when the time is scaled with respect to the depletion timescale T = t/t s1 . Thus, it is apparent from the dimensionless equations (21a)-(22b) that if ε 1, then not only will the RSA hold, but the QSSA also holds. In fact the RSA (i.e., ε 1) is more restrictive than separation of timescales. After some algebraic calculations, the separation of timescales (t c1 /t s1 1) is equivalently expressed