Electrochem 2

Question 1

Slide 1 calc

Answer 1

Okay

Question 2

What is amperometry

Answer 2

The current (in amps) is measured throughout the oxidation reduction reaction

We measure the current at a specific time mutiple times since the current changes with time

Question 3

In anoerometry what is the current proportional to

Answer 3

Proportional to the analyte concentration

As concentration increases, Amps incresse

Question 4

What does it mean is the current becomes zero

Answer 4

The analyte concentration is zero meaning it fully reacted

Question 5

Give an example of how a amperometry experiment can work

Answer 5

There are two working electrodes in a glucose monitor

The first working electrode is coated in an enzyme glucose oxidase which makes the reaction of glucose with O2 to h2o2 go forward

Then the h202 reacted at the working electrode and the current was measured throughout he reaction to see the amount of h202 in the solution

If current is proportional to h202 then it’s proportional to the glucose since the h202 came from glucose’s

This is how we can tell the amount of glucose

Question 6

Why is a mediator used in the glucose amperometry analysis

Answer 6

The reaction of glucose to h202 depends on the amount of o2 in the environment

So if the o2 is low then the reaction to h202 doesn’t work and it makes it seem like there is no glucose when there actually is

To stop this dependence on o2, you substitute o2 with a mediator

Question 7

What is a mediator

Answer 7

A thing that moves electrons from the analyte to the working electrode

Replaces the thing that the reaction is dependent on

Question 8

In amperometry does all of the spangle need to be consumed to get the graph

Answer 8

No because the current is measured at each time interval, don’t need entire reaction do finish

Also because the current isn’t stochimetricslly related to the analyte (doesn’t need to do a full reaction to get proper values)

Question 9

What are things that effect the measured current in amperometry

Answer 9

The analyte concentration (larger concentration, larger current)

But even if same concentration of ions, the current is diff for each because of

mobility of the ions

E standard vs E of working electrode

Question 10

How do amperometric detectors work for hplc

Answer 10

You hold the working electrode at a specific potential that matches your target analyte that you think will elute

Then you monitor the current as the eluate passes over the electrode

The current will tell you what type of thing passed through and its concentration

Question 11

What is volametry

Answer 11

You’re changing the voltage at the working electrode then measuring the current as the reaction progresses

Question 12

What does the current in volametry depend on

Answer 12

The faradaic contributions

The capacitive contributions

Question 13

What are faradaic contributions to current

Answer 13

current is flowing through the electrode because of electron transfer from a reaction happening at its surface

Question 14

What are capacitive contributions to current in voltametry

Answer 14

because the potentiostat is changing the voltage

The ions in the solution and at the double layer (near the electrode) move and change the current

Question 15

Where would the reactants that are consumed in a reaction be

Answer 15

More of it is far away from the electrode and comes close to the electrode from the bulk of the solution

Question 16

Where would the products that are made in a reaction be

Answer 16

They would be close to the electrode when their concentration is high

Then far away as their concentration decreases and time passes and they diffuse away from the electrode

Question 17

What is the mass transport limit

Answer 17

When the reactant is consumed faster than it can move toward the surface of the electrode

This changes the maximum current that we observe since some didn’t react at the electrode

Question 18

What is a rotating disk electrode

What is it made of

Answer 18

A disk shaped electrode that rotates vary fast

It’s inert so it’s made of pt au or C

Question 19

How does a rotating disk electrode work

Answer 19

It’s rotations stir the solution near the electrode surface

This brings fresh solution to the electrode but not completely

The analyte needs to move last few distance from the electrode by diffusion

Question 20

What is the limiting current of a rotating disk electrode

When does the value of max current change

Answer 20

It’s the maximum current that is observed at an electrode, also called the diffusion limit

If a concentration of analyte increases, limiting current increase

If the rotation of the electrode increases , limiting current increase

Question 21

What is linear scan voltametry

Answer 21

The potential (E) at the working electrode is scanned overtime

This gives a linear graph

When the reaction begins, the current increases on the current vs E (or time) graph and we can see at what E the reaction can start

Question 22

What does the current (I) vs E graph look like with a rotation disk electrode

Answer 22

First around zero straight, then increase at a certain E, then reaches a max (diffusion limit)

The max current is proportional to the concentration of analyte

Question 23

What does the current (I) vs E graph look like with a planar electrode

Answer 23

Reaches a max then goes a bit lower,

Doesn’t stay at the max because there’s still some reactant drifting in toward the electrode

The max current is proportional to the concentration of analyte

Question 24

With a planar electrode what is special

Answer 24

It has no stirring

Eventually all the reactant near the surface of the electrode is used up and more can only come in through diffusion or convection (stirring)

Question 25

In scanning voltametry what is a half wave potential and what does it help with

Answer 25

It’s the (E) potential at the half way point of the curve of current vs E

We use this to IDENTIFY analytes

The max current is related to the concentration of what your analyzing (higher max, higher concentration)

Question 26

In scanning voltametry what is a peak current and what does it help with

Answer 26

It’s a graph of each analytes highest/max current vs its concentration

We use this to QUANTIFY analytes because it’s a calibration curve

Question 27

What is cyclic voltametry

Answer 27

The potential at the working electrode is scanned back and forth over time

Back and forth as in the analyte would be oxidized then reduced back and forth

This can tell us if the reaction is reversible or not

Question 28

What type of electrode is cyclic voltametry done with

Answer 28

Planar/regular electrodes

Question 29

What does the current vs potential graph look like for reversible reactions in cyclic voltametry

Answer 29

The reduction peak is lower happens backwards
The oxidation peak is higher and forwards

The peaks are almost overlapping , looks like a duck

Question 30

What does the graph look like for irreversible reactions in cyclic voltametry

Answer 30

The current peaks are more separated broad and uneven

The top part is reductions (Cathodic peak)

Question 31

For cyclic volametry if you see only the bottom part of the peak what does this mean

Answer 31

This means that only oxidation is happening and the reaction is irreversible

The analyte doesnt get replenished through reduction

Question 32

What are electrochemical biosensors

Answer 32

It’s when Antibodies and aptamers bind to the target molecules and change their redox properties to make them more or less able to do redox

They are sensitive and specific

Question 33

How do electrochemical biosensors work

Answer 33

The aptamers (synthetic dna) bind to the target reactant molecule to bring it closer to the analyte

Since their closer, redox is more easy and the peaks in cyclic voltametry get bigger