Glossary of instrumentationfinal

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What is elctrochemistry?
the measureent of the movement of electrons in an electrolytic solution
What are 4 necessary components for electrochemistry?
1. an intact pathway
2. moving electrons
3. a potential dffnce between 2 points
4. a measuring device
what is the measuring device in electrochemistry?
an electrode
What does an electrochemistry device measure?
a change in voltage and or current.
What is EMF and what does it depend on?
Voltage; depends on reactant and product concentrations.
what predicts the output of an electrochemical cell?
the nernst equation.
What gas law is important for the electrochemical cell?
Ficke's law:
Vol of gas = area of membrane/thickness x D x Pressure difference
What is polarography and what are 2 other names for it?
-Voltamitry; Polarogram.
A dual measurement of I and V using a Clarke type electrode.
What is polarography used for measuring, and what electrode?
Measures PO2 using the Clarke electrode.
Explain the principle of the clark-type electrode:
see paper
What are the 5 parts of a clark type electrode?
1. Platinum cathode
2. Ag Agcl anode (reference)
3. Electrolyte reservoir of buffered phosphate soln
4. Semi-permeable membrane O2
5. Temp controlld module 37'C
What is the clnical application of the Clarke type electrode?
Measuring Respiration
What 4 factors affect accuracy in the clarke electrode?
1. Calibration
2. Sensitivity
3. Temperature
4. Sample procurement
How is the clarke electrode calibrated?
With gas; this has different MATRIX than blood, so there's a 1-2% bias.
What decreases the sensitivity of electrochemical measurement?
A Clogged membrane from protein in blood.
Why is temperature so closely regulated on the BGE?
because there is a 6-7% change in PO2 from a body for every degree difference from body temp.
How does the sample need to be procured in order for blood gas measurement?
-from the artery and kept anaerobic; bedside.
-cannot use capillary/venous blood.
If there's a delay in transfer of the blood, what should be done?
Keep on ice to prevent O2 consumption.
How is the clark electrode calibrated?
By bubbling Hi gas and Lo gas over it. The Hi gas sets zero, the lo gas sets the high value.
How does the gas used for calibration do so?
It corrects for the vapor pressure of water by using an internal barometer and subtracting 47 mm Hg.
What is potentiometric used for measuring?
Everything except PO2
Explain what potentiometric measurement is.
A voltage measurement in the absence of current flowing. It uses a high resistance meter to negate any I generated.
What are the 3 components of a potentiometric electrode?
-Measuring electrode
-Reference electrode
-Measuring device with high resistance.
What is vital about the reference electrode in a potentiometric electrode?
It has to always given an IDENTICAL, SAME, CONSTANT, STABLE value. Millivolt reading.
What are the 3 clinical applications of the potentiometric electrode?
pH, pCO2, electrolytes - all except the pO2.
What is the measuring electrode routinly used for pH?
a Glass membrane electrode.
What gives the sensitivity and specificity of a glass membrane electrode?
the glass composition - can be made to measure Li, Lanthanum, Cesium, or Sodium silicate.
What are the 3 components of a pH glass electrode?
1. Half cell
2. Buffer
3. pH sensitive glass membrane.
What is the name of the reference electrode used for potentiometric measurements?
Calomel reference
What are 2 types of calomel reference electrodes?

What are the 3 components of a calomel reference electrode?
1. Half cell
2. Ceramic plug
3. Cellulose membrane
How is the reference electrode measurement kept constant?
By having a saturated solution of KCl
What is the porous plug on the sample end for in the calomel reference electrode?
It allows for SOME Cl- ions to go into the patient sample when the oxidation occurs, but no change occurs b/c of the saturated solution.
What is the electrolyte reservoir in the calomel reference again?
SATURATED solution of KCl.
What is the specific name for the pCO2 electrode?
a Severinghaus electrode - a modified pH electrode.
What is contained in the pCO2 electrode?
Measuring electrode: Ag/AgCl2
Reference electrode: Ag/AgCl2
What accuracy factor plays a role in calibrating electrochemical electrodes?
-Because the gas is moving, the temperature can change 4.5% and causes accuracy reduction.
Describe the pH meter again
A meter that has high resistance so that current does not flow. If current did flow, it would prevent measurement of Voltage.
You don't want current to flow in pH measurement; where DO you want it to flow?
In pO2 measurement.
Other than glass, what are 4 other types of ion selective electrodes?
1. Salt replacement - for glass
2. Solid state
3. Liquid ion exchange
4. Enzymatic
What is an example of a liquid ion exchange electrode commonly used? How does it operate briefly?
Electrode for measuring K+
-The ionophore is Valinomycin
-Valinomycin attracts K+ from the patient sample.
What problem is encountered with electrodes only at alkaline pHs?
Sodium Alkaline error - mistaking singly charged ions for H+, falsely elevating the acidity of the solution (falsely decreased pH).
In what 3 situations do you NEVER have alkaline error?
If you're not working with
1. Glass membrane
2. 50% silicate membrane
3. In alkaline pH
Other than measuring pO2, pCO2, and electolytes, what does the IL-BGE measure? How?
Hematocrit. By conductivity.
What's a tonometer?
A device for which you bubble a whole gas sample.. problem is that it expses the tech to bloodborne pathogens.
whats the main source of error in electrochemistry?
protein in the membrane.

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