Biochemical instrumental analysis - 6 Dr. Maha Al-Sedik 2015 CLS 332

Osmosis: If two aqueous solutions with different concentrations of particles are separated from each other by a semipermeable membrane, then water will move across the membrane from the solution with the lower concentration to the solution with the higher concentration.

Factors affecting osmosis:  The difference in the concentration of the particles.  The nature of permeability of the membrane.

Osmotic pressure : The pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane. It is also defined as the minimum pressure needed to nullify osmosis.

Clinical importance of osmotic pressure: It is an important factor affecting cells.  Hypertonicity is the presence of a hypertonic solution that causes cells to shrink.  Hypotonicity is the presence of a hypotonic solution that causes cells to swell.  Isotonicity is the presence of a solution that produces no change in cell volume.

Osmolarity and osmolality: Osmolarity is a measure of the number of particles in one liter of solution. Osmolality is a measure of the number of particles in one Kg of solution. e.g., 1 mole of NaCl  2 osmoles … NaCl (1 for Na + 1 for Cl).

What is the molarity of NaCl, HCL and CuCl 2 ? NaCL osmoles HCL osmoles CuCL Osmoles Think with me

 Molarity = one mole of substance in a liter total volume (total volume solution = 1000 ml).  Molality = one mole of substance in a kilogram total wt (total weight solution = 1000 grams). What is the difference between osmolarity and osmolality?

When we consider osmolarity is the same as osmolality?

If the solvent is water → osmolarity means osmolality One liter of water = One Kg water SO

1 mole of NaCl would weigh grams molecular weights: Na = 23, Cl = 35 1 mole of HCL would weight grams molecular weights: H = 1, Cl = 35 Think with me

1 mole of substance is its gram molecular weight 1 mole of NaCl would weight 58 grams ( ). 1 mole of HCl would weight 36 grams.

How many grams of NaCl I have to put to prepare normal saline = 0.9 molar solution NaCl molecular weights: Na = 23, Cl = 35. Think with me

I need 58 gm of NaCl is needed to prepare a molar solution, so, how many grams I need to prepare 0.9 molar solution ??? X 58 ??? = = 52.2 gm 100

What will happen if a solute is dissolved in a solvent The following properties of the solvent change:  Osmotic pressure increases.  Vapor pressure decreases.  Boiling point increases.  Freezing point decreases. COLLIGATIVeCOLLIGATIVe

 These are known as colligative properties and are all related to the total number of solute particles per mass of solvent, i.e. the osmolality.  Any of the four colligative properties could be used as a basis for the measurement of concentration of the substances.  The most commonly used method in the case of physiological fluids is freezing point depression.

For example, the freezing point of salt water is lower than that of pure water, due to the presence of the salt dissolved in the water. To a good approximation, it does not matter whether the salt dissolved in water is sodium chloride or potassium nitrate; if the molar amounts of solute are the same and the number of ions are the same, the freezing points will be the same.

Principle:  The presence of a solute lowers the freezing point of a solution.  The decrease in the freezing point will be directly proportional to concentration of the substance. For example: pure water freezes at 0°C; if one dissolves 10 grams of sodium chloride in 100 ml of water, the freezing point goes down to −5.9°C. Freezing Point Osmometer

 Super cooled the sample by bath containing an antifreeze solution that is maintained at about -5° C.  Inside the sample there will be thermometer to measure FP.  The freezing point is determined and osmolality is shown on the digital display.  The measurement value is stored in the memory.

Vapor Pressure osmometry

Principle:  The presence of a solute lowers the vapor pressure of a solution at the same temperature and pressure.  The decrease in vapor pressure is directly proportional to the concentration of substance.

Vapor Pressure and Boiling Vapor Pressure: the pressure exerted by a vapor in equilibrium with its liquid state. Liquid molecules at the surface escape into the gas phase. These gas particles create pressure above the liquid in a closed container.

Vapor Pressure increases with increasing temperature. 20 o C 80 o C  As temperature increases, the amount of vapor generated by a liquid in a closed container increases.