Analytical Electrodes

Question 1

What must the analyte be in order to use electrodes?

Answer 1

Must be electroactive (oxidative or reductive)

Question 2

Oxidation occurs at the ______. Reduction occurs at the ______.

Answer 2

Oxidation occurs at the anode. Reduction occurs at the cathode.

Question 3

What is the standard cell potential equal to?

Answer 3

Eo = Ered + Eox

Question 4

Which equation relates concentration to potential?

Answer 4

Nernst Equation

Question 5

If you are measuring a saturated solution of copper with some amounts of Zn, what does the potential depend on? What can you plot to see this?

Answer 5

[Zn]

E vs. log(Zn)

Question 6

Potentiometry measures….?
Amperometry measures….?
Coulometry measures…..?

What are these examples of?

Answer 6

Potentiometry measures electrical potential under no control
Amperometry measures current under a fixed applied voltage
Coulometry measures total accumulated charge following electrochemical reaction

These are examples of analytical uses for electrochemical cells

Question 7

What is the Calomel Electrode and what does it do? What is the reaction that goes on?

Answer 7

It is a reference electrode that applies constant potential

Hg2Cl2 +2e → 2Hg + 2Cl-

Question 8

What is different about the biocatalytic electrode?

Answer 8

It contains an enzyme layer that convert substrates to ionic species

Question 9

What are main differences between reflectance and electrochemical glucose monitors?

Answer 9

Reflectance

• uses photometry
• needs frequent calibration
• uses dyes
• must clean thoroughly

Electrochemical

• uses voltage to drive reaction
• more sensitive and faster
• has a mediator (has higher reductive properties)

-both use glucose oxidase

Question 10

What is the difference between 2 vs 3 electrode glucometers? (other than the number of electrodes)

Answer 10

2 electrodes
- Has indicator and reference electrode

3 electrodes
- Indicator, reference, and background correction electrode

Question 11

Which electrode in the 3 electrode system has no glucose oxidase?

Answer 11

Background correction electrode

Question 12

Why does using coulometry better than amperometry?

Answer 12

Because accumulated charge you are oxidizing all of the glucose in the sample (compared to amperometry which is just measuring a rate)

• allows for smaller sample sizes
• less temperature flucuations

Question 13

Why are smaller sample sizes better?

Answer 13

Allows for alternate sites (other than pricking your finger)

Question 14

Which glucometers are glucose dehydrogenases used in? Osmium as mediators?

Answer 14

Coulometric glucometers for both

Question 15

What are some things to keep in mind when handling reflectance monitors? Coulometric and amperometric?

Answer 15

Reflectance - must clean before each use

Coulometric and amperometric - don’t touch contacts before use

Question 16

What is the Glucowatch? How does it work? What must you do before you use the watch?

Answer 16

It is a SUPPLEMENT to the finger stick and is a non invasive method of glucose measurement.

Current is applied to skin and glucose is drawn up to skin and measures glucose.

You have to calibrate the watch every 12 hours

Question 17

What is the Medtronic Minimed? Which population it is used for? What modes are there?

Answer 17

It is a glucose sensor that communicates with an insulin pump that gives out insulin when a certain level of glucose is reached.

Open loop - patient looks at a value and gives insulin
Closed loop - automatic dosing

Question 18

How does the Medtronic Minimed work?

Answer 18

Pulls glucose in the sensor and glucose oxidase processes and eventually spits out an electron to which a detector measures this