A stereo headset interface that is compatible with mono for an audio playback device. Multiple embodiments of varying apparatus are presented for completing four steps of the method. The passageway is positioned passing through a first wall of first gastrointestinal organ and a second wall of a second gastrointestinal organ with the inlet end disposed within an interior of the first gastrointestinal organ and with the outlet disposed within an interior of the second gastrointestinal organ. Moreover, the probe card has fine impedance matching and channels separating to raise testing efficiency and reduce signal loss. A controller in communication with a pH sensor may be configured to generate a control signal to adjust the pH level of the aqueous mixture in response to the pH sensor registering a pH level outside a predetermined pH solubility range for a selected catalyst.