Potassium potentiometric method

Potentiometric Methods. - Potassium trithiocarbonate has been used as a reductant (-S-S- reduction cleavage) for the potentiometric (and spectrophoto-metric) determination of the disulfides of dithio-phosphinic acids in DMF-H2O medium at millimolar levels.The protonation equilibria for N,N -diethylami-nomethylenephosphonic acid (88) were elucidated from both potentiometric titration and determination of the pH dependence of the NMR chemical shift (83 ip), and protonation constants for aminoalkanephosphonates RCH(NH2)P(0)(0Et)2 and the acidity constant of di(2-ethylhexyl)thiopho-sphoric acid (111) have also been obtained potentiometrically. 

Papers devoted to the studies of metal-oxide solubilities in molten potassium halides are few. In particular, Guyseva and Khokhlov reported the determination of the solubility product of MgO in molten KC1 in the 1067-1195 K temperature range [374], The study was performed by the potentiometric method using the Pt(02) gas-oxygen electrode. The experimental method consisted of the addition of a known quantity of MgCl2 to the pure melt, and measurements of e.m.f. for the following cell ... 

In the lUPAC method 2.201 (Paquot, 1979a), two methods are described for the determination of the free fatty acid content acid value by the indicator method , a method comparable to the method described in Section 6.2.9, and acid value by the potentiometric method . In the latter method, the free fatty acids are titrated potentiometrically in a non-aqueous medium with a solution of potassium hydroxide in isopropanol. This method is employed for the determination of free acidity in highly coloured oils and fats. 

The potentiometric method should be employed for the determination of the saponification value of highly coloured oils and fats. It is based on reflux boiling of the sample with isopropanolic potassium hydroxide solution and potentiometric titration of the excess of potassium hydroxide by hydrochloric acid in a non-aqueous medium. 

In potentiometric methods, the potential between a reference and an indicator electrode is measured, which corresponds to the analyte activity. Because of their usefulness in food analysis, ion-selective electrodes (ISEs) that measure anions like bromide, chloride, and fluoride or cations like potassium, sodium, and calcium stand out among indicator electrodes. The characteristics and advantages of ISE include the ability to measure different anions and cations directly, the fact that they do not consume the analyte, the fact that analyses are independent of sample volume when taking direct measurements, and that moreover turbidity, color, and viscosity do not affect the measurement. Potentiometric methods are also... 

ISO 11427 1993 Determination of silver jewelry alloys - volumetric (potentiometric) method using potassium bromide... 

During the last years in the clinical laboratory potentiometric methods using ion-sensitive electrodes (ISEs) have been introduced. It must be considered that with these methods ion activities are measured and not ion concentrations [18-21]. The methodic differences resulting from this fact have to be considered in the interpretation of the results or have to be eliminated in the process of evaluation of the method [22]. Ion-sensitive electrodes are practicable in single apparatuses as well as in automatic analyzers. Even in analyzers using the technique of dry reagent chemistry, slides for direct potentiometric determination of sodium and potassium are used [23]. 

The gravimetric determination of potassium as its barely soluble tetraphenylborate is recommended and described here. This method has also been applied to seawater for an ocean-wide survey of the element (see Table 11-1). The procedure is preferred because of its high accuracy and precision and the minimum amount of equipment required to perform the analysis. Basically, the method outlined here is that developed by Wittig (1950) and Raff and Brotz (1951). A brief description of a potentiometric method is presented in Section 11.2.3.6. 

The iron-carbon system has been investigated in our laboratory. The powders were subjected to thermal treatment and next they were investigated by the potentiometric method in powder electrodes, and by the metallographic method using grinds and corrosions of the powder in shellac. Both the carbon content and the structure of the system had an influence on the rates of change and the value of the powder electrode potential in aqueous solution of potassium sulphate. The potentiometric measurements enabled us to define the structure when the quantitative composition of an alloy was known. 

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. 

A weighed amount of sample is dissolved in a mixture of propanone and ethanoic acid and titrated potentiometrically with standard lead nitrate solution, using glass and platinum electrodes in combination with a ferro-ferricyanide redox indicator system consisting of 1 mg lead ferrocyanide and 0.5 ml 10% potassium ferricyanide solution. The endpoint of the titration is located by graphical extrapolation of two branches of the titration plot. A standard solution of sodium sulfate is titrated in the same way and the sodium sulfate content is calculated from the amounts of titrant used for sample and standard. (d) Water. Two methods are currently available for the determination of water. 

Measurement of Reaction Rates by Titrimetry. The rates of cerium(IV) consumption by each of Cr(C204)3 3, m-Cr(OH2)2(C204)2 and Cr(0H2)4C204+ were also measured by a direct titrimetric method. Solutions were prepared and mixed as for the spectrophotometric procedure. At appropriate times aliquots of the reactant solutions were quenched with known volumes of standard ferrous sulfate, and the excess ferrous ion was titrated potentiometrically with standard potassium dichromate,... 

Tartaric Acid. Quantitative measures of total tartrate are useful in determining the amount of acid reduction required for high acid musts and in predicting the tartrate stability of finished wines. Three procedures may be used. Precipitation as calcium racemate is accurate (85), but the cost and unavailability of L-tartaric acid are prohibitive. Precipitation of tartaric acid as potassium bitartrate is the oldest procedure but is somewhat empirical because of the appreciable solubility of potassium bi-tartrate. Nevertheless, it is still an official AO AC method (3). The colorimetric metavanadate procedure is widely used (4, 6, 86, 87). Tanner and Sandoz (88) reported good correlation between their bitartrate procedure and Rebeleins rapid colorimetric method (87). Potentiometric titration in Me2CO after ion exchange was specific for tartaric acid (89). 

Polymer-polymer complexation is generally detected via conductometric or potentiometric titrations. Colloid titration represents an inverse-system where a polymer with known characteristics, such as potassium poly (vinylalcohol-sulfate) or poly(diallyldimethylam-moniumchloride), are used to quantify the concentration of polycation or polyanion, hence relying on a 1 1 stoichiometry. Using the cationic dye, tol-uidine blue, as an indicator, a metachromatic end point is detected. Both methods are volumetric. 

The hydroxyl number is very important for the synthesis of polyurethane. It is defined as the number of milligrams of potassium hydroxide equivalent to the hydroxyl content of one gram of the sample. The principle of the analytical method is that the hydroxyl group is esterified with a solution of phthalic anhydride in pyridine. The excess reagent is back-titrated with standard sodium hydroxide solution, and a blank is run on the reagents to determine the amount of anhydride consumed. The phenolphthalein is an indicator for the titrate. Because the color of recycled polyol is dark brown, the faint pink endpoint is not clear, so a potentiometric titrate can be applied. 

Part 4 of ISO 787 specifies the method of determination and Part 3 specifies how the extract should be prepared. The material for testing is extracted in boiling water for 5 minutes and filtered to obtain a clear filtrate. An aliquot of filtered extract is titrated either with hydrochloric acid or sodium or potassium hydroxide solution in the presence of an indicator or evaluated by potentiometric determination. 

Values of/x = Ac/A may be calculated from Kohlrausch s measurements of electrical conductivity of hydrochloric acid solutions. /h and fci can be evaluated from the potentiometric measurements on hydrochloric acid solutions performed by Scatchaed. These data are very reliable since the concentration chain was so arranged as to eliminate diffusion potentials. In this way, ScATCHARD determined the mean activity coefficient V/h/ci instead of the individual ion activities. If we assume that in a potassium chloride solution/ = /ci— which is plausible when we recall that both ions have the same structure—and that fci is the same in hydrochloric acid solutions and potassium chloride solutions of the same concentration, then we can calculate/h and fci in hydrochloric acid solutions. Naturally these values are not strictly correct since the effect of the potassium ions on the activity of the chloride ions probably is different from that of the hydrogen ions at the same ionic strength. In the succeeding table are given values of /x, /h, and fci calculated by the above method. 

To determine the acid number by the potentiometric titration method (ASTM D-664, IP 177), the sample is dissolved in a mixture of toluene and isopropyl alcohol containing a small amount of water and titrated poten-tiometrically with alcoholic potassium hydroxide using a glass indicating electrode and a calomel reference electrode. The meter readings are plotted... 

Acidity is determined through the acid number, which is the quantity of base, expressed in milligrams of potassium hydroxide per gram of sample, required to titrate a sample in the solvent from its initial meter reading to a meter reading corresponding to a freshly prepared nonaqueous basic buffer solution or a well-defined inflection point as specified in the test method. Test methods include potentiometric titration (ASTM D-66, IP 177) and indicator-indicator titration (ASTM D-974, IP 139) in addition to inorganic acidity (IP 182) and total acidity (IP 1) methods. 

A potentiometric titration method for obtaining the solubility of silver chloride in potassium nitrate solutions has been used by Brown and Maclnnes.28 These workers used the cell... 

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