This construction also allows the use of filters to remove particulates before {HEAD ~ the sample} reaches {TAIL ~ the chromatographic medium} 
reaches
This construction also allows the use of filters to remove particulates before { HEAD ~ the sample } reaches { TAIL ~ the chromatographic medium }
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