A review of sensor-based methods for monitoring hydrogen sulfide Sudhir Kumar Pandey, Ki-Hyun Kim, Kea-Tiong Tang We review sensor-based methods commonly employed for monitoring hydrogen sulfide (H 2 S), and recent developments in H 2 S-sensing instrumentation. We evaluate the basic quality-assurance parameters of different sensor types for quantifying H 2 S in terms of major operational criteria (e.g., response time, limit of detection, common operating range of concentrations, and stability). We also describe the applicability of these sensor-based methods with respect to practicality in various environmental settings. Finally, we highlight the limitations and the future prospects of these sensor-based methods. ª 2011 Elsevier Ltd. All rights reserved. Keywords: Chemical sensor; Environmental analysis; Hydrogen sulfide; Limit of detection; Malodor; Nuisance; Real-time monitoring; Sensor-based method; Sensor response time; Toxicity 1. Introduction Hydrogen sulfide (H 2 S) is a toxic gas with a characteristic malodor of rotten eggs [1]. It is also commonly referred to as sewer gas, stink damp, swamp gas, and manure gas [2]. It occurs naturally in crude petroleum, natural gas, hot springs, and foods. H 2 S gas is commonly formed in nature and released during the decay of organic matter (e.g., human and animal wastes) in septic or sewer systems by bacterial breakdown [3]. Furthermore, it is also produced in large quantity from such industrial activities and places as petroleum/natural gas drilling and refining, wastewater treatment, coke ovens, tanneries, kraft paper mills, and landfills [4,5]. H 2 S is rapidly absorbed by the lungs, once exposed via inhalation [2]. A variety of occupational epidemiological studies on humans has indicated that exposure to H 2 S (at high concentrations) has profound health effects on the respiratory system, which could then lead to unconsciousness with attendant neurological sequelae and, sometimes, death [e.g., 6]. It has also been associated with cardiovascular related deaths [7]. Further, it can cause a mal- odor-nuisance problem even at relatively low concentrations [8]. As a first step towards the management of this gaseous pollutant, one has to monitor its behavior in various environ- mental settings. To determine this noxious gas in environmental samples, gas chro- matography (GC)-based methods have been employed most frequently [9]. These quantification methods have proved their reliability in terms of high detectability and precision. However, application of these methods is not simple, as it involves a multi-stage protocol starting from sam- pling and going to final determination. As such, this approach is not convenient to track down short-term variations in behavior due to the dynamics of varying environmental conditions. Moreover, off- line analytical protocols of H 2 S analysis can also suffer from a number of biases (e.g., sorptive loss in association with its high reactivity) [9]. Hence, it has always been a big challenge to measure H 2 S accurately with the least amount of bias under field conditions. Chemical sensors have been widely used in a number of applications (e.g., critical care, safety, industrial hygiene, process control, product-quality control, human comfort controls, emissions monitoring, automotive industry, clinical diagnostics, home-safety alarms, and homeland secu- rity) [10]. For real-time monitoring of harmful pollutants that can cause a nui- sance, numerous chemical sensors have been developed and employed. These sen- sors have mainly been based on semicon- ducting metal-oxide, electrochemical Sudhir Kumar Pandey + , Ki-Hyun Kim* Dept. of Environment and Energy, Sejong University, 98 Gun-Ja Dong, Gwang-Jin Gu, Seoul 143-747, Republic of Korea Kea-Tiong Tang Department of Electrical Engineering, National Tsing Hua University, No. 101, Sec. 2, Kuang-Fu Road, Hsinchu 30013, Taiwan * Corresponding author. Tel.: +82 2 499 9151; Fax: +82 2 3408 4320.; E-mail: khkim@sejong.ac.kr + Presently at: Depart- ment of Botany, Guru Ghasidas Central University, Bilaspur (C.G.) 495009, India Trends in Analytical Chemistry, Vol. 32, 2012 Trends 0165-9936/$ - see front matter ª 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.trac.2011.08.008 87