The present invention still further provides labeled compounds, of the structure Ar—S—C*D2−xHx—O—R where Ar is an aryl group, C* is a 13C labeled carbon atom, D is a 2H, x is 0 or 1, and R is selected from a C1 C5 lower alkyl group or an acyl group including a C1 C5 lower alkyl group substituent, i.e., the acyl group is where {HEAD ~ R1} is {TAIL ~ a C1 C5 lower alkyl} 
is
The present invention still further provides labeled compounds , of the structure Ar — S — C*D2−xHx — O — R where Ar is an aryl group , C * is a 13C labeled carbon atom , D is a 2H , x is 0 or 1 , and R is selected from a C1 C5 lower alkyl group or an acyl group including a C1 C5 lower alkyl group substituent , i.e. , the acyl group is where { HEAD ~ R1 } is { TAIL ~ a C1 C5 lower alkyl }
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 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 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 HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL