Amperometric Sensing of NO[sub x] with Cyclic Voltammetry

Abstract

Cyclic voltammetry ͑CV͒ techniques were used to measure the concentration of nitric oxide ͑NO͒ and nitrogen dioxide (NO 2 ) in air using an amperometric gas sensor. A porous gold membrane working electrode in sulfuric acid electrolyte was used with a counter electrode of bare Pt wire and quasi-reference electrode of electrodeposited Pt on a Pt wire. The anodic peak current (i pa ) was proportional to the concentration of NO at various bias sweep rates. The limit of detection was about 4.8 ppm for NO in air or 31 ppm for NO 2 in air for the CV methods. A parameter related to the diffusion coefficient and membrane permeability can be determined from CV measurements and was at the high range, 2.4 ϫ 10 Ϫ4 cm 2 s Ϫ1 , of reported values of diffusion constants. Simple models of combined effects of gas and liquid mass-transport and electrokinetic current limiting mechanisms complicate explanation of observed currents with porous gas electrodes.Nitric oxide, NO, is a human hormone necessary for healthy metabolic processes at parts per billion levels, and NO inhalation is now used to treat some conditions, but at high levels it can damage the human respiratory system. 1 The U.S. Occupational Safety and Health Administration and Department of Labor recommended exposure limit is 25 ppm NO in air. Symptoms of excess NO exposure are eye, nose, and throat irritations, drowsiness, and unconsciousness. Chronic health effects are methemoglobinemia, central nervous system effects, and delayed lung damage. 2 NO is formed in processes of combustion and found in effluents from coal-fired power plants and automobiles. 3,4 NO 2 can also cause adverse health effects 5 and causes environmental impact when reacting with water vapor in the atmosphere to contribute to acid rain. Therefore, sensitive and selective detection methods for these gases are required.Detection methods from colorimetric to electrochemical have been reported for NO, and references to electroanalytical approaches 6-10 can be found, but it has been some time since the earliest amperometric gas sensors ͑AGS͒ for NO and NO 2 were reported 9 in this journal. This early commercial NO/NO 2 sensor had a large 25 cc electrolyte reservoir and a design adapted from the amperometric ethanol 11 and CO 12,13 sensors of the time that used a composite Pt/tetrafluoroethylene ͑TFE͒ porous fuel cell-type electrode. The early NO sensor replaced the working electrode ͑WE͒ of the CO sensor with a powdered Au/TFE composite electrode to avoid interference from CO. Selectivity was achieved by reducing NO 2 at a potential too cathodic for NO oxidation and too anodic for NO reduction. 6,9 Since then, this system for ambient NO/NO 2 detection has been studied and used in several different embodiments. Later an electrode of powdered Au on Nafion was built 14 and the performance of this system was characterized and compared 7 to a thin-film low surface area ͑LSA͒ Au electrode on Nafion, both at constant potential. It was found that the LSA electrode offered a faster response and parts per billion...

Gas Diffusion Electrodes for Use in an Amperometric Enzyme Biosensor

“…Gold or platinum were deposited by e-beam evaporation on to PTFE membranes (˘25 mm) at the optics workshop of the University of Bayreuth using a Balzers evaporation system (type BA 510) with a rotating sample holder, according to a procedure similar to that given by Roh and Stetter [22]. The vacuum was 10 À5 -10 À6 mbar, the deposition rate was 1 nm/s for Au and 3 /s for Pt.…”

Exploration of gas sensing possibilities with edge plane pyrolytic graphite electrodes: nitrogen dioxide detection

“…This concentration of acid was chosen since Stetter et al report this for their detection of nitrogen dioxide using a gold working electrode observing an oxidation wave at +0.2 V (vs. platinum wire) but no corresponding reduction wave. 3,13 The voltammetric response (shown in Fig. 1) at the edge plane electrode was found to produce a reduction wave at ca.…”

“…Nitrogen dioxide is an extremely toxic gas, and an environmental pollutant, generated from combustion processes. [1][2][3][4] Nitrogen dioxide accumulates in enclosed spaces such as ice rinks 5 from ice surface renewal machines and in kitchens or apartments from using a gas stove. 6 Exposure to NO 2 may exacerbate a pre-existing pathogenic condition in people who spend a large amount of time in such places 5 and/or cause respiratory health problems; 7 consequently continuous monitoring is imperative.…”

“…12 Recently Stetter et al have described the amperometric detection of nitrogen monoxide, NO and nitrogen dioxide, NO 2 using gold film electrodes. 3,13 However an alternative might be through the use of carbon based electrodes. These are preferred in electroanalysis due to their low background currents, wide potential windows and especially low cost.…”