For example, a disulfide bond is not reduced at {HEAD ~ the S—S bond} but is displaced to yield {TAIL ~ an R—S—S fragment ion} 
For example , a disulfide bond is not reduced at { HEAD ~ the S — S bond } but is displaced to yield { TAIL ~ an R — S — S fragment ion }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL