Gran evaluation

In the Gran evaluation the mass balance equations given above are used together with the experimental variables volume of acid added (vmL) and measured emf (E mV)- Linear functions, F2 and Fi, which are valid for limited parts of the titration, are calculated from the titration variables and mass balance equations. Each of the two functions corresponds to a main reaction associated with an equivalence point which is mainly determined by the carbonate protonation ... 

For the purpose of estimation of At only, a rapid titration procedure based on a five point potentiometric titration with Gran evaluation has been suggested for large (40 mL) as well as small (1 mL) sample volumes (Haraldsson et aL, 1997). 

Gran-plot (multiple standard addition with 10iE/s vs. concentration) 0.1-3% 0-1-3% less accurate if interfering ions are present best results if many points between 30 and 80% of a titration curve are evaluated and discordant points are eliminated... 

Cabiedes, L., P. Arcos and F. Alvarez de Toledo (1995), Evaluation del coste incremental del servicio farmaceutio respecto a la distribution de medicamentos en oficinas de farmacia , in Libro de Ponencias del V Congreso Nacional de Economla, Economia de la salud, 5-7 December, Las Palmas de Gran Canaria, Espana, Madrid Consejo General de Colegios de Economistas de Espana, pp. 163-70. 

A computer program has been used to calculate the magnitude of systematic errors incurred in the evaluation of equivalence points in hydrochloric acid titrations of total alkalinity and carbonate in seawater by means of Gran plots. Hansson [13] devised a modification of the Gran procedure that gives improved accuracy and precision. The procedure requires approximate knowledge of all stability constants in the titration. 

Chloride can also be estimated by potentiometric titration using standard silver nitrate [27]. The results are recorded directly and evaluated by means of a computer program based on the Gran extrapolation method. The determinations have a precision of 0.02% and since many samples can be titrated simultaneously, the time for a single determination can be reduced to less than 5 min. 

Total dissolved inorganic carbon can also be evaluated from the potentiometric titration method described in Section 8.4.1, if it is performed in a closed cell. However, this technique does not give the highest precision possible and thus the coulometiic method first described by Johnson et al. (1985) and outlined here is nowadays the method of choice. Nevertheless, Ct can be evaluated from the potentiomettic titration curve, either Gran function linearization (Section 8.4.2.3 Gran evaliiation ) or by a curve fitting procedure (Section 8.4.2.3 Non-linear curve-fitting ). 

Gran, B.A., Bye, R., Nyheim, O.M., Okstad, E.H., Seljelid, X, Sklet, S., Vatn, J. Vinnem, XE. 2012. Evaluation of the Risk OMT model for maintenance work on major offshore process equipment. Journal of Loss Prevention in the Process Industries 25(3) 582-593. 

In instances where the ion to be determined is directly indicated, one of two techniques may be chosen The addition technique described above can be used, or a titration can be carried out in which the amount of indicated ion is quantitatively diminished. In this case, of course, the Gran titration curve will increase from right to left. For trace analyses the first technique should be used, and with larger amounts of material the second is more convenient. With very high concentrations, large end point jumps and negligible symmetry errors, the usual titration method is recommended for the simpler evaluation procedure. 

In addition to overcoming all these problems in the actual measurement and in the evaluation method, this technique also avoids a series of chemical titration problems. These arise with other techniques when too large a solubility product or too small a complex formation constant in dilute solutions result in poorly defined end points in the usual titration curves. With the Gran method, with which an excess of titrating... 

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