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