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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It establishes the preference with which the sensor responds to the analyte in the presence of various interfering ions from the sample. Free fatty acids are a measure of evaluating fats and oils, submitted to abusive conditions, besides being a quality characteristic of edible vegetable oils. If for example metal buffers are used to eliminate the effectswhich lead to the contamination of very dilute solutions it is fundwmentos to enhance the detection potencilmetria down to M.
An ion-selective membrane is the fundmaentos component of all potentiometric ion sensors. How to cite this article. New York,vol. No processo de refino, por ex. 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: Typical calibration curve of a potentiometric sensor determined in this way is shown in figure 2.
Different methods of the selectivity determination can be found in the literature. At high and very low target ion activities there are deviations from linearity.
Alterando as quantidades de amostra utilizadas. The official method of determination AOCS Ca 5a, is based on titration, using phenolphthalein as an indicator.
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.
Industrial Processing of Cotton-Seed apud ref. New York,cap. According to the nature of the binding sites, the membranes can be classified as: Negative values indicate a preference for the target ion relative to the interfering ion. Funeamentos tipos de erros podem ter ocorrido: However, a membrane truly selective for a single funvamentos an ion and completely non-selective for other ions does not exist.
Most often it is expressed as the logarithm of Kxy.
Meaning of “potenciometria” in the Portuguese dictionary
Moreover, in many investigationsthe response time of the overall measuring system is determined, which influences on the response time of the ISE. Ea experimental selectivity coefficients depend on the activity and a method of their determination. Positive values of log Kxy indicate the preference of an electrode for theinterfering ion. It is important to note that this is a measurement at zero current i. Typically such a poteniometria contains an analyte-selective component whichis responsible for the recognition process.
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Potentiometric titration applied to free fatty acid determination of edible oils and fats. Funsamentos the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License. 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.
The linear range of the calibration curve is usually applied to determine the activity of the target ionin any unknown solution. potenciomehria
[Potencio & Conduto] Aula – Métodos Eletroquímicos e Titulação Potenciométrica (Guts)
Typically, the electrode calibration curve exhibits linear potenciometra range between Dx and M. Each of them has got advantages and drawbacks, and there are not general rules pointing which method gives the true result. Nova17 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.
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: Release 10 for WindowsMinitab: In practice, detection limit on the order of M is measured for most of ion-selective electrodes.
However, in certain applications the value of the electrode slope is not criticaland potenciomefria value does not exclude its usefulness. However, it should be pointed out that only at constant ionic strength a linearrelationship between the signal measured and fundamejtos concentration of the analyte is maintained because of the clear cut relationship between ion activity and concentration, occurring in such condition.
Europa’s Quality Acceptance apud ref. However, it should be pointed out that a single time constant does not describe the form of the electrode response function.
The measured signal is the sum of different potentials generated at all solid-solid, solid-liquid and liquid-liquid interfaces. Eletrodos Ion-Seletivos The potential difference can be measured between two identical reference electrodes placed in the two phases. 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. This membrane can be prepared as:
