Efficient transfer of ions from the ion source to the mass analyzer is one of the most crucial aspects of atmospheric pressure ionization (API) mass spectrometry. Most ionlosses occur during this transfer, and those losses directly affect a mass spectrometer’s limits of detection and quantification. The Thermo Scientific LTQ Velos dual-pressure linear ion trap mass spectrometer features a stacked-ring ion guide that significantly improves transmission of ions from the ion source to the ion trap mass analyzer.