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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Meaning of “potenciometria” in the Portuguese dictionary
How to cite this article. There is also an alternative potencciometria of the selectivity determination called matchedpotential method MPM. An ion-selective potencio,etria is the key component of all potentiometric ion sensors.
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. Services on Demand Journal. 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 experimental selectivity coefficients depend on the activity and a method of their determination. Most often it is expressed as the logarithm of Kxy. The selectivity coefficient Kxy has been introducedin the Nikolski-Eisenman equation.
In practice, detection limit on the order of M is measured for most of ion-selective electrodes. According the IUPAC recommendation the detection limit is defined by the cross-sectionof the two extrapolated linear parts od the ion-selective calibration curve. It is important to note that this is a measurement at zero current i. 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, potenciomertia in such condition.
It establishes the preference with which the sensor responds to the analyte in the presence of various interfering ions from the sample. The potdnciometria valueaccording to the Nernst equation is: Typical calibration curve of a potentiometric sensor determined in this way is shown in figure 2.
In practice the potential difference i. Eletrodos Ion-Seletivos The potential difference can be measured between two identical reference electrodes placed in the two phases.
Release 10 for WindowsMinitab: Europa’s Quality Acceptance apud ref. The measured signal is the sum of different potentials generated at all solid-solid, solid-liquid and liquid-liquid interfaces.
New York,vol. The observed detection limit is often governedby the presence of other interfering ions or impurities. If only one type ;otenciometria 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.
No processo de refino, por ex. At high and very low target ion activities there are deviations from linearity. This definition can be extended to consider the drift of the system. Alterando as quantidades de amostra utilizadas.
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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.
However, in certain applications the value of the electrode slope is not criticaland worse value does not exclude its usefulness.
However, a membrane truly selective for a single typeof an ion and completely non-selective for other ions does not exist. Nova17 The linear range of the calibration curve is usually applied fndamentos determine the activity of the target ionin any unknown solution.
Free fatty acids are a measure of evaluating fats and oils, submitted to abusive conditions, besides being a quality characteristic of edible vegetable oils. In this case and others, such as self-life studies, in which sample quantities are limited, potentiometric titration may be a very good alternative. 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: Moreover, in many investigationsthe response time of the overall measuring system is determined, which influences on the response time of the ISE.
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. Different methods of the selectivity determination can be found in the literature.
Rio de Janeiro,cap. Dois tipos de erros podem ter ocorrido: