Toward the Required Detection Limits for Volatile Organic Constituents in Marine Environments with Infrared Evanescent Field Chemical Sensors

Abstract

A portable sensor system for the simultaneous detection of multiple environmentally relevant volatile organic compounds (VOCs) in real seawater based on Fourier transform infrared fiber-optic evanescent wave spectroscopy (FT-IR-FEWS) was developed. A cylindrical silver halide (AgX) fiber with an ethylene/propylene copolymer (E/P-co) coated flattened segment was used as an active optical transducer. The polymer membrane enriches the hydrophobic analytes, while water is effectively excluded from the penetration depth of the evanescent field. Determination of multicomponent mixtures (i.e., 10 VOCs in real-world seawater samples) collected in Arcachon Bay, France revealed a high accuracy and reproducibility with detection limits down to 560 ppb. The measurement showed no significant influence from changing water conditions (e.g., salinity, turbidity, and temperature or other interfering substances). The time constants for 90% saturation of the polymer ranged from 20 to 60 min. The sensor system is capable of being transported for on-site monitoring of environmental pollutants in aqueous matrices with efficient long-term stability, thus showing great potential to be utilized as an early warning system.

Toward Chalcogenide Platform Infrared Sensor Dedicated to the In Situ Detection of Aromatic Hydrocarbons in Natural Waters via an Attenuated Total Reflection Spectroscopy Study

“…The detection limit obtained during this study using PIB coating directly on a ZnSe prism or on GeSbSe planar waveguide on a ZnSe prism for ATR-FTIR spectroscopy still needs to be improved, but it is of the same order of magnitude as other results found in the literature concerning the detection of hydrocarbons in aqueous media by means of infrared spectroscopy. Indeed, if detection techniques based on gas chromatography and microextraction allow detecting hydrocarbons at concentrations lower than 1 ppb [7,44,45], the detection of these molecules using ZnSe-ATR prism [11,36] and waveguide (planar [14], fiber [9,46]) in aqueous media (distilled and natural water) reaches limits of detection (LODs) ranging from a few tens to several hundreds of ppb. It is important to underline that the detection limit should be lower when using the chalcogenide waveguide, opening interesting perspectives for infrared microsensors based on the chalcogenide platform.…”

Mid-IR sensing platform for trace analysis in aqueous solutions based on a germanium-on-silicon waveguide chip with a mesoporous silica coating for analyte enrichment

“…To the best of our knowledge, the state-of-the-art for on-chip absorption spectroscopy in CMOScompatible long-wave mid-infrared platforms is limited to a few reported proofs-of concept [11][12][13][14][15][16][17][18] showing the potential for sensing, but until today there are no reports on the detection of ppm-concentrations of an analyte neither in gas phase nor in liquid phase. Compared to a standard attenuated total internal reflection (ATR) unit were the evanescent field is interacting with the analyte at a limited number of locations in an ATR crystal [19], the use of waveguides can enhance the sensitivity by increasing the effective interaction length [1,20,21]. However, the requirements on LOD and the strong absorption of the aqueous matrix in the mid-infrared prevents the use of water-clad waveguide structures for sensing.…”

“…To assure a safe environment, novel water monitoring technologies are needed for all types of water including process water, wastewater as well as drinking water. In particular organic contaminants are one of the major pollutants of water [1] and their detection concerns the identification of a complex mixture of many different molecules. In this regard, mid-infrared (mid-IR) spectroscopy has proven to be a very suitable sensing method since it provides direct information on the molecular fingerprint of the analytes [2][3].…”

Determination of Volatile Organic Compounds in Water by Attenuated Total Reflection Infrared Spectroscopy and Diamond-Like Carbon Coated Silicon Wafers

“…ATR-FTIR waveguide materials include crystals, e.g., zinc selenide (ZnSe), zinc sulfide (ZnS), silicon (Si), and germanium (Ge) and thin film waveguides based on gallium arsenide/aluminum gallium arsenide (GaAs/AlGaAs), mercury-cadmium-telluride (MCT), and diamond [12][13][14][15]. Alternatively, optical fiber waveguide materials were already reported, e.g., chalcogenide, silver and tellurium halide [10,[16][17][18][19][20][21][22]. In particular, silver halide fibers are one of the most promising materials due to their flexibility and transparence in the entire mid-infrared (MIR) spectral regime [23].…”

“…At the same time, this polymer layer acts as protective coating of the silver halide fiber [24][25][26]. Various types of hydrophobic polymer membranes were already investigated, e.g., low-density polyethylene (LDPE) [17,27,28], Teflon ® AF [29][30][31], poly(dimethylsiloxane) (PDMS) [32][33][34], polyisobutylene (PIB) [17,[35][36][37], and E/P-co polymer [16,35,[38][39][40][41]. However, within harsh environments the polymer coating can come off.…”