Glossary of Osmometry
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- What is an Osmometer?
- An instrument for measuring solute particles in a solution
- What properties have to be considered in osmometry?
- Colligative; how each would need to change to incr. osmolality.
- What are the 4 colligative properties? Which concern osmometry?
- 1. Osmotic pressure
2. Vapor pressure - this.
3. Boiling point
4. Freezing point - & this.
- How does Vapor pressure vary with increasing osmolality?
- For every mOsm, Pvap decreases 0.3 mm Hg
- How does Freezing pnt vary with increasing osmolality?
- For every mOsm, freezing pnt decreases 1.86 ' C.
- What IS vapor pressure?
- The pressure needed to prevent molecules from escaping from a liquid.
- What happens to Pvap when you add solute?
- Decreases; need less pressure to keep from evaporating.
- On what principle does an osmometer operate?
- the principle of freezing point depression.
- What is the name of the most common brand of osmometer?
- What are the 5 components of an osmometer?
- 1. Cooling bath
3. Thermister probe
5. Measuring potentiometer
- What's in the cooling bath? How does it work?
- Antifreeze; the patient sample gets lowered into it.
- What 2 things stick into the patient sample?
- -Stirrer to agitate vigorously
- How does a thermistor probe work?
- Its resistance changes with temperature changes, giving a readout that is proportional.
- On what point of the temp versus time curve is the osmolarity reading taken?
- at the plateau region - the heat of fusion, equilibrium temp between thawing and freezing.
- On the osmometer, what is the
- Input = thermistor
Output = Wheatstone bridge
- How do you calibrate the osmometer?
- By first using a standard of 300 mOsm; setting one potentiometer on the wheatstone brdg at 300;
Use 500 mOsm standard and do same w/ other POT.
Use Calibrated pot to set zero;
Measure patient sample, adjust final Pot for value.
- How does the Wescor Vapor pressure osmometer work?
- Same concept as the osmometer, but you replace the graph values of heat of fusion for "Heat of condensation", between liquid and pressure.
- What are 2 problems with osmometry?
- -Sample volume the holder holds 2-3 ml of plasma
-Vat of Antifreeze maintanence.
- What are 3 advantages of Osmometry?
- -Small sample size
-Short time period of measurement.
-Sample is not altered in anyway.
- What is the Dew point?
- The temperature at which vapor in air goes into the liquid phase because of atmospheric pressure.
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