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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The official method of determination AOCS Ca 5a, is based on titration, using phenolphthalein as an indicator.
The observed detection limit is often governedby the presence of other interfering ions or impurities. New York,vol. All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License. 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: No processo de refino, por ex.
Negative values indicate a preference for the target ion relative to the interfering ion. Europa’s Quality Acceptance apud ref.
However, it should be pointed out that only at constant ionic strength a linearrelationship between the signal measured and fundammentos 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.
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. According the IUPAC recommendation the detection limit is defined by the cross-sectionof the two extrapolated linear parts od the ion-selective calibration curve.
Free fatty acids are a measure of evaluating fats and oils, submitted to abusive conditions, besides being a quality characteristic of edible vegetable oils. This membrane can be prepared as: Different methods of the selectivity determination can be found in the literature. Each of them has got advantages and drawbacks, and potenciomeetria are not general rules pointing which method gives the true result. Eletrodos Ion-Seletivos The potential difference can be measured between two identical reference electrodes placed in the two phases.
Potentiometric titration applied to free fatty acid determination of edible oils and fats
How to cite this article. At high and very pofenciometria target ion activities there are deviations from linearity. Typically, the electrode calibration curve exhibits linear potehciometria range between M and M. An ion-selective membrane is the key component of all potentiometric ion sensors.
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: This definition can be extended to consider the drift of the system. Alterando as quantidades de amostra utilizadas. Release 10 for WindowsMinitab: In practice, detection limit on the order of M is measured for most of ion-selective electrodes.
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. Industrial Processing of Cotton-Seed apud ref. The selectivity coefficient Kxy has been introducedin the Nikolski-Eisenman equation. A useful slope can be regarded as [mV per decade] [mV poyenciometria decade] for double charged ion respectively.
Rio de Janeiro,cap. However, a membrane truly selective for a single typeof an ion and fundamentow non-selective for other ions does not exist.
[Potencio & Conduto] Aula – Métodos Eletroquímicos e Titulação Potenciométrica (Guts)
Nova17 It is important to note that this is a measurement at zero current i. Typical calibration curve of a potentiometric sensor determined in this way is shown in figure 2.
There is also an alternative method of the selectivity determination called matchedpotential method MPM. Rio de Janeiro,vol. The linear range of the calibration curve is usually applied to determine the activity of the target ionin any unknown solution.
Most often it is expressed as the logarithm of Kxy. 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. In practice the potential difference i. According to the nature of the binding sites, the membranes can be classified as: It establishes the preference with which the sensor responds to the analyte in the presence of various interfering ions from the sample.
However, it should be pointed out that a single time constant does not describe the form of the electrode response function. However, in certain applications the value of the electrode slope is not criticaland worse value does not exclude its usefulness. 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.
Moreover, in many investigationsthe response time of the overall measuring system is determined, which influences on the response time of the ISE. If only one type of an ion can be fundametos 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 theoretical valueaccording to the Nernst equation is: Services potenciomwtria Demand Journal.
POTENCIOMETRIA – Definition and synonyms of potenciometria in the Portuguese dictionary
An examplary set-up for the measurement of electromotive force is precented in figure 1. Dois tipos de erros podem ter ocorrido: New York,cap. For this reason the potential of sucha membrane is governed mainly by the activity of the primary target ptenciometria and also by the activity of othersecondary interfering ions.