First, the response of a non-injective sensor arrays places potentially useful constraints on the gas composition. For example, consider the single HKUST-1 sensor in Fig. . The response under CH 4 /CO 2 /N 2 mixtures places tight bounds on the mole fraction of CO 2 in the mixture. On the other hand, the response under CH 4 /CO 2 /C 2 H 6 mixtures cannot delineate between dominantly CH 4 /CO 2 and CH 4 /C 2 H 6 mixtures (see Fig. ). Nevertheless, the response does place tight bounds on the sum of the CO 2 and C 2 H 6 mole fractions and, hence, the CH 4 mole fraction. See Fig. . This tight bound on x CH 4 could be very useful and sufficient for certain applications.