Chemical reaction schemes are typically simplified by considering the contr
olling steps of the process, the 'fast' reactions being taken into account
by quasi-equilibrium assumptions. Traditionally, intuitive reasoning is emp
loyed to arrive at the simplified system. This may, however, be cumbersome
and sometimes misleading. In this paper a systematic approach is presented
that guarantees that the simplified model coincides with the asymptotics of
the original one. (C) 1999 Elsevier Science Ltd. All rights reserved.