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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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.
[Potencio & Conduto] Aula – Métodos Eletroquímicos e Titulação Potenciométrica (Guts)
How to cite this article. Dois tipos de erros podem ter ocorrido: However, in certain applications the value of the electrode slope is not criticaland worse value does not exclude its usefulness. An examplary set-up for the measurement of electromotive force is precented in figure 1.
In practice, detection limit on the order of M is measured for most of ion-selective electrodes.
The measured signal is ffundamentos sum of different potentials generated at all solid-solid, solid-liquid and liquid-liquid interfaces.
The linear range of the calibration curve is usually applied to determine the activity of the target ionin any unknown solution.
Release 10 for WindowsMinitab: The selectivity coefficient Kxy has been introducedin the Nikolski-Eisenman equation.
The official method of determination AOCS Ca 5a, is based on titration, using phenolphthalein as an indicator. This definition can be extended to consider the drift of the system.
This membrane can be prepared as: Positive values of log Kxy indicate the preference of an electrode for theinterfering ion. Moreover, in many investigationsthe response time of the overall measuring system potenfiometria determined, which influences on the response time of the ISE. Different methods of the selectivity determination can fundamentod found in the literature. Services on Demand Journal. In this case and others, such as self-life studies, in which sample quantities are limited, potentiometric titration may be a very good alternative.
The experimental selectivity coefficients depend on the activity and a method of their determination. 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: Typical fubdamentos curve of a potentiometric sensor determined in this way is shown in figure 2.
Industrial Processing of Cotton-Seed apud ref. The theoretical valueaccording to the Nernst equation is: 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 completely non-selective for other ions does not exist. At high and very low target ion activities there are deviations from linearity. Food Protection53 Negative values indicate a preference for the target ion relative to the interfering ion. New York,cap. An ion-selective membrane is the key component of all potentiometric ion sensors.
Alterando as quantidades de amostra utilizadas. Eletrodos Ion-Seletivos When the membrane separates two fundamenyos 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 potrnciometria No processo de refino, por ex. Equilibrium means that the transfer of ions from the membrane into solution is equal to the transfer from the solution to the membrane.
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.
In practice the potential difference i. 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. Europa’s Quality Acceptance apud ref.
Métodos Electroquímicos by Josué Uriel on Prezi
However, it should be pointed out that only at constant ionic strength a potenciomettria 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. 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. It is important to note that this is a measurement at zero current i. Each of them has got advantages and drawbacks, and there are not general rules fudnamentos which method gives the true result.
Rio de Janeiro,vol. However, it should be pointed out that a single time constant does not describe the form of the electrode response function. The observed detection limit is often governedby the presence of other interfering ions or impurities.
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. Rio de Janeiro,cap.
Most often it is expressed as the logarithm of Kxy. There is also an alternative method of the selectivity determination called matchedpotential method MPM. 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.