Product Description EDTA anticoagulant tube purple cap, ethylenediamine tetraacetic acid (EDTA, molecular weight 292), and its salt are amino polycarboxylic acids that can effectively chelate calcium ions in blood samples. Cheating calcium or removing the calcium reaction site will block and terminate the endogenous or exogenous coagulation process to prevent the coagulation of blood... https://www.edtatube.com/product/10ml-edta-tube-with-purple-top/