Sodium ion selective electrode

D. One commercial glass-membrane sodium ion-selective electrode has a selectivity coefficient H+ = 36. When this electrode was immersed in 1.00 mM NaCI at pH 8.00, a potential of —38 mV (versus S.C.E.) was recorded. 

EN18 Daniel, D., Bakos, J., Casper, S., Kissel, T., Kozuch, S., Murawski, J., Roth, J.,Toner, ]. and Van Brunt, N. (1991). Development of a new thin-film sodium ion selective electrode with improved specificity. Clin. Chem. 37, 946, Abstr. 174. 

The Na" concentration of a solution was determined by measurement with a sodium ion-selective electrode. The electrode system developed a potential of -0.2331 V when immersed in 10.0 mL of the solution of unknown concentration. After addition of 1.00 mL of 2.00 X 10 M NaCI, the potential changed to — 0.1846 V. Calculate the Na" concentration of the original solution. 

In preparing all solutions, the distilled, deionized water was boiled to remove C02 prior to its use. All samples were then kept sealed to prevent any absorption of C02 during equilibration. For the Sephadex, a 3-4-day period was sufficient to achieve equilibrium with the IRC-50, however, the equilibrium interval exceeded 2 weeks. At equilibrium, pH and pNa measurements at 25° 0.1 °C were made with the system under a nitrogen atmosphere. All pH measurements were made with a glass electrode using a Radiometer Model 4 pH meter. A sodium-ion selective electrode was used to measure pNa. A saturated calomel electrode was used as the reference electrode. 

A cation-sensitive electrode is used to determine the activity of calcium in the presence of sodium. The potential of the electrode in 0.0100 M CaCl2 measured against an SCE is +195.5 mV. In a solution containing 0.0100 M CaCl2 and 0.0100 M NaCl, the potential is 201.8 mV. What is the activity of calcium ion in an unknown solution if the potential of the electrode in this is 215.6 mV versus SCE and the sodium ion activity has been determined with a sodium ion-selective electrode to be 0.0120 M Assume Nemstian response. 

Mean sodium chloride activity coefficients have been determined [41] with a sodium ion-selective electrode and silver-silver chloride reference electrode system in mixed sodium chloride-calcium chloride solutions within the range of sodium chloride and calcium chloride levels (0.05-0.5 mol dm ) encountered in extracellular fluids. These show that at constant ionic strength, log /Naci varies linearly with the ionic strength of calcium chloride in the mixture in accordance with Harned s rule [45] ... 

Suzuki K, Hayashi K, Tohda K, et al. (1991) Sodium ion-selective electrodes based on lipophilic 16-crown-5-derivatives. Analytical Letters 24 1085-1091. 

Lin, J.L., Hsu, H.Y. Study of sodium ion selective electrodes and differential stractures with anodized indium tin oxide. Sensors 10, 1798-1809 (2010)... 

Figure 6.4. Typical working calibration curve for glass membrane sodium-ion-selective electrode.

Diamond, D., G. Svehla, E.M. Seward, and M.A. McKervey. 1988. A sodium ion-selective electrode based on p-t-butylcalix[4]aryl acetate as the ionophore. Anal. Chim. Acta 204 223-231. 

Tsujimura, Y., T. Sunagawa, A. Yokoyama, and K. Kimura. 1996. Sodium ion-selective electrodes based on silicone-rubber membranes covalently incorporating neutral carriers. Awa/yj f 121 1705-1709. 

This experiment describes the preparation and evaluation of two liquid-membrane Na+ ion-selective electrodes, using either the sodium salt of monensin or a hemisodium ionophore as ion exchangers incorporated into a PVG matrix. Electrodes prepared using monensin performed poorly, but those prepared using hemisodium showed a linear response over a range of 0.1 M to 3 X 10 M Na+ with slopes close to the theoretical value. 

Procedure. Prepare a set of external standards containing 0.5 g/L to 3.0 g/L creatinine (in 5 mM H2SO4) using a stock solution of 10.00 g/L creatinine in 5 mM H2SO4. In addition, prepare a solution of 1.00 x 10 M sodium picrate. Pipet 25.00 mL of 0.20 M NaOH, adjusted to an ionic strength of 1.00 M using Na2S04, into a thermostated reaction cell at 25 °C. Add 0.500 mL of the 1.00 x 10 M picrate solution to the reaction cell. Suspend a picrate ion-selective electrode in the solution, and monitor the potential until it stabilizes. When the potential is stable, add 2.00 mL of a... 

