Final answer:
Capillary Hydrodynamic Fractionation separates bound and unbound drug fractions using capillary hydrostatic pressure (CHP) and blood colloid osmotic pressure (BCOP) to drive substances through or against a semi-permeable membrane based on molecular size.
Step-by-step explanation:
Capillary Hydrodynamic Fractionation is a laboratory technique used to separate bound from unbound drugs in a protein solution. The mechanism by which this separation occurs involves capillary hydrostatic pressure and blood colloid osmotic pressure. During the process, a semi-permeable membrane separates an upper chamber, which holds the drug-protein solution, from a lower chamber. Centrifugation, typically at around 2000 x g, is then used, taking advantage of the larger molecular size of the compound-protein complex, which prevents it from passing through the membrane. This results in separation of the bound and unbound fractions, where the free drug concentration can be measured in the lower chamber, and the total drug concentration before ultrafiltration is assessed.
Within the capillaries, capillary hydrostatic pressure (CHP) is the force that drives fluid out of the capillaries and into the tissues. It begins high as the blood enters the capillary bed from the arterioles (about 35 mm Hg) and decreases towards the venous end (approximately 18 mm Hg). Contrarily, the blood colloidal osmotic pressure (BCOP) remains roughly constant throughout the capillary (around 25 mm Hg) due to the suspended plasma proteins. The interaction of these pressures dictates the net filtration pressure (NFP), which therefore decides how much and in which direction the fluid will be transported between capillaries and tissues.