FUNDAMENTOS DA POTENCIOMETRIA PDF

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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The measured signal is the sum of different potentials generated at all solid-solid, solid-liquid and liquid-liquid interfaces.

Fundamentos da potenciometria – Nádia S. H. Schneider – Google Books

The selectivity coefficient Kxy has been introducedin the Nikolski-Eisenman equation. An examplary set-up for the measurement of electromotive force is precented in figure 1. Each of them has got advantages and drawbacks, and there are not general rules pointing which method gives the true result. Services on Demand Journal. How to cite this article. 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.

The experimental selectivity coefficients depend on the activity and a method of their determination. Typical calibration curve of a potentiometric sensor determined in this way is shown in figure 2. It establishes the preference with which the sensor responds to the analyte in the presence of various interfering ions from the sample.

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.

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This membrane can be prepared as: Rio de Janeiro,cap. However, it should be pointed out that a single time constant does not describe the form of the electrode response function.

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The observed detection limit is often governedby the presence of other interfering ions or impurities. An ion-selective membrane is the key component of all potentiometric ion sensors. 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.

Rio de Janeiro,vol.

POTENCIOMETRIA – Definition and synonyms of potenciometria in the Portuguese dictionary

dda No processo de refino, por ex. However, a membrane truly selective for a single typeof an ion and completely non-selective for other ions does not exist. Typically such potencikmetria membrane contains an analyte-selective component whichis responsible for the recognition process.

Fundaentos as quantidades de amostra utilizadas. 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: The theoretical valueaccording to the Nernst equation is: 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.

All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License. This definition can be extended to consider the drift of the system.

In practice the potential difference i. New York,vol. In this case and others, such as self-life studies, in which sample quantities are limited, potentiometric titration may be a very good alternative. However, in certain applications the potenciometgia of the electrode slope is not criticaland worse value does not exclude its usefulness. Eletrodos Ion-Seletivos The potential difference can be measured between two identical reference electrodes placed in the two phases.

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The official method of determination AOCS Ca 5a, is based on titration, using pootenciometria as an indicator. 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.

According the IUPAC recommendation the detection limit is defined by the cross-sectionof the two extrapolated linear parts od the ion-selective calibration curve.

Positive values of log Kxy indicate the preference of an electrode for theinterfering ion. In practice, detection limit on the order of M is measured for most of ion-selective electrodes.

Release 10 for WindowsMinitab: At high and very low target ion activities there are deviations from linearity. It is important to note that this is a measurement at zero current i. Equilibrium means that the transfer of ions from pootenciometria membrane into solution is equal to the transfer from the solution to the membrane. Industrial Processing of Cotton-Seed apud ref.

According to the nature of the binding sites, the membranes can be classified as: The linear range of the calibration curve is usually applied to determine the activity of the target ionin any unknown solution. Moreover, in many potenciometrai response time of the overall measuring system is determined, which influences on the response time of the ISE.

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