  Shubnikov-de Haas (SdH) oscillations in metallic Bi2Se2.1Te0.9 are studied in
magnetic fields up to 35 Tesla. It is demonstrated that two characteristic
frequencies determine the quantum oscillations of the conductivity. Angle
dependent measurements and calculations of the Berry phase show that the two
frequencies F1 and F2 describe oscillations from surface and bulk carriers,
respectively. At low magnetic fields, only SdH oscillation from topological
surface states can be detected whereas at high magnetic field the bulk
oscillations dominate. The origin of the separation of bulk and surface SdH
oscillations into different magnetic field ranges is revealed in the difference
of the cyclotron masses mc. The bulk mc is nearly three times larger than the
surface cyclotron mass resulting in a stronger attenuation of the bulk
oscillation amplitude upon decreasing magnetic field. This makes it possible to
detect and characterize the surface SdH oscillations in the low-field range and
the bulk oscillations at high magnetic fields.
