This application describes an antibody that specifically binds to a synthetic oligomer (e.g., an oligonucleotide or oligopeptide) having a organic protecting group covalently bound thereto, which antibody does not bind to that synthetic oligomer when the organic protecting group is not covalently bound thereto. Methods of making and using such antibodies are also disclosed, along with cells for making such antibodies and articles carrying immobilized oligomers that can be used in assay procedures with such antibodies.