Silica sol-gels that are processed at room temperature contain residual solute. By selection of salts that have the properties of a humidistat in the sol, the resulting gel will contain a controlled amount of water, thereby making the resistance of the sol-gel independent of humidity of a contacting gas phase. Further, when the processing conditions result in a mesoporous sol-gel, diffusion coefficients of electroactive species that are encapsulated therein are in the 10 -6 cm 2 s -1 range. The latter is illustrated by the cyclic voltammetry of hexacyanoferrate when a solid-state cell is fabricated to incorporate three electrodes in the silica matrix. This design is extended to the voltammetry of gas-phase species by extending the working electrode beyond the sol-gel so that a three-phase boundary is formed. In this manner the detection of carbon monoxide, hydrazine, and hydrogen peroxide by amperometry is achieved. This cell design was evaluated as an amperometric detector for gas chromatography. Initial experiments were in the flow injection mode with He flowed at 0.63 mL min -1 as the carrier gas and100- µL injections of H 2 comprised the sample. Wirh a Pt working electrode at 0.5 V vs. a Pt quasi-reference electrode, linear response to concentration over range 1.7 x 10 -6 g to 7.6 x 10 -6 g was observed. Extensions to 1,2-ethandithiol, phenol, p-cresol, and thioanisole yielded detection limits of 4, 1, 3, and 70 ppmv (k = 3 criterion), respectively, when operating the working electrode at 800 mV. Application to aqueous samples in the absence of supporting electrolyte also were achieved; however, a problem is that leaching of the electrolyte from the sol-gel cell was a limitation. To address this problem, the sol-gel matrix is being modified to contain a macromolar cation (anion) of a size that is greater than the ca. 0.5 nm pore size of the silica. An example is to immobilize 3,4- ethyelenedioxythiophene (EDOT) in the sol-gel and oxidize it to the polymeric form, PEDOT. Results on the polymerization process will be shown, and the efficacy of the resulting composite as a matrix for a probe to determine various species in water in the absence of supporting electrolyte will be presented.

ZnO nanoparticles were successfully synthesized within the free volume of an ethylene vinyl acetate (EVA) polymer sheet. Using a process termed nanoinfusion, nanoparticles are created in situ. Vapor phase nanoparticle precursors first filled the polymer free volume. Nucleated components of the precursor molecule within the free volume enabled nanoparticle formation and immobilization within the polymer. Trapped nanoparticles were accessible to gas diffusion and can be modified as was demonstrated by the successful conversion of nanoinfused ZnO to ZnS nanoparticles. Successful nanoparticle formation was confirmed through fluorescence spectroscopy and the amount of material nanoinfused was obtained through thermal gravimetric analysis. The nanoinfused ZnO and ZnS exhibited unexpectedly high fluorescent quantum yields, significantly higher than that observed for comparable materials. (c) 2013 Society of Plastics Engineers

A sensor system for the automatic, in-line, determination of chlorite ion is reported. Electroanalytical measurements were performed in electrolyte-free liquids by using an electrochemical probe (EC), which enables in-line detection in high-resistance media such as disinfected water. Cyclic voltammetry scan rate studies suggest that the current arising from the oxidation of chlorite ion at an EC probe is mass-transfer limited. By coupling FIA with an EC probe amperometric cell, automated analysis was achieved. This sensor is intended to fulfill the daily monitoring requirements of the EPA DBP regulations for chlorite ion. Detection limits of 0.02-0.13 mg/L were attained, which is about one order of magnitude below the MRDL. The sensor showed no faradaic signal for perchlorate, chlorate, or nitrate. The lifetime and stability of the sensor were investigated by measuring calibration curves over time under constant-flow conditions. Detection limits of <0.1 mg/L were repeatedly achieved over a period of three weeks.

Terahertz (THz) time-domain spectroscopy was used to monitor collective mode shifts in l-serine, l-serine-2,3,3-d(3), l-serine-d(4), and l-serine-d(7) at both room and liquid nitrogen (LN(2)) temperatures. Increasing the molecular mass by deuteration caused an expected absorbance red-shift; however, the magnitude of the displacement could not be predicted using normal mode analysis. Both modes at 67.8 cm(-1) and 91.4 cm(-1) demonstrated a greater peak shift upon deuterium substitution at non-hydrogen bonding sites than at sites that participated in hydrogen bonding. This is evident in the larger peak shifts observed in l-serine-d(3) than in l-serine-d(4), despite a smaller increase in mass. This leads to the conclusion that both peaks present in the room temperature spectra of l-serine likely arise primarily from other intermolecular interactions with <50% contribution from hydrogen bonding. This goes against the prediction that peaks in the THz spectra of amino acids are predominantly due to the hydrogen bonding network that makes up the crystal lattice.

Terahertz (THz) time-domain reflectance spectroscopy is evaluated as a technique for nondestructive analysis of sol–gels over the first week of aging without directly contacting or disturbing the sol–gels. In the sol–gels analyzed, tetramethyl orthosilicate (TMOS) is the precursor and polyamidoamine (PAMAM) dendrimers are incorporated into each of two sol–gel sample groups; a third control group contains no dendrimer. The study reports data acquired during sol–gel aging in contrasting humidity and ventilation conditions and determines statistically whether the inclusion of a particular dendrimer and/or the humidity and air circulation of the environment produce significant differences in the THz reflectance intensity observed throughout the first week of sol–gel aging. The results of this study are correlated with previous studies of the same three species analyzed using AFM, impact testing and nitrogen adsorption. The correlations are used to interpret the THz reflectance intensity differences between the sol–gel groups studied using the previously reported results from established methods of analysis regarding the influence of each dendrimer on polymer density, pore size and distribution, and homogeneity of the resulting amorphous silica monoliths.

A sensitive, rapid, and rugged liquid chromatography with tandem mass spectrometry (LC-MS/MS) method for measuring concentrations of perchlorate, chlorate, and bromate ions in concentrated sodium hypochlorite solutions is presented. The LC-MS/MS method offers a practical quantitation limit (PQL) of 0.05 microg L(-1) for ClO(4)(-), 0.2 microg L(-1) for BrO(3)(-), and 0.7 microg L(-1) for ClO(3)(-) and a sample analysis time of only 10 min. Additionally, an iodometric titration technique was compared with the LC-MS/MS method for measurement of chlorate ion at high concentration. The LC-MS/MS method was the most reproducible for chlorate concentrations below 0.025 M while the iodometric titration method employed was the most reproducible above 0.025 M. By using both methods, concentrations of chlorate can be measured over a wide range, from 0.7 microg L(-1) to 210 g L(-1) in hypochlorite ion solutions. Seven quenching agents were also evaluated for their ability to neutralize hypochlorite ion, thereby stopping formation of perchlorate ion in solution, without adversely impacting the other oxyhalide ions. Malonic acid was chosen as the quenching agent of choice, meeting all evaluation criteria outlined in this manuscript.

A new dispersive vapor extraction (DVE) technique for rapid removal of selected volatile organic compounds (VOCs) from gaseous mixtures was investigated. In this technique, less than 1.0 mL of a volatile solvent was vaporized for 8 min in a 250-mL flask containing a gaseous mixture. The flask was then cooled under running tap water for 2–3 min to induce condensation of the vapor and co-extraction of the VOCs from the headspace. The technique was tested over a concentration range of 4–23 ppb, and resulted in extraction efficiencies ranging from 80 to 97% for the VOCs tested. Because of its simplicity and the relatively short sampling time, DVE could potentially lead to high sample throughput and rapid air analysis.

A new dispersive vapor extraction (DVE) technique for rapid removal of selected volatile organic compounds (VOCs) from gaseous mixtures was investigated. In this technique, less than 1.0mL of a volatile solvent was vaporized for 8min in a 250-mL flask containing a gaseous mixture. The flask was then cooled under running tap water for 2–3min to induce condensation of the vapor and co-extraction of the VOCs from the headspace. The technique was tested over a concentration range of 4–23ppb, and resulted in extraction efficiencies ranging from 80 to 97% for the VOCs tested. Because of its simplicity and the relatively short sampling time, DVE could potentially lead to high sample throughput and rapid air analysis.

We have observed collective mode frequency shifts in deuterium-substituted L-alanine, three of which have previously only been calculated. Terahertz (THz) absorbance spectra were acquired at room temperature in the spectral range of 66-90 cm(-1), or 2.0-2.7 THz, for L-alanine (L-Ala) and four L-Ala compounds in which hydrogen atoms (atomic mass = 1 amu) were substituted with deuterium atoms (atomic mass = 2 amu): L-Ala-2-d, L-Ala-3,3,3-d(3), L-Ala-2,3,3,3-d(4), and L-Ala-d(7). The absorbance maxima of two L-Ala collective modes in this spectral range were recorded for multiple spectral measurements of each compound, and the magnitude of each collective mode frequency shift due to increased mass of these specific atoms was evaluated for statistical significance. Calculations were performed which predict the THz absorbance frequencies based on the estimated reduced mass of the modes. The shifts in absorbance maxima were correlated with the location(s) of the substituted deuterium atom(s) in the L-alanine molecule, and the atoms contributing to the absorbing delocalized mode in the crystal structure were deduced using statistics described herein. The statistical analyses presented also indicate that the precision of the method allows reproducible frequency shifts as small as 1 cm(-1) or 0.03 THz to be observed and that these shifts are not random error in the measurement.

Gold nanoislands interact with gaseous ozone to produce a surface plasmon resonance shift, similarly to the interaction of ozone and gold nanoparticles in water. Gold nanoislands are produced by sputtering, which significantly simplifies the synthesis and produces controlled size for the gold nanoislands. The shift of surface plasmon resonance peak was monitored while gold nanoislands were exposed to variable concentration of gaseous ozone. The shift was then correlated with ozone concentration. Our current results indicate sensing gaseous ozone at concentration of as low as 20 microg/L is achievable. Gold nanoislands were reversed to their original wavelength and were able to cycle between the wavelengths as ozone was introduced and removed. Potentially, this system can be useful as a sensor that identifies the presence of ozone at low part-per-billion concentrations of ozone in gaseous media.

The quantitative measurement of jet fuel additives in the field is of interest to the Air Force. The "smart nozzle" project was designed as a state-of-the-art diagnostics package attached to a single-point refueling nozzle for assessing key fuel properties as the fuel is dispensed. The objective of the work was to show proof of concept that a layer-by-layer thin film and long period grating fibers could be used to detect the presence of water in jet fuel. The data for the nafion/PDMA film and a long period grating fiber is a combination capable of quantitative measurement of water in kerosene. The average response (spectral loss wavelength shift) to the kerosene sample ranged from -6.0 for 15 ppm to -126.5 for 60 ppm water. The average calculated value for the check standard was 21.71 and ranged from 21.25 to 22.00 with a true value of 22.5 ppm water. Potential interferences were observed and are judged to be insignificant in real samples.

Aqueous foam drainage has been studied using terahertz (THz) spectroscopy. Water is highly absorbing of THz radiation, allowing drainage to be determined based on water content at respective foam height. These drainage profiles were validated using a model constructed from published equations and tailored to this specific study. In addition, a slow-draining foam was scanned to produce a two-dimensional foam image.

Foams are important in many industrial applications and as such require appreciable characterization techniques. Current methods used to investigate foam properties, including drainage and structure, cannot fully contribute sufficient information. The work expressed in this paper details the application of terahertz (THz) spectroscopy to studying foam drainage by way of transmissive radiation absorption, Data shown support the wealth of information obtained including both static and kinetic data of foam drainage.

In aqueous, un-buffered solution at a potential where H+ is generated in a tetraethylorthosilicate sol, nm-scale deposits of silica on electrodes are formed. Inclusion of beta-cyclodextrin in the sol promotes electrochemical activity, presumably by producing channels in the otherwise-passivating film. With the additional provision of inclusion of a redox mediator, Rh-II, the electrochemical oxidation of a representative phospholipid (PL), phosphatidylcholine (PC), is demonstrated; the process occurs without the passivation that otherwise precludes the voltammetric determination of PLs. By cyclic voltammetry, current proportional to PC concentration in the range 1 - 100 mu M is achieved with the described electrode.

Microwave radiation simplifies synthesis methods by reducing reaction times, requiring fewer materials, and also controlling reaction processes. We have successfully synthesized nanoparticles of iron oxide and zinc oxide coated on zeolite A using microwaves. The radiation assisted in displacing either ferrous or zinc ions from the pre-loaded zeolite network and increasing reaction speed with solution at the interface. Products were characterized by TEM, XRD, VSM, ICP-AES, and fluorescence. We demonstrate the ability of using cation-exchanged zeolites as microreactors to bias reactions onto the zeolite surface. Efficient structure-directed surface reactions are a potential route to making unique supported nanomaterials for applications such as sensors, environmental remediation, and chemical catalysis.

Sensors based on changes of refractive index in response to sorption of an analyte on the coating or film of a long period grating fiber (LPG) fiber have recently been reported. In most prior work the coating or film swelled during interaction with the analyte. The swelling mechanism produced a kinetic response that slowed both the sensor's time for steady-state measurement and the reversibility of the sensor. Here, the analytical utility of fabricating these nanometer thin films using the layer-by-layer (LBL) electrostatic assembly method is evaluated using Cu(II) as the test analyte and Cibacron Blue as the reagent immobilized in the LBL assembly; a generation-4 poly(amidoamine) dendrimer served as the spacer in the assembly. Detection of 1.3mgCu(II)L(-1) was observed when six bilayers comprised the coating. The stable response was achieved with 0.6mgL(-1) in less than 1min. When 0.1M HCl was used as the rinsing solution, this LPG sensor was reversible and the signal to similar concentrations of Cu(II) reproducible.

Ozone is a drinking water disinfectant that quickly and efficiently kills many types of pathogens. However, the ozonation of bromide ion containing waters can form the disinfection byproduct, bromate ion. Bromate ion is a possible human carcinogen that is regulated by the US EPA at a Maximum Contaminant Level (MCL) of 10 micrograms per liter (μg/L). The lifetime risk at the MCL was calculated from studies where laboratory animals received large doses of bromate ion that would produce effects in their lifetimes. The data from these large doses was fitted to a low-dose linear extrapolation (also called a linearized dose-response) model. The model assumes there is a finite, albeit small, risk at any dose above zero of a genotoxic carcinogen. The validity of the linearized dose-response model projection at low doses is being questioned (i.e., the actual shape and slope of the dose/response as the dose approaches zero). The test system is bromate ion in synthetic and real gastric juices. The results reported here show that the bromate ion half-life, in the presence of typical H+, Cl−, and H2S concentrations found in the stomach, is 1.5–2 minutes. Thus, as much as 99% of the ingested bromate ion should be decomposed, while it is retained in the stomach. The results of these experiments will be used in the development of a more scientifically rigorous methodology for determining low level effects of bromate ion.

This study was designed to identify and quantify the effects of reducing agents on the rate of bromate ion reduction in real and synthetic gastric juice. This could be the first element in the sequence of a pharmacokinetic description of the fate of bromate ion entering the organism, being metabolized, and subsequently being tracked through the system to the target cell or eliminated. Synthetic gastric juice containing H+ and Cl- did exhibit reduced bromate ion levels, but at a rate that was too slow for a significant amount of bromate to be reduced under typical stomach retention time conditions. The reaction orders for Cl- and H+ were 1.50 and 2.0, respectively. Addition of the reducing agents hydrogen sulfide (which was shown to be present and quantified in real gastric juice), glutathione, and/or cysteine increased the rate of bromate ion loss. All of the reactions showed significant pH effects. Half-lives as short as 2 min were measured for bromate ion reduction in 0.17 M H+ and Cl- and 10(-4) M H2S. Therefore, the lifetime of bromate ion in solutions containing typical gastric juice concentrations of H+, Cl-, and H2S is 20-30 min. This rate should result in as much as a 99% reduction of bromate ion during its residence in the stomach. Bromate ion reduction in real gastric juice occurred at a rapid rate. A comparison of real and synthetic gastric juice containing H+, Cl-, cysteine, glutathione, and hydrogen sulfide showed that the component most responsible for the considerable decrease of the concentration of bromate ion in the stomach is hydrogen sulfide.

Unmodified and modified gold nanoparticles are proposed as sensors using the red to blue transition as an indicator. This work indicates that ionic content is an important variable to track in analytical samples and during the sensor fabrication processes. Mono and multivalent salts where the titrants for a standard gold nanoparticle solution. Multivalent cation salt titrants exhibited a greater sensitivity to color change than monovalent cation salts. The data suggest that specific surface adsorption is the predominant mechanism for the red to blue color change not aggregation. The 3–7 nm Debye length for divalent cations versus the 0.5–1.5 nm for monovalent cations indicates surface electrodynamic resonance effects are an important factor in the observed color changes.