Module 10: Osmometry Flashcards
When a solute is dissolved in a solvent, osmotic pressure is:
Increased
When a solute is dissolved in a solvent, vapor pressure is:
Decreased
When a solute is dissolved in a solvent, boiling point is:
Increased
When a solute is dissolved in a solvent, freezing point is:
Decreased
Colligative properties
Directly related to the total number of solute particles
The total number of individual solute particles determines:
Total osmotic pressure of the solution
Thermister
Temperature sensor
Constant current applied
Change in temperature produces a change in voltage proportional to the resistance change of the thermistor
Osmometry instrument/operator errors
Prefreeze
Incorrect sample volume
Cleaned with alcohol and not sufficiently rinsed (false increase)
Sample carryover due to improper cleaning between
Osmometry sample errors
Plasma used instead of serum (heparinized plasma OK)
Turbid samples - centrifuge to prevent prefreeze
Two types of solutes that determine plasma osmotic pressure with examples
Crystalloids - small electrolyte and non electrolyte particles
Colloids - large particles eg. proteins
What is the effect of freezing point of dissolving 1 mole of non dissociated solute in 1 kg of water?
Decreased by 1.86 degrees C
Steps in freezing point depression measurement
Sample cooled below its freezing point (supercooled)
Stirring rod is pulsed to induce crystal formation and freezing
Heat of fusion released by crystal formation raises temperature to equilibrium temperature at which both freezing and thawing take place
Equilibrium temperature measured as freezing point depression and compared to standards
Serum osmolality reference range
280-300 mOsm/kg
Normal random urine osmolality reference range
300-900 mOsm/kg
Osmolal gap reference range
=10 mOsm/kg
