Electroanalytical chemistry
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Chapter 3. Electroanalytical Chemistry. Best seen broken into four categories. Part 1: Ion Selective Electrodes. Part 2: Amperometric Sensors. Part 3: Step Voltammetry. Part 4: Cyclic Voltammetry. (1) Ion Selective Electrodes.

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Electroanalytical Chemistry

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Electroanalytical chemistry

Chapter 3

Electroanalytical Chemistry


Best seen broken into four categories

Best seen broken into four categories

Part 1:

Ion Selective Electrodes

Part 2:

Amperometric Sensors

Part 3:

Step Voltammetry

Part 4:

Cyclic Voltammetry


1 ion selective electrodes

(1) Ion Selective Electrodes

Electroanalytical devices that measure concentration of a selected ion in a sample by virtue of electric potential difference due to concentration of that ion.

There are many applications (cba to list)

And many analytical advantages! (again cba to list)

Naming is Trivial!!!!!!

ISE to detect F-Fluoride selective electrodes

ISE to detect Ca2+Calcium selective electrodes etc

Note ISE to detect H+pH electrodes


General outline of an ise

General Outline of an ISE

Morgan. T. 2014, Summary of Electrodes, www.che-revision.weebly.com


The different types of ise

The different types of ISE

Summary of Electrodes at CHE-Revision

Highly Recommended!

Documentary on The Crazy Nastyass Honey Badger

Not Recommended!

May result in procrastination

Click button below to visit the ‘Summary of Electrodes’ page on the revision website. Just re-open the presentation afterwards.

If you are confident enough on this topic (AS IF!!!!!) then alternatively continue through the presentation.


How do ises work nernst equation

How do ISEs Work?Nernst Equation

RGas Constant 8.314 J K-1 mol-1

TAbsolute Temperature K

jCharge on ion being detected

FFaraday Constant 96484 C mol-1

When T = Room Temperature (25°C)


Prediction of nernstian responses

Prediction of Nernstian Responses

For aUni-Cation (ie Na+) at 25’C

For a Di-Anion (ie O2-) at 25’C

EISE

EISE

Gradient = 0.059 V

per log10[X]

Gradient = - (0.059/2) V per log10[X]

Log10[X]

Log10[X]


Example questions

Example Questions

A Ca2+ selective electrode reads an EISE value of 0.473 V in a sample containing 3 x 10-3 M Ca2+ at 25’C. Calculate Cellconstant for this electrode.


Example questions1

Example Questions

Calculate EISE for this

electrode in a sample containing 30 x 10-2 M Ca2+ at 25’C.

Note Cellconstant was calculated to be 0.547 V


Example questions2

Example Questions

What is the Ca2+ concentration when EISE reads 0.347 V at 25’C?

Note Cellconstant was calculated to be 0.547 V


What do you need to know

What do you need to know

Can you describe what an ISE is to someone who knows nothing about chemistry? How do you name them?

Can you illustrate a simple design of an ISE?

Can you recall all the different types of ISE with illustrations?

Do you remember and can you use the Nernst Equation?

Can you predict graphical responses of Nernst relationships?

Best go back and revise it again then!


Best seen broken into four categories1

Best seen broken into four categories

Part 1:

Ion Selective Electrodes

Part 2:

Amperometric Sensors

Part 3:

Step Voltammetry

Part 4:

Cyclic Voltammetry


2 amperometric sensors

(2) Amperometric Sensors

Electroanalytical devices that measure the concentration of a selected redox active species in a sample. Concentration determined by virtue of flow of electrical current due to oxidation or reduction.

There are many applications of Amperometric Sensors

Dissolved Oxygen

Glucose

Neurotransmitters

They also have many analytical advantages (same as ISE)

BUT MORE EFFECTED BY SURFACE DETERMINATION (revisit later)


Oxidation and reduction

Oxidation and Reduction

Really?

If you want me to go through this, I don’t even think you should be here :L But ill explain briefly:

Remember GCSE: OILRIG

Lets try some questions!

Is species A reduced or oxidised?

A- + B  A + B-

Its OXIDISED AS ITS LOST AN ELECTRON!

That is it!


Oxidation reduction in solution and at electrode surface

Oxidation / Reduction in Solution and at electrode surface

Can you spot the mistake?

Solution

No net direction of electron transfer

Electrode

All electron transfer in same direction to give a flow of electrical current!

TADA!


The different types of amperometric sensors

The different types of Amperometric Sensors

Summary of Electrodes at CHE-Revision

Highly Recommended!

Documentary on The Crazy Nastyass Honey Badger

Not Recommended!

May result in procrastination

Click button below to visit the ‘Summary of Electrodes’ page on the revision website. Just re-open the presentation afterwards.

If you are confident enough on this topic (AS IF!!!!!) then alternatively continue through the presentation.


Direction of current

Direction of Current


Equation on amperometrics

Equation on Amperometrics

RGas Constant

TTemperature

NNumber of electrons transferred in half cell

FFaraday Constant

[O]/[R]Concentration of Oxidised and Reduced Species


Questions on amperometrics

Questions on Amperometrics

Dopamine is oxidised in a

two-electron process that has a reduction

potential E0 of 0.2 V vs SHE. Which of the potentials below would be best applied to a sample to induce dopamine oxidation at 25’C?


Questions on amperometrics1

Questions on Amperometrics

Calculate the percentage of dopamine at the electrode surface when it has equilibrated at the potential given to your answer above.


Relationships between current and concentration

Relationships between Current and Concentration

Current is proportional to Area of Electrode

Concentration is proportional to Current

|i| Current Magnitude

AArea of electrode

khetHeterogeneous electron transfer rate consatant


Questions on amperometrics2

Questions on Amperometrics

A clark electrode with a sensor electrode area of 0.2 cm2 measured a current magnitude of 10 x 10-8Amps in a stirred solution containing 10x10-6 M dissolved oxygen.

What is the dissolved oxygen concentration in a stirred solution for which the same clark electrode measured a current magnitude of 3 x 10-8 Amps?


Questions on amperometrics3

Questions on Amperometrics

A clark electrode with a sensor

electrode area of 0.2 cm2 measured a current magnitude of 10 x 10-8Amps in a stirred solution containing 10x10-6 M dissolved oxygen.

What current magnitude is predicted to be measured in a stirred solution containing 10x10-6 M dissolved oxygen with a clark electrode having sensor electrode area of 0.05 cm2?


Questions on amperometrics4

Questions on Amperometrics

A clark electrode with a sensor

electrode area of 0.2 cm2 measured a current magnitude of 10 x 10-8Amps in a stirred solution containing 10x10-6 M dissolved oxygen.

What is the sign (positive or negative) of the current measured during the detection of oxygen with a clark electrode?


What do you need to know1

What do you need to know?

Can you describe an amperometric sensor to someone who doesn’t do chemistry?

Do you know the principals of oxidation and reduction?

Do you know the direction of current and their signs?

Can you illustrate the basic design of an amperometric sensor and recall different types?

Can you recall and use equations of relationships between sensor response and concentrations?

Best go back and revise it again then!


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