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Abstract

An analyte recognition system uses an array (16) of ion-selective electrode (ISE) sensors, each sensitive to a different ion in a downstream flow path (32) therethrough to a coupling (30) which provides a ground or bias electrode. Another flow path (34) is upstream through an ISE sensor (26) which provides a reference electrode and the coupling. The coupling has a flow path, provided by a sidearm, to an outlet (40) going to a drain (35) for both the upstream and downstream flow paths. The upstream flow path reference electrode is a conduit for a reference fluid, and measurements from the other electrodes are made with respect to the reference electrode. Contamination and permanent poisoning of certain of the electrodes in the downstream path may occur if reversal of the flow were to take place, or if the reference fluid flowing in the upstream path were to flow into the downstream path. Reversal of flow is prevented by inclusion of a one-way valve, desirably a duckbill valve (75) in the coupling in the downstream path to the sidearm. Poisoning of the ISE sensors is prevented because the duckbill valve reduces the likelihood of a reversal of the normal downstream flow and reduces flow of the reference fluid in the upstream direction through the array of ion-selective electrodes.

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