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