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Rio de Janeiro,cap. In practice, detection limit on the order of M is measured ffundamentos most of ion-selective electrodes. The observed detection limit is often governedby the presence of other interfering ions or impurities.

Meaning of “potenciometria” in the Portuguese dictionary

However, a membrane truly selective for a single typeof an ion and completely non-selective for other ions does not exist. 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. 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.

Food Protection53 Rio de Janeiro,vol. An examplary set-up for the measurement of electromotive force is precented in figure 1. Negative values indicate a preference for the target ion relative to the interfering ion.

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 linear range of the calibration curve is usually applied to porenciometria the activity of the target ionin any unknown solution.

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

Positive values of log Kxy indicate the preference of an electrode for theinterfering ion. How to cite this article. The measured signal is the sum of different potentials generated at all solid-solid, solid-liquid and liquid-liquid interfaces.

At high and very low target ion activities there are deviations from linearity. Alterando as quantidades de amostra utilizadas.

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It is important to note that this is a measurement at zero current i. Potentiometric titration applied to free fatty acid determination of edible oils and fats. If ions can penetrate the boundary betweentwo phases, then an electrochemical equilibrium will be reached, in potenciometrai different potentials in the two phases fyndamentos formed.

Typical calibration curve of a potentiometric sensor determined in this way is shown in figure 2. Typically, the electrode calibration curve exhibits linear response range between M and M.

This membrane can be prepared as: However, in certain applications the value of the electrode slope is not criticaland worse value does not exclude its usefulness. In practice the potential difference i. 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: Each of them has got advantages and drawbacks, and there are not general rules pointing which method gives the true result.

Industrial Processing of Cotton-Seed apud ref.

Europa’s Quality Acceptance apud ref. New York,vol. New York,cap. Dx 10 for WindowsMinitab: A useful slope can be regarded as [mV per decade] [mV per decade] for double charged ion respectively.

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However, it should be pointed out that a single time constant does not describe the form of the electrode response function. Free fatty acids are a measure of evaluating fats and oils, submitted to abusive conditions, besides being a quality characteristic of edible vegetable oils. All the contents of this journal, except where otherwise ea, is licensed under a Creative Commons Attribution License. Typically such a membrane contains an analyte-selective component whichis responsible for the recognition process.

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.

Eletrodos Ion-Seletivos The fundwmentos difference can be measured between two identical reference electrodes placed in the two phases. Services on Demand Journal. Different methods of the selectivity determination can be found in the literature. Most often it is expressed as the logarithm of Kxy. The experimental selectivity coefficients depend on the activity and a method of their determination. Moreover, in many investigationsthe response time of the overall measuring system is determined, which influences on the response time of the ISE.

An potenciometrua membrane is the key component of all potentiometric ion sensors. The theoretical valueaccording to the Nernst equation is: This definition can be extended to consider the drift of the system.