Volatile Organic Compounds In Aqueous Solutions Research Articles

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

Volatile organic compounds (VOCs) are one of the most commonly detected contaminants in water. The occurrence is mainly in gasoline and other petroleum-based products, fumigants, paints and plastics. Releases into the environment and the widespread use have an impact on the ecosystem such as humans and animals due to their toxicity, mutagenicity, and carcinogenicity. VOCs may persist in groundwater and may enter drinking water supplies. In this paper, a diamond-like carbon (DLC)-coated silicon waveguide in combination with a polymer film (ethylene/propylene copolymer, E/P-co) for enrichment of analytes was investigated to determine its suitability for ATR-FTIR (attenuated total reflection Fourier transform infrared) spectroscopic detection of VOCs. The DLC film was fluorine-terminated enhancing the adhesion of the hydrophobic polymer to the waveguide surface. The analytes diffuse into the hydrophobic polymer whereas water is excluded from the emanating evanescent field. Therefore, direct detection in aqueous systems is enabled. Nine VOCs, i.e., ethylbenzene (EB), trichloroethylene (TCE), tetrachloroethylene (TeCE), the xylene isomers (p-xylene, pXYL; m-xylene, mXYL; o-xylene, oXYL), naphthalene (NAPH), toluene (TOL), and benzene (BENZ), were evaluated simultaneously qualitatively and quantitatively showing the potential of DLC coatings revealing high sensitivities in the low ppb to ppm concentration range, i.e., 50 ppb for TeCE. To the best of our knowledge, this is the first time of IR spectroscopic detection of VOCs in aqueous solutions using DLC-coated waveguides in combination with a hydrophobic polymer. By utilizing a DLC-coated waveguide, a versatile sensor for real-time monitoring in harsh environments such as effluents, leaking pipelines, and underground storage tanks is feasible due to response times within a few minutes.

A sandwich temperature control membrane inlet mass spectrometer for dissolved gases and volatile organic compounds in aqueous solution

A sandwich temperature control membrane inlet system based on a miniature mass spectrometer is presented that demonstrates improved analytical performance for the measurement of dissolved gases and volatile organic compounds (VOCs) in aqueous solution. Aqueous solution is directly brought to the monolayer flat membrane interface at a constant flow rate. A heating resistor and a thermocouple are fixed on the side of the membrane and aqueous solution respectively. This new strategy allows for a temperature compensation method, affording an improvement of sensitivity and a reduction of response time compared with the conventional heating solution temperature control strategy. Furthermore, a static heating mode is applied to effectively remove the memory effect. Automatic sampling and measurement are achieved by using the membrane inlet system with silicone sheeting of 50 μm thickness. The vacuum is below 3 × 10−5 Torr, which can make the instrument work normally. A good linear response is observed for benzene in the range of 0.1 ppm–10 ppm and the detection limit is 50 ppb. The analytical capacity of this system is demonstrated by the on-line analysis of VOCs in aqueous solution, in which the dominant ions are detected rapidly. The results indicate that the sandwich temperature control membrane inlet mass spectrometer (STC-MIMS) has a potential application for on-line analyzing organic pollution in aquatic environments.

Development of a printed sensor for volatile organic compound detection at μg/L-level

The detection of volatile organic compounds (VOCs) at low μg/L levels in aqueous solution is accomplished using a resistive sensor. In particular, a flexible sensor manufactured by printing techniques is presented: its electrodes are defined with silver nanoparticles ink by inkjet printing, while its sensitive layer based on graphite and polystyrene is deposited by screen printing. The influence of different manufacturing parameters is analyzed: mesh density of the screen, ink composition and electrode configuration. The lower the mesh density of the screen is, the higher the resolution obtained and the lower the resistance value achieved. Inks with higher graphite content results in lower resistance values and better time responses. Higher resistance values are obtained with the serpentine electrode. In addition, the response of the sensor to different VOCs in aqueous solution is shown, finding the highest sensitivity to benzene, followed by o-xylene, p-xylene, m-xylene and toluene, in this order. All these results foresee that it is a promising device.

Permeation of Volatile Organic Compounds through EVOH Thin Film Membranes and Coextruded LLDPE/EVOH/LLDPE Geomembranes

Abstract Coextruded geomembranes with an inner ethylene vinyl alcohol (EVOH) layer are gaining attention as potential improved barriers to volatile organic compounds (VOCs) when used in barrier systems that would traditionally use high-density polyethylene (HDPE) geomembranes. The permeation characteristics of nine common VOCs in aqueous solutions through the EVOH layer are investigated for two thin films: a 0.015-mm-thick, 32 mol% EVOH and a 0.02-mm-thick, 44 mol% EVOH. The VOCs included aromatic hydrocarbons [benzene, toluene, ethylbenzene, and xylenes (BTEX)] and chlorinated hydrocarbons [1,2-dichloroethane (1,2-DCA), dichloromethane (DCM), trichloroethylene (TCE), and tetrachloroethylene (PCE)]. The BTEX permeation coefficients, P g , range from 1.4 × 10 − 14 to 25 × 10 − 14 m 2 ⋅ s − 1 depending on the contaminant and mol% EVOH. When a 0.02-mm-thick, 38 mol% EVOH thin film layer is coextruded with linear low-density polyethylene (LLDPE) to form a 0.53-mm-thick geomembrane, the BTEX permeation v...

Application of gold complexes in the development of sensors for volatile organic compounds

Two different kinds of sensors have been developed by using the same kind of vapochromic complexes. The vapochromic materials [Au2Ag2(C6F5)4L2]n have different colours depending on the ligand L. These materials change, reversibly, their optical properties, colour and fluorescence, in the presence of the vapours of volatile organic compounds (VOCs). For practical applications, two different ways of fixing the vapochromic material to the optical fibre have been used: the sol-gel technique and the electrostatic self-assembly method (ESA). With the first technique the sensors can even be used to detect VOCs in aqueous solutions, and using the second method it has been possible to develop nanosensors.

Cooled internal reflection element for infrared chemical sensing of volatile to semi-volatile organic compounds in the headspace of aqueous solutions

In this study, the cooling effect was applied to an evanescent wave type infrared (IR) chemical sensing method to effectively trap volatile organic compounds (VOCs), which have been absorbed in the hydrophobic film coated around the internal reflection element (IRE). The detection of VOCs in aqueous solutions was taken in the headspace of the aqueous solution. This method eliminates the long-term instability of hydrophobic film soaked in an aqueous solution and the potential spectral interference caused by the matrix of the aqueous solution. Thermal energy has been applied to the aqueous solution to assist in the evaporation of VOCs out of the aqueous matrix. By applying a cooling system to the IRE, the excess thermal energy can be removed leading to more stable IR signals. After examination of organic compounds with vapour pressure ( P v) ranging from 0.017 to 150 Torr, significant differences were found between IR signals from cooled and un-cooled systems. Because the thermal conductivity of the IRE used in IR detection is typically low; the efficiency in removing the thermal energy is limited. By heating the aqueous solutions to different temperatures, the IR signals showed that the sample temperature was limited to around 80 °C. The IR signal determination results for five different volatility organic compounds indicated that the optimal heating temperature was not necessary to match with the volatilities of organic compounds in cooling system. The linear regression coefficient ( R 2) of the standard curve for sample concentrations in the range 5–200 μg ml −1 was generally higher than 0.991 and the detection limit was around a few hundred ng ml −1, which was two to three times lower than that of un-cooled system.