RESUMEN

This paper describes the synthesis of a nano-porous multilayered film consisting of Au@SiO2 nanoparticles. This film was used to miniaturize the size of a localized surface plasmon resonance (LSPR)-based capillary gas chromatograph (GC) detector. A layer-by-layer (LbL) approach with proper surface reaction sequences was used to create a multilayer structure that consisted of as many as five layers of Au@SiO2 nanoparticles. The center wavelength of LSPR was shifted from 520 to 634 nm due to the approximation of additional layers of nanoparticles. The vapor response time for this Au@SiO2 multilayer LSPR sensor was identical to that of an Au nanoparticle monolayer, which confirmed that this multilayer structure has a high level of gas permeability. The multilayer was synthesized inside a glass capillary for use as a GC detector. Due to the enhancement of absorbance, the gas chromatographic signal was obtained via a single spotlight that penetrated one side of the glass capillary and was then reflected by a silver mirror coated on the opposite side. The detection limits were ≤20 ng for cyclohexanone and m-xylene.

RESUMEN

This paper presents the design, assembly, and evaluation of a novel gas chromatographic detector intended to measure the absorbance of the localized surface plasmon resonance (LSPR) of a gold nanoparticle monolayer in response to eluted samples from a capillary column. Gold nanoparticles were chemically immobilized on the inner wall of a glass capillary (i.d. 0.8 mm, length = 5-15 cm). The eluted samples flowed through the glass capillary and were adsorbed onto a gold nanoparticle surface, which resulted in changes in the LSPR absorbance. The LSPR probing light source used a green light-emitting diode (LED; λ(center) = 520 nm), and the light traveled through the glass wall of the capillary with multiple total reflections. The changes in the light intensity were measured by a photodiode at the rear of the glass capillary. The sensitivity of this detector can be improved by using a longer spiral glass capillary. The detector is more sensitive when operated at a lower temperature and at a slower carrier velocity. The calibration lines of 8 preliminary test compounds were all linear (R(2) > 0.99). The detection limits (3σ) ranged from 22 ng (n-butanol) to 174 ng (2-pentanone) depending on the volatility of the chemicals and the affinity to the citrate lignads attached to the gold nanoparticle surface. This detector consumed a very low amount of energy and could be operated with an air carrier gas, which makes this detector a promising option for portable GC or µGC.

RESUMEN

This paper reports the results from a field study that used a micro gas chromatograph (µGC) in conjunction with single gas chromatography-mass spectrometry (GC-MS) analysis to obtain the time-dependent concentration changes of individual volatile organic compounds (VOCs). The µGC is capable of performing sub-ppb analysis every 15min and has a total weight of only 3kg, which includes an embedded tablet computer. The field study was conducted in an elementary school near a chemical industrial area. Six VOCs including acetone, 2-butanone, methyl acetate, toluene, m-xylene and isobutyl acetate, were detected at low ppb levels via canister/GC-MS analysis. Five of the six chemicals were successfully quantified using the µGC. The lone exception was acetone, which prematurely breakthrough on the preconcentrator of the µGC because of its high volatility. The continuous analyses performed by the µGC revealed the individual temporal trends of the concentrations for the remaining 5 chemicals. The establishment of real-time trends for each of the chemicals enabled a detailed examination of their correlations.

Asunto(s)

Contaminantes Atmosféricos/análisis , Contaminación del Aire Interior/análisis , Monitoreo del Ambiente/métodos , Compuestos Orgánicos Volátiles/análisis , Contaminación del Aire Interior/estadística & datos numéricos , Butanonas/análisis , Cromatografía de Gases , Cromatografía de Gases y Espectrometría de Masas , Instituciones Académicas , Xilenos/análisis

RESUMEN

A dual-chip, multidimensional micro gas chromatographic module was designed, built and evaluated. Column chips were fabricated on a silicon wafer with an etched rectangular channel 100 µm (width) × 250 µm (depth) using a deep reactive ion etching (DRIE) process. The column chip for the first GC dimension was 3 m long and was coated with polydimethylsiloxane (DB-1) as the stationary phase. The columns on the second dimensional chip were etched with the same width and depth as the first chip, but the flow channel was split into three parallel columns, 1 m long, on the same sized silicon chip (i.e., 3 cm × 3 cm). These three parallel columns on the second chip were coated with polyethylene oxide (DB-Wax), trifluoropropylpolymethylsilicone (OV-210) and cyanopropylmethylphenylmethylpolysilicone (OV-225), accordingly, in order to provide diversified chromatographic retention. These two chips were connected via a stop-flow configuration to simultaneously generate multiple two-dimensional gas chromatograms for every analysis. This stop-flow µGC × µGCs design allowed the first column to function as a pre-separator and as a sequencing injector for the second parallel-separation chip. Fifteen volatile organic compounds with boiling points that ranged from 80-131 °C with various functional groups were tested using this µGC × µGCs module. Three discrete 2-D chromatograms were generated simultaneously, which demonstrated the advantages of simultaneously combining GC × GC with parallel separation GCs in microchip chromatography. The total traveling length in the column was only 4 m for each eluted peak and fully resolved separation was achieved through the cross reference among triplet 2-D chromatograms.

RESUMEN

Aspects of the design, fabrication, and characterization of a chemiresistor type of microdetector for use in conjunction with gas chromatograph are described. The detector was manufactured on silicon chips using microelectromechanical systems (MEMS) technology. Detection was based on measuring changes in resistance across a film comprised of monolayer-protected gold nanoclusters (MPCs). When chromatographic separated molecules entered the detector cell, the MPC film absorbed vapor and undergoes swelling, then the resistance changes accordingly. Thiolates were used as ligand shells to encapsulate the nano-gold core and to manipulate the selectivity of the detector array. The dimensions of the µ-detector array were 14(L)×3.9(W)×1.2(H)mm. Mixtures of eight volatile organic compounds with different functional groups and volatility were tested to characterize the selectivity of the µ-detector array. The detector responses were rapid, reversible, and linear for all of the tested compounds. The detection limits ranged from 2 to 111ng, and were related to both the compound volatility and the selectivity of the surface ligands on the gold nanoparticles. Design and operation parameters such as flow rate, detector temperature, and width of the micro-fluidic channel were investigated. Reduction of the detector temperature resulted in improved sensitivity due to increased absorption. When a wider flow channel was used, the signal-to-noise ratio was improved due to the larger sensing area. The extremely low power consumption and small size makes this µ-detector array potentially useful for the development of integrated µ-GC.