The applied field comprises {HEAD ~ a first, external magnetic gradient} which moves {TAIL ~ magnetically responsive particles} to a region of a collection vessel 
moves
The applied field comprises { HEAD ~ a first , external magnetic gradient } which moves { TAIL ~ magnetically responsive particles } to a region of a collection vessel
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH