Extension of the Q Orbitrap intrascan dynamic range by using a dedicated customized scan

The intrascan dynamic range of modern Orbitrap instrumentation is specified to reach 1:5000, while the interscan dynamic range is significantly larger due to the utilization of the automatic gain control feature. There are some applications (e.g. residue analysis in complex matrices, metabolomics or structural elucidation) where a wider intrascan dynamic range is desirable.

The Application Programming Interface (API) of the Q Exactive Orbitrap mass spectrometer has been used to program a customized scan in order to cover a larger intrascan dynamic range. Different approaches were used, which were all based on the variation of the isolation time of low-abundance versus high-abundance mass range segments. The differently attenuated mass range segments isolated by the quadrupole were sequentially forwarded to the C-trap. Finally, the accumulated mass segments were measured within the Orbitrap analyzer.

The spectra obtained by the customized scans show an enlarged dynamic range. This has been demonstrated by monitoring the higher isotope mass peaks (first and second isotope) of a low intensity analyte. Furthermore, a practical application (veterinary drugs in bovine kidney) has been investigated with the proposed customized scan. Analytes eluting within the retention time region of very intense matrix peaks (e.g. peptides) showed improved detectability when utilizing the customized scan.

The extension of the intrascan dynamic range by a customized scan is helpful when analyzing residues which happen to elute together with a dominating matrix peak or within a high ion abundance region (e.g. dead volume). Furthermore, this feature helps in the process of determining the elemental composition of compounds by permitting the investigation of low-abundance ions (e.g. belonging to the isotopic fine structure of the investigated compound).