Final answer:
EDTA is commonly used in blood collection tubes to prevent clotting and preserve cells by binding calcium ions, which are essential for coagulation. Potassium oxalate and lithium heparin are also used as anticoagulants but for different specific purposes in sample preparation.
Step-by-step explanation:
The substance used in blood collection tubes to prevent clots and preserve cells is often an anticoagulant that can chelate calcium ions, removing them from the blood sample and thus preventing coagulation. Substances such as citrates, oxalates, and ethylenediaminetetraacetic acid (EDTA) are commonly used for this purpose. In particular, EDTA is a strong chelating agent and is frequently used in blood collection tubes to preserve blood cells and plasma by binding calcium ions essential for the coagulation process.
While lithium heparin is used as an anticoagulant, its primary purpose is for preparing plasma samples rather than specifically preserving cells. Potassium oxalate also acts as an anticoagulant by precipitating calcium ions as calcium oxalate. It is necessary in cases where a complete removal of calcium is required to halt the coagulation cascade.