The most popular device for fluoride analysis is the ion-selective electrode (see Electro analytical techniques). Analysis usiag the electrode is rapid and this is especially useful for dilute solutions and water analysis. Because the electrode responds only to free fluoride ion, care must be taken to convert complexed fluoride ions to free fluoride to obtain the total fluoride value (8). The fluoride electrode also can be used as an end poiat detector ia titration of fluoride usiag lanthanum nitrate [10099-59-9]. Often volumetric analysis by titration with thorium nitrate [13823-29-5] or lanthanum nitrate is the method of choice. The fluoride is preferably steam distilled from perchloric or sulfuric acid to prevent iaterference (9,10). Fusion with a sodium carbonate—sodium hydroxide mixture or sodium maybe required if the samples are covalent or iasoluble. 

The sodium hydroxide is titrated with HCl. In a thermometric titration (92), the sibcate solution is treated first with hydrochloric acid to measure Na20 and then with hydrofluoric acid to determine precipitated Si02. Lower sibca concentrations are measured with the sibcomolybdate colorimetric method or instmmental techniques. X-ray fluorescence, atomic absorption and plasma emission spectroscopies, ion-selective electrodes, and ion chromatography are utilized to detect principal components as weU as trace cationic and anionic impurities. Eourier transform infrared, ft-nmr, laser Raman, and x-ray... 

Sodium and chloride may be measured using ion-selective electrodes (see Electro analytical techniques). On-line monitors exist for these ions. Sihca and phosphate may be monitored colorimetricaHy. Iron is usually monitored by analysis of filters that have had a measured amount of water flow through them. Chloride, sulfate, phosphate, and other anions may be monitored by ion chromatography using chemical suppression. On-line ion chromatography is used at many nuclear power plants. 

Cyanide compounds are classified as either simple or complex. It is usually necessary to decompose complex cyanides by an acid reflux. The cyanide is then distilled into sodium hydroxide to remove compounds that would interfere in analysis. Extreme care should be taken during the distillation as toxic hydrogen cyanide is generated. The cyanide in the alkaline distillate can then be measured potentiometricaHy with an ion-selective electrode. Alternatively, the cyanide can be determined colorimetricaHy. It is converted to cyanogen chloride by reaction with chloramine-T at pH <8. The CNCl then reacts with a pyridine barbituric acid reagent to form a red-blue dye. 

Individual polyethers exhibit varying specificities for cations. Some polyethers have found appHcation as components in ion-selective electrodes for use in clinical medicine or in laboratory studies involving transport studies or measurement of transmembrane electrical potential (4). The methyl ester of monensin [28636-21 -7] i2ls been incorporated into a membrane sHde assembly used for the assay of semm sodium (see Biosensors) (5). Studies directed toward the design of a lithium selective electrode resulted in the synthesis of a derivative of monensin lactone that is highly specific for lithium (6). 

In some systems, known as continuous-flow analy2ers, the reaction develops as the sample —reagent mixture flows through a conduit held at constant temperature. In such systems, the reaction cuvettes are replaced by optical reading stations called flow cells. In most analy2ers, whether of discrete- or continuous-flow type, deterrnination of electrolyte tests, eg, sodium and potassium levels, is done by a separate unit using the technique of ion-selective electrodes (ISE) rather than optical detection. 

The majoiity of the various analyte measurements made in automated clinical chemistry analyzers involve optical techniques such as absorbance, reflectance, luminescence, and turbidimetric and nephelometric detection means. Some of these ate illustrated in Figure 3. The measurement of electrolytes such as sodium and potassium have generally been accomphshed by flame photometry or ion-selective electrode sensors (qv). However, the development of chromogenic ionophores permits these measurements to be done by absorbance photometry also. 

Ion Selective Electrodes Technique. Ion selective (ISE) methods, based on a direct potentiometric technique (7) (see Electroanalytical techniques), are routinely used in clinical chemistry to measure pH, sodium, potassium, carbon dioxide, calcium, lithium, and chloride levels in biological fluids. 

Ion-selective electrodes are available for the electro analysis of most small anions, eg, haUdes, sulfide, carbonate, nitrate, etc, and cations, eg, lithium, sodium, potassium, hydrogen, magnesium, calcium, etc, but having varying degrees of selectivity. The most successful uses of these electrodes involve process monitoring, eg, for pH, where precision beyond the unstable reference electrode s abiUty to deUver is not generally required, and for clinical apphcations, eg, sodium, potassium, chloride, and carbonate in blood, urine, and semm. 

Where-high purity MU is provided for higher pressure WT boiler plant FW, some form of continuous analyzers for measuring treated water pH and conductivity are almost always installed, as are sodium (Na) ion-selective electrodes for detection of sodium leakage. Automatic online silica analyzers also may be installed, but they measure only reactive (ionizable) silica (Si02), not colloidal or total silica, so caution is required where unforeseen silica leakage may present a problem. 

EXAMPLE 5-5 Calculate the error caused by sodium ion, aNa = 0.01, in the measurement of lithium, au = 0.01, using a lithium ion-selective electrode... 

Vlasov YG, Bychkov EA (1989) Sodium ion-selective chalcogenide glass electrodes. Anal Lett 22 1125-1144... 

Sodium, Na(I) has a normal concentration in human serum of 136-145 mmol/L (Tohda 1994) and makes up about 90 % of the cations present. (Many extracellular body fluids possess ranges from 7 mmol/L [mature milk] via 33 [saliva] to 145 mmol/ L [bile]). The reference method for determination is potentiometry with ion-selective electrodes (PISE). 

Especially sensitive and selective potassium and some other ion-selective electrodes employ special complexing agents in their membranes, termed ionophores (discussed in detail on page 445). These substances, which often have cyclic structures, bind alkali metal ions and some other cations in complexes with widely varying stability constants. The membrane of an ion-selective electrode contains the salt of the determined cation with a hydrophobic anion (usually tetraphenylborate) and excess ionophore, so that the cation is mostly bound in the complex in the membrane. It can readily be demonstrated that the membrane potential obeys Eq. (6.3.3). In the presence of interferents, the selectivity coefficient is given approximately by the ratio of the stability constants of the complexes of the two ions with the ionophore. For the determination of potassium ions in the presence of interfering sodium ions, where the ionophore is the cyclic depsipeptide, valinomycin, the selectivity coefficient is Na+ 10"4, so that this electrode can be used to determine potassium ions in the presence of a 104-fold excess of sodium ions. 

It has been emphasized repeatedly that the individual activity coefficients cannot be measured experimentally. However, these values are required for a number of purposes, e.g. for calibration of ion-selective electrodes. Thus, a conventional scale of ionic activities must be defined on the basis of suitably selected standards. In addition, this definition must be consistent with the definition of the conventional activity scale for the oxonium ion, i.e. the definition of the practical pH scale. Similarly, the individual scales for the various ions must be mutually consistent, i.e. they must satisfy the relationship between the experimentally measurable mean activity of the electrolyte and the defined activities of the cation and anion in view of Eq. (1.1.11). Thus, by using galvanic cells without transport, e.g. a sodium-ion-selective glass electrode and a Cl -selective electrode in a NaCl solution, a series of (NaCl) is obtained from which the individual ion activity aNa+ is determined on the basis of the Bates-Guggenheim convention for acr (page 37). Table 6.1 lists three such standard solutions, where pNa = -logflNa+, etc. 

Lindell H, Jappinen P, Savolainen H. 1988. Determination of sulphide in blood with an ion-selective electrode by pre-concentration of trapped sulphide in sodium hydroxide solution. Analyst 113 839-840. 

Buchberger et al. [104] carried out a selective determination of iodide in brine. The performance of a potentiometric method using an ion-selective electrode and of liquid chromatography coupled with ultraviolet detection at 230 nm were compared as methods for the determination of iodide in the presence of other iodide species. Satisfactory results were obtained from the potentiometric method provided the solution was first diluted tenfold with 5 M sodium nitrate, and external standards were used. Better reproducibility was, however, achieved with HPLC, provided precautions were taken to prevent reduction of iodine to iodide in the mobile phase, for which extraction of iodine with carbon tetrachloride prior to analysis was recommended. This was the pre-... 

In Nebraska, state regulations require that the chemical makeup of animal feed sold in the state be accurately reflected on the labels found on the feed bags. The Nebraska State Agriculture Laboratory is charged with the task of performing the analytical laboratory work required. An example is salt (sodium chloride) content. The method used to analyze the feed for sodium chloride involves a potentio-metric titration. A chloride ion-selective electrode in combination with a saturated calomel reference electrode is used. After dissolving the feed sample, the chloride is titrated with a silver nitrate standard solution. The reaction involves the formation of the insoluble precipitate silver chloride. The electrode monitors the decrease in the chloride concentration as the titration proceeds, ultimately detecting the end point (when the chloride ion concentration is zero). 

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