Precise tuning of MCP-based ion detector using isotope ratios with software correction

A method for calculating an optimum bias voltage for a microchannel plate (MCP) detector of a mass spectrometer, comprising:

• continuously receiving and ionizing a calibration sample that includes a known compound that has at least a first isotope and a second isotope with a known abundance ratio using an ion source device, producing an ion beam;
• receiving the ion beam, selecting and mass analyzing a mass range that includes a first ion of the first isotope and a second ion of the second isotope, controlling the ion beam so that an MCP detector detects only multiple-ion strikes for the first ion and only single-ion strikes for the second ion, and producing one or more mass spectra for the mass range as a bias voltage of the MCP is stepped through a sequence of one or more different voltages that affect the number of the first ion and the number of the second ion that the MCP detects using a mass spectrometer that includes the MCP;
• and,
• for each voltage of the sequence of voltages, determining a first intensity of the first ion and a second intensity of the second ion from the one or more mass spectra, calculating a measured ratio of the first intensity and the second intensity, comparing the measured ratio to the known abundance ratio, and, when the measured ratio is within a predetermined threshold of the known abundance ratio, calculating an optimum voltage for the MCP using one or more measured ratios calculated for voltages of the sequence of voltages using a processor.

A computer program product, comprising a non-transitory tangible computer-readable storage medium whose contents include a program with instructions being executed on a processor so as to perform a method for calculating an optimum bias voltage for a microchannel plate (MCP) detector of a mass spectrometer, comprising:

• providing a system, wherein the system comprises one or more distinct software modules, and wherein the distinct software modules comprise a control module and an analysis module;
• instructing an ion source device to continuously receive and ionize a calibration sample that includes a known compound that has at least a first isotope and a second isotope with a known abundance ratio using the control module, producing an ion beam;
• instructing a mass spectrometer that includes an MCP detector to receive the ion beam, select and mass analyze a mass range that includes a first ion of the first isotope and a second ion of the second isotope, control the ion beam so that the MCP detects only multiple-ion strikes for the first ion and only single-ion strikes for the second ion, and produce one or more mass spectra for the mass range as a bias voltage of the MCP is stepped through a sequence of one or more different voltages that affect the number of the first ion and the number of the second ion that the MCP detects using the control module;
• and,
• for each voltage of the sequence of voltages, determining a first intensity of the first ion and a second intensity of the second ion from the one or more mass spectra, calculating a measured ratio of the first intensity and the second intensity, comparing the measured ratio to the known abundance ratio, and, when the measured ratio is within a predetermined threshold of the known abundance ratio, calculating an optimum voltage for the MCP using one or more measured ratios calculated for voltages of the sequence of voltages using the analysis module.