Gran’s plot

A number of commercial titrators are available in which the electrical measuring unit is coupled to a chart recorder to produce directly a titration curve, and by linking the delivery of titrant from the burette to the movement of the recorder chart, an auto-titrator is produced. It is possible to stop the delivery of the titrant when the indicator electrode attains the potential corresponding to the equivalence point of the particular titration this is a feature of some importance when a number of repetitive titrations have to be performed. Many such instruments are controlled by a microprocessor so that the whole titration procedure is, to a large extent, automated. In addition to the normal titration curve, such instruments will also plot the first-derivative curve (AE/AV), the second-derivative curve (A2 E/AV2), and will provide a Gran s plot (Section 15.18). 

Lee Y. H. and Brosset C. (1978) The slope of Gran s plot a useful function in the examination of precipitation, the water-soluble part of airborne particles, and lake water. Water Air Soil Pollut. 10, 457-469. 

H. Li, Improvement of Gran s Plot Method in Standard Addition and Subtraction Methods by a New Plot Method, Anal. Lett., 24 (1991) 473. 

In the second step the value is used as and the procedure is repeated. The successive Gran s plots are calculated as long as the difference between the values is smaller than the assumed accuracy. Usually the first approximation is sufficiently good, but it is recommended to check at least one more step. 

Known addition, known subtraction and Gran s plot methods are other ways of using ion-selective electrodes [14,20—27]. In the standard addition to sample method, the potential, o,of the ion-selective electrode with respect to a suitable reference electrode is measured for the sample solution of volume, Fo, and total concentration, Co, of the sought species ... 

Computation of the left-hand side of Equation (11) is avoided by using semiantilog Gran s Plot Paper supplied by Orion Research Incorporated which has been corrected for limited volume changes, that is, for (Fo-i- F,), and which assumes sufficiently dilute solutions and that x, = 1. Hence, all that is required is to plot the emf response on the ordinate against the volume of standard addition on the abscissa when the intercept, Fe, is easily discernible. 

Mascini M (1980) Uses of known addition, Gran s plot and the related methods with ion-selective electrodes. Ion-Selective Electrode Reviews 2 17-71. 

The potentiometric detection of sulfate can be performed by Gran s plot titration of the sulfate solution with a commercially available barium-selective electrode (17), Sulfate-selective electrodes based on solid state crystals have also been reported (18), More recently, polymeric-membrane sulfate-selective electrodes have been developed using imidazole and thiourea derivatives as ionophores (19, 20),... 

A graphical method for determining concentrations has been developed which is also useful in titration determinations. This method, known as Gran s plots, involves the use of a proprietary plotting paper (Orion, 1973). 

A potentiometric SIA method was developed to quantify the nitrite contained in cured meat products. The assessment of nitrite concentration was accomplished by using the Gran s plot approach using a nitrite-selective electrode. A silver sulfate solution was used to remove the salt present in the samples since chloride ion is one of the most important interferents (Zarate et al., 2009). 

Zarate, N., M. P. Ruiz, R. Perez-Olmos, A. N. Araujo, M. Conceiqao, and B. S. M. Montenegro. 2009. Development of a sequential injection analysis system for the potentiometric determination of nitrite in meat products by using a Gran s plot method. Microchim. Acta 165 117-122. 

Fig. 10.2 Gran s plot corresponding to the titration of the weak acid HA with sodium hydrojdde (Co = 6 10 mol/L, Vb = 40 ml, C = 0.1 moVL, pK = 5.40—see text)...

Figure P.6 Differential titration curve, (a) First differential titration curve, (b) Second differential titration curve, (c) Gran s plot... 

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