a) placing an aliquot of {HEAD ~ sample} onto {TAIL ~ a test element comprising}, in overlying relation, 
onto
a ) placing an aliquot of { HEAD ~ sample } onto { TAIL ~ a test element comprising } , in overlying relation ,
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH