A method of determining, for a target ion mass, a bandpass range of an ion filter for a mass spectrometer, the method comprising: introducing at least two ion species into the ion filter; characterized in that the method further comprises: scanning a mass range of each ion species by changing at least one filter parameter; determining an ion intensity associated with each scanned mass using the mass spectrometer; registering the ion intensities and the associated filter parameters of each scanned mass range; for each scanned mass range, determining a maximum ion intensity and the associated centre mass; for each scanned mass range, determining (669, 671): a first mass associated with a first ion intensity corresponding with a first fraction of the respective maximum intensity, and a second mass associated with a second ion intensity corresponding with a second fraction of the respective maximum intensity, wherein the first mass is lower than the centre mass of the ion species and the second mass is higher than the centre mass of the ion species; and for the target ion mass having a known centre mass, deriving the masses having the associated first ion intensity and second ion intensity from the determined first ion intensities and second ion intensities of the scanned masses, wherein the deriving comprises: interpolating, from the first mass for each of the at least two ion species, a first expected mass having the associated first ion intensity using a first interpolant function; and interpolating, from the second mass for each of the at least two ion species, a second expected mass having the associated second ion intensity using a second interpolant function. introducing at least two ion species into the ion filter; characterized in that the method further comprises: scanning a mass range of each ion species by changing at least one filter parameter; determining an ion intensity associated with each scanned mass using the mass spectrometer; registering the ion intensities and the associated filter parameters of each scanned mass range; for each scanned mass range, determining a maximum ion intensity and the associated centre mass; for each scanned mass range, determining (669, 671): a first mass associated with a first ion intensity corresponding with a first fraction of the respective maximum intensity, and a second mass associated with a second ion intensity corresponding with a second fraction of the respective maximum intensity, wherein the first mass is lower than the centre mass of the ion species and the second mass is higher than the centre mass of the ion species; and for the target ion mass having a known centre mass, deriving the masses having the associated first ion intensity and second ion intensity from the determined first ion intensities and second ion intensities of the scanned masses, wherein the deriving comprises: interpolating, from the first mass for each of the at least two ion species, a first expected mass having the associated first ion intensity using a first interpolant function; and interpolating, from the second mass for each of the at least two ion species, a second expected mass having the associated second ion intensity using a second interpolant function. scanning a mass range of each ion species by changing at least one filter parameter; determining an ion intensity associated with each scanned mass using the mass spectrometer; registering the ion intensities and the associated filter parameters of each scanned mass range; for each scanned mass range, determining a maximum ion intensity and the associated centre mass; for each scanned mass range, determining (669, 671): a first mass associated with a first ion intensity corresponding with a first fraction of the respective maximum intensity, and a second mass associated with a second ion intensity corresponding with a second fraction of the respective maximum intensity, a first mass associated with a first ion intensity corresponding with a first fraction of the respective maximum intensity, and a second mass associated with a second ion intensity corresponding with a second fraction of the respective maximum intensity, wherein the first mass is lower than the centre mass of the ion species and the second mass is higher than the centre mass of the ion species; and for the target ion mass having a known centre mass, deriving the masses having the associated first ion intensity and second ion intensity from the determined first ion intensities and second ion intensities of the scanned masses, wherein the deriving comprises: interpolating, from the first mass for each of the at least two ion species, a first expected mass having the associated first ion intensity using a first interpolant function; and interpolating, from the second mass for each of the at least two ion species, a second expected mass having the associated second ion intensity using a second interpolant function. interpolating, from the first mass for each of the at least two ion species, a first expected mass having the associated first ion intensity using a first interpolant function; and interpolating, from the second mass for each of the at least two ion species, a second expected mass having the associated second ion intensity using a second interpolant function.