Melvin Findlay

Monitoring of electrochemically inactive compounds by amperometric gas sensors

Abstract Electrochemical sensors have many useful applications in air and toxic gas monitoring, but they are extremely limited in the gaseous species that they can detect. To extend the applicability of amperometric gas-sensing instruments to electrochemically inactive compounds, gas samples were exposed to a heated platinum or gold filament before being introduced into the sample chambers of several different amperometric sensors. The sensors were of the three-electrode type, having platinum-black reference and counter electrodes and sensing electrodes made of platinum black, powdered gold or vapor-deposited platinum or gold on porous tetrafluoroethylene membranes. All three electrodes were in contact with a 25 – 30 wy.% sulfuric acid solution. The responses of four different sensors to various compounds at 20°C were measured at sensing electrode potentials ranging from 0.9 V to 1.4 V versus RHE (reversible hydrogen electrode in the same electrolyte), with and without a heated platinum filament at the sample inlet. Of 10 compounds tested, only two elicited significant responses without the filament. With the filament heated to about 700 °C, each of the tested compounds elicited a significant response under certain conditions. Moreover, the particular sensors and electrode potentials corresponding to the strongest responses were different for each compound. Qualitatively similar, but quantitatively more pronounced, responses were obtained with the same filament heated to 800 °C or 1050 ± 50 °C, or with a gold filament heated to 950 ± 50 °C. The responses were proportional to concentration in the 0 – 50 ppm range, and usually proportional in the 0 – 200 ppm range.

Sensor array and catalytic filament for chemical analysis of vapors and mixtures

Abstract An amperometric sensor array has been interfaced to a catalytic microreactor. The apparatus has been automated so that frequency- and amplitude-modulated concentrations can be produced for subsequent detection by the sensor array. The response of the CO sensor to modulated concentrations of CO, benzene, TCE, formaldehyde and perchloroethylene has been studied at different frequencies. The results reveal the operating principles and suggest that a simplified modulator-sensor system may provide enough information to identify and quantify individual compounds in simple mixtures.

High performance gas sensing of CO: comparative tests for (SnO2-based) semiconducting and for electrochemical sensors

Abstract A comparison of the stability and sensitivity for two different sensor types (semiconductor SnO 2 devices and amperometric electrochemical sensors) has been performed. Sensitivities and drifts in the signal and in the background for various concentrations of CO have been studied for thick film SnO 2 sensors (undoped, Pt and Pd doped) over a period in excess of 8 months. Similar performance data have been recorded for amperometric sensors over a period in excess of 3 years. The two sensor types investigated here were also compared to well known commercial SnO 2 -based sensors at similar concentrations.

A Prototype Active End-of-Service-Life Indicator for Respirator Cartridges

Abstract Respirator cartridges are used to allow workers to remain in an environment that contains gases which would be harmful to breathe. One of the problems users face is determining when the cartridge service life has ended. Air-purifying respirators for use with vapors are certified by the National Institute for Occupational Safety and Health (NIOSH). When the cartridge is no longer reducing the toxic gas concentration below the minimum permissible level, a ‘warning’ may take the form of an odor; an irritation to the eyes, nose, or throat; or perhaps dizziness. From the viewpoint of a user, the most desirable cartridge should have an indicator that actively and unambiguously notifies the operator when the cartridges useful service life is almost ended. In 1984, NIOSH published standards for certification of Active-End-of-Service-Life-Indicators (AESLI) to encourage the development of AESLI systems. AESLI should provide advance warning to the user that the cartridge is 90 percent expended. To this da...