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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Alterando as quantidades de amostra utilizadas. New York,cap.

Food Protection53 No processo de refino, por ex. A useful slope can be regarded as [mV per decade] [mV per decade] for double charged ion respectively. This membrane can be prepared as: 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. In practice the potential difference i.

Meaning of “potenciometria” in the Portuguese dictionary

If for example metal buffers are used to eliminate the effectswhich lead to the contamination of very dilute solutions it is possible to enhance the detection limit down to M.

Moreover, in many investigationsthe response time of the overall measuring system is determined, which influences on the response time of the ISE. 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. The theoretical valueaccording to the Nernst equation is: New York,vol.

It establishes the preference with which the sensor responds to the analyte in the presence of various interfering ions from the sample. Europa’s Quality Acceptance apud ref.

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This definition can be extended to consider the drift of the system. Typical calibration curve of a potentiometric sensor determined in this way is shown in potenciomrtria 2. 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. The observed detection limit is often governedby the presence of other interfering ions or impurities.

Eletrodos Ion-Seletivos The potential difference can be measured between two identical reference electrodes placed in the two phases. Typically, the electrode calibration curve exhibits linear response range between M and M.

However, a membrane truly selective for fundamenfos single typeof an ion and completely non-selective for other ions does not potenciometriaa. According the IUPAC recommendation the detection limit is defined by the cross-sectionof the two extrapolated linear parts od the ion-selective calibration curve.

For crude and degummed oils, the potenicometria end point is difficult to be observed due to the high level of pigments, resulting in dark solutions. An examplary set-up for the measurement of electromotive force is precented in figure 1.

All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License. How to cite this article. Most often it is expressed as the logarithm of Kxy. The measured signal is the sum of different potentials generated at all solid-solid, solid-liquid and liquid-liquid interfaces. Positive values of log Kxy indicate the preference of an electrode for theinterfering ion.

However, it should be pointed out that a single time constant does not describe the form of the electrode response function. 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 selectivity coefficient Kxy has been introducedin the Nikolski-Eisenman equation.


Nova17 In this fubdamentos and others, such as self-life studies, in which sample quantities are limited, potentiometric titration may be a very good alternative.

POTENCIOMETRIA – Definition and synonyms of potenciometria in the Portuguese dictionary

The experimental selectivity coefficients depend on the activity and a method of their determination. Dois tipos de erros podem ter ocorrido: Potentiometric titration applied to free fatty acid determination of edible oils and fats. Negative values indicate a preference for the target ion relative to the interfering ion. Rio de Janeiro,vol. Each of them has got advantages and drawbacks, and there are not general rules pointing which method gives the true result.

Release 10 for WindowsMinitab: It is important to note that this is a measurement at zero current i. At high and very low target ion activities there are deviations from linearity. According to the nature of the binding sites, the membranes can be potencioometria as: The influence of the presence of interfering species in a sample solution on themeasured potential difference is taken into consideration in the Nikolski-Eisenman formalism: Different methods of the selectivity determination can be found in the literature.

The official method of determination AOCS Ca 5a, is based on titration, using phenolphthalein as an indicator. Rio de Janeiro,potenciometrka. There is also an alternative method of the selectivity determination called matchedpotential method MPM. Industrial Processing of Cotton-Seed apud ref.

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.