Gold Film Amperometric Sensors for NO and NO[sub 2]

Abstract

A porous gold membrane working electrode was evaluated for amperometric sensing of NO or NO 2 in air. The Au electrode was evaporated by E-beam onto a porous Teflon substrate and tested in two different geometries: a lab-built universal ͑U͒ and a housing ͑C͒ used in building sensors for commercial sale. The optimum bias for NO 2 reduction was determined to be Ϫ150 mV vs. Pt/air quasi-reference electrode ͑Pt/air-QRE͒ and was ϩ400 mV for NO oxidation. Sensor signals were independent of gas flow rate in both housings at flow rates over 30 cm 3 /min. NO sensitivity in the U and C housing was 180 and 43 nA/ppm, respectively, and the NO 2 sensitivity was Ϫ100 and Ϫ38 nA/ppm, respectively. The U sensor had a limit of detection ͑LOD͒ for NO 2 of 1.3 ppb ͑signal-to-noise ratio 3͒. The sensor housing design and operating conditions can be directly related to observed analytical performance characteristics.The air pollutant gases nitrogen oxide, nitrogen dioxide, nitrous acid, and peroxyacetyl nitrate constitute a nuisance to many people and a danger to those with respiratory conditions such as asthma and emphysema. Oxides of nitrogen are generated by internal combustion 1 and are therefore commonly encountered in urban atmospheres. Monitoring of these gases is important for the protection of human health. Moreover, because emissions are subject to government regulations, industry, especially the automotive industry, has an interest in monitoring for these chemicals.There are numerous methods for detecting NO/NO 2 gases including wet chemical, 2,3 electrochemical, 4-11 infrared ͑IR͒ and ultraviolet ͑UV͒ spectrometric, 12,13 chemiluminescent, 14,15 mass spectrometric ͑MS͒, 16 and gas chromatographic ͑GC͒ 17,18 techniques. Each method has advantages and limitations for particular applications. No method has sufficiently low power, high sensitivity, low cost, and still high performance to meet modern automotive requirements for monitoring in severe environments. Real-time electrochemical sensors, such as amperometric, 4-8 potentiometric, 9,10 and electric impedance based devices, 11 represent a convenient option for NOx measurement and can be incorporated into portable and process control instruments. The amperometric gas sensor ͑AGS͒ has attractive costs, selectivity, and low power. The AGS is limited by modest detection limits and slow response time for many applications. 7 Improvements in performance can be best achieved only by a thorough understanding of the chemical and physical processes that control the amperometric mechanism.Sedlak and Blurton 5 studied an AGS for NO and NO 2 and reported results in this journal. They used a composite Teflon-bonded gold powder working electrode and found the best potential for oxidation of NO at 1.5 V and reduction of NO 2 at 0.8 V ͑vs. a reversible hydrogen electrode, RHE͒. Electrode structure and the serpentine gas exposure geometry limited the sensors analytical performance to part-per-million level determinations. Here, we studied a gold membrane electrode and compared it to earli...

Development of a multiparametric (bio)sensing platform for continuous monitoring of stress metabolites

“…Herein, NO2was detected amperometrically owing to the use of catalyst (Meldola Blue) modifiedcarbon electrode [38]. By applying a potential of +0.863 V vs Ag/AgCl, NO2ions issued from NO secretions are electrochemically oxidized to NO3at the electrode surface as follow [61,62]: Figure 5a shows the amperometric response of nitrite in PBS (1x, pH 7,4) medium under flow rate conditions (100 µL.min -1 ). As expected, the detection of NO2depends linearly on the concentration of the analyte (Fig.…”

Gas Diffusion Electrodes for Use in an Amperometric Enzyme Biosensor

“…The graphite/PTFE layer was deposited by vacuum filtration of a respective aqueous suspension of graphite and PTFE according to a procedure similar to that given by Roh and Stetter [23], and Chao et al [24]. In short, the PTFE membrane (˘25 mm) was tightly fixed in a self-made filter holder, then the sonicated (30 min) graphite /PTFE suspension was applied and filtrated using a water-jet pump.…”

Electrochemical reduction of NO2 at a Pt/membrane electrode—Application to amperometric NO2 sensing

“…The sensitivity, detection limit and response time (t 95 ) of this sensor were 400 nA/ppm, 50 ppb and 50 s, respectively. In Roh and Stetter's work [7], NO 2 was reduced at a Au electrode at 0.15 V (vs. Pt/air electrode). The sensitivity and detection limit of the sensing device were 100 nA/ppm and 1.3 ppb, respectively.…”

“…The reported sensitivity to NO 2 gas (52 nA/(ppm cm 2 )) was rather low. In fact, the reduction of NO 2 at different electrodes has also been studied by many researchers [3][4][5][6][7][8][9][10]. The generally accepted mechanism for cathodic reduction of NO 2 involves transfer of two electrons and can be expressed as…”