How can we remedy non-injective gas sensors to give a determined inverse problem? The observed response of a non-injective gas sensor generally places an insufficient number of constraints on the gas composition to give the inverse problem a unique solution. We can make a non-injective sensor array injective by (i) retrofitting it with additional sensing elements (MOFs), (ii) designing sensing elements (MOFs) that do not respond appreciably to interferents in the gas that we are not concerned about, or (iii) imposing additional assumptions on the gas composition as in eqn. 17.