Final answer:
The EDTA tube acts by chelating metal ions, specifically calcium, to prevent blood coagulation during blood sample collection, allowing for stable plasma samples for diagnostic tests.
Step-by-step explanation:
The mode of action for an EDTA tube centers on its ability to chelate metal ions. EDTA, or ethylenediaminetetraacetic acid, is a chelating agent that binds tightly to metal ions, forming a stable hexadentate complex. In medical applications, EDTA tubes are commonly used for blood collection because EDTA effectively prevents coagulation by chelating calcium ions, which are necessary for blood clotting. When EDTA binds to calcium, it removes it from the clotting process, resulting in a stable and unclotted blood sample that can then be centrifuged to obtain plasma for various diagnostic tests.