Agilent 6540 Accurate-Mass Q-TOF: Superior Mass Accuracy for High-Confidence Characterisation of Unknowns

Quadrupole time-of-flight (Q-TOF) instruments are invaluable for characterisation of unknown compounds. They offer a combination of unbeatable separation speed and resolution as well as superior qualitative MS and MS/MS capabilities. However, even with their ability to give high resolution accurate mass data, it is common to get multiple candidate molecular formula for the [M+H]+ ion, or several elemental compositions for a given ion in the MS/MS spectra. High quality Q-TOF data helps to eliminate unlikely and incorrect formula. The Agilent 6540 Accurate-Mass QTOF LC/MS System provides outstanding mass accuracy and isotopic fidelity, which reduces the number of formula for unknown samples. The system’s high resolution can also resolve charge states or pinpoint small changes in structure.

Excellent MS Mass Accuracy Limits Number of Possible Formula
To test the capability of the instrument, a laboratory submitted a sample described as a compound with a nominal molecular weight 218. The test was to determine the correct molecular formula. The sample was analyzed
using the Agilent 6540 Accurate-Mass Q-TOF. Figure 1 shows the resulting MS spectrum, and analysis using Agilent Molecular Formula Generation (MFG) software,1 part of Agilent MassHunter Qualitative Analysis software. The theoretical value for [M+H]+ ion is m/z 219.0764. Because the mass error was only 0.33 ppm and the isotope abundance match was excellent, MFG was able to select the correct formula, i.e. C11H10N2O3, from among the many potential candidates.