Ppt-Level Detection of Aqueous Benzene with a Portable Sensor Based on Bubbling Extraction and UV Spectroscopy

Abstract

Benzene (EPA, 1993), sometimes also referred to as part of BTX or BTEX, which stands for benzene, toluene, ethylbenzene, and xylenes, is widely used in industrial activities despite being a known carcinogen that can easily contaminate different media (gas, water, and soil). It can be inhaled, ingested, and absorbed through the skin and therefore represents a potential threat to human health, even at trace levels. With respect to benzene toxicity, national regulations have been established in an effort to minimize its impact on human health. Water regulations cover drinking water and wastewater, with levels varying from one country to another but falling within the same order of magnitude. Wastewater regulations give the maximum concentration allowed for disposal, about a few hundred parts per billion (ppb) (Volume) (110 ppbV in Japan (Ministry of the Environment in Japan, 2008)). Below this level, the impact on the environment is assumed to be negligible. This level is sometimes referred to as the alarm level. Drinking water regulations, which are aimed at water for human consumption, stipulate permissible levels in the low ppbV range, two orders of magnitude lower than for wastewater (11, 5 and 1 ppbV in Japan, America, and Europe, respectively (Ministry of Health, Labour and Welfare in Japan, 2003) (EPA, 2006) (European Council, 1998)). Laboratory procedures for detecting benzene concentrations in water involve several consecutive steps: (i) extraction by inert-gas stripping or heating to transfer benzene to the vapor phase, (ii) trapping to enhance the concentration, and (iii) detection by gas chromatography combined with either flame ionization, photo-induced detection or massspectrometry (respectively GC/ FID, GC/ PID, and GC/ MS) (Martinez et al., 2002) (Serrano & Gallego, 2004) (Richardson & Ternes, 2005). The detected thresholds far exceed the requirements, but the procedures are complex and involve the use of expensive equipment. The required apparatuses are also not compatible with the requirements for on-site measurements, which means samples have to be collected in the field and sent to a laboratory for analysis (Richardson & Ternes, 2005). To prevent contamination of samples or changes in their characteristics due to long contact-exposure to the container (with transportation time to the laboratory varying from a few hours to a few days), complex and error-prone procedures have been established (Namiesnik et al., 2005), which, depending mainly on the potential contaminants, include choosing an appropriate container material,