  The de Haas - van Alphen effect in quasi-two-dimensional metals is studied at
arbitrary parameters. The oscillations of the chemical potential may
substantially change the temperature dependence of harmonic amplitudes that is
usually used to determine the effective electron mass. Hence, the processing of
the experimental data using the standard Lifshitz-Kosevich formula (that
assumes the chemical potential to be constant) may lead to substantial errors
even in the limit of strong harmonic damping. This fact may explain the
difference between the effective electron masses, determined from the de Haas -
van Alphen effect and the cyclotron resonance measurements. The oscillations of
the chemical potential and the deviations from the Lifshitz-Kosevich formula
depend on the reservoir density of states, that exists in organic metals due to
open sheets of Fermi surface. This dependence can be used to determine the
density of electron states on open sheets of Fermi surface. We present the
analytical results of the calculations of harmonic amplitudes in some limiting
cases that show the importance of the oscillations of the chemical potential.
The algorithm of the simple numerical calculation of the harmonic amplitudes at
arbitrary reservoir density of states, arbitrary warping, spin-splitting,
temperature and Dingle temperature is also described.
