Comparative analysis of multipole ion guide transmission performance under consistent benchmark conditions

Radio-frequency (RF) multipole ion guides transfer ions between pressure stages in mass spectrometers, but pole-number comparisons are often confounded by changes in aperture, guide length, and instrument layout. We established a common SIMION benchmark for quadrupole, hexapole, and octopole guides using the same inscribed radius (r₀ = 5.24 mm), axial length, mass grid, waveform convention, and response definitions. Interchangeable quadrupole and hexapole cartridges were also evaluated at the same ion-guide position in a laboratory-built electrospray ionization time-of-flight mass spectrometer (ESI-TOFMS); the octopole was a numerical extension only. Across the sampled amplitude grid, mass-averaged transmission over m/z 50-2000 was the greatest at 300 V for the quadrupole and 200 V for both higher-order guides. In the separate frequency scan, the best sampled settings were 1.0, 1.5, and 2.0 MHz, with pointwise maximum transmission efficiencies of 56%, 65%, and 79%, respectively. Increasing pole number broadened the simulated transmission window but increased the root-mean-square (RMS) exit radius. Increasing the pressure from 1 to 2 Pa reduced the matched-mass mean RMS radius by 51.8%, 32.7%, and 29.1% for the three guides. In the experimental RF-amplitude scans, the within-ion hexapole-to-quadrupole relative instrument-response ratio, calculated from maximum mean integrated peak areas, ranged from 1.33 to 2.78 across five diagnostic ions. For every monitored ion, the best sampled mean peak area was higher and the RSD was lower with the hexapole. The paired maxima could occur at different RF amplitudes and are not absolute transmission efficiencies. The benchmark therefore quantifies an order-dependent design trade-off between mass acceptance and exit-beam confinement and shows how it is expressed in fixed-platform signal response and repeatability.