Selektifitas membran

Summary

This lecture discusses the concept of membrane selectivity in ion selective electrodes (ISEs). It explains how an electrode's membrane responds to multiple ions, with greater selectivity to a primary ion (e.g., H+). The lecture delves into the significance of the selectivity coefficient, illustrating its role in determining the electrode's response to different ions. Experimental methods to measure this coefficient are outlined, including the use of varying concentrations and potential measurements. The selectivity coefficient indicates the degree of an electrode's preference for a particular ion over others, with smaller values showing higher selectivity.

Takeaways

• 😀 Ion-selective electrodes (ISEs) respond to a range of ions, not just one specific ion.
• 😀 ISEs exhibit selectivity towards certain ions, but they may also respond to interfering ions present in the solution.
• 😀 The selectivity of an ISE towards an analyte ion is quantified using a selectivity coefficient, which is typically less than 1.
• 😀 A smaller selectivity coefficient means the electrode is more selective towards the target ion and less responsive to interfering ions.
• 😀 The selectivity coefficient can be experimentally determined by preparing solutions with varying analyte concentrations and measuring cell potential.
• 😀 In a potentiometric measurement using an ISE, the cell potential depends on all ions present in the solution, with the target ion's response typically being dominant.
• 😀 The selectivity coefficient formula involves the ratio of analyte concentration to interfering ion concentration, which helps determine the electrode's response.
• 😀 Ion-selective electrodes are characterized by their ability to differentiate between ions based on their concentration, allowing accurate measurements.
• 😀 A plot of cell potential against analyte concentration reveals how the electrode’s response changes as the concentration of the target ion varies.
• 😀 Manufacturers provide selectivity coefficient data for ISEs, which helps users understand the degree of interference from other ions in their measurements.
• 😀 When calculating the selectivity coefficient, the intersection point of a tangent line on a potential-concentration curve is used to determine the value, helping quantify electrode selectivity.

Q & A

What is the primary focus of the lecture in the provided transcript?

The primary focus of the lecture is membrane selectivity, particularly in ion-selective electrodes, and how these electrodes respond to different ions in a solution.

What is an ion-selective electrode (ISE), and how does it function?

An ion-selective electrode is designed to measure the concentration of a specific ion in a solution. However, it does not respond solely to that ion; it also responds to other ions present, with a greater response to the target ion. The electrode generates a cell potential based on the concentrations of various ions in the solution.

What is the significance of the selectivity coefficient in ion-selective electrodes?

The selectivity coefficient quantifies the electrode's preference for one ion over others. A smaller selectivity coefficient indicates that the electrode is more selective for the target ion and less responsive to interfering ions.

How is the selectivity coefficient determined experimentally?

The selectivity coefficient is determined by measuring the potential difference between the ion-selective electrode and a comparison electrode in solutions with varying concentrations of the target and interfering ions, and using a specific equation based on the concentrations of these ions.

What does a selectivity coefficient of 0.01 signify in terms of ion response?

A selectivity coefficient of 0.01 means that if both the target ion (A) and an interfering ion (I) are present in equal concentrations, 99% of the response is due to the target ion (A), and only 1% is due to the interfering ion (I).

Why is the selectivity coefficient important when selecting an ion-selective electrode?

The selectivity coefficient is crucial because it helps determine how well the electrode can differentiate between the target ion and interfering ions. A lower selectivity coefficient ensures more accurate and reliable measurements of the target ion in the presence of other ions.

What experimental method is used to determine the selectivity coefficient for an ion-selective electrode?

The experimental method involves preparing several solutions with varying concentrations of the analyte (target ion) and a constant concentration of interfering ions, then measuring the potential difference for each solution. The data is plotted to determine the selectivity coefficient.

How does the concentration of the target ion (A) affect the cell potential in the context of ion-selective electrodes?

When the concentration of the target ion (A) is much higher than the interfering ions, its contribution to the cell potential becomes dominant, resulting in a higher and more variable potential. If the concentration of the target ion is lower, the interference from other ions becomes more significant.

How does the concentration of the interfering ion (I) affect the response of the ion-selective electrode?

When the concentration of the interfering ion (I) is higher than that of the target ion, the potential difference becomes more constant, and the electrode becomes less sensitive to the target ion, which can affect the accuracy of measurements.

What role does the comparison electrode play in the measurement process with an ion-selective electrode?

The comparison electrode serves as a reference during the measurement process, providing a stable reference potential against which the ion-selective electrode's potential is measured to determine the concentration of the target ion.