  The asymptotic limit-cycle analysis of mathematical models for oscillating
chemical reactions is presented. In this work, after a brief presentation of
mathematical preliminaries applied to the biased Van der Pol oscillator, we
consider a two-dimensional model of the Chlorine dioxide Iodine Malonic-Acid
(CIMA) reactions and the three-dimensional and two-dimensional Oregonator
models of the Belousov-Zhabotinsky (BZ) reactions. Explicit analytical
expressions are given for the relaxation-oscillation periods of these chemical
reactions that are accurate within 5\% of their numerical values. In the
two-dimensional CIMA and Oregonator models, we also derive critical parameter
values leading to canard explosions and implosions in their associated limit
cycles.
