Model reduction by extended quasi-steady-state approximation

We extend the quasi-steady-state approximation (QSSA) with respect to the c lass of differential systems as well as with respect to the order of approx imation. We illustrate the first extension by an example which cannot be tr eated in the frame of the classical approach. As an application of the seco nd extension we prove that the trimolecular autocatalator can be approximat ed by a fast bimolecular reaction system. Finally we describe a class of si ngularly perturbed systems for which a higher order QSSA can easily be obta ined.