Before revision: We revisit the scaling analysis and commonly accepted conditions for the validity of the standard, reverse and total quasi-steady-state approximations (sQSSA, rQSSA and tQSSA) through the lens of dimensional Tikhonov--Fenichel small parameters and their respective critical manifolds.
After revision: We revisit the scaling analysis and commonly accepted conditions for the validity of the standard, reverse and total quasi-steady-state approximations (sQSSA, rQSSA and tQSSA) through the lens of dimensional Tikhonov-Fenichel parameters and their respective critical manifolds.