2 research outputs found
Mid-Infrared Spectroscopic Method for the Identification and Quantification of Dissolved Oil Components in Marine Environments
The
use of mid-infrared sensors based on conventional spectroscopic
equipment for oil spill monitoring and fingerprinting in aqueous systems
has to date been mainly confined to laboratory environments. This
paper presents a portable-based mid-infrared attenuated total reflectance
(MIR-ATR) sensor system that was used to quantify a number of environmentally
relevant hydrocarbon contaminants in marine water. The sensor comprises
a polymer-coated diamond waveguide in combination with a room-temperature
operated pyroelectric detector, and the analytical performance was
optimized by evaluating the influence of polymer composition, polymer
film thickness, and solution flow rate on the sensor response. Uncertainties
regarding the analytical performance and instrument specifications
for dissolved oil detection were investigated using real-world seawater
matrices. The reliability of the sensor was tested by exposition to
known volumes of different oils; crude oil and diesel samples were
equilibrated with seawater and then analyzed using the developed MIR-ATR
sensor system. For validation, gas chromatographic measurements were
performed revealing that the MIR-ATR sensor is a promising on-site
monitoring tool for determining the concentration of a range of dissolved
oil components in seawater at ppb to ppm levels
Using Plasticizers to Control the Hydrocarbon Selectivity of a Poly(Methyl Methacrylate)-Coated Quartz Crystal Microbalance Sensor
Chemical sensors based on a polymer coated quartz crystal
microbalance
(QCM) generally present poor molecular selectivity for compounds that
contain similar functional groups and possess the same chemical properties.
This paper shows for the first time that the selectivity and sensitivity
of a polyÂ(methyl methacrylate) (PMMA) based QCM sensor can be significantly
enhanced for aromatic hydrocarbons by incorporating a plasticizer
into the polymer film. The sensor was fabricated by spin coating PMMA
onto a quartz crystal, and the influence of plasticizer type and amount
on the response was evaluated. It was shown that the hydrocarbon sensitivity
of plasticizer-free PMMA is negligible, while the sensitivity of plasticized
PMMA was similar to or in some cases greater relative to highly responsive
rubbery polymers such as polyisobutylene (PIB). Detection limits of
4.0, 1.5, 0.4, 0.6, and 0.1 ppm were obtained on a PMMA film containing
25% w/w diÂ(2-ethylhexyl) phthalate for benzene, toluene, ethylbenzene, <i>p</i>-xylene, and naphthalene, respectively. We found that at
low plasticizer levels (∼10% w/w) the PMMA film was more sensitive
toward ethylbenzene and <i>p</i>-xylene over naphthalene
when compared to a PIB film under similar measurement conditions.
Attenuated total reflectance Fourier transform infrared spectroscopy
(ATR-FTIR) measurements were performed to understand the sensing mechanism,
and these studies confirmed a higher hydrocarbon uptake by PMMA in
the presence of plasticizer. Positron annihilation lifetime spectroscopy
(PALS) studies detected variations in the free volume properties of
the polymer films as a function of plasticizer content. The accessible
free volume as measured by PALS was significantly less in the PMMA
films compared to the PIB, and this result correlates favorably with
differences in the QCM response pattern. The QCM results have been
rationalized in terms of free volume theory which is responsible for
the higher hydrocarbon diffusion/sorption with increased plasticizer
content