Quantitative Solid-Phase Microextraction (SPME)–Raman Spectroscopy for the Detection of Trace Organics in Water

Abstract

Solid-phase microextraction (SPME) was used along with Raman spectroscopy to quantify the partitioning of trace organics into polydimethylsiloxane (PDMS) matrices. PDMS has previously been utilized with SPME-Raman to pre-concentrate trace benzene, toluene, ethyl-benzene, and xylene fuel components from contaminated water, thereby enhancing detected Raman signals. Here, we show that SPME can increase Raman signals more than two orders of magnitude for the compounds investigated. We also demonstrate the quantitative features of SPME-Raman by estimating PDMS-organic partition coefficients for benzene [log(K) = 1.90 ± 10] and toluene [log(K) = 2.35 ± 20] by using linear regression fits in the dilute limit of concentrations. The K values obtained are within the range of values obtained with other quantitative SPME techniques. The method was also used to characterize quinoline, a pyridine-based organic, which yielded reasonable K values [log(K) = 1.20 ± 20]. Combining PDMS-based SPME with a technique such as Raman spectroscopy potentially enhances optical detection methods used in microfluidic systems, wherein PDMS is a common material of construction.

Rational design of polymer-based absorbents: application to the fermentation inhibitor furfural

“…Also included in Figure 1 are experimental values of found in the literature for the partitioning of toluene into five different polymer phases. Symbols x and o represent experimental values from our work [ 16 ] and literature sources [ 28 - 31 ], respectively. From these data, we can see that the Flory-Huggins theoretical predictions adequately estimate the partition coefficient of toluene across several different polymer extraction phases.…”

“…A key thermodynamic parameter that describes the potential of a polymer to separate a target molecule is the partition coefficient [ 13 - 18 ]. Tailoring the traits of the polymer to the trace aqueous component is a common strategy for environmental contaminants like toluene and benzene, where hydrophobic polymers are used to extract low-solubility non-polar molecules from the aqueous solvent [ 16 , 19 , 20 ]. In contrast, polar fermentation inhibitors like furfural in the pre-fermentation broths will require a more polar polymeric species for an effective separation scheme.…”

“…The critical parameter that quantifies the absorption partitioning for a species ( i ) between a polymer ( p ) and a solvent (water = w ) is the equilibrium partition coefficient ( ), which can be expressed experimentally by [ 16 ]; where C p is the equilibrium concentration of the target compound in the polymer phase and C w is its equilibrium concentration in the water phase. The larger the value, the greater the affinity the target molecule has for the chosen polymer phase.…”

Raman Spectroscopy for In-Line Water Quality Monitoring—Instrumentation and Potential

“…Microfluidic devices have been used for miniaturized pre-concentration of chemicals and contaminants for rapid and direct chemical analysis [ 62 , 63 ]. In [ 64 ], PDMS was used with SPME to pre-concentrate organic compounds, and the Raman signal intensity was reported to be increased by more than two orders of magnitude. However, most of the pre-concentration strategies are time consuming and the setups are complex.…”

Microfluidics and Solid-phase Microextraction Effects in SERS Chips for Rapid and Sensitive Malathion Detection

“…Many efforts had been carried out to increase the active concentration of analyte on the surface of nanostructure or nanoparticles substrates using well designed photonic crystal fiber, as well as using active or passive microfluidic techniques such as electrical/magnetic field, nanofluidic channel, nanoporous silica microspheres, and flow-through microhole array [1,2]. By utilizing Solid Phase Micro-Extraction (SPME) effect for pre-concentration, a PDMS microfluidcs chip with quasi-3D (Q3D) gold plasmonic nanostructure arrays, which serve as SERS-active substrates, was experimentally proved to be sensitive and efficient for detecting malathion, a widely used organophosphate insecticide that can contaminate waterways after application in agricultural areas [3,4].…”