Análise potenciométrica de redissolução com ultramicroeletrodos: fundamentos e aplicações na determinação de metais traços. Quím. Nova [online]. 09/02/ la química analítica es la parte de la química que estudia, diseña, desarrolla, optimiza y aplica métodos y técnicas que se materializan en. fundamentos fisioquímicos grado farmacia us métodos químicos: son todos aquellos que se basan casi exclusivamente en reacciones químicas en los que la.

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No processo de refino, por ex. In practice the potential difference i. Potentiometric titration applied to free fatty acid determination of edible oils and fats. Eletrodos Ion-Seletivos The potential difference can be measured between two identical reference electrodes placed in the two phases. Dois tipos de erros podem ter ocorrido: In this case and others, such as self-life studies, in which sample quantities are limited, potentiometric titration may be a very good alternative. There is also an alternative method of the selectivity determination called matchedpotential method MPM.

According the IUPAC recommendation the detection limit is defined by the cross-sectionof the two extrapolated linear parts od the ion-selective calibration curve. Eletrodos Ion-Seletivos When the membrane separates two solutions of different ionic activities a1 and a2 and provided the membrane is only permeable to this single type of ion, the potential difference E across the membrane is described by the Nernst equation: Alterando as quantidades de amostra utilizadas.

This definition can be extended to consider the drift of the system. This membrane can be prepared as: If ions can penetrate the boundary betweentwo phases, then an electrochemical equilibrium will be reached, in which different potentials in the two phases are formed.

Most often it is expressed as ptoenciometria logarithm of Kxy.

Potentiometric titration applied to free fatty acid determination of edible oils and fats

According to the nature of the binding sites, the membranes can be classified as: Each of them has got advantages and drawbacks, and there are not general rules pointing which method gives the true result. An examplary set-up for the measurement of electromotive force is precented in figure 1. The observed detection limit is often governedby the presence of other interfering ions or impurities. Different methods of the selectivity determination can be found in the literature.


How to cite this article. Rio de Janeiro,cap. If only one type of an ion can be exchanged between the two phases, then the potential difference formed between the phases is governed only by theactivities of this target ion in these phases. Equilibrium means that the transfer of ions from the membrane into solution is equal to the transfer from the solution to the membrane.

Negative values indicate a preference for the target ion relative to the interfering ion. Nova17 Typically, the electrode calibration curve exhibits linear response range between M and M. However, a membrane truly selective for a single typeof an ion and ad non-selective for other ions does not exist. Typical calibration curve of potehciometria potentiometric sensor determined in this way is shown in figure 2.

Moreover, in many investigationsthe response time of the overall measuring system is determined, which influences on the response time of the ISE.

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All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License. Europa’s Quality Acceptance apud ref. Food Protection potencometria, 53 Positive values of log Kxy indicate the preference of an electrode for theinterfering ion. The official method of determination AOCS Ca 5a, is based on titration, using phenolphthalein as an indicator.

At high and very low target ion activities there are potenciomerria from linearity. The selectivity is one of the most important characteristics of an electrode, as it oftendetermines whether a reliable measurement in the sample is possible or not. It establishes the preference with which the sensor responds to the analyte in the presence of various interfering ions from the sample.


Services on Demand Journal. New York,vol. The selectivity coefficient Kxy has been introducedin the Nikolski-Eisenman equation.

For crude and degummed oils, the titration end point is difficult to be observed due to the high level of pigments, resulting in dark solutions.

Typically such a membrane contains an analyte-selective component whichis responsible for the recognition process. The theoretical valueaccording to the Nernst equation is: The experimental selectivity coefficients depend on the activity and a method of their determination.

It is important to note that this is a measurement at zero current i. New York,cap.

[Potencio & Conduto] Aula – Métodos Eletroquímicos e Titulação Potenciométrica (Guts)

Rio de Janeiro,vol. The measured signal is the sum of different potentials generated at all solid-solid, solid-liquid and liquid-liquid interfaces. However, it should be pointed out that only at constant ionic strength a linearrelationship between the signal measured and the concentration of the analyte is maintained because of the clear cut relationship between ion activity and concentration, occurring in such condition.

Release 10 for WindowsMinitab: An ion-selective membrane is the key component of all potentiometric ion sensors. For this reason the potential of sucha membrane is governed mainly by the activity of the primary target ion and also by the activity of othersecondary interfering ions.