Dynamic range improvement for isotope ratio mass spectrometry

A mass spectrometer, comprising:

• a mass-to-charge dispersive element, configured to receive ions and separate the ions spatially according to their mass-to-charge ratios, to provide a dispersed ion beam thereby, wherein the mass to charge dispersive element comprises a magnetic sector mass analyzer;
• the ion detection arrangement for detecting ions in the dispersed ion beam, including at least one primary ion detector, each arranged to detect spatially separated ions having mass-to-charge ratios within a respective desired range and each configured to provide a respective main beam signal based on its respective detected ions, and at least one secondary ion detector, each arranged to detect ions having mass-to-charge ratios outside all of the desired ranges simultaneously with the at least one primary ion detector detecting the spatially separated ions and each of the at least one secondary ion detectors being configured to provide a respective background signal based on its respective detected ions;
• and,
• a processor, configured to provide at least one mass intensity measurement for the received ions having a mass-to-charge ratio within the desired range, based on the at least one main beam signal and the at least one background signal, wherein the background signal is subtracted from the main beam signal in order to correct the main beam signal.