改写下列句子避免与原文出现连续3个单词重复：Whole blood was collected from each subject in tubes with EDTA and centrifuged at 2500 rpm 4°C for 15 min to obtain plasma aliquoted in 250 μL and stored at −80°C

Plasma aliquots of 250 μL were obtained by collecting whole blood from each subject in tubes containing EDTA. The blood was then centrifuged at 2500 rpm, 4°C for 15 min and stored at −80°C.