Direct analysis of oxidizing agents in aqueous solution with attenuated total reflectance mid-infrared spectroscopy and diamond-like carbon protected waveguides

A novel approach for the direct detection of oxidizing agents in aqueous solution is presented using diamond-like carbon (DLC) protected waveguides in combination with attenuated total reflectance (ATR) mid-infrared spectroscopy. Pulsed laser deposition was applied to produce high-quality DLC thin films on ZnSe ATR crystals with thicknesses of a few 100 nm. Scanning electron microscopy and X-ray photoelectron spectroscopy has been used to investigate the surface properties of the DLC films including the sp(3)/sp(2) hybridization ratio of the carbon bonds. Beside excellent adhesion of the DLC coatings to ZnSe crystals, these films show high chemical stability against strongly oxidizing agents. IR microscopy was utilized to compare differences in the chemical surface modification of bare and protected ATR waveguides when exposed to hydrogen peroxide, peracetic acid, and peroxydisulfuric acid. The feasibility of DLC protected waveguides for real-time concentration monitoring of these oxidizing agents was demonstrated by measuring calibration sets in a concentration range of 0.2-10%. Additionally, principal component regression has been applied to analyze multicomponent mixtures of hydrogen peroxide, acetic acid, and peracetic acid in aqueous solution. Due to high chemical stability and accurate monitoring capabilities, DLC protected waveguides represent a novel approach for directly detecting oxidizing agents in aqueous solution with promising potential for industrial process analysis.     

Detection of anions by normal Raman spectroscopy and surface-enhanced Raman spectroscopy of cationic-coated substrates

The use of normal Raman spectroscopy and surface-enhanced Raman spectroscopy (SERS) of cationic-coated silver and gold substrates to detect polyatomic anions in aqueous environments is examined. For normal Raman spectroscopy, using near-infrared excitation, linear concentration responses were observed. Detection limits varied from 84 ppm for perchlorate to 2600 ppm for phosphate. In general, detection limits in the ppb to ppm concentration range for the polyatomic anions were achieved using cationic-coated SERS substrates. Adsorption of the polyatomic anions on the cationic-coated SERS substrates was described by a Frumkin isotherm. The SERS technique could not be used to detect dichromate, as this anion reacted with the coatings to form thiol esters. A competitive complexation method was used to evaluate the interaction of chloride ion with the cationic coatings. Hydrogen bonding and pi-pi interactions play significant roles in the selectivity of the cationic coatings.     

Electrochemical oxidation of histamine and serotonin at highly boron-doped diamond electrodes

The electrochemistry of histamine and serotonin in neutral aqueous media (pH 7.2) was investigated using polycrystalline, boron-doped diamond thin-film electrodes. Cyclic voltammetry, hydrodynamic voltammetry, and flow injection analysis (FIA) with amperometric detection were used to study the oxidation reactions. Comparison experiments were carried out using polished glassy carbon (GC) electrodes. At diamond electrodes, highly reproducible and well-defined cyclic voltammograms were obtained for histamine with a peak potential at 1.40 V vs SCE. The voltammetric signal-to-background ratios obtained at diamond were 1 order of magnitude higher than those obtained for GC electrodes at and above 100 microM analyte concentrations. A linear dynamic range of 3-4 orders of magnitude and a detection limit of 1 microM were observed in the voltammetric measurements. Well-defined sweep rate-dependent voltammograms were also obtained for 5-hydroxytryptamine (5-HT). The characteristics of the voltammogram indicated lack of adsorption of its oxidation products on the surface. No fouling or deactivation of the electrode was observed within the experimental time of several hours. A detection limit of 0.5 microM (signal-to-noise ratio 13.8) for histamine was obtained by use of the FIA technique with a diamond electrode. A remarkably low detection limit (10 nM) was obtained for 5-HT on diamond by the same method. Diamond electrodes exhibited a linear dynamic range from 10 nM to 100 microM for 5-HT determination and a range of 0.5-100 microM for histamine determination. The FIA response was very reproducible from film to film, and the response variability was below 7% at the actual detection limits.     

Voltammetric characterization of a N,N'-diphenyl-p-phenylenediamine-loaded screen-printed electrode: a disposable sensor for hydrogen sulfide

The voltammetric response of a 10% (by weight) N,N'-diphenyl-p-phenylenediamine (DPPD) and 90% (by weight) carbon and binder screen-printed electrode has been examined in aqueous media over a range of pH using cyclic voltammetry both in the presence and in the absence of sulfide. In the absence, the screen-printed electrode undergoes an initial oxidative process on the surface of the solid organic particles to form an insoluble layer of the corresponding cation radical salt, DPPD(*)(+)X(-), where X(-) is an anion present in the solution. The charge transfer is thought to occur at the three-phase boundary between solid DPPD, carbon, and the aqueous solution. At higher potentials, a second oxidative wave is observed that is attributed to the oxidation of the bulk DPPD with intercalation of the anion species present to form a solid phase of DPPD(*)(+)X(-). The two voltammetric processes were found to stabilize after repetitive scanning, after which time, sulfide was added to the solution. The voltammetric response was found to respond to sulfide by showing a decrease in both the oxidative and reductive waves, which can be attributed to the sulfide effectively blocking the three-phase boundary. The response was found to be independent of the electrode used and at pH 4 produced a linear range from 20 to 165 microM, and a limit of detection of 7.5 microM for sulfide detection was achieved.     

Application of mid-infrared spectroscopy: measuring hydrogen peroxide concentrations in bleaching baths

The presented work applies mid-infrared attenuated total reflection (ATR) spectroscopy to the measurment of hydrogen peroxide in aqueous matrices. The performance of different ATR crystals mounted in flow cells was investigated in the presence of aqueous hydrogen peroxide solutions. Quantitative determination has been achieved by evaluation of specific OH stretching and deformation vibrations with linear correlation between peak areas or peak heights and hydrogen peroxide concentration in the range of 1-10% (weight in water). Important aspects such as chemical stability of the waveguide material and influences of pH and ionic strength on the performance are discussed. Feasibility for the investigation of real world samples is demonstrated by measuring industrial bleaching solutions with known concentrations of hydrogen peroxide fitting well with calibration graphs established with neat hydrogen peroxide solutions. The presented sensor system is capable of determining hydrogen peroxide within complex matrices and clearly corroborates the potential of providing an in situ measurement concept for on-line hydrogen peroxide detection.     

Efficient charge carrier control on single walled carbon nanotube thin film transistors using water soluble polymer coatings

SWCNT-based thin-film transistors (TFTs) typically display unipolar p-type electrical characteristics in ambient condition due to the O₂/H₂O redox couple. However, complementary circuits that combine both p and n channels are preferred due to lower power requirements. Typical approaches with small molecule or polymeric dopants often yield ambipolar devices, or unstable n-type devices while concomitantly suppressing the on-current and mobility. Herein, we demonstrate a charge carrier control strategy using aqueous-based polymeric coatings that enable n-type devices with comparable performance to p-type devices. Specifically, we used a polyvinyl alcohol (PVA) coating layer containing a minority fraction of polyethyleneimine (PEI) (0.06–1.1?% w/w) to effectively switch the transfer characteristics from p-type to n-type, while maintaining decent electrical characteristics. Moreover, we demonstrate the ability to fine-tune the n branch threshold voltage via the annealing temperature. A similar strategy provides a balanced p branch on-current by incorporating PVA as a minor component (0.1-6?% w/w) into a polyacrylic acid (PAA) matrix. Through effective n-type conversion and p-type balancing, we demonstrate a simple SWCNT-based inverter. Considering the low-cost, environmentally friendly compositions and aqueous processability, this approach is attractive for large scale complementary printable circuits.

     

Combining the tape-lift method and Fourier transform infrared spectroscopic imaging for forensic applications

Conventional Fourier transform infrared (FT-IR) spectroscopy and microscopy have been widely used in forensic science. New opportunities exist to obtain chemical images and to enhance the spatial resolution using attenuated total reflection (ATR) FT-IR spectroscopy coupled with a focal-plane array (FPA) detector. In this paper, the sensitivity limits of FT-IR imaging using three different ATR crystals (Ge, ZnSe, and diamond) in three different optical arrangements for the detection of model particles is discussed. Model systems of ibuprofen and paracetamol particles having sizes below 32 mum were studied. The collection of drug particles was achieved with the aid of two different tapes: common adhesive tape and a film of polydimethylsiloxane (PDMS). The surface of the film with collected particles was measured directly via ATR-FT-IR imaging. Since the removal of tape from porous surfaces can be difficult, the application of micro ATR-FT-IR imaging directly to the surface of a newspaper contaminated with particles of model drugs is also discussed. In order to assess the feasibility of the chosen method in a forensic case study, the detection of diacetylmorphine hydrochloride traces in PDMS matrix and the finger surface is investigated. The scenarios considered were that of the detection of evidence collected at a crime scene with the tape lift method and the analysis of the finger of an individual after drug handling. The results show broad implications in the detection of drugs of abuse.     

Effect of supersaturation on the morphology of hydroxyapatite crystals deposited by electrochemical deposition on titanium

Cathodic deposition of calcium phosphate coating on titanium using electrochemical method was investigated in our study and well-defined hexagonal rod-like hydroxyapatite (HAp) crystals were synthesized. Scanning electron microscopic photographs of HAp coatings under different deposition durations revealed the morphology change of the HAp crystals in the coating film with the experimental process: from cone-like structure to hexagonal prism with sharp-angled tip, and finally turns to rod-like one with regular hexagonal cross section. It was suggested that both morphology and longitudinal length of the HAp crystals in the coating could be regulated by an accurate control of the degree of supersaturation of the aqueous system.     

Combined determination of the thermo physical properties of vaporized materials

A nonsteady method is proposed for determining the thermophysical characteristics of poor heat conductors in the form of thin-film vaporized coatings. The heat conduction problem is solved for a system consisting of a bounded and a semibounded rod with a plane heat source of constant power using a thin-film coating with known characteristics as standard.     

Grazing angle attenuated total reflection spectroscopy: fields at the interface and source of the enhancement

With the tremendous growth in the semiconductor and coatings industries, spectroscopic methods of examining extremely thin films on high refractive index substrates have become increasingly important. One infrared method for analyzing monolayers on substrates such as silicon and gold that has recently gained popularity is 'grazing' or high angle of incidence attenuated total reflection (ATR) spectroscopy. This paper investigates the directional electric field strengths and the extraordinary sensitivity achieved by using the grazing angle ATR method for analyzing monolayers on silicon substrates.     

All-nanoparticle thin-film coatings

All-nanoparticle thin-film coatings that exhibit antireflection, antifogging (superhydrophilicity), and self-cleaning properties have been prepared via layer-by-layer deposition of TiO(2) and SiO(2) nanoparticles. The porosity and chemical composition of the coatings were determined using a simple method that is based on ellipsometry and does not require any assumptions about the refractive indices of the constituent nanoparticles. The presence of nanopores in the TiO(2)/SiO(2) nanoparticle coatings results in superhydrophilicity as well as antireflection properties. The superhydrophilicity of contaminated coatings could also be readily recovered and retained after ultraviolet irradiation.     

An analytical method for trifluoroacetic Acid in water and air samples using headspace gas chromatographic determination of the methyl ester

An analytical method has been developed for the determination of trace levels of trifluoroacetic acid (TFA), an atmospheric breakdown product of several of the hydrofluorocarbon (HFC) and hydrochlorofluorocarbon (HCFC) replacements for the chlorofluorocarbon (CFC) refrigerants, in water and air. TFA is derivatized to the volatile methyl trifluoroacetate (MTFA) and determined by automated headspace gas chromatography (HSGC) with electron-capture detection or manual HSGC using GC/MS in the selected ion monitoring (SIM) mode. The method is based on the reaction of an aqueous sample containing TFA with dimethyl sulfate (DMS) in concentrated sulfuric acid in a sealed headspace vial under conditions favoring distribution of MTFA to the vapor phase. Water samples are prepared by evaporative concentration, during which TFA is retained as the anion, followed by extraction with diethyl ether of the acidified sample and then back-extraction of TFA (as the anion) in aqueous bicarbonate solution. The extraction step is required for samples with a relatively high background of other salts and organic materials. Air samples are collected in sodium bicarbonate-glycerin-coated glass denuder tubes and prepared by rinsing the denuder contents with water to form an aqueous sample for derivatization and analysis. Recoveries of TFA from spiked water, with and without evaporative concentration, and from spiked air were quantitative, with estimated detection limits of 10 ng/mL (unconcentrated) and 25 pg/mL (concentrated 250 mL:1 mL) for water and 1 ng/m(3) (72 h at 5 L/min) for air. Several environmental air, fogwater, rainwater, and surface water samples were successfully analyzed; many showed the presence of TFA.     

Gas-Assisted IR-ATR Probe for Detection of Volatile Compounds in Aqueous Solutions

The application of the principle of solid-phase microextraction (SPME) to attenuated total reflectance (ATR) infrared (IR) probes can provide a convenient and sensitive way to detect volatile organic compounds (VOCs) in aqueous solutions. In this paper a new method to increase the performance of this type of sensing device is proposed. A stream of gas purges out VOCs from aqueous solution. These compounds are directed to an internal-reflection sensor. Several advantages are recognized by this new method as compared with a conventional liquid probe; these include a longer lifetime for the probe, higher selectivity in the detection of VOCs, less limitation in the sample volume, and easier regeneration of the sensing probe.     

Planar fiber-optic chips for broadband spectroscopic interrogation of thin films

A planar fiber-optic chip (FOC) has been developed using side-polished optical fibers and characterized for broadband absorbance and fluorescence detection of molecular films. FOC technology combines the sensitivity of an attenuated total reflection (ATR) element with the ease of use of fiber-optic-based spectrometers and light sources to create an improved platform for spectroscopic analysis of molecular adsorbates. A multi-mode optical fiber (core diameter = 50 mum, numerical aperture = 0.22, stepped refractive index profile) mounted in a glass V-groove block was side-polished to create a planar platform that allows access to the evanescent field escaping from the fiber core. For this generation of FOC technology, the exposed evanescent field has an interaction length of approximately 17.2 mm. The FOC platform was independently characterized through measurements of thin-film and bulk absorbing samples. The device performance was compared to the existing ATR technology and methods for increasing sensitivity of the FOC were investigated and validated. Additionally, we have demonstrated the ability of the FOC to both evanescently excite and collect fluorescence through guided modes of the optical fiber for a surface-confined luminescent semiconductor nanoparticle film (4 nm diameter, ligand capped, CdSe core). The FOC described here with a supported planar interface can facilitate the use of conventional planar deposition technologies and provide a robust planar platform that is amenable for incorporation into various sensor technologies.     

环境功能负离子涂料的制备及抗菌性能研究

采用溶胶-凝胶法以Na2SiO3为包覆剂成功地制备了分散性优良负离子粉体，通过不同的添加量，研制能够产生最大负离子浓度的功能涂料。进行了负离子涂料的抗菌性研究，实验结果表明负离子材料具有抗菌性，抗菌效果与涂料的负离子产生量、负离子材料粒径、涂料的距离密切相关，并从微观上对负离子杀菌进行了分析，验证了负离子的生物学效应。     

Thermoluminescence centres created selectively in MgO crystals by fast neutrons

A possibility of using the thermoluminescent detection of collision-created interstitial centres in MgO by the TL peak at 700 K, arising at the radiative recombination of anion interstitials with F+ centres, for the selective detection of fast neutrons in mixed neutron-gamma fields, is examined. Selectivity and sensitivity of such a detector are discussed. For the present time, the sensitivity of the thermoluminescent detection of anion interstitials created by neutron irradiation is comparable to that of the EPR detection of F+ centres, the main limitations of the thermoluminescence method being connected with the background thermoluminescence and absence of suitable luminescence centres in this temperature region, when undoped and untreated MgO crystals are used. Possible ways to overcome these shortcomings are discussed.     

Measurement system to determine the total and angle-resolved light scattering of optical components in the deep-ultraviolet and vacuum-ultraviolet spectral regions

An instrumentation for total and angle-resolved scattering (ARS) at 193 and 157 nm has been developed at the Fraunhofer Institute in Jena to meet the severe requirements for scattering analysis of deep- and vacuum-ultraviolet optical components. Extremely low backscattering levels of 10(-6) for the total scattering measurements and more than 9 orders of magnitude dynamic range for ARS have been accomplished. Examples of application extend from the control of at-wavelength scattering losses of superpolished substrates with rms roughness as small as 0.1 nm to the detection of volume material scattering and the study into the scattering of multilayer coatings. In addition, software programs were developed to model the roughness-induced light scattering of substrates and thin-film coatings.     

Attenuated total reflection surface-enhanced infrared absorption microspectroscopy for identification of small thin layers on material surfaces

Attenuated total reflection surface-enhanced infrared absorption microspectroscopy (micro-ATR-SEIRA) was developed for the identification of sub-mm size and nm-thick layers on material surfaces by using gold island films deposited on the surface of micro-ATR crystals. A thin layer of triphenyl phosphate (TPP) on a poly(tetrafluoroethylene) (PTFE) membrane filter was used to evaluate the enhancement of the absorption bands. Three types of crystals: diamond, silicon, and germanium, were evaluated. Diamond gave the greatest enhancement with a 12 nm thick gold island film. The enhancement factor was 200 times compared to bare diamond crystal, whereas it was 10 times for germanium crystal. This variation of enhancement factor according to crystal types was presumed to be due to the morphology of the gold films on the crystals. We also obtained an enhanced ATR map over an area of approximately 2 x 6 mm for a thin layer (approximately 1 nm thick) of di-2-ethylhexylphthalate on PTFE using gold-coated hexagonal silicon micro-ATR crystals. This micro-ATR-SEIRA technique has major potential for analyzing small and thin substances on material surfaces.     

PVD薄膜传感器裂纹检测概率测定与分析

为利用PVD(physical vapor deposition)薄膜传感器对金属结构裂纹的检测能力进行定量化表征,首先采用正交实验优化后适用于LY12-CZ铝合金的工艺参数,在3组中心孔板实验件上分别制备币状、1mm宽同心双环状、0.5mm宽同心三环状3种不同形状的PVD薄膜传感器。随后,在实验室条件下开展疲劳裂纹在线监测实验,对比分析PVD薄膜传感器电位输出信号和显微镜观测结果。最后,采用改进的裂纹尺寸间隔法和二项分布检测模型绘制PVD薄膜传感器总体与不同形状的裂纹检测概率曲线。PVD薄膜传感器在95%置信水平下,对长度大于0.99mm的裂纹检出概率可达93.56%;相比于币状薄膜传感器,同心环状薄膜传感器对小于0.5mm的裂纹更为敏感,且传感器通道宽度越细,对小尺寸裂纹的检测概率越高。     

Measurement of cosmogenic 35S activity in rainwater and lake water

Although cosmogenic 35S (t(1/2) = 87 d) has been found to be a unique and excellent radioactive tracer for stable S in atmospheric and aqueous environments, its application has been very limited because an analytical method for its detection has not been well-documented. Here, we report a rapid and robust method for analyzing extremely low levels of 35S in rainwater and lake water samples. About 20-L water samples were preconcentrated using an anion exchange column. The purified 35S was precipitated as BaSO4, and the precipitates were collected using a GF/B filter. The 35S in precipitates on the filter was directly counted using a super-low-background liquid scintillation counter with cocktail. We successfully measured 35S in precipitation and lake water samples using this method, which promises future diverse applications of the 35S tracer to S cycling in the environment and to age determination of lake water and shallow groundwater.