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The fundamental transport theory for ion mobility spectrometry is modified to include effects of space charge. The new theory is then applied to describing the performance of 'inverse ion mobility spectrometry' recently reported in Tabrizchi, M.; Jazan, E. Anal. Chem. 2010, 82, 746-750 using a discharge ionization source. The improved separation capabilities arise from space charge repulsion of the greater number of ions that are introduced into the drift tube by the technique. A larger effective diffusion coefficient and additional displacement velocides for the leading and trailing edges of the ion mobility peak account for the results. Performance is compared to conventional linear ion mobility spectrometry, with and without a radioactive source for ionization. 10.1021/ac100240t

The ion mobility spectrometry (IMS) methods are grouped into conventional IMS, based on the absolute ion mobility, and differential or field asymmetric waveform IMS (FAIMS), based on mobility differences between strong and weak electric fields. A key attraction of FAIMS is substantial orthogonality to mass spectrometry (MS). Although several FAIMS/MS platforms were commercialized, their utility was limited by FAIMS resolving power, typically ~10-20. Recently, gas mixtures comprising up to 75% He have enabled resolving power >100 that permits separation of numerous heretofore 'coeluting' isomers. This performance opens major new proteomic and other biological applications. Here, we show that raising the separation field by ~35% over the previous 21 kV/cm provides similar or better resolution (with resolving powers of >200 for multiply charged peptides) using only 50% He, which avoids problems due to elevated pressure and He content in the mass spectrometer. The heating of ions by the separation field in this regime exceeds that at higher He content but weaker field, inducing greater izomerization of labile species. 10.1021/ac101413k

Cavity ring-down spectroscopy is a spectroscopic method that uses a high quality optical cavity to amplify the optical loss due to the light absorption by a sample. In this presentation we highlight two applications of phase-shift cavity ring-down spectroscopy that are suited for absorption measurements in the condensed phase and make use of waveguide cavities. In the first application, a fiber loop is used as an optical cavity and the sample is introduced in a gap in the loop to allow absorption measurements of nanoliters of solution at the micromolar level. A second application involves silica microspheres as high finesse cavities. Information on the refractive index and absorption of a thin film of ethylene diamine on the surface of the microresonator is obtained simultaneously by the measurements of the wavelength shift of the cavity mode spectrum and the change in optical decay time, respectively. Key words: cavity ring-down spectroscopy, microresonator, microsphere, fiber loop. La spectroscopie a cavite ring-down est une meethode spectroscopique qui utilise une cavite optique de haute qualite pour amplifier la perte optique due a l'absorption de lumiere par l'echantillon. Durant cette presentation, nous mettons en evidence deux applications de la spectroscopie a cavite; ring-down avec deeplacement de phase qui convient aux mesures d'absorption en phase condenseee et fait usage de caviteesa guide d'onde. Dans la premiere application, une boucle de fibre est utiliseie comme cavite optique et l'eechantillon est introduit dans un intervalle de la boucle pour permettre des mesures d'absorption sur des nanolitres de solution au niveau micromolaire. Une seconde application est basee sur des microspheres de silice comme caviteesa haute finesse. Des informations sur l'index de refraction et l'absorption d'un film mince d'ethylene diamine sur la surface d'un micro-resonateur sont obtenues simultaneement par des mesures de deplacement de longueur d'onde du spectre modal de la cavite et de changement de temps de decroissance optique, respectivement. Mots-cles: spectroscopie a cavite; ring-down, micro-resonateur, microsphere, boucle de fibre., In the past years, absorption spectroscopy has undergone a rapid change and the absorption spectrometers that are developed in many research labs have little in common with the teaching instruments [...]

Analyses of complex mixtures and characterization of ions increasingly involve gas-phase separations by ion mobility spectrometry (IMS) and particularly differential or field asymmetric waveform IMS (FAIMS) based on the difference of ion mobility in strong and weak electric fields. The key advantage of FAIMS is substantial orthngonality to mass spectrometry (MS), which makes FAIMS/MS hybrid a powerful analytical platform of broad utility. However, the potential of FAIMS has been constrained by limited resolution. Here, we report that the use of gas mixtures comprising up to 75% He dramatically increases the FAIMS separation capability, with the resolving power for peptides and peak capacity for protein digests reaching and exceeding 100. The resolution gains extend to small molecules, where previously unresolved isomers can now be separated. These performance levels open major new applications of FAIMS in proteomic and other biomolecular analyses. 10.1021/ac902852a

Spectroelectrochemical sensors combine three modes of selectivity in a single device (electrochemistry, spectroscopy, and selective partitioning). A thin polymer film is coated onto the sensing platform in order to facilitate chemically selective transport to the electrode. The film is an essential part of the sensor because it provides an increase in selectivity and sensitivity by selectively pre-concentrating the analyte. Here, we report the next step in the characterization of partially sulfonated polystyrene-block-poly(ethylene-ran-butylene)block-polystyrene (SSEBS) films for the purpose of chemical sensing by examining the selectivity of the sensor fabricated with this novel thin film material. Binaw mixtures using model analytes were used to demonstrate the sensor's ability to detect an analyte in the presence of a direct interference. The binary mixtures consisted of Ru[(bpy).sub.3.sup.2+]/Fe[(CN).sub.6.sup.3-], Ru[(bpy).sub.3.sup.2+]/ Fe[(bpy).sub.3.sup.2+], and Ru[(bpy).sub.3.sup.2+]/Cu[(bpy).sub.2.sup.2+]. Demonstration of the selective partitioning mode using the Ru[(bpy).sub.3.sup.2+]/Fe[(CN).sub.6.sup.3-] mixture and absorption detection showed the SSEBS film's preference for Ru[(bpy).sub.3.sup.2+] over Fe[(CN).sub.6.sup.3-], and therefore, Fe[(CN).sub.6.sup.3-] did not interfere with the sensor's response to Ru[(bpy).sub.3.sup.2+]. Furthermore, the importance of the use of three modes together was demonstrated by analysis of the Ru[(bpy).sub.3.sup.2+]/Fe[(bpy).sub.3.sup.2+] and the Ru[(bpy).sub.3.sup.2+]/Cu[(bpy).sub.2.sup.2+] test mixtures, where both selection of a specific wavelength for absorption and selection of a specific potential window were required to reduce or eliminate the signal from the interference. Finally, analysis of the Ru[(bpy).sub.3.sup.2+]/Fe[(bpy).sub.3.sup.2+] test mixture was also demonstrated using fluorescence detection. 10.1021/ac901595b

The ability of luminescent species in the near-field to both induce and couple to surface plasmons has been known for many years, with highly directional emission from films (Surface Plasmon Coupled Luminescence, SPCL) facilitating the development of sensitive near-field assay sensing platforms, to name but just one application. Because of the near-field nature of the effect, only luminescent species (fluorescence, chemiluminescence and phosphorescence) within a few hundred nanometers from the surface play a role in coupling, which in terms of biosensing, provides for limited penetration into optically dense media, such as in whole blood. Another attractive feature is the highly polarized and angular dependent emission which allows both fixed angle and wavelength dependent emission angles to be realized at high polarization ratios. In this paper, a generic procedure based on theoretical Fresnel calculations, which outlines the step-by-step selection of an appropriate metal for SPCL applications is presented. It is also shown that 11 different metals have differing properties in different spectral regions and offer either fixed angle or wavelength-dependent angular shifts in emission. In addition, it is shown that both chemiluminescence and phosphorescence can also be observed in a highly directional manner similar to coupled fluorescence.

The maximum electric field intensity (E) in field asymmetric waveform ion mobility spectrometry (FAIMS) analyses was doubled to E > 60 kV/cm. In earlier devices with >0.5 mm gaps, such strong fields cause electrical breakdown for nearly all gases at ambient pressure. As the Paschen curves are sublinear, thinner gaps permit higher E: here, we established 61 kV/cm in [N.sub.2] using microchips with 35 [micro]m gaps. As FAIMS efficiency is exceptionally sensitive to E, such values can in theory accelerate analyses at equal resolution by over an order of magnitude. Here we demonstrate FAIMS filtering in ~20 [micro]s or ~1% of the previously needed time, with a resolving power of about half that for 'macroscopic' units but sufficing for many applications. Microscopic gaps enable concurrent ion processing in multiple (here, 47) channels, which greatly relaxes the charge capacity constraints of planar FAIMS designs. These chips were integrated with a [beta]-radiation ion source and charge detector. The separation performance is in line with first-principles modeling that accounts for high-field and anisotropic ion diffusion. By extending FAIMS operation into the previously inaccessible field range, the present instrument advances the capabilities for research into ion transport and expands options for separation of hard-to-resolve species.

A simple method for increasing the efficiency of multidimensional ion mobility spectrometry (IMS--IMS) measurements (as defined by the number of two-dimensional data sets necessary to sample all of the ions in a complex mixture) is illustrated. In this approach, components from a packet containing a mixture of ions are introduced into the first IMS drift region where they are separated based on differences in mobility. At the exit of this region, narrow distributions of ions having identical mobilities are selected, subjected to gentle activation conditions that are intended to induce conformational changes, and transmitted into a second IMS drift region where the new conformations are separated. Here, we describe a simple timing sequence associated with selection and activation of multiple distributions at the entrance of the second drift region in a systematic fashion that improves the efficiency of two-dimensional IMS--IMS by a factor of ~8. The method is illustrated by examination of a mixture of tryptic peptides from human hemoglobin.

A specific biominetic diiron compound is examined by using X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations in four protonation states. The protonation of the putative azadithiolate (adt) ligand might cause the bridging CO to move to a terminal position in the iron-only hydrogenases, thereby preparing the active site for hydride binding en route to [H.sub.2] formation.

Redox state-dependent protonable sites are examined over a wide pH range by ATR-FTIR spectroscopy. Two sharp IR modules on reduction of the enzyme were observed, one of which is sensitive to H/D isotope exchange and the other to both H/D and [H.sub.2][16.sup.O]/[H.sub.2][18.sup.O] exchange.

Field asymmetric waveform ion mobility spectrometry (FMMS) is emerging as a major analytical tool, especially in conjunction with mass spectrometry (MS), conventional ion mobility spectrometry (IMS), or both. In particular, FAIMS is used to separate protein or peptide conformers prior to characterization by IMS, MS/MS, or H/D exchange. High electric fields in FMMS induce ion heating, previously estimated at < 10 [degrees]C on average and believed too weak to affect ion geometries. Here we use a FAIMS/ IMS/MS system to compare the IMS spectra for ESI-generated ubiquitin ions that have and have not passed FAIMS and find that some unfolding occurs for most charge states. These data and their comparison with the reported protein unfolding in a Paul trap imply that at least some structural transitions observed in FAIMS, or previously in an ion trap, are not spontaneous. The observed unfolding is similar to that produced by heating of ~50[degrees]C above room temperature, consistent with the calculated heating of ions at FAIMS waveform peaks. Hence, the ion isomerization in FAIMS likely proceeds in steps during the 'hot' periods, especially right after entering the device. The process distorts ion geometries and causes ion losses by a 'self-cleaning' mechanism and thus should be suppressed as much as possible. We propose achieving that via cooling FAIMS by the amount of ion heating; in most cases, cooling by ~75[degrees]C should suffice.

In this paper, emission spectra of both positive column (PC) and negative glow (NG) regions of the dc glow discharge have been measured at different pressures and currents. The intensity of the lines in the NG is in the order of five times of that corresponding lines' intensity in the PC region. It is found that the line intensity increases linearly with the discharge current, while it increases as [P.sup.[alpha]] with the gas pressure. The electron temperature [T.sub.e] has been estimated using the line-to-line-intensity-ratio technique. It is found that [T.sub.e] derived by this technique generally decreases with the pressure. Also, [T.sub.e] in NG region is about 3/2 of that in the PC. Index Terms--Diagnostics, electron temperature, gas discharge, plasma, probes, spectroscopy.

Stable, homogeneous, aqueous dispersions of single-walled carbon nanotubes (SWNTs) are prepared by non-specific physical adsorption of surfactants enhanced by sonication. Upon centrifugation, supernatant and precipitate phases are obtained. The initial weights of the SWNTs and the surfactant are divided between these two phases, and the respective SWNT concentration in each phase is unknown. The focus of this work is on the determination of the true concentration of raw, exfoliated HiPCO SWNTs in the supernatant phase. A UV--visible absorption-based approach is suggested for a direct measurement of the SWNT and the surfactant concentration in the supernatant. UV--visible absorbance spectra of SWNTs--surfactant dispersions and surfactants alone reveal that the intensity of a certain peak, attributed to the [pi]-plasmon resonance absorption, is unaffected by the presence of most surfactants. A calibration plot is then made by monitoring the intensity of the peak as a function of the true concentration of the exfoliated SWNTs. Thus, we are able to determine the unknown concentration of surfactant-dispersed HiP-CO SWNTs in the supernatant solution, simply by measuring its optical absorbance. Moreover, we can now calculate the surfactant efficiency in dispersing SWNTs. Cryogenic-transmission electron microscopy and thermo-gravimetric analysis techniques are used for the characterization of these dispersions and to complement the UV visible measurements.

X-ray absorption near-edge structure (XANES) suffers from core-hole lifetime broadening at a higher energy absorption edge, such as Sn K (29 keV, [[GAMMA].sub.K] = 8.49 eV). To overcome this problem, emitted Sn K[[alpha].sub.1] fluorescence from sample was counted using high-energy-resolution fluorescence spectrometer in the XANES measurements. Experimental energy resolution (5.0 eV) was consistent with theoretical values based on the Rowland configuration of the spectrometer. The absorption edge became steeper compared to conventional spectra. The white-line peak due to [Sn.sup.II] species became remarkably sharper and more intense in the Sn K[[alpha].sub.1]-detecting Sn K-edge XANES for Pt-Sn/Si[O.sub.2]. To support the semiclassical theory of resonant Raman scattering for the explanation of observed elimination of lifetime width, more resolved XANES data at Cu K, Pb [L.sub.3], and Sn K in this work were convoluted (filtered) with a Lorentzian of each core hole lifetime width. The processed data resembled generally well corresponding XANES spectrum measured in transmission mode. The verification based on ab initio XANES calculations was also performed.

The exceptional ability of the Ru(sub 2)-(DMBA)(sub 4) unit in mediating electron mobility between ferrocenium and ferrocene reporter groups by voltammetric and spectroelectrochemical studies of the trans-(FcC (sub 2n))Ru(sub 2)(Y-DMBA)(sub 4) (C(sub 2m) Fc) series is demonstrated. The results obtained of charge transfer across carbon-rich bridges provide the validation of the proposal to realize molecular wires based on Ru(sub 2)-alkynyl oligomers.

The focus of this study is the quantification of multianalyte mixtures in water by the use of sensor arrays based on polymer layers. Reflectometric interference spectroscopy is used as a optical sensor system for temporal-resolved measurements of the interaction kinetics of analytes in water with the polymer layers. The principles and widespread possibilities of this approach are demonstrated using the quantification of quaternary aqueous mixtures of low alcohols from methanol up to 1-butanol. The sensitive layers consist of two hyperbranched polyesters and one microporous polyimide. Different time-dependent sensor signals are evaluated by artificial neural networks. Because the kinetics of sorption and desorption of the analytes differ significantly, the number of sensors needed for a quantification of analytes in mixtures can be reduced. A feature extraction allows identification of the most important differences of kinetic patterns of the analytes and allows improvement of the multivariate calibration. It is shown that a quantification of quaternary mixtures of methanol, ethanol, 1-propanol, and 1-butanol is possible on the basis of only two polymer sensors.

A combined atomic force microscope (AFM) and Raman spectrometer is presented as a microfluidic device for pumping, sampling, and trace chemical analysis. The AFM tip-cantilever provides a mechanism for sheardriven pumping of fluids in microchannels. Shear-driven pumping allows rapid flow rates and avoids the limitations of conventional pumping. The AFM's ability to translate sub-femtoliter volumes of fluid also proves a mechanism for fluidic switching and sample injection. In addition, the AFM is used to image liquid surfaces in microchannels and remove samples for very sensitive spectral analysis. Surface-enhanced Raman spectroscopy localized near the AFM tip provides chemical information of the sampled fluids. The results demonstrate the feasibility of integrating the AFM with microfluidic circuits and shear-driven chromatography and the potential for nanometer-scale chromatography.

Understanding molecular adsorption at a chromatographic interface is of great interest for addressing the tailing problem in chemical separations. Single-molecule spectroscopy and confocal fluorescence correlation imaging are used to study the adsorption sites of [C.sub.18] silica beads under RPLC chromatographic conditions. The experiments show that cationic molecule rhodamine 6G laterally diffuses through the chromatographic interface of a [C.sub.18] hydrocarbon monolayer and acetonitrile with occasional reversible strong adsorptions. Fluorescence correlation imaging extracts the rare strong adsorption events from large data sets, revealing that the strong adsorption sites are randomly distributed throughout the silica beads. Virtually every imaging pixel of silica beads adsorbs molecules. Single-molecule spectroscopy of the 584 strong adsorption events observed indicates that the strong adsorptions persist on the time scales from several milliseconds to seconds, having an average desorption time of 61 ms. The strong adsorption events are rare, comprising 0.3% of the total observation time. The sizes of strong adsorption sites are within the optical resolution of confocal imaging.

Mass transfer of an alkyl sulfate anion with a (ferrocenylmethyl)trimethylammonium cation from water into single oil microdroplets was kinetically studied by microcapillary injection, fluorescence microspectroscopy, and microelectrochemistry. The partitioning ratio and the extraction rate significantly depended on the alkyl chain length of the alkyl sulfate anion. The extraction rate for the n-dodecyl sulfate or n-tridecyl sulfate ion was proportional to both the alkyl sulfate ion and ferrocene derivative concentrations while that for the n-undecyl sulfate ion was proportional to the anion concentration alone. The results are discussed in terms of transfer of the individual ions across the microdroplet/water interface and adsorption/ ion pair formation of the alkyl sulfate ion at the microdroplet/water interface.

Imaging of a coimmobilized diaphorase and albumin surface was investigated by scanning electrochemical microscopy (SECM) with shear force based tip-substrate distance control. A microelectrode tip was attached to a commercially available tuning fork to detect the shear force between the microelectrode tip and the surface. We used the standing approach mode, which repeats an approach and retraction at each data point of the surface to obtain simultaneous current and topographic images. To check the performance of our SECM system, we imaged a platinum-patterned array electrode and a diaphorase/albumin coimmobilized glass surface. Since the system acquires current when the tip is retracted to a desired distance, this mode is useful for a relatively large microelectrode (~10 [micro]m) and for scanning a large area (few hundreds of micrometers). Furthermore, by retracting the tip when the tip moves laterally to the next data point to avoid contact between the tip and sample surface, we successfully imaged the surface without destroying its morphology.

Spectral reconstruction from multicomponent spectroscopic data is the frequent primary goal in chemical system identification and exploratory chemometric studies. Various methods and techniques have been reported in the literature. However, few algorithms/methods have been devised for spectral recovery without the use of any a priori information. In the present studies, a higher dimensional entropy minimization method based on the BTEM algorithm (Widjaja, E.; Li, C.; Garland, M. Organometallies 2002, 21, 1991-1997.) and related techniques were extended to large-scale arrays, namely, 2D NMR spectroscopy. The performance of this novel method had been successfully verified on various real experimental mixture spectra from a series of randomized 2D NMR mixtures (COSY NMR and HSQC NMR). With the new algorithm and raw multicomponent NMR alone, it was possible to reconstruct the pure spectroscopic patterns and calculate the relative concentration of each species without recourse to any libraries or any other a priori information. The potential advantages of this novel algorithm and its implications for general chemical system identification of unknown mixtures are discussed.

In this work, a simple, robust, and automated microfluidic chip-based FIA system with gravity-driven flows and liquid-core waveguide (LCW) spectrometric detection was developed. The high-throughput sample introduction system was composed of a capillary sampling probe and an array of horizontally positioned microsample vials with a slot fabricated on the bottom of each vial. FI sample loading and injection were performed by linearly moving the array of vials filled alternately with 50-[micro]L samples and carder, allowing the probe inlet to enter the solutions in the vials through the slots sequentially and the sample and carder solution to be introduced into the chip driven by gravity. The performance of the system was demonstrated using the complexation of o-phenanthroline with Fe(II) as a model reaction. A 20-mm-long Teflon AF 2400 capillary (50-[micro]m i.d., 375-[micro]m o.d.) was connected to the chip to function as a LCW detection flow cell with a cell volume of 40 nL and effective path length of 1.7 cm. Linear absorbance response was obtained in the range of 1.0-100 [micro]M Fe(II) ([r.sup.] = 0.9967), and a good reproducibility of 0.6% RSD (n = 18) was achieved. The sensitivity was comparable with that obtained using conventional FIA systems, which typically consume 10 000-fold more sample. The highest sampling throughput of 1000 [h.sup.-1] was obtained by using injection times of 0.08 and 3.4 s for sample and carrier solution, respectively, with a sample consumption of only 0.6 nL for each cycle.

We describe here the implementation of the statistical total correlation spectroscopy (STOCSY) analysis method for aiding the identification of potential biomarker molecules in metabonomic studies based on NMR spectroscopic data. STOCSY takes advantage of the multicollinearity of the intensity variables in a set of spectra (in this case [sup.1]H NMR spectra) to generate a pseudo-two-dimensional NMR spectrum that displays the correlation among the intensities of the various peaks across the whole sample. This method is not limited to the usual connectivities that are deducible from more standard two-dimensional NMR spectroscopic methods, such as TOCSY. Moreover, two or more molecules involved in the same pathway can also present high intermolecular correlations because of biological covariance or can even be anticorrelated. This combination of STOCSY with supervised pattern recognition and particularly orthogonal projection on latent structure--discriminant analysis (O-PLS-DA) offers a new powerful framework for analysis of metabonomic data. In a first step O-PLS-DA extracts the part of NMR spectra related to discrimination. This information is then cross-combined with the STOCSY results to help identify the molecules responsible for the metabolic variation. To illustrate the applicability of the method, it has been applied to 1H NMR spectra of urine from a metabonomic study of a model of insulin resistance based on the administration of a carbohydrate diet to three different mice strains (C57BL/6Oxjr, BALB/cOxjr, and 129S6/SvEvOxjr) in which a series of metabolites of biological importance can be conclusively assigned and identified by use of the STOCSY approach.

Laser-scattering techniques are utilized for the first time to visualize the aerosol droplets in an inductively coupled plasma (ICP) torch from the nebulizer tip to the site of analytical measurements. The resulting images provide key information about the spatial distribution of the aerosol introduced by direct injection and conventional sample introduction devices: (1) a direct injection high-efficiency nebulizer (DIHEN); (2) a large-bore DIHEN; and (3) a MicroFlow PFA nebulizer with a PFA Scott-type spray chamber. Moreover, particle image velocimetry is used to study the in situ behavior of the aerosol before interaction with the plasma, while the individual surviving droplets are explored by particle tracking velocimetry. Directly introduced aerosols are highly scattered across the plasma torch as a result of their radial motion, indicating less than optimum sample consumption efficiency for the current direct injection devices. Further, the velocity distribution of the surviving droplets demonstrates the importance of the initial droplet velocities in complete desolvation of the aerosol for optimum analytical performance in ICP spectrometries. These new observations are critical in the design of the next-generation direct injection devices for lower sample consumption, higher sensitivity, lower noise levels, suppressed matrix effects, and developing smart spectrometers.

A novel method for applying cavity ring-down spectroscopy in the liquid phase, compatible with LC analyses, is presented. The core of the setup is a home-built cavity ring-down flow cell (cell volume 12 [micro]L) that is constructed using a silicon rubber spacer, which is clamped leak-tight between two high-reflectivity mirrors. The mirrors are in direct contact with the liquid flow, which provides for a small path length and short ring-down times. Inside the cavity there are no windows, reflection losses, or Brewster angles to be considered. Due to the small size of the presented cavity geometry, the setup can be implemented in conventional-size LC apparatuses. With a flow injection setup, a detection limit of 2.5 nM was obtained for Crystal Violet in ethanol, and the linear dynamic range of the system is at least 2 orders of magnitude. The method has the potential to become a powerful alternative for commercial LC UV/visible absorbance detectors.

We describe the use of liquid-phase continuous-wave cavity ring-down spectroscopy for the detection of an HPLC separation. This technique builds on earlier work by Snyder and Zare using pulsed laser sources and improves upon commercially available UV--visible detectors by a factor of up to 50. The system employs a compact doubled-diode single-mode continuous-wave laser operating at 488 nm and a previously described Brewster's-angle flow cell. Ring-down time constants as long as 5.8 [micro]s were observed with liquid samples in a 0.3-mm path length cell. The baseline noise during an HPLC separation was only 2 x [10.sup.-7] absorbance units (AU) peak to peak, as compared to 1 x [10.sup.-5] AU for a state-of-the-art commercial UV--visible detector.

As the physical limits of silicon-based microelectronics are reached, a need for new materials is required in order to continually improve processor speed. Carbon nanotubes have been suggested as a material to fill in where silicon technology leaves off, due to their small dimensions and unique metallic and semiconductor properties. In order to better understand the conditions in which carbon nanostructures are formed, a detailed plasma analysis has been performed on a gaseous electronics conference (GEC) plasma chamber. This analysis includes plasma composition, rotational temperatures, and spatially resolved hydrogen actinometry during carbon nanostructure growth. Index Terms--Carbon-based plasmas, hydrogen actinometry, nanotechnology, plasmas, rotational temperature, spectroscopy.

Microdielectric spectroscopy with planar fringe-effect (FE) interdigital sensors is a useful method for noninvasive characterization of the interfacial properties of the materials. Unfortunately, obtaining an accurate dielectric spectrum is difficult because of the complexity of the probing electrical field created by the FE sensor and the contribution of the sensor substrate and stray elements to the overall measurements. Previously, quantitative microdielectric spectroscopy required the calibration of the FE sensor with standard materials that are known to be dielectrically similar to an unknown sample of interest. This limitation complicates the application of microdielectric spectroscopy, particularly in cases where the monitored sample undergoes a transformation that changes its dielectric permittivity. A standard-independent method for quantitative FE microdielectric measurements is proposed in this paper. The developed method is based on comparison of the theoretically predicted admittance of the FE sensor with the sample of known dielectric properties and the measured sensor admittance. Comparison of the theoretical predictions with the admittance measurements reveals the contribution of the unknown stray elements. The measurements with an unknown sample are then adjusted for the strays. The contribution of the sensor substrate to the sensor measurements is removed using the theoretical model derived from the electroquasistatie approximation of Maxwell equations. The dielectric permittivity of the material being tested is calculated by successively solving the system of complex nonlinear equations for each frequency at which the sensor admittance is measured. The developed method is illustrated by applying it to the dielectric measurements of several dissimilar samples. The results are in excellent agreement with those obtained using the gold standard parallel-plate measurement method over the entire range of frequencies.

We present initial results obtained from an optical absorption sensor for the monitoring of ambient atmospheric nitrogen dioxide concentrations (0-200 ppb). This sensor utilizes cavity attenuated phase shift spectroscopy, a technology related to cavity ringdown spectroscopy. A modulated broadband incoherent light source (a 430-nm LED) is coupled to an optically resonant cavity formed by two high-reflectivity mirrors. The presence of N[O.sub.2] in the cell causes a phase shift in the signal received by a photodetector that is proportional to the N[O.sub.2] concentration. The sensor, which employed a 0.5-m cell, was shown to have a sensitivity of 0.3 ppb in the photon (shot) noise limit. Improvements in the optical coupling of the LED to the resonant cavity would allow the sensor to reach this limit with integration times of 10 s or less (corresponding to a noise equivalent absorption coefficient of < 1 x 10 s [cm.sup.-1] [Hz.sup.1/2]). Over a 2-day-long period of ambient atmospheric monitoring, a comparison of the sensor with an extremely accurate and precise tunable diode laser-based absorption spectrometer showed that the CAPS-based instrument was able to reliably and quantitatively measure both large and small fluctuations in the ambient nitrogen dioxide concentration.

A portable thermal lens spectrometer with a precise focusing system was developed. Astigmatism of the reflected excitation beam from the microchip was used for depth direction focusing. For width direction focusing, the scattering effect of the transmitted probe beam by a microchannel edge was used. The focusing system was evaluated with a 250 [micro]m wide x 50 [micro]m deep microchannel. Focusing resolutions for depth and width directions were 1 and 10 [micro]m, respectively. The repeatability of the thermal lens signal (40 [micro]M xylenecyanol solution) was proved to be ~1% coefficient of variance when using these focusing methods. The limit of detection for a xylenecyanol solution was 30 nM, and the absorbance was 4.7 x [10.sup.-6] AU. The sensitivity was 20-100 times higher than that obtained by spectrophotometry. In consequence, a practical thermal lens spectrometer was realized.

In general, applications of metabonomics using biofluid NMR spectroscopic analysis for probing abnormal biochemical profiles in disease or due to toxicity have all relied on the use of chemometric techniques for sample classification. However, the well-known variability of some chemical shifts in [sup.1]H NMR spectra of biofluids due to environmental differences such as pH variation, when coupled with the large number of variables in such spectra, has led to the situation where it is necessary to reduce the size of the spectra or to attempt to align the shifting peaks, to get more robust and interpretable chemometric models. Here, a new approach that avoids this problem is demonstrated and shows that, moreover, inclusion of variable peak position data can be beneficial and can lead to useful biochemical information. The interpretation of chemometric models using combined back-scaled loading plots and variable weights demonstrates that this peak position variation can be handled successfully and also often provides additional information on the physicochemical variations in metabonomic data sets.

Field asymmetric waveform ion mobility spectrometry (FAIMS) has significant potential for post-ionization separations in conjunction with MS analyses. FAIMS fractionates ion mixtures by exploiting the fact that ion mobilities in gases depend on the electric field in a manner specific to each ion. Nearly all previous work has used pure gases, for which FAIMS fundamentals are understood reasonably well; however, unexpected phenomena observed in some gas mixtures (e.g., [N.sub.2]/C[O.sub.2]) but not in others ([N.sub.2]/[O.sub.2]) remain unexplained. Here, we introduce and experimentally test a universal model for FAIMS separations in mixtures, derived from formalisms that determine high-field mobilities in heteromolecular gases. Overall, the theoretical findings are consistent with data for [N.sub.2]/C[O.sub.2] (although quantitative discrepancies remain), while results for [N.sub.2]/[O.sub.2] fit Blanc's law, in agreement with measurements. Calculations for He/[N.sub.2] and He/C[O.sub.2] are also consistent with observations and suggest why adding He to the working gas generally enhances FAIMS performance. As predicted, mixtures of gases with extremely disparate molecular masses and collision cross sections, such as He/S[F.sub.6], exhibit spectacular non-Blanc effects, which greatly improve the resolution and peak capacity of technique. Understanding FAIMS operation in gas mixtures is expected to enable the rational design of media for both targeted and global analyses.

A method is presented for the use of SAM layers as internal standards for calibration in surface-enhanced Raman spectroscopy. Three cyano-containing compounds were attached to gold colloids via a metal--sulfur bond and evaluated for spectral stability and normalization capacity. The results show that the analyte, rhodamine 6G, and the internal standard signal enhancement covaried, and it was possible to quantify the analyte with PLS. The fact that the enhancing substrate was chaotic assemblies with large variation in signal enhancement shows the versatility of this method.

Quantitative detection of small volatile organic compounds in ambient air is demonstrated using a combination of continuous wave cavity ring-down spectroscopy (cw-CRDS) and the preconcentration of air samples with an adsorbent trap. The trap consists of a zeolite molecular sieve, selected for efficient trapping of the test compounds ethene (ethylene) and ethyne (acetylene). Upon heating of the trap, these organic compounds desorb into a small-volume ring-down cavity, and absolute concentrations are measured by CRDS at 6150.30 [cm.sup.-1] (ethene) and 6512.99 [cm.sup.-1] (ethyne) without the need for calibration. The efficiency of the trapping and desorption was tested using commercial standard gas mixtures and shown to be 100% in the case of ethene, whereas some ethyne is retained under the current operating conditions. Samples of indoor and outdoor air were analyzed for ethene content, and measurements were made of mixing ratios as low as 6 ppbv. Removal of water vapor and C[O.sub.2] from the air samples prior to trapping was unnecessary, and the selectivity of the trapping, desorption, and spectroscopic detection steps eliminates the need for gas chromatographic separation prior to analysis. With anticipated improvements to the design, measurements of these and other trace atmospheric constituents should be possible on time scales of a few minutes.

Two novel laser-based imaging techniques centered on particle image velocimetry and optical patternation are used to map and contrast the size and velocity distributions for indirect and direct pneumatic nebulizations in plasma spectrometry. The flow field of droplets is illuminated by two pulses from a thin laser sheet with a known time difference. The scattering of the laser light from droplets is captured by a charge-coupled device (CCD), providing two instantaneous images of the particles. Pointwise cross-correlation of the corresponding images yields a two-dimensional velocity map of the aerosol velocity field. For droplet size distribution studies, the solution is doped with a fluorescent dye and both laser-induced florescence (LIF) and Mie scattering images are captured simultaneously by two CCDs with the same field of view. The ratio of the LIF/Mie images provides relative droplet size information, which is then scaled by a point calibration method via a phase Doppler particle analyzer. Two major findings are realized for three nebulization systems: (1) a direct injection high-efficiency nebulizer (DIHEN); (2) a large-bore DIHEN; and (3) a PFA microflow nebulizer with a PFA Scott-type spray chamber. First, the central region of the aerosol cone from the direct injection nebulizers and the nebulizer-spray chamber arrangement consists of fast (> 13 and >8 m/s, respectively) and fine (25 [micro]m) droplets in the fringes. Second, the spray chamber acts as a momentum separator, rather than a droplet size selector, as it removes droplets having larger sizes or velocities. The concepts and results presented in this research may be used to develop smart-tunable nebulizers, for example, by using the measured momentum as a feedback control for adjusting the nebulizer, i.e., its operating conditions, its critical dimensions, or both.

Micro-Raman spectroscopy, infrared absorption microspectroscopy, and AFM images of nano--or microsized micelles formed by fulvic acid (FA) solutions, prepared at different pHs, and cast on glass slides or gold island films, are reported. FA films cast on gold islands are characterized by surface-enhanced infrared absorption (SEIRA), surface-enhanced infrared reflection absorption, and surface-enhanced Raman scattering (SERS). Based on spectral evidence, it is expected that the chemisorption of FA on gold island films takes place through thiol groups, which become more active as pH increases. The SEIRA spectra of these films show increased peak intensity, as well as improved band resolution. Microspectroscopy SERS studies show that, at pH 5, FA form small aggregates on gold surfaces. At pH 8, FA tends to expand due to electrostatic repulsion, giving rise to a fractal surface composed of different domains. SERS studies of these domains reveal that the most polar molecules are located on the external faces. At pH 11, fractal conformations are even more pronounced and give rise to radial patterned structures. At this pH, the position of fulvic acid molecules in the fractal micelles is the same as observed at pH 8. In this way, SERS can be viewed as a powerful tool for the analysis of the composition, apparent contribution of the surface functional groups of FA films, and the FA building blocks (i.e., catechol, gallic, salicylic, or ftalic acids) in the structures of these materials.

Multivariate curve resolution is proposed for the study of complex chemical reactions monitored by two-dimensional (2D) NMR spectroscopy. In particular, in this work, multivariate curve resolution is applied to the study of the reaction between 15N-labeled cisplatin and the amino acid-nucleotide hybrid (Phac-Met-linker-pSdG). At several stages of the reaction, 2D [[sup.1]H,[sup.15]N] HSQC NMR spectra were acquired and stored in data matrices. In a first step, multivariate curve resolution was applied to analyze individually each one of these 2D spectra, allowing the resolution of the corresponding [sup.1]H and [sup.15]N one-dimensional correlation spectra. In a second step, the whole set of 2D spectra recorded along the reaction were simultaneously analyzed by multivariate curve resolution, allowing the resolution of the kinetic concentration profiles and of the pure 2D NMR spectra of each of the species detected along the reaction. Results finally obtained confirmed previously postulated reaction mechanisms involving the existence of two monofunctional adducts and of two bifunctional adducts, with the structure of one of them not completely resolved.

Fiber-loop ring-down spectroscopy (FLRDS) is a recently developed absorption spectroscopic technique suitable for very small liquid samples. It is based on measurements of the optical decay constant of laser intensity in a loop made of optical waveguide material. This decay constant changes as small liquid samples containing absorbing species are introduced into the loop. In this report, it is demonstrated that one can also obtain the optical decay constant using a continuous wave laser beam that is intensity modulated and then coupled into an optical fiber loop. The inherent exponential decay in the fiber loop introduces a phase shift of the light emitted from the loop with respect to the pumping beam. By measuring rids phase shift, one can readily determine the concentration of the analyte introduced between the two fiber ends and a model is established to describe the relationship. It is demonstrated that this technique, dubbed phase-shift fiber-loop ring-down spectroscopy (PS-FLRDS), is well suited as an absorption detector for any flow system in which the optical absorption path is limited by the instrument architecture. By measuring the phase angle as a function of concentration of 1, 1'-diethyl-4,4'-dicarbocyanine iodide in dimethyl sulfoxide, the detection limit was determined as ~6 [micro]M for a 30-40-[micro]m absorption path. A temporal resolution of ~100 ms was demonstrated by a rapid displacement of the solutions between the two fiber ends. Proof-of-principle use of the PS-FLRDS detection in capillary flow systems using a commercial four-way microcross established that the alignment of the fiber and the capillary can be made simple and effective, while retaining both a low detection limit and a fast response.

This study describes the development of a surface plasmon fluorescence spectroscopy (SPFS)-based sandwich immunoassay, for the detection of free prostate-specific antigen (f-PSA). The commercial CM5 chip (Biacore) was integrated into the SPFS-based assay making use of its three-dimensionally extended dextran architecture, which offers a large protein retention capacity and alleviates the metal-induced fluorescence quenching. The performance of the f-PSA assay was investigated in buffer and in human plasma, respectively. In the human plasma, the limit of detection of f-PSA was estimated to be ~80 fM for 40 min of contact time, which adequately meets clinical requirements.

Pulsed electric fields (PEFs) above a certain voltage threshold cause electroporation for microsecond pulses and intracellular effects for submicrosecond pulses. Models describing these effects often depend on the electrical properties of the cell, which are altered by the PEF. We used time domain dielectric spectroscopy to provide data for these models and to measure effects on cell suspension conductivity. We applied single 50-[micro]s and 10-ns pulses to HL-60 cells, with the voltages chosen so the pulses have approximately the same energy. For 1.l-kV/cm, 50-[micro]s pulses, the conductivity rose within a minute after the pulse and dropped dramatically approximately 40 min after the pulse. For 78-kV/cm, 10-ns pulses, we observed a brief delay prior to the conductivity rise and noted the same drop in conductivity after approximately 40 min. For both pulse durations, higher voltages frequently led to membrane potation followed by a gradual recovery approximately 30--40 min after the pulse. For 2-kV/cm, 50-[micro]s pulses, we observed significantly more scatter in Trypan Blue uptake measurements due to stronger effects on the cell membrane. By using a cell model, we showed that a 50-[micro]s pulse caused a much larger rise in membrane conductivity than a 10-ns pulse of the same energy. Index Terms--Bioelectric phenomena, biological cells, biological effects of electromagnetic radiation, biomembranes, dielectric measurements, pulse power systems.

High spatial- and temporal-resolution spectroscopic methods are employed to perform detailed studies of the interaction between the propagating magnetic field and a multi-ion-species plasma. The experiment is performed in a plasma-opening-switch configuration, in which a 150-kA current of ~400 ns duration is conducted through a plasma. Recent observations demonstrated a new phenomenon of simultaneous rapid magnetic field penetration into the heavy-ion plasma and specular reflection of the light-ion plasma, leading to ion-species separation. Additionally, noticeable inconsistencies between experimental results and theories were found. The current paper summarizes these recent results and discusses the aspect of the role of the plasma composition in the magnetic field evolution and ion dynamics. In order to systematically investigate the effect of the plasma composition, a method for producing plasmas with controllable compositions, based on spatial species separation and electrode heating, is presented. This method allows for achieving plasmas with varying proton-to-carbon ion ratios, however, at different electron densities. Measurements are described for studying the relation between the magnetic field propagation velocity and the plasma composition and density; however, this relation is not yet satisfactorily clear. Index Terms--Magnetic field-plasma interaction, multi-ion species plasma, plasma devices, plasma spectroscopy.

A microfabricated drift tube for differential mobility spectrometry (DMS) was used with pyrolysis-gas chromatography (py-GC) to chemically characterize bacteria through three-dimensional plots of ion intensity, compensation voltage from differential mobility spectra, and chromatographic retention time. The DMS analyzer provided chemical information for positive and negative ions simultaneously from chemical reactions between pyrolysis products in the GC effluent and reactant ions of [H.sup.+]([H.sub.2]0).sub.n] and [O.sub.2]-([H.sub.2]O).sub.n] in air at ambient pressure. Authentic standards for chemicals formed in the pyrolysis of bacteria showed favorable matches with plots from py-GC/DMS analysis and were supported by py-GC/MS results. These and other yet-unidentified constituents provided a means to distinguish Escherichia coli from Micrococcus luteus. A Gram-positive spore former (Bacillus megaterium) was distinguished by an abundant peak for crotonic acid evident in positive and negative ions and not observed with M. luteus. In contrast, plots from py-GC/DMS of lipid A and lipoteichoic acid showed poor matches to plots for a Gram-negative (E. coli) bacterium and a Gram-positive (M. luteus) bacterium and the differences were attributed to differences in genus sources of the biopolymers. A significant percentage of the chemical information available in py-GC/DMS is unidentified, and the analytical utility must be established. Precision in the chemical measurement was determined as [+ or -] 0.2 V, 10% relative standard deviation (RSD), and [+ or -] 0.05 min for compensation voltage, peak intensity, and retention time, respectively. The minimum number of total bacteria (cell forming units) detected was 6000 though detection limits and resolution could be varied by the magnitude of the separation voltage in the differential mobility spectrometer.

Differential mobility spectrometry (DMS) of nitro-organic explosives and related compounds exhibited the expected product ions of [M.sup.-] or M x N[O.sup.-.sub.2] from atmospheric pressure chemical ionization reactions in purified air at 100 [degrees]C. Peaks in the differential mobility spectra for these ions were confined to a narrow range of compensation voltages between -1 to +3 V which arose through a low dependence of mobility for the ions in electric fields at E/N values between 0 and 120 Td (1 Td = [10.sup.-7] V [cm.sup.2]). The field dependence of ions, described as an [alpha] parameter, ranged from -0.005 to 0.02 at a separation field of 100 Td. The [alpha] parameter could be controlled through the addition of organic vapors into the drift gas and was increased to 0.08-0.24 with 1000 ppm of methylene chloride in the drift gas. This modification of the drift gas resulted in compensation voltages of +3 to +21 V for peaks. The improved separation of peaks was consistent with a model of ion characterization by [DELTA]K or [K.sub.1] - [K.sub.h], where [K.sub.1] is the mobility coefficient of ions clustered with vapor neutrals during the low-field portion of the separation field waveform and [K.sub.h] is for the same core ion when heated and declustered during the high-field portion of waveform.

A simple and powerful method based on UV--visible spectroscopy is presented for studying the stability of the inner electrically conducting polyaniline (PANI) solid contact (SC) layer in all-solid-state ion-selective electrodes (ISE). The influence of the plasticized poly(vinyl chloride) (PVC) membrane (ISM) composition and the pH of the sample solution on the stability of the solid contact is reported. PANI is used as a model compound in this study, but the method presented is universal and can be applied to different types and combinations of SCs and ISMs. It provides a tool for finding the best combination of conducting polymer and ISM for solid contact ISEs. PANI is deposited electrochemically either on glassy carbon or quartz glass covered with a thin layer of tin oxide, and a [K.sup.+]-selective ISM is deposited on top of the PANI layer. The short-term stability of the inner PANI layer is good for all membrane types in buffer solutions with pH 2, 6, and 9, indicating that the outer plasticized PVC membrane hinders the emeraldine salt-emeraldine base transition of the highly pH sensitive PANI layer. The solid contact [K.sup.+]-selective electrodes studied showed a Nernstian response of 58.2 [+ or -] 0.1 mV/log [a.sub.K]. Significant differences are observed in the long-term stability of the inner PANI layer between the different membrane types. This indicates that water uptake of the PVC membrane and its permeability to OH- ions are critical parameters affecting the stability of the PANI layer. The solid contact electrodes based on PANI may require a composition of the PVC membrane different from those typically used in conventional ISEs with an inner solution.

A direct method for the speciation of Sn compounds in solid environmental samples by X-ray absorption near-edge structure spectroscopy (XANES) has been developed. It was found that the method can provide the 'organic extent', the average number of organic ligands bound to Sn, for environmental samples. For Sn XANES at the [L.sub.III], [L.sub.I], and K edges, systematic variations were found in the spectra for butyl-, phenyl-, and methyl-substituted Sn compounds depending on the organic extent. A quantitative relationship between the organic extent and the characteristics in the XANES spectra was determined based on the peak position, peak area ratio, and peak width. The detection limit was better than 10/[micro]g/g Sn when using the K edge, which is sensitive enough for some environmental samples, e.g., sediments, biological samples, and antifouling paints, and the sensitivity will be better if a more intense X-ray source such as an undulator or Wiggler beamline is used. The present XANES method is totally nondestructive, having the advantage that no complicated pretreatment procedures are needed, whereas such procedures are essential in conventional chromatographic analyses, which may cause experimental error by alteration of Sn species and poor recovery during analyses. Although the XANES method only provides the average number of organic ligands, the direct speciation using XANES will be helpful for estimating roughly the ratio of organic and inorganic Sn species, which can be used to study organotin transformations in sediment cores and inspection of organotin compounds in antifouling paints. In particular, micro-XANES analysis based on the present method is a promising tool in obtaining the distribution of organotin species in biological samples and specific phases in sediments.

Advances in manufacturing technology for microstructures are allowing new opportunities for vacuum electron devices producing radio-frequency (RF) radiation. Specifically, the capability to produce small circuit structures is allowing development of RF devices at frequencies impractical with traditional machining technology. This is generating increased interest in applications in the submillimeter and terahertz frequency range. High-power RF devices in this frequency range are needed for medical, communications, defense, and homeland security applications. This paper describes the most promising microfabrication techniques applicable to high-frequency RF devices and examples of recent applications. Index Terms--Backward wave oscillator (BWO), cold cathode, deep reactive ion etching (DRIE), electrical discharge machining (EDM), field emission, field emitter array (FEA), focused ion beam (FIB), LIGA, radiation, RF source, spectroscopy, SU-8.

The ability to estimate low-dose human exposure to commonly used pesticides often is requested in epidemiologic studies. Therefore, fast and robust methods are necessary that can measure many analytes in the same sample. We have developed a method for high-throughput analysis of 19 markers of commonly used pesticides in human urine. The analytes were seven specific metabolites of organophosphorus pesticides, five metabolites of synthetic pyrethroids, six herbicides or their metabolites, and one insect repellant. Human urine (2 mL) was spiked with stable isotopically labeled analogues of the analytes, enzymatically hydrolyzed, extracted using solid-phase extraction, concentrated, and analyzed using high-performance liquid chromatography-tandem mass spectrometry. The sample was divided into two portions and analyzed on two different mass spectrometers, one using atmospheric pressure chemical ionization (APCI) and the other using turbo ion spray atmospheric pressure ionization (TIS). All analytes except the pyrethroid metabolites were analyzed using APCI. The detection limits for all analytes ranged from 0.1 to 1.5 ng/mL of urine, with the majority (17) below 0.5 ng/mL. The analytical precision for the different analytes, estimated as both the within-day and between-day variation, was 3-14 and 4-19%, respectively. The extraction recoveries of the analytes ranged from 68 to 114%. The throughput, including calibration standards and quality control samples, is ~50 samples a day. However, the analysis time with the TIS application is much shorter, and if only pyrethroid metabolite data are of interest, the throughput can be increased to 100-150 samples/day.

A novel method is presented that is capable of collecting time-resolved vibrational spectroscopic information with sub-100-[micro]s temporal resolution. Unlike previous step scan FT-IR approaches, the phenomena under study do not necessarily need to be repeatable. The methodology described herein is based on the planar array infrared (PA-IR) technique, which utilizes a spectrograph for wavelength dispersion and a mid-infrared focal plane array (FPA) detector for simultaneous detection of multiple wavelengths. Unlike previous PA-IR approaches, a rolling mode FPA is employed. This unique data readout mode, where data are read out of the array two rows at a time, is exploited to generate increased temporal resolution. The capabilities of this technique are demonstrated using the example of the electric field-induced Freedericksz transition of a nematic liquid crystal. It is shown that the orientational dynamics of a single transition can be tracked over a spectral range of 154 [cm.sup.-1] with a temporal resolution of 99.17 [micro]s while requiring a total experimental time of less than 1 s.

Linear and nonlinear wavelet compression of ion mobility spectrometry (IMS) data are compared and evaluated. IMS provides low detection limits and rapid response for many compounds. Nonlinear wavelet compression of ion mobility spectra reduced the data to 4-5% of its original size, while eliminating artifacts in the reconstructed spectra that occur with linear compression, and the root-mean-square reconstruction error was 0.17-0.20% of the maximum intensity of the uncompressed spectra. Furthermore, nonlinear wavelet compression precisely preserves the peak location (i.e., drift time). Small variations in peak location may occur in the reconstructed spectra that were linearly compressed. A method was developed and evaluated for optimizing the compression. The compression method was evaluated with in-flight data recorded from ion mobility spectrometers mounted in an unmanned aerial vehicle (UAV). Plumes of dimethyl methylphosphonate were disseminated for interrogation by the UAV-mounted IMS system. The daublet 8 wavelet filter exhibited the best performance for these evaluations.

Development of a new quantitative method for determining low concentrations of aqueous polyatomic anions using attenuated total reflectance (ATR) FTIR spectroscopy is described. Evaporated thin-film coatings of anion-selective tetraalkylated ferrocenium salts were applied to the surface of ATR crystals, which enabled anion detection limits to be lowered up to 23 000-fold below those achieved using the commercially available spectrometer with identical uncoated ATR crystals. Linear calibration curves based on d(absorbance)/dt, which is related to the rate of anion exchange in the thin film, were established in the 0.04-30 [micro] M range. Limits of detection (10-min analyses) for perchlorate, chlorate, trifluoromethanesulfonate, perfluoro-n-butanesulfonate, perfluoro-n-octanesulfonate, tetrafiuoroborate, hexafluorophosphate, and pinacolylmethylphosphonate in aqueous solution were 0.03, 0.2, 0.05, 0.07, 0.06, 0.06, 0.6, and 0.7 [micro] M, respectively, using the thin-film coatings. This simple detection/quantification method afforded good reproducibility with relatively fast detection times.