Families of compositions are provided as labels, referred to as eTag reporters for attaching to polymeric compounds and assaying based on release of the eTag reporters from the polymeric compound and separation and detection. For oligonucleotides, the eTag reporters are synthesized at the end of the oligonucleotide by using phosphite or phosphate chemistry, whereby mass-modifying regions, charge-modifying regions and detectable regions are added sequentially to produce the eTag labeled reporters. By using small building blocks and varying their combination large numbers of different eTag reporters can be readily produced attached to a binding compound specific for the target compound of interest for identification. Protocols are used that release the eTag reporter when the target compound is present in the sample.