Abstract: Accurate mass measurements of 20 drugs were conducted using MassWorks software on a TSQ Quantum Ultra mass spectrometer. All Q1 scan mass spectral data were collected in profile mode with full width at half-maximum (FWHM) set at 0.7 Da. The mass errors of all 20 drugs (molecular weight between 135 and 810) were within the range from -22.4×10^-6 to 36.1×10^-6, among them 90% of the drugs achieved a mass accuracy better than 10×10^-6. The new method can provide accurate mass measurements on unit mass resolution mass spectrometers.