As a matter of {HEAD ~ course}, cation exchange membranes permit selective permeation of {TAIL ~ cations} alone 
As a matter of { HEAD ~ course } , cation exchange membranes permit selective permeation of { TAIL ~ cations } alone
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH