Development of an aerosol chemiluminescent detector coupled to capillary electrophoresis for saccharide analysis

A novel aerosol chemiluminescent (CL) detector coupling to capillary electrophoresis (CE) for the detection of saccharides is reported. This CL detector is composed of a postcapillary nebulizer and porous alumina as catalyzer in quartz tube. The CL emission could be generated due to the catalyzing oxidization of saccharides on the surface of porous alumina. The saccharides such as sucrose, alpha-lactose, maltose, raffinose, galactose, xylose, and glucose with only weak UV absorbance can be successfully detected. The linear ranges of those saccharides are from 30-2000 to 50-2000 mg/L; relative standard deviations range from 2.1 to 3.7% (200 mg/L, n = 11). Compared with the traditional UV detector currently used in CE, this novel detector shows the advantage of high sensitivity to the compounds with only weak UV absorption. Thus, it could be an important supplement of CE detectors for UV-lacking compounds.     

Vortex configuration flow cell based on low-temperature cofired ceramics as a compact chemiluminescence microsystem

The integration of optical detection methods in continuous flow microsystems can highly extend their range of application, as long as some negative effects derived from their scaling down can be minimized. Downsizing affects to a greater extent the sensitivity of systems based on absorbance measurements than the sensitivity of those based on emission ones. However, a careful design of the instrumental setup is needed to maintain the analytical features in both cases. In this work, we present the construction and evaluation of a simple miniaturized optical system, which integrates a novel flow cell configuration to carry out chemiluminescence (CL) measurements using a simple photodiode. It consists of a micromixer based on a vortex structure, which has been constructed by means of the low-temperature cofired ceramics (LTCC) technology. This mixer not only efficiently promotes the CL reaction due to the generated high turbulence but also allows the detection to be carried out in the same area, avoiding intensity signal losses. As a demonstration, a flow injection system has been designed and optimized for the detection of cobalt(II) in water samples. It shows a linear response between 2 and 20 microM with a correlation of r > 0.993, a limit of detection of 1.1 microM, a repeatability of RSD = 12.4%, and an analysis time of 17 s. These results demonstrate the suitability of the proposal to the determination of compounds involved in CL reactions by means of an easily constructed versatile device based on low-cost instrumentation.     

Gold nanoparticle-catalyzed luminol chemiluminescence and its analytical applications

Gold colloids with nanoparticles of different sizes were found to enhance the chemiluminescence (CL) of the luminol-H2O2 system, and the most intensive CL signals were obtained with 38-nm-diameter gold nanoparticles. UV-visible spectra, X-ray photoelectron spectra, and transmission electron microscopy studies were carried out before and after the CL reaction to investigate the CL enhancement mechanism. The CL enhancement by gold nanoparticles of the luminol-H2O2 system was supposed to originate from the catalysis of gold nanoparticles, which facilitated the radical generation and electron-transfer processes taking place on the surface of the gold nanoparticles. The effects of the reactant concentrations, the size of the gold nanoparticles. and some organic compounds were also investigated. Organic compounds containing OH, NH2, and SH groups were observed to inhibit the CL signal of the luminol-H2O2-gold colloids system, which made it applicable for the determination of such compounds.     

Development and testing of a detection method for liquid chromatography based on aerosol charging

Aerosol-based detection methods for HPLC in which HPLC effluent is converted to an aerosol and detected optically have been employed in the past. This paper describes a new aerosol-based detection method for HPLC, which we name aerosol charge detection. This detection method also involves generation of an aerosol but with aerosol detection by charging aerosol particles and measuring the current from the charged particle flux. A commercial electrical aerosol size analyzer was used for the aerosol detection. The constructed detector was tested using flow injection analysis with water as the mobile phase, and the signal response was found to be linear for sodium sulfate over the concentration ranges of 0.2-100 microg mL(-1) using one of the nebulizers. Minimum mass and concentration detection limits using the more efficient nebulizer were estimated to be 0.2 ng and 10 ng mL(-1), respectively. Behavior for most of the other compounds tested was similar with some differences in sensitivity. Testing the detector using reversed phase HPLC for glucose gave a range of linear response and detection limits that were similar to the flow injection analysis studies. Under most HPLC conditions, the noise will primarily be a function of solvent impurities; however, the electrical aerosol size analyzer allows the removal of small charged particles to improve the signal-to-noise ratio.     

Dielectric barrier discharge-induced chemiluminescence: potential application as GC detector

Atmospheric pressure dielectric barrier discharge (DBD) plasma can be used to split low molecular weight organic compounds, and the DBD-split/excited species can be swept into luminol solution to induce chemiluminescence (CL) emission. Based on this observation, a novel optical detector was proposed and preliminarily tested as a potential gas chromatographic (GC) detector in this work. The advantages of this new type of detector include the following: direct detection, fast response, high sensitivity, versatility (sensitive to a broad range of volatile organic compounds), simple and easy instrumentation, compactness (3.0 mm i.d. x 4.0 mm o.d. x 20 mm length of the DBD device), and low power (less than 5 W). Twelve volatile organic compounds, including methanol, ethanol, propanol, formaldehyde, acetaldehyde, benzene, dichloromethane, trichloromethane, tetrachloromethane, tetrahydrofuran, carbon bisulfide, and ethyl ether, were tested with this detector, and each of them produced a large signal. It was found that the CL signal was proportional to the analyte concentration and affected by the DBD parameters. Under the optimized experimental conditions, the limits of detection down to the tens of nanogram level were achieved for methanol, ethanol, propanol, formaldehyde, and acetaldehyde. It was then preliminarily tested as a GC detector for the separation of formaldehyde, ethanol, and propanol. This is the new application of DBD in analytical chemistry, and CL was for the first time generated in this way. The new detector can be a potential GC detector suitable for a wide range of volatile organic compounds.     

Effect of particles on ultraviolet light penetration in natural and engineered systems

The effect of light scattering on measurement of UV absorbance and penetration of germicidal UVC irradiance in a UV reactor were studied. Using a standard spectrophotometer, absorbance measurements exhibited significant error when particles that scatter light were present but could be corrected by integrating sphere spectroscopy. Particles from water treatment plants and wastewater effluents exhibited less scattering (20%-30%) compared with particles such as clay (50%) and alumina (95%-100%). The distribution of light intensity in a UV reactor for a scattering suspension was determined using a spherical chemical actinometry method. Highly scattering alumina particles increased the fluence rate in the reactor near the UV lamp, whereas clay particles and absorbing organic matter reduced the fluence rate. A radiative transfer fluence rate model reasonably predicted the fluence rate of absorbing media and highly scattering suspensions in the UV reactor.     

Quantification of fluorophore concentration in tissue-simulating media by fluorescence measurements with a single optical fiber

Quantifying fluorescent compounds in turbid media such as tissue is made difficult by the effects of multiple scattering and absorption of the excitation and emission light. The approach that we used was to measure fluorescence using a single 200-microm optical fiber as both the illumination source and the detector. Fluorescence of aluminum phthalocyanine tetrasulfonate (AlPcS4) was measured over a wide range of fluorophore concentrations and optical properties in tissue-simulating phantoms. A root-mean-square accuracy of 10.6% in AlPcS4 concentration was attainable when fluorescence was measured either interstitially or at the phantom surface. The individual effects of scattering, absorption, and the scattering phase function on the fluorescence signal were also studied by experiments and Monte Carlo simulations.     

Extending ATOFMS measurements to include refractive index and density

An absolute calibration of the light scattering region in an aerosol time-of-flight mass spectrometer (ATOFMS) has been performed enabling a direct comparison of the average experimentally measured light scattering intensity to theory. A fitting procedure allows for the determination of both refractive index and density for spherical homogeneous particles. The scattering information has been correlated with the other single-particle information measured by the ATOFMS. Size, chemical composition, and scattering intensity can all be linked to establish a better understanding of the relationships between the chemical and physical properties of aerosol particles. Currently, inputs into climate models are derived from data acquired from bulk aerosol composition measurements, and therefore, assumptions must be made regarding the chemical associations within individual particles (mixing state) to enable modelers to calculate the relevant aerosol optical properties. These new measurements aim for the goal of directly testing the model assumptions by utilizing single-particle chemical information to derive the optical properties of the different particle classes.     

Moving beyond traditional UV-visible absorption detection: cavity ring-down spectroscopy for HPLC

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 micros 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(-7) absorbance units (AU) peak to peak, as compared to 1 x 10(-5) AU for a state-of-the-art commercial UV-visible detector.     

Chemiluminescence determination of chlorinated volatile organic compounds by conversion on nanometer TiO2

A novel method based on conversion of chlorinated volatile organic compounds (CVOCs) to chlorine using a new type of column packed with nanometer TiO2 coupled with chemiluminescence (CL) has been developed for determination of them in workplace air. CVOCs are converted to chlorine by nanometer TiO2 at 220 degrees C. The Cl2 that is produced is selectively enriched on the column and subsequently released from the column at 600 degrees C. The Cl2 that is released is determined using a postcolumn CL detector. The CL intensity was linear with CCl4 in the range of 0.1-380 ppm, and the detection limit was 40 ppb (S/N = 3). Higher sensitivity could be acquired by using a larger volume of enrichment A similar procedure could be used for the determination of other CVOCs. CL intensities of CH2Cl2, CHCl3, and CCl4 at the same concentration increased in the order CH2Cl2 < CHCl3 < CCl4. The method has been successfully applied to the determination of CCl4 in workplace air, where 0.15-150 ppm CCl4 would be detected. The possible mechanism for the long lifetime of the column packed with nanometer TiO2 was tested using Raman spectrometer, X-ray powder diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The results showed that the column packed with nanometer TiO2 could be operated in the reversible mode for determination of CVOCs under the present conditions. The method would be potentially applied to the analysis of other chlorinated compounds in environment, such as persistent organic pollutants.     

氧化铝薄膜在发光方面的研究进展

对近十几年来Al2O3薄膜在发光方面的研究进展分4个方面进行了介绍:(1)多孔阳极氧化铝薄膜基质的光致发光(PL)及其发光机理研究;(2)退火温度对多孔阳极氧化铝薄膜发光性能的影响;(3)氧化铝薄膜基质中掺杂稀土离子或过渡金属离子后的光致发光研究;(4)Al2O3薄膜的电致发光(EL)研究.此外,还对氧化铝薄膜发光方面的发展前景进行了展望.     

Polarization of skylight in the O(2)A band: effects of aerosol properties

Motivated by several observations of the degree of linear polarization of skylight in the oxygen A (O(2)A) band that do not yet have a quantitative explanation, we analyze the influence of aerosol altitude, microphysics, and optical thickness on the degree of linear polarization of the zenith skylight in the spectral region of the O(2)A band, between 755 to 775 nm. It is shown that the degree of linear polarization inside the O(2)A band is particularly sensitive to aerosol altitude. The sensitivity is strongest for aerosols within the troposphere and depends also on their microphysical properties and optical thickness. The polarization of the O(2)A band can be larger than the polarization of the continuum, which typically occurs for strongly polarizing aerosols in an elevated layer, or smaller, which typically occurs for depolarizing aerosols or cirrus clouds in an elevated layer. We show that in the case of a single aerosol layer in the atmosphere a determination of the aerosol layer altitude may be obtained. Furthermore, we show limitations of the aerosol layer altitude determination in case of multiple aerosol layers. To perform these simulations we developed a fast method for multiple scattering radiative transfer calculations in gaseous absorption bands including polarization. The method is a combination of doubling-adding and k-binning methods. We present an error estimation of this method by comparing with accurate line-by-line radiative transfer simulations. For the Motivated by several observations of the degree of linear polarization of skylight in the oxygen A (O(2)A) band that do not yet have a quantitative explanation, we analyze the influence of aerosol altitude, microphysics, and optical thickness on the degree of linear polarization of the zenith skylight in the spectral region of the O(2)A band, between 755 to 775 nm. It is shown that the degree of linear polarization inside the O(2)A band is particularly sensitive to aerosol altitude. The sensitivity is strongest for aerosols within the troposphere and depends also on their microphysical properties and optical thickness. The polarization of the O(2)A band can be larger than the polarization of the continuum, which typically occurs for strongly polarizing aerosols in an elevated layer, or smaller, which typically occurs for depolarizing aerosols or cirrus clouds in an elevated layer. We show that in the case of a single aerosol layer in the atmosphere a determination of the aerosol layer altitude may be obtained. Furthermore, we show limitations of the aerosol layer altitude determination in case of multiple aerosol layers. To perform these simulations we developed a fast method for multiple scattering radiative transfer calculations in gaseous absorption bands including polarization. The method is a combination of doubling-adding and k-binning methods. We present an error estimation of this method by comparing with accurate line-by-line radiative transfer simulations. For the O(2)A band, the errors in the degree of linear polarization are less than 0.11% for transmitted light, and less than 0.31% for reflected light. band, the errors in the degree of linear polarization are less than 0.11% for transmitted light, and less than 0.31% for reflected light.     

Measuring scatter with a cryogenic probe and an ICCD camera: recording absorption spectra in Shpol'skii matrixes and fluorescence quantum yields in glassy solvents

Recording absorption spectra via transmittance through frozen matrixes is a challenging task. The main reason is the difficulty in overcoming the strong scattering light reaching the detector. This is particularly true when thick samples are necessary for recording absorption spectra of weak oscillators. In the case of strongly fluorescent compounds, additional errors in absorbance measurements arise from the emission reaching the detector, which might have an intensity comparable to that of the transmitted light. This article presents a fundamentally different approach to low-temperature absorption measurements as the sought for information is the intensity of laser excitation returning from the frozen sample to the ICCD. Laser excitation is collected with the aid of a cryogenic fiber optic probe. The feasibility of our approach is demonstrated with single-site and multiple-site Shpol'skii systems. The 4.2 K absorption spectra show excellent agreement with their literature counterparts recorded via transmittance with closed-cycle cryogenators. Fluorescence quantum yields measured at room temperature compare well to experimental data acquired in our laboratory via classical methodology. Similar agreement is observed between 77 K fluorescence quantum yields and previously reported data acquired with classical methodology. We then extend our approach to generate original data on fluorescence quantum yields at 4.2 K.     

Semi-infinite linear diffusion spectroelectrochemistry on an aqueous micro-drop

We report a technique for conducting semi-infinite diffusion spectroelectrochemistry on an aqueous micro-drop as an easy and economic way of investigating spectroelectrochemical behavior of redox active compounds and correlating spectroscopic properties with thermodynamic potentials on a small scale. The chemical systems used to demonstrate the aqueous micro-drop technique were an absorbance based ionic probe [Fe(CN)(6)](3-/4-) and an emission based ionic probe [Re(dmpe)(3)](2+/+). These chemical systems in a micro-drop were evaluated using cyclic voltammetry and UV-visible absorbance and luminescence spectroscopies.     

Light-scattering studies of packed stationary phases for capillary electrochromatography

Multiply scattered light through turbid media, packed particles, or compressed powders will inherently have a significantly longer optical path length than that of light which is not scattered. The concept of using the multiply scattered light potentially generated in the packed stationary phase of a capillary electrochromatography (CEC) column for enhanced detection as a result of its increased optical path length was examined. Ultraviolet (UV) light at 365 nm or laser light at 635 nm was focused to a small spot onto the packed section of a 3 microns spherisorb ODS1 CEC column (100 microns i.d.). The light was transported inside the capillary, and an image of the multiply scattered light several millimeters along the capillary was collected using a charged-couple device detector. Even if the spot size was less than 100 microns in diameter, evidence of light scattering was observed at a detection spatial off-set distance of 1-2 mm from the illumination point. When the calcium channel blocking drug felodipine was flushed through the column, the light intensity value dropped (increase in absorbance) to a greater degree at a spatial off-set (1.5 mm) than at the illumination point. The greater absorbance values at the spatial off-set were examined experimentally when felodipine was eluted from the column in the CEC mode in 6 min using MeCN/50 mM TRIS (pH 8.0) (80:20, v/v) at an applied voltage of 300 V/cm and an injection time of 2 s at 10 kV. A factor of 8.5 increase in absorbance was observed at a spatial off-set of 1 mm compared to the value obtained at the illumination point. An efficiency value of approximately 234,000 plates m-1 was obtained for this higher felodipine peak. Higher noise values, however, were also observed with this increase in absorbance. Using a spectrophotometer or an open capillary to obtain reference values for optical length, it was possible to estimate the average optical path length of light traveled through the packed stationary phase when transmitted at a spatial off-set. It was concluded that, although an increase in absorbance of 8.5 was observed at a spatial off-set, this most likely arises from the light being "redirected" and scattered in a straightforward fashion along the capillary. It was expected that if substantial multiple scattering did occur inside the packed stationary phase, a significantly larger absorbance increase would be attained. A number of proposals are thus given to explain the relatively low degree of multiple scattering in this stationary phase and suggestions offered on means to attain even higher absorbance increases at a spatial off-set. Additional potential applications are also discussed.     

Effects of aerosol scattering phase function formulation on point-spread-function calculations

The quality of the image produced by an outdoor optical system is affected by the presence of atmospheric aerosols between object and receiver. The properties of the point-spread function that result from aerosol particles were calculated by a new Monte Carlo code called MEDIA (an acronym for Modélisation des Effets de Diffusion Inhérents à l'Atmosphère). The influence of the scattering phase function's angular dependence on the irradiance of the focal plane of a detector was studied. Calculations were performed by use of Mie theory and of the Henyey-Greenstein formulation for the same asymmetry parameter and various detector optical characteristics and atmospheric conditions. Major variations were observed for strong forward-peaked scattering phase functions and a large detector field of view.     

Separation and determination of iron-containing proteins via liquid chromatography-particle beam/hollow cathode-optical emission spectroscopy

Presented here is a method for the quantitative determination of iron-containing metalloproteins. Four iron-containing metalloproteins (transferrin, myoglobin, hemoglobin, and cytochrome c) were separated by high-performance liquid chromatography (HPLC) and determined through particle beam/hollow cathode-optical emission spectroscopy (PB/HC-OES) by the Fe (I) 371.9 nm optical emission. Parametric optimization of sample introduction, nebulization, and hollow cathode source conditions is performed for the suite of Fe-metalloproteins. Response curves for the Fe (I) emission were obtained under optimized conditions with detection limits for triplicate injections occurring on the nanogram level for iron ( approximately 24 ng) with variability of <7% RSD over the concentration range of 0.1-100 microg/mL iron in the metalloproteins. Response curves for S (I) emission yielded similar analytical characteristics. Optical emission detection of the liquid chromatography separations of the iron-containing metalloproteins demonstrates the feasibility of the PB/HC-OES system as a simple element-specific detector for liquid chromatography. The retention times of the four analytes are similar to those determined by UV absorbance (216 nm), demonstrating the ability of the PB interface to preserve the chromatographic integrity of the separation. Additionally, empirical formula calculations based on Fe (I) and S (I) emission response ratios provide a much higher level of specificity than single-element protein determination.     

A dc microplasma on a chip employed as an optical emission detector for gas chromatography

A micromachined plasma chip is coupled to a conventional gas chromatograph to investigate its performance as an optical emission detector. The device employs a 180-nL plasma chamber in which an atmospheric pressure dc glow discharge is generated in helium. Applied power is 9 mW (770 V, 12 microA) and helium flow rate 320 nL s(-1). A number of carbon-containing compounds are detected in the column effluent by recording the emission at 519 nm. For hexane, the detector has a linear dynamic range of over two decades and a minimum detectability of 10(-12) g s(-1) (800 ppb). The detector signal shows a marked peak broadening and tailing when compared with the signal of a flame ionization detector. This is mainly attributed to dead volumes and chromatographic processes introduced by the connecting tubing and the chip glass channels. The device was operated for more than 24 h without a significant change in performance. Operation is stable and instrumental requirements are simple. Future use of the detector chip in conventional gas chromatography or as an integrated detector in on-chip gas chromatography is discussed.     

Chemiluminescent reaction of fluorescent organic compounds with KHSO5 using cobalt(II) as catalyst and its first application to molecular imprinting

The decomposition of peroxomonosulfate (HSO5-) has been investigated by chemiluminescence (CL). A weak CL was observed during mixing the HSO5- solution with the Co2+ solution in unbuffered conditions. An appropriate amount of fluorescent organic compounds (FOCs), such as dansyl amino acids and pyrene, was added to the KHSO5/Co2+ solution, a strong CL was recorded. A possible CL mechanism, based on studies of the fluorescence, CL, and UV-visible spectra and comparison of Co3+ oxidation ability with the SO4.- radical ion, was discussed. The CL from HSO5-/Co2+ is the emission of singlet oxygen produced from the catalytic decomposition of HSO5-. It was suggested that the decomposition of HSO5- in aqueous solution with Co2+ proceeds via one-electron transfer to yield SO4.- radical ion. The FOC was attacked by SO4.- radical ion and oxidized to decompose into small molecules. During this proceeding, CL emission was given out. The present CL system has been developed as a flow injection analysis for FOCs. The detection limits (S/N = 3) were in the concentration range 10(-9)-10(-7) M for FOCs. Oxidation decomposition and CL emission of the analytes have been used in the molecular imprinting recognition. As an initial attempt, dansyl-L-phenylalanine was used as a template molecule and methacrylic acid and 2-vinylpyridine were used as functional monomers. The network copolymer imprinted with dansyl-L-phenylalanine exhibits an affinity for the template molecule. When the flowing streams of HSO5- and Co2+ solutions mixing through the molecularly imprinted polymer particles filled the flow cell, the template molecule, dansyl-L-phenylalanine reacted with the HSO5-/Co2+ solution and CL was emitted. The dansyl-L-phenylalanine was decomposed during the CL process, and the cavities of a defined shape and an arrangement of functional groups complementary to the template in the polymer were left for the next sample analysis.