Patent ID: 8211636

Claim:
A method comprising (a) selecting a nucleic acid target comprising at least one loop, bulge, kink, stem structure, or mismatched base pair, wherein the mass of the nucleic acid target is known; (b) forming a first complex comprising a standard binding compound and the nucleic acid target; (c) combining the first complex with a mixture of two or more test ligands under competitive binding conditions such that a mixture comprising at least one second complex is formed, wherein the mass of each of the test ligands is known; (d) subjecting the mixture comprising at least one second complex to mass spectrometry; (e) collecting mass spectral data for the mixture comprising at least one second complex, wherein the mass spectral data comprises an ion abundance and a mass to charge ratio for an ion of the at least one second complex; (f) calculating the mass of the at least one second complex; and (g) determining the identity of one or more of the test ligands bound on the at least one second complex, based on the mass of each of the test ligands and the mass of the at least one second complex.