Signal suppression of lower abundance proteins by high abundance proteins presents {HEAD ~ a significant challenge} to {TAIL ~ SELDI mass spectrometry} 
to
Signal suppression of lower abundance proteins by high abundance proteins presents { HEAD ~ a significant challenge } to { TAIL ~ SELDI mass spectrometry }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL