Final answer:
Substances like EDTA or potassium oxalate are used to remove Ca2+ from donated blood to prevent clotting. Potassium oxalate works by forming an insoluble precipitate with calcium, eliminating its potential to induce coagulation.
Step-by-step explanation:
To prevent clots in donated blood, a substance that removes Ca2+, such as EDTA or potassium oxalate, may be added to the blood. Removing calcium ions from the blood is essential for stopping the blood coagulation process because calcium activates the conversion of prothrombin into thrombin, which then contributes to the formation of a blood clot.
When looking at a specific example, if a 10 mL blood sample that is 55% serum by volume is to be treated, we must calculate the mass of potassium oxalate required to reduce the concentration of Ca2+ to 1% of its original value in the serum to prevent clotting. This is critical since the presence of calcium is what allows the coagulation cascade to proceed.