While {HEAD ~ the exclusion} of sodium has received {TAIL ~ the most attention} because of its ubiquitous presence and high mobility, the other alkali metal ions, especially potassium and lithium, are also desirably kept to acceptable levels 
While { HEAD ~ the exclusion } of sodium has received { TAIL ~ the most attention } because of its ubiquitous presence and high mobility , the other alkali metal ions , especially potassium and lithium , are also desirably kept to acceptable levels
OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH