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

A.V. Loboda^{1}, V.I. Kozlovski^{1}, E.V. Chardakova^{1}, A.V. Tolmachev^{1}, I.V. Sulimenkov^{1},
A.F. Dodonov^{1} and H. Wollnik^{2}

^{1}Institute of Energy Problem of Chemical Physics (Branch), R.A.C.,

142432, Chernogolovka, Moscow Region, Russia

^{2}II.Physikalisches Institut Justus-Liebig Universitat Giessen, Germany

Received 5 November 1997; Accepted 14 November 1997

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 2+, gramicidin S 2+ and 1+, multicharged ions of apomyoglobin and cytochrome c) were measured and compared with literature values.

*© 1998 by John Wiley & Sons, Ltd.*