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., {HEAD ~ the acyl group} is where {TAIL ~ R1} is a C1 C5 lower alkyl 
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. , { HEAD ~ the acyl group } is where { TAIL ~ R1 } is 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 HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH