A fluid sample is brought into {HEAD ~ contact} with {TAIL ~ a pair} of spaced apart electrodes and a voltage is applied across the electrodes 
with
A fluid sample is brought into { HEAD ~ contact } with { TAIL ~ a pair } of spaced apart electrodes and a voltage is applied across the electrodes
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH