Lecture 3: Osmometry (Biomedical Techniques)

Biomedical Techniques CLSB-222 Dr. Ahmad Alamri, M.H.S, Ph.D. Assistant professor of clinical laboratory sciences [email protected] Osmometry  Osmosis Osmosis is the diffusion of water molecules from a low concentration solution to high concentration solution, across a semi-permeable...

Biomedical Techniques CLSB-222 Dr. Ahmad Alamri, M.H.S, Ph.D. Assistant professor of clinical laboratory sciences [email protected] Osmometry  Osmosis Osmosis is the diffusion of water molecules from a low concentration solution to high concentration solution, across a semi-permeable membrane. 3  Osmosis Solution A solution is a homogeneous mixture consisting of Solute Solvent. The solute is the substance that is being dissolved, while the solvent is the dissolving medium. 4  Osmosis: Important Process for cell survival Cell survives by balancing water uptake and loss Cell membrane is made of phospholipids and is semi-permeable (Selectively permeable) Control what molecules or ions to pass through the phospholipid bilayer in the cell & what goes out of the cell. Process of osmosis is important as cells can burst if they take on too much water or collapse if they lose too much. Osmotic pressure is the pressure required to stop water from diffusing through a membrane by osmosis. 5  Osmosis An isotonic solution is one that has the same concentration of solutes both inside and outside the cell. A hypertonic solution is one that has a higher solute concentration outside the cell than inside A hypotonic solution is the one that has a higher solute concentration inside the cell than outside. 6  Osmolarity Osmolarity is the number of osmoles of solute per liter of solution Explanation: An osmole is 1 mol of particles that contribute to the osmotic pressure of a solution. For example, NaCl dissociates completely in water to form Na⁺ ions and Cl⁻ ions. Thus, each mole of NaCl becomes two osmoles in solution: 1 mol of Na⁺ and 1 mol of Cl⁻. A solution of 1 mol/L NaCl has an osmolarity of 2 Osmol/L. A solution of 1 mol/L CaCl2 has an osmolarity of 3 Osmol/L (1 mol Ca2+ and 2 mol Cl-). 7  Cells cannot survive if the osmolarity if their surroundings is much different Osmolarity from their own If the osmolarity of the Extracellular fluid (ECF) becomes too low (hypotonic), water will fill the cells. This increases their volume and may lead to their rupture (cytolysis) If the osmolarity of the ECF becomes too high (hypertonic), water will leave the cells. This decreases volume and may lead to their shrinking (crenation 8  Osmolality Osmolality is the number of solute particles in 1 kg of solvent Osmolarities are expressed as milliosmoles per kilogram of water (mOsm/kg H 2O). Higher osmolality means more particles in the solution. Lower osmolality means particles more diluted. Blood osmolality : A normal result is typically 275 to 295 milliosmoles per kilogram. 9 Osmolality Osmolality increases when we are dehydrated and decreases when we have a fluid buildup. Our body has a unique way to control osmolality. Plasma osmolality : determine several conditions like diabetes, dehydration and shock 10  Colligative Properties Depend only on the number of solute particles present not the identity of the solute particle Vapour Pressure Depression Freezing Point Depression Boiling Point Elevation Osmotic Pressure Colligative properties are used for the measurement of the osmolality of solution (when solute is added) Osmometer Used to measure the osmolality in various biological samples, from blood plasma to human tears Measures osmotic concentration on the scale of milliosmoles (mOsm) per unit of weight (mOsm/kg) 13  Type of Osmometers Freezing Point Vapour Pressure Membrane Depression Osmometer Osmometers Osmometer measure Measure vapor Measure the freezing point pressure of the osmotic pressure depression solution of a solution separated by a semi-permeable membrane 14 Freezing Point Depression Osmometer Principle : Based on the colligative property of freezing point depression. If concentration of the solute is increased, it will lower its freezing point of solution relative to pure solvent e.g., water freezes at 0 °C , If we dissolve 10gm of NaCl to 10 ml of water , the freezing point go down to -5.9c Most used method for measuring the osmolality of serum or urine in clinical laboratory. 15  Freezing Point Depression Osmometer: Process During this process, the solution is supercooled below 0 °C At a certain temperature, the freezing process is initiated by a rotation of the stirring wire. The formation of ice crystals causes the release of thermal energy, thus rising the temperature of the sample. After equilibrium is reached, melting and thawing of ice crystals are balanced and the sample’s temperature stays constant. This marks the real freezing point of the sample. 16  Vapor Pressure Osmometer Determine the concentration of osmotically active particles that reduce vapor pressure of solution Principle  At a given temperature the vapor pressure of a solution is less than that of the pure solvent.  The vapor pressure osmometer operates on the principle of differential vapor pressure between a pure solvent and a solution 17 Vapor Pressure Osmometer Application: Drawback: Monitoring diuretic Volatile gases if therapy present will increase Quantitation: Sodium the vapor pressure of in isotonic solutions solvent) Studying colligative Hence not properties of recommended for parenteral solution clinical laboratory 18