The study of chemical action of electricity and the production of electricity by chemical reactions. Involves reduction and oxidation.
Initially, the copper is a shiny coper color and the solution (silver nitrate 2%) is clear. In less than one hour, the solution is light blue and the wire is covered with shiny silver needles.
What was reduced and what was oxidized?
Copper was oxidized and became copper ions in the solution (blue color). Silver ions became a silver metal and it was reduced.
Potentiometry
Electrical potential difference between two electrodes in an electrochemical cell is ameasured. The electrical potential difference between two electrodes in an electrochemical cell is measured. We measure potential values relative to a standard or reference electrode.
Amperometry
Constant voltage (potential) is applied, current is measured (rate of flow in amps).
Coulometry- coulometric titration
Current applied (constant); measure time required to reach the end point of a titration. Measure of time is related to concentration.
What is the device that produces an electromotive force measured in voltage?
Electrochemical cell
There are different two electrochemical cells. Name them. What are the concepts behind them?
Galvanic cell - consists of two electrodes connected by an electrolyte solution. A spontaneous current occurs (from a chemical reaction) which produces a potential difference, and the current is measured.
Electrolytic cell - a current is applied from the outside.
Electrolyitc cell is basis for __________ measurement.
D. b and c
Galvanic cell is the basis for ____________ measurement.
C. potentiometric
Nernst Equation is associated with which cell?
C. Galvanic cell
What's the Nernst Equation used for?
Allows us to calculate the potential (voltage) of a galvanic cell for any given concentrations of materials making up the electrodes.
Why do we need Reference Electrodes aka Standard electrode.
With an indicator electrode, we measure the potential values (from our sample) relative to a reference electrode. The reference value will help us find out what's the unknown concentration in the solution. The reference electrode and indicator electrode work together in one system.
This electrode consists of a silver wire coated with silver chloride, with an electrolyte solution of saturated potassium chloride and silver nitrate.
C. Ag/AgCl standard electrode
This electrode uses metalic mercury in direct contact with calomel paste, in a KCl solution.
A. Calomel electrode
What connects the reference electrode and indicator electrode together?
A liquid junction where the electrolyte solution can travel back and forth between the two electrodes. This sets up a junction potential providing an electrical connection between the two electrodes.
If an indicator electrode detects hydrogen ions (creating a potential difference), what might the reference electrode measure?
pH
This is a reference electrode. It is specialized in potentiometric electrodes that use slectively permeable membranes- membranes that only let a single type of ion pass through.
Ion-selective electrodes.
In an ISE, electrical potential due to the activity of ____ is measured.
B. Ions
ISE - Ion selective electrodes (potentiometric measurement)
Glass electrodes
Glass membranes that are selective for specific elements. The glass electrodes are usually made of silicon dioxide and something else.
True or False: Sodium ISEs are also glass electrodes
True
For sodium measurement in sodium electrodes, there can be issues. Direct reading or indirect reading can be an issue in order to retrieve concentration reading. What's does this mean?
Direct - sample not diulted.
Indirect - sample is heavily diluted; elevated proteins/lipids can skew sodium test results giving an artificially lower result.
Indirect reading is so common that people who do direct readings will have to recalibrate in relation to indirect reading results.
Solid State Electrodes (ISE)
A crystal of "something" that can react or be sensetive to the ion we're looking for.
An example are silver chlorde membrane electrodes used for measuring sweat chlorde directly on the skin surface.
Liquid ion exchange electrones (ISE)
It is a membrane that is an inert solvent, and it has ion selective carrier substances dissolved in it.
Valinomycin (antibiotic) is a liquid ion exchange electrode (ISE). What kind of ions is it looking for discussed in class?
B. Potassium
Which is not an Ion-selective electrode.
a. Glass Electrode
b. Solid State Electrode
c. Liquid Ion Exchange Electrode
e. Enzyme Electrode
They all are Ion-selective electrode.
This ISE electrode can measure analytes like glucose and BUN.
a. Glass Electrode
b. Solid State Electrode
c. Liquid Ion Exchange Electrode
e. Enzyme Electrode
e. Enzyme electrode
What's the popular ISE method that measures BUN (blood urea nitrogen) concentration.
Urea ISE method
PO2 measurement is _____________.
B. Amperometric
The current flow is proportional to the amount of oxygen present at the membrane.
What's a common issue with Amperometric measurement when measuring partial pressure oxygen?
Proteins covering the membrane. This can cause the reading to be inaccurate.
The best instrument used to measure chloride is...
chloridometer, does only coulometric chloride titrations.
What stops the titration of chloride in coulometry.
When all chloride ions are removed from solution, an excess of silver ions is detected by sensor and the titration is stopped. The amount of time required to remove all chloride ions is directly proportional to concentration. The chloride is a variable while the silver is constant.
Chloridometer - Three Unique Components
Electrode assembly - silver electrode actually has a spool of silver wire as the anode.
The sample vial is placed on a platform andholds the acid reagent and sample, in contact with the electrode assembly.
A timer- since the amount of time to remove all chloride ions is directly proportional to concentration.
Blood gas instruments tests whole blood for three components. What are they.
pH - potentiometry
PCO2 - potentiometry
PO2 - amporometry
pH electrode is calibrated with ______.
B. phosphate buffer
PO2 and PCO2 testing is calibrated with _________.
D. gas mixture
All of the following are sources of pre-analytical error in blood gas measurements except for...
D. none of the above
Co-oximetry
Looking for different kinds of hemoglobin in blood sample.
