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46 Cards in this Set
- Front
- Back
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What is elctrochemistry?
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the measureent of the movement of electrons in an electrolytic solution
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What are 4 necessary components for electrochemistry?
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1. an intact pathway
2. moving electrons 3. a potential dffnce between 2 points 4. a measuring device |
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what is the measuring device in electrochemistry?
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an electrode
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What does an electrochemistry device measure?
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a change in voltage and or current.
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What is EMF and what does it depend on?
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Voltage; depends on reactant and product concentrations.
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what predicts the output of an electrochemical cell?
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the nernst equation.
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What gas law is important for the electrochemical cell?
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Ficke's law:
Vol of gas = area of membrane/thickness x D x Pressure difference |
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What is polarography and what are 2 other names for it?
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-Voltamitry; Polarogram.
A dual measurement of I and V using a Clarke type electrode. |
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What is polarography used for measuring, and what electrode?
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Measures PO2 using the Clarke electrode.
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Explain the principle of the clark-type electrode:
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see paper
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What are the 5 parts of a clark type electrode?
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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 |
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What is the clnical application of the Clarke type electrode?
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Measuring Respiration
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What 4 factors affect accuracy in the clarke electrode?
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1. Calibration
2. Sensitivity 3. Temperature 4. Sample procurement |
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How is the clarke electrode calibrated?
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With gas; this has different MATRIX than blood, so there's a 1-2% bias.
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What decreases the sensitivity of electrochemical measurement?
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A Clogged membrane from protein in blood.
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Why is temperature so closely regulated on the BGE?
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because there is a 6-7% change in PO2 from a body for every degree difference from body temp.
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How does the sample need to be procured in order for blood gas measurement?
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-from the artery and kept anaerobic; bedside.
-cannot use capillary/venous blood. |
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If there's a delay in transfer of the blood, what should be done?
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Keep on ice to prevent O2 consumption.
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How is the clark electrode calibrated?
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By bubbling Hi gas and Lo gas over it. The Hi gas sets zero, the lo gas sets the high value.
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How does the gas used for calibration do so?
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It corrects for the vapor pressure of water by using an internal barometer and subtracting 47 mm Hg.
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What is potentiometric used for measuring?
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Everything except PO2
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Explain what potentiometric measurement is.
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A voltage measurement in the absence of current flowing. It uses a high resistance meter to negate any I generated.
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What are the 3 components of a potentiometric electrode?
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-Measuring electrode
-Reference electrode -Measuring device with high resistance. |
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What is vital about the reference electrode in a potentiometric electrode?
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It has to always given an IDENTICAL, SAME, CONSTANT, STABLE value. Millivolt reading.
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What are the 3 clinical applications of the potentiometric electrode?
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pH, pCO2, electrolytes - all except the pO2.
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What is the measuring electrode routinly used for pH?
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a Glass membrane electrode.
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What gives the sensitivity and specificity of a glass membrane electrode?
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the glass composition - can be made to measure Li, Lanthanum, Cesium, or Sodium silicate.
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What are the 3 components of a pH glass electrode?
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1. Half cell
2. Buffer 3. pH sensitive glass membrane. |
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What is the name of the reference electrode used for potentiometric measurements?
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Calomel reference
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What are 2 types of calomel reference electrodes?
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-Ag/AgCl
-Hg2/Hg2Cl2 |
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What are the 3 components of a calomel reference electrode?
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1. Half cell
2. Ceramic plug 3. Cellulose membrane |
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How is the reference electrode measurement kept constant?
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By having a saturated solution of KCl
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What is the porous plug on the sample end for in the calomel reference electrode?
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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.
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What is the electrolyte reservoir in the calomel reference again?
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SATURATED solution of KCl.
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What is the specific name for the pCO2 electrode?
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a Severinghaus electrode - a modified pH electrode.
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What is contained in the pCO2 electrode?
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Measuring electrode: Ag/AgCl2
Reference electrode: Ag/AgCl2 |
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What accuracy factor plays a role in calibrating electrochemical electrodes?
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-Because the gas is moving, the temperature can change 4.5% and causes accuracy reduction.
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Describe the pH meter again
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A meter that has high resistance so that current does not flow. If current did flow, it would prevent measurement of Voltage.
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You don't want current to flow in pH measurement; where DO you want it to flow?
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In pO2 measurement.
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Other than glass, what are 4 other types of ion selective electrodes?
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1. Salt replacement - for glass
2. Solid state 3. Liquid ion exchange 4. Enzymatic |
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What is an example of a liquid ion exchange electrode commonly used? How does it operate briefly?
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Electrode for measuring K+
-The ionophore is Valinomycin -Valinomycin attracts K+ from the patient sample. |
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What problem is encountered with electrodes only at alkaline pHs?
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Sodium Alkaline error - mistaking singly charged ions for H+, falsely elevating the acidity of the solution (falsely decreased pH).
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In what 3 situations do you NEVER have alkaline error?
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If you're not working with
1. Glass membrane 2. 50% silicate membrane 3. In alkaline pH |
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Other than measuring pO2, pCO2, and electolytes, what does the IL-BGE measure? How?
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Hematocrit. By conductivity.
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What's a tonometer?
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A device for which you bubble a whole gas sample.. problem is that it expses the tech to bloodborne pathogens.
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whats the main source of error in electrochemistry?
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protein in the membrane.
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