New Method for Ion Mobility Determination by Stability Threshold Measurement in Gas Filled Radio Frequency Quadrupoles

A new method is proposed for determining ion mobility by use of a RF-only quadrupole equipped with a longitudinal electrical field along its axis (RFQLEF). This method is based on measuring the transmission threshold for the ions of interest as a function of the RF voltage and frequency. The method is based on the analysis of the equation of the motion of ions under the RF-only quadrupolar electrical field and the friction force due to collisions of the ions with the buffer gas molecules. The stability diagram for this equation was found numerically by a modified matrix method. According to the stability diagram the threshold values of the RF voltage and frequency determine the mobility coefficient for the ions of interest. Mobility coefficients for electrosprayed ions of several substances (bradykinin 2a, gramicidin S 2a and 1a, multicharged ions of apomyoglobin and cytochrome c) were measured and compared with literature values. # 1998 John Wiley & Sons, Ltd.