Fractionation of a sample reduces {HEAD ~ the complexity} of {TAIL ~ the constituents} of each fraction 
Fractionation of a sample reduces { HEAD ~ the complexity } of { TAIL ~ the constituents } of each fraction
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH