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One-base substitution has been detected on the polymerase chain reaction (PCR) products amplified from human mutated DNA for the first time by using mass spectrometry. PCR fragments of 52 base pairs were produced on a collagen gene of an osterogenesis imperfecta patient's heterozygous DNAs. The products were digested with EcoRI restriction enzyme to liberate 3'-end adducts and purified by phenol + chloroform extraction, ammonium acetate addition and ethanol precipitation to remove sodium ions from the phosphoric acid backbone of the DNAs. Purified products were examined using an electrospray ionization mass spectrometer. Mass spectra showed four groups of fragment peaks with the expected molecular masses, which originate from the sense and antisense strands of the heterozygous DNAs.
