The present disclosure relates to the determination of analytes in a sample using chromatography. The present disclosure provides methods of separating an analyte from a sample. A mobile phase is flowed through a chromatography column. The mobile phase includes about 0.005% (v/v) to about 0.20% (v/v) difluoroacetic acid and less than about 100 ppb of any individual metal impurity. A sample including the analyte is injected into the mobile phase. The analyte is separated from the sample.