We set s 2 (t s1 ) = s 0 1 to match the inner solution (38a) and outer solution (38b). The validity of the matched asymptotic solution is dependent not only on the prerequisite that λ 1 (and that δ S 1), but also on the qualifier that σ 1 be sufficiently large. This is because matching the inner solution with the outer solution requires that s 1 (t s1 ) = 0. Consequently, the accuracy of the matched solution depends on the accuracy of t s1 as a completion timescale for the non-observable reaction. Generally, the larger σ 1 becomes, the more accurate the depletion timescale becomes in approximating the time it takes the nonobservable reaction to complete. Numerical simulations once again confirm the validity of the approximations given in (38a) and (38b) (see Figs. Once again, it is important to note that if δ S 1 and λδ S ∝ (1+κ 2 )(1+σ 2 ), then the approximate time it takes for the indicator reaction to reach QSS is