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