Accurate mass measurements of some glucuronide derivatives by electrospray low resolution quadrupole mass spectrometry

The measurement of exact masses using negative‐ion quadrupole low resolution electrospray mass spectrometry (ESMS) is demonstrated with p‐nitrophenol, entacapone, mitecapone and 1‐hydroxypyrene glucuronides. The results are compared with those obtained by high resolution fast‐atom bombardment mass spectrometry (FAB‐MS). The errors with ESMS between measured and calculated values ranged from −1.7 to 3.1 ppm (−0.8 to 1.2 milli‐mass units (mmu). The standard deviations of the measurements were between ±1.1 and 4.8 ppm (±0.5 and 2.3 mmu). The errors with high resolution FAB‐MS were between −2.5 and 3.2 ppm (−1.1 and 1.0 mmu). These results show that accurate mass measurements using low resolution quadrupole ESMS are comparable to those achievable in practice using high resolution instruments. A precondition for a successful measurement with low resolution mass spectrometry is that the sample ion be completely separated from background ions, since even very small levels of unresolved ions can interfere with the accuracy of mass analysis.