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The laboratory value measures the freezing point depression, properly called osmolality while the calculated value is given in units of osmolarity. Even though these values are presented in different units, when there is a small amount of solute compared to total volume of solution, the absolute values of osmolality vs. osmolarity are very close.
The osmol gap is typically calculated with the following formula (all values in mmol/L): = = ([+] + [] + []) In non-SI laboratory units: Calculated osmolality = 2 x [Na mmol/L] + [glucose mg/dL] / 18 + [BUN mg/dL] / 2.8 + [ethanol/3.7] [3] (note: the values 18 and 2.8 convert mg/dL into mmol/L; the molecular weight of ethanol is 46, but empiric data shows that it does not act as an ideal ...
Note: NaCl does not dissolve completely in water at standard temperature and pressure, so the solution will be comprised of Na+ ions, Cl- ions, and some NaCl molecules, with actual osmolality = Na+ concentration x 1.75] Another example is magnesium chloride (MgCl 2), which dissociates into Mg 2+ and 2Cl − ions.
For liquid solutions, the osmotic coefficient is often used to calculate the salt activity coefficient from the solvent activity, or vice versa. For example, freezing point depression measurements, or measurements of deviations from ideality for other colligative properties, allows calculation of the salt activity coefficient through the osmotic coefficient.
For most non-electrolytes dissolved in water, the van 't Hoff factor is essentially 1. For most ionic compounds dissolved in water, the van 't Hoff factor is equal to the number of discrete ions in a formula unit of the substance. This is true for ideal solutions only, as occasionally ion pairing occurs in solution. At a given instant a small ...
Serum sample preparation requires about 30 minutes of waiting time before it can be centrifuged and then analyzed. [23] However, coagulation can be hastened down to a few minutes by adding thrombin or similar agents to the serum sample. [25] Compared to serum, 15–20% larger volume of plasma can be obtained from a blood sample of certain size.
Osmotic pressure is the basis of filtering ("reverse osmosis"), a process commonly used in water purification. The water to be purified is placed in a chamber and put under an amount of pressure greater than the osmotic pressure exerted by the water and the solutes dissolved in it.
Oncotic pressure values are approximately 290 mOsm per kg of water, which slightly differs from the osmotic pressure of the blood that has values approximating 300 mOsm /L. [citation needed] These colloidal solutions are typically used to remedy low colloid concentration, such as in hypoalbuminemia, but is also suspected to assist in injuries ...