Optimal pressure conditions for unbiased external ion accumulation in a two-dimensional radio-frequency quadrupole for Fourier transform ion cyclotron resonance mass spectrometry

When combined with on-line separations (e.g., capillary liquid chromatograp hy (LC)), Fourier transform ion cyclotron resonance mass spectrometry (FTIC R-MS) provides a powerful tool for biological applications, and particularl y proteomic studies. The sensitivity, dynamic range, and duty cycle provide d by FTICR-MS have been shown to be increased by ion trapping and accumulat ion in a two-dimensional (2D) radio-frequency (rf)-only multipole positione d externally to an FTICR cell. However, it is important that ions be detect ed across the desired m/z range without a significant bias. In this work we found that pressure inside the accumulation rf-quadrupole plays an importa nt role in obtaining 'unbiased' ion accumulation. Pressure optimization was performed in both pulsed and continuous modes. It was found that unbiased accumulation in a 2D rf-only quadrupole could be achieved in the pressure r ange of 5 X 10(-4) to 5 x 10 (-3) Torr. External ion accumulation performed at the optimal pressure resulted in an increase in both the spectrum acqui sition rates and dynamic range. Copyright (C) 2001 John Wiley & Sons, Ltd.