This work addresses whether a reaction network, taken with mass-action kinetics, is multistationary, that is, admits more than one positive steady state in some stoichiometric compatibility class. We build on previous work on the effect that removing or adding intermediates has on multistationarity, and also on methods to detect multistationarity for networks with a binomial steady state ideal. In particular, we provide a new determinant criterion to decide whether a network is multistationary, which applies when the network obtained by removing intermediates has a binomial steady state ideal. We apply this method to easily characterize which subsets of complexes are responsible for multistationarity; this is what we call the multistationarity structure of the network. We use our approach to compute the multistationarity structure of the n-site sequential distributive phosphorylation cycle for arbitrary n. is multistationary or not; indeed, it suffices to find the set of inputs of our network and check whether it belongs to the multistationarity structure.The method applies to core networks that are binomial (the ideal generated by the steady state polynomials is binomial). For these networks, a method to decide on multistationarity was introduced in [13], based on the computation of sign vectors. Under some extra assumptions, another method relying on the computation of a symbolic determinant and inspection of the sign of its coefficients is presented in [12] (see Theorem 2.7).The first main result of this paper is Theorem 3.11, where we combine the results in [8,12] into a new determinant criterion for multistationarity that applies to extended networks for which the core network is binomial, even though the original network might not be binomial.The second main result is Theorem 4.2, which removes the technical realization condition in [8] for concluding that an extended network is multistationary provided the core network is. Instead, we require that both the core and the extended networks are binomial (in a compatible way).The third main contribution is Algorithm 4.8, which returns the multistationarity structure of a binomial core network based on the determinant criterion. The algorithm relies on the study of the signs of a polynomial obtained after the computation of the determinant of a symbolic matrix. Our approach is more direct than testing if the extended network is multistationary for all subsets of input complexes. We apply our method to find the multistationarity structure of the n-site distributive sequential phosphorylation cycle for arbitrary n in §4.3. This illustrates how our results allow us to study a family of networks at once.We conclude with an investigation of when the technical realization conditions in [8] are satisfied. In particular, we show that the conditions hold for typical types of intermediates like the Michaelis-Menten mechanism above. The structure of the paper is as follows. In §1 we introduce basic concepts on reaction networks and multistationarity. In §2 we introduce (co...