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
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
-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
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
- 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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