely low solubility of lead phosphate in water (about 6 x 10 15m) again suggests potentiometric analysis. Selig57,59 determined micro amounts of phosphate by precipitation with lead perchlorate in aqueous medium. The sample was buffered at pH 8.25-8.75 and a lead-selective electrode was used to establish the end-point. The detection limit is about 10 pg of phosphorus. Anions which form insoluble lead salts, such as molybdate, tungstate or chromate, interfere with the procedure. Similar direct potentiometric titrations of phosphate by precipitation as insoluble salts of lanthanum(III), copper(II) or cadmium(II) are suggested, the corresponding ion-selective electrodes being used to detect the end-point. 

Fig. 1. Simultaneous separation and detection of anions and cations on a latex agglomerate column. Column Dionex HPIC-CS5 cation exchange column (250X2 mm) with precolumn HPIC-CG5 (50 X 4 mm) eluent 0.5 mM copper sulfate, pH 5. 62 flow rate 0.5 ml/min sample volume 20 gl containing 0.1 m M of each ion detection two potentiomet-ric detectors equipped with different ion-selective electrodes in series. Peaks (1) chloroacetate, (2) chloride, (3) nitrite, (4) benzoate, (5) cyanate, (6) bromide, (7) nitrate, (8) sodium, (9) ammonium, (10) potassium, (11) rubidium, (12) cesium, (13) thallium. Reprinted with permission from [10].

Bresnahan, W.T., Grant, C.L. and Weber, 3.H., 1978. Stability constants for the complexation of copper (II) ions with water and soil fulvic acids measured by an ion selective electrode. Anal. Chem., 50 1675-1679. 

The fluorescence properties of two fulvic acids, one derived from the soil and the other from river water, were studied. The maximum emission intensity occurred at 445-450 nm upon excitation at 350 nm, and the intensity varied with pH, reaching a maximum at pH 5.0 and decreasing rapidly as the pH dropped below 4. Neither oxygen nor electrolyte concentration affected the fluorescence of the fulvic acid derived from the soil. Complexes of fulvic acid with copper, lead, cobalt, nickel and manganese were examined and it was found that bound copper II ions quench fulvic acid fluorescence. Ion-selective electrode potentiometry was used to demonstrate the close relationship between fluorescence quenching and fulvic acid complexation of cupric ions. It is suggested that fluorescence and ion-selective electrode analysis may not be measuring the same complexation phenomenon in the cases of nickel and cobalt complexes with fulvic acid. 

Various workers [28,34,41] have used different extraction solutions in the ion-selective electrode method, depending on the soil being analysed. The most important are [28,32,35-37] potassium sulfate [39], aluminium sulfate [30], copper (II) sulfate [32], calcium hydroxide [33], and copper sulfate(II) with aluminium and silver resins [41 ]. 

Cabaniss, S. E., and Shuman, M. S. (1986). Combined ion-selective electrode and fluorescence quenching detection for copper-dissolved organic-matter titrations. Anal. Chem. 58(2), 398 101. 

In some studies the main aim is identification of the chemical form of an element which has toxic properties, or which translocates within an ecosystem (e.g. a nutrient species). For example, the hydrated Cu2+ ion is considered to be more toxic than the other copper species normally found in waters, and measurement of the level of this ion using an ion-selective electrode would meet the speciation challenge . 

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).

Shuman, M.S., Collins, B.J., Fitzgerald, RJ. and Olson, D.L. (1983) Distribution of stability constants and dissociation rate constants among binding sites on estuarine copper-organic complexes rotated disk electrode studies and an affinity spectrum analysis of ion-selective electrode and photometric data. In Aquatic and Terrestrial Humic Materials (eds Christman, R.F. and Gjessing, E.T.). Ann Arbor Science, Ann Arbor, MI, pp. 349-370. 

---