Analytical Electrodes Flashcards
What must the analyte be in order to use electrodes?
Must be electroactive (oxidative or reductive)
Oxidation occurs at the ______. Reduction occurs at the ______.
Oxidation occurs at the anode. Reduction occurs at the cathode.
What is the standard cell potential equal to?
Eo = Ered + Eox
Which equation relates concentration to potential?
Nernst Equation
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?
[Zn]
E vs. log(Zn)
Potentiometry measures….?
Amperometry measures….?
Coulometry measures…..?
What are these examples of?
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
What is the Calomel Electrode and what does it do? What is the reaction that goes on?
It is a reference electrode that applies constant potential
Hg2Cl2 +2e → 2Hg + 2Cl-
What is different about the biocatalytic electrode?
It contains an enzyme layer that convert substrates to ionic species
What are main differences between reflectance and electrochemical glucose monitors?
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
What is the difference between 2 vs 3 electrode glucometers? (other than the number of electrodes)
2 electrodes
- Has indicator and reference electrode
3 electrodes
- Indicator, reference, and background correction electrode
Which electrode in the 3 electrode system has no glucose oxidase?
Background correction electrode
Why does using coulometry better than amperometry?
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
Why are smaller sample sizes better?
Allows for alternate sites (other than pricking your finger)
Which glucometers are glucose dehydrogenases used in? Osmium as mediators?
Coulometric glucometers for both
What are some things to keep in mind when handling reflectance monitors? Coulometric and amperometric?
Reflectance - must clean before each use
Coulometric and amperometric - don’t touch contacts before use
What is the Glucowatch? How does it work? What must you do before you use the watch?
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
What is the Medtronic Minimed? Which population it is used for? What modes are there?
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
How does the Medtronic Minimed work?
Pulls glucose in the sensor and glucose oxidase processes and eventually spits out an electron to which a detector measures this
