R. Kellner

Investigation of Different Polymers as Coating Materials for IR/ATR Spectroscopic Trace Analysis of Chlorinated Hydrocarbons in Water

Polymer-coated attenuated total reflection (ATR) elements have been used to compare the diffusion behavior and enrichment from aqueous solutions of three different chlorinated hydrocarbons (CHCs) — monochlorobenzene (MCB), chloroform (CF), and tetrachloroethylene (TeCE)—into different polymers. The influence of polymer properties such as glass transition temperature and crystallinity and the effect of the polymer background IR absorption and varying thicknesses of the polymer membranes to the detectability were investigated. The crystallinity and the glass transition temperature have a very pronounced influence on the velocity of the diffusion process, whereas the partition coefficient influences the amount of CHC diffusing into the polymer membrane. The time constants for 90% saturation of the polymer with the test analytes are in the range of 8 to 40 min, depending on the nature of the polymer and analyte. A linear calibration graph was obtained for simultaneous detection of all three test analytes in the range from 5 mg/L to 100 mg/L CHC with detection limits of 1.5 to 2 mg/L. Coefficients for CHC partitioning between water and polymers measured by ATR/IR were in good agreement with values determined by GC/MS.

Fiber optic sensor for chlorinated hydrocarbons in water based on infrared fibers and tunable diode lasers

A novel fiber optic evanescent wave spectroscopy (FEWS) system is based on a tunable diode laser (TDL) source, on a polymer‐coated AgClBr infrared transmitting fiber, and on a mercury cadmium telluride detector. This system was used for sensing low levels of chlorinated hydrocarbons in water. The detection limit was 100 μg/l (100 ppb), which is an improvement by a factor of 50 in comparison to a similar system that is based on a Fourier transform infrared spectrometer, and the measurement time was reduced by a factor of 3. The TDL‐FEWS system shows significant potential for in situ monitoring of ground water.

New IR Fiber-Optic Chemical Sensor for in Situ Measurements of Chlorinated Hydrocarbons in Water

In this work the development and validation of a new MIR fiber-optic physicochemical sensor system for the continuous in situ analysis of chlorinated hydrocarbons (CHCs) in water is described. This study took advantage of the selectivity and sensitivity of fiber evanescent wave spectroscopy (FEWS) and the recent development of polycrystalline silver halide fibers. Since these fibers are transparent up to 20 μm, it was possible for the first time to develop a fiber-optic sensing system for CHCs, which have their strongest absorption bands > 10 μm. The silver halide fibers were coated with low-density polyethylene (LDPE) to enrich the CHC within the evanescent wave and to exclude the IR absorbing water from the measurement. For the quantitative in situ FEWS measurements, the coated silver halide fibers were coupled to a Fourier transform infrared (FT-IR) spectrometer using an off-axis parabolic mirror and a fiber-detector coupling system. This setup enabled the simultaneous in situ detection of the most common chlorinated hydrocarbons in concentrations between 1 to 50 mg/L in water by employing a fiber sensing part only 10 cm in length. A comparative analysis of waste water samples under participation of two experienced head space-gas chromatography (HSGC) laboratories showed good agreement of this continuous sensor system with the established standard techniques. The resulting working curve for tetrachloroethylene showed a correlation coefficient of r2 = 0.968 and a relative standard deviation of 17% in the range from 1 to 10 ppm.

Polymer coated silver halide infrared fibers as sensing devices for chlorinated hydrocarbons in water

Fiberoptic evanescent wave spectroscopy (FEWS) based on AgClBr fibers and a Fourier transform infrared (FTIR) spectrometer was used for the first time to measure chlorinated hydrocarbons (CH) in water. A minimum detection limit lower than 10 mg/l was achieved by coating the fiber with low density polyethylene (LDPE), which shows reversible enrichment of CH. The response of the sensor to CH diffusion through the polymer layer was analyzed theoretically and the results were found to be in good agreement with the experiments.

Infrared attenuated total reflection spectroscopic investigations of the diffusion behaviour of chlorinated hydrocarbons into polymer membranes

Abstract The response behaviour of a sensor for chlorinated hydrocarbons (CHC) in water was evaluated practically and theoretically. The sensor consisted of polymer-coated attenuated total reflection (ATR) elements coated with different polymers such as low-density polyethylene polyisobutylene and ethylene/propylene copolymer and was based on the diffusion behaviour of the CHC in different polymer layers. The purpose of the polymer coating was to enrich chlorinated hydrocarbons and to exclude water from the information depth of the penetrating infrared (IR) radiation. The coated ATR crystals were mounted in a flow-through cell and placed inside the sample chamber of the Fourier transform infrared spectrometer equipped with a mercury-cadmium-telluride detector. Measurements were performed by filling the cell with aqueous solutions of CHC and recording a series of spectra with constant time offset. The aim of this study was to investigate the diffusion behaviour and to determine the diffusion coefficient of three CHC (monochlorobenzene, tetrachloroethylene and chloroform) in polymer matrices in order to optimize the sensor response. For that reason an already existing theoretical model was modified. Using this new model numerical simulations of the diffusion processes occurring in the aqueous and polymer phase with respect to different partition coefficients, different diffusion coefficients and different thicknesses were performed. A classical Fickian response was found to be the dominant diffusion behaviour observed for the diffusion of chlorinated hydrocarbons into the polymers. This work showed the importance to understand the diffusion processes in different polymer materials for optimizing a fiber optic sensing system for CHCs in water.

Flow-injection analysis for total cholesterol with photometric detection

Abstract The level of total cholesterol in human blood serum samples is determined by flow-injection analysis. A. 70-μl sample is injected into a phosphate buffer stream, pH 7.0, and led through an enzymatic reactor, which contains cholesterol esterase and cholesterol oxidase immobilized on controlled pore glass. The enzymatically released hydrogen peroxide is detected with 2,2′-azinobis(3-ethylbenzthiazoline-6-sulfonate) in a peroxidase catalyzed reaction. A linear calibration is obtained in the clinically important range from 0.11 to 8.6 mmol 1−1. The indicator system is compared to the commonly used aminoantipyrine-phenol reagent. The potential interferents studied include bilirubin, triglycerides, haemolyzed serum, glucose, urea, uric acid, and citric acid. The accuracy of the method is established by comparison with a clinically established method based on spectrophotometric endpoint evaluation.

Enhancing the Sensitivity of Chemical Sensors for Chlorinated Hydrocarbons in Water by the Use of Tapered Silver Halide Fibers and Tunable Diode Lasers

Tapered silver halide fibers were used for the first time for high-sensitivity fiber evanescent wave spectroscopic (FEWS) measurements of chlorinated hydrocarbons (CHCs) in water at trace level. The sensor arrangement consisted of a tunable diode laser (TDL) source, a polymer-coated and tapered silver halide fiber, and a direct fiber/mercury cadmium telluride (MCT) detector coupling. A minimum detection limit of 50 μg L−1 was achieved by using a polyisobutylene-coated fiber with a 1:4 tapering ratio. The sensor response is in the minute range and shows reversible analyte enrichment.

FTIR-ATR-spectroscopic investigation of the silanization of germanium surfaces with 3-aminopropyltriethoxysilane

SummaryThe adsorption of 3-aminopropyltriethoxysilane (3-APTS) on germanium crystals was investigated using Attenuated Total Reflection (ATR) spectroscopy. Ethanol, which is produced by the hydrolysis of 3-APTS in water, adsorbs on germanium prior to 3-APTS. This can be checked by the CH3-modes at 1150 cm−1 and 2975 cm−1. The structure differences between chemisorbed and physisorbed 3-APTS can be observed by the shift of the Si-O-Si bands of the silane molecules. The asymmetric and symmetric stretch bands for chemisorbed 3-APTS occurs at 1096 cm−1 and 1022 cm−1, whereas, the bands for physisorbed 3-APTS are found at 1115 cm−1 and 1038 cm−1. The amino groups of physisorbed 3-APