The Practical Significance of Isotopes (Isotopically Displaced Ions) and Mass Resolution

Isobars are ions that have the same (or very similar) mass-to-charge ratio but differ in elemental composition and chemical structure. For example, CO and N₂ both have a nominal m/z of 28, whilst C₂H₄ and N₂ are also quite similar. In the analysis of mixtures, if the instrument’s resolution is insufficient, the peaks of these ions will overlap to form a ‘combined peak’, leading to the misidentification of two substances as one, or to cross-interference during quantification.

Mass resolution (R = m/Δm) directly determines whether isobars can be separated. The higher the resolution, the smaller the m/z difference that can be distinguished. The Xinceyuan ProC series explicitly states in its description that it ‘can distinguish isomers in air’, relying precisely on the high resolution provided by dual-field reflection TOF. For example, to assign several components such as CO, N₂ and C₂H₄, all near m/z 28, to their respective identities, a sufficiently high R value must be combined with mass accuracy; otherwise, a single composite peak will obscure the true composition.

In practical applications, distinguishing isomers serves two key purposes. Firstly, in environmental monitoring and industrial gas analysis, it enables the correct identification of each peak, preventing the confusion of pollutants with background gases—for example, nitrogen oxides and certain hydrocarbon fragments may fall within a similar m/z range; failure to distinguish between them could lead to misjudgements regarding emission sources. Secondly, in mass spectrometry imaging, it enables the correct identification of structurally similar lipids and metabolites, preventing the distribution of one substance from being mistakenly attributed to another; this is particularly important in complementary analysis of positive and negative ion modes.

Therefore, resolution and mass accuracy (see the section on mass accuracy) are two complementary parameters: resolution is responsible for ‘separating’, whilst mass accuracy is responsible for ‘identifying’ . High resolution alone, coupled with poor calibration of the mass axis, results in peaks being separated but incorrectly identified; conversely, high mass accuracy alone, with low resolution, means overlapping peaks cannot be separated in the first place, rendering identification impossible. New Ceyuan pursues both simultaneously in its dual-field reflection TOF mass spectrometer precisely to ensure that ‘comprehensive coverage in a single scan’ does not come at the expense of ‘accurate identification of every substance’.