360 - Osmometry Flashcards

1
Q

define molarity

A

the concentration of a solution expressed as the number of moles of solute per litre of solvent

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2
Q

define molality

A

the concentration of a solution expressed as the number of moles of solute per kilogram of water or solvent

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3
Q

What is an osmole?

A

the amount of a substance that dissociates to produce 1 mole of particles in a solution

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4
Q

the concentration of a solution expressed as the number of osmoles of particles per litre of water

A

Osmolarity

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5
Q

the concentration of a solution expressed as the number of osmoles of particles per kilogram
of water

A

Osmolality

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6
Q

a phenomenon in which the addition of solutes molecules to a solution lowers
the temperature at which a solution will freeze

A

Freezing Point Depression

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7
Q

Osmolality is measured in the clinical laboratory to assess several conditions such as….

A

renal function
ingestion of toxins

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8
Q

the amount of solute that dissociates to produce 1 mole of particles in a solution with each particle in a
solution contributing equally to the total osmolality of a solution

A

an osmole

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9
Q

a property which is influenced by the number of particles in the
solution

A

colligative property

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10
Q

define the osmotic pressure of a solution

A

it is the hydrostatic pressure caused by a difference in the
amounts of solutes between solutions that are separated by a semi-permeable membrane

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11
Q

The four colligative properties

A

increase in: osmotic pressure and boiling pt [directly proportional]

decrease in: vapour pressure, freezing pt

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12
Q

the measurement
of a solution’s tendency to move from a liquid to a gas state as temperature rises

A

vapour pressure

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13
Q

the temperature at
which the solution’s vapour pressure is equal to the pressure of the gas above it

A

boiling pt

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14
Q

the temperature at which the solution changes from a liquid into a solid

A

freezing pt

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15
Q

The freezing point of a solution
decreases _.__°C for each osmole of particles/kg of solution.

A

1.86

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16
Q

how is vapour pressure measured?

A

it’s measured indirectly by measuring the dew point of a solution; the temperature at which condensation of water from a vapour state occurs

17
Q

T or F. Vapour pressure measurements do not measure volatile substances

A

T! and the method is sensitive to changes in air temperature

18
Q

Why is measuring boiling pt not suitable for biological samples

A

bc endogenous proteins are denatured and alter the nature of the sample

19
Q

the four main components of freezing pt osmometers

A

cooling mechanism, a thermistor to measure the temperature, a mechanism to initiate freezing and a readout display

20
Q

describe the processes of freezing pt depression osmometry

A
  • 20 uL into cooling chamber
  • temp decreased below expected freezing pt; approx. -7C (SUPERCOOLING)
  • physical shock; vigorous stirring = ice crystal formation (SEEDING)
  • sample solidifies and releases heat
  • thermistor detects a decrease in resistance as the temperature
    increases
  • temp increases until plateau = true freezing pt of sample
  • = osmolality (mOsm/kg)
21
Q

how is a freezing pt osmometer calibrated?

A
  • sodium chloride solutions of known concentrations to ensure accurate results
  • calibration performed at same temp as used for patient samples
  • additional calibration of injection syringes and pump systems may also be required
22
Q

these sources of error can increase the variation in results

A
  • pipetting different sample volumes
  • air bubbles in samples
  • preparing samples too early = evaporation
23
Q

presence of particulate matter in a sample may initiate …

A

seeding and adversely affect osmolality results

24
Q

T or F. Osmolality measurements are not affected by lipemia or hemolysis

25
major osmotically active components of serum
sodium chloride bicarbonate glucose urea
26
what is osmolality used to evaluate?
- the ability of the kidney to concentrate urine - monitor kidney disease - monitor fluid and electrolytes therapy - aid in the diagnosis of hypernatremia and hyponatremia - to evaluate the secretion of and renal response to anti-diuretic hormone
27
define osmolal gap:
the difference between the measured plasma or serum osmolality and the calculated osmolality - normally close to 0 - increases in presence of unmeasured molecules or ions - can be used to screen for exogenous substances: ethanol, methanol, ethylene glycol, isopropanol -may also be increased in the presence of ketones or mannitol
28
decreased osmolal gaps are usually the result of this
lab error
29
Unaccounted osmolal gap values above ___ mmol/kg are flagged as High
10 mmol/kg
30
Causes of an elevated unaccounted osmolal gap
diabetic, alcoholic and starvation ketoacidosis, sepsis, toxic alcohol poisoning and a variety of drugs (e.g. isoniazid, mannitol, propylene glycol, contrast dyes, glycerol)