Absorption of sulfur dioxide gas in moistened porous material on a suspended gold leaf electrochemical sensor

This work describes an unconventional voltammetric detection in a gas medium using a suspended electrode unit. A paper moistened with the supporting electrolyte is used to absorb the gas. This concept was demonstrated for the in-situ detection of SO2 gas to quantify sulfite residue in samples of frozen shrimp. The gas is generated by the acidification of an aqueous suspension of shrimp tissues. The porosity of facial tissue paper is employed to provide a liquid layer of supporting electrolyte for the operation of the gold leaf electrochemical sensor. The absorbed gas is also dissolved in this liquid layer. The gold leaf sensor is reusable by replacing the tissue disc and rinsing the electrodes with water. The electrochemical sensor does not require refrigeration or pre-conditioning as with commercial biosensors and is thus suitable for point-of-need purposes. Production of the gold leaf sensor is only ca. 0.2 USD per unit and can be used regularly for up to 3 months. The linear calibration range of spiked negative control shrimp samples is from 3 to 240 mg kg-1 SO2 for a 30 mL solution of an extract of 5.0 g ho-mogenized defrosted shrimp. The limit of detection (3 xSDintercept/slope) for spiked samples is 2 mg kg-1 SO2. This is the first electrochemical sensor in a gas medium exploiting the entrapment of electrolyte solution inside a porous substrate.