Accurate mass measurements and ultrahigh-resolution: evaluation of different mass spectrometers for daily routine analysis of small molecules in negative electrospray ionization mode.

Six mass spectrometers based on different mass analyzer technologies, such as time-of-flight (TOF), hybrid quadrupole-TOF (Q-TOF), orbitrap, Fourier transform ion cyclotron resonance (FT-ICR), and triple quadrupole (QqQ), installed at independent laboratories have been tested during a single day of work for the analysis of small molecules in negative electrospray ionization (ESI) mode. The uncertainty in the mass measurements obtained from each mass spectrometer has been determined by taking the precision and accuracy of replicate measurements into account. The present study is focused on calibration processes (before, after, and during the mass measurement), the resolving power of the mass spectrometers, and the data processing for obtaining elemental formulae. The mass range between m/z 100 and 600 has been evaluated with a mix of four standards. This mass range includes small molecules usually detected in food and environmental samples. Negative ESI has been tested as there is almost no data on accurate mass (AM) measurements in this mode. Moreover, it has been used because it is the ESI mode for analysis of many compounds, such as pharmaceutical, herbicides, and fluorinated compounds. Natural organic matter has been used to demonstrate the significance of ultrahigh-resolution in complex mixtures. Sub-millidalton accuracy and precision have been obtained with Q-TOF, FT-ICR, and orbitrap achieving equivalent results. Poorer accuracy and precision have been obtained with the QqQ used: 11 mDa root-mean-square error and 6-11 mDa standard deviation. Some advice and requirements for daily AM routine analysis are also discussed here.