Exact mass measurement of polar organic molecules at low resolution using electrospray ionization and a quadrupole mass spectrometer.

Hitherto, exact mass measurement experiments have usually been performed using high-resolution mass spectrometry. However, under the right circumstances, measurements with comparable accuracy may be made at low resolution. Here we demonstrate the use of a low-resolution single-quadrupole mass spectrometer to accurately mass measure organic samples analyzed by electrospray ionization, using a variety of glycol polymers for internal calibration. Results are presented from 11 samples which yield molecular signals in the m/z range 190-750, including data for positive, negative, and multiply-charged sample and reference ions. Replicate determinations of the masses of 12 ions gave values within 4.5 ppm (1.1 millimass units, mmu) of their calculated values, with standard deviations no larger than 3 ppm (1.7 mmu). From a total of 88 individual 1 min measurements, 83 were within 5 ppm, and 87 within 2 mmu of the theoretical mass. The accuracy, precision, and sensitivity shown here are comparable to those achievable using high-resolution mass spectrometers, with the added benefits of simpler instrumentation and analytical technique afforded by the quadrupole mass analyzer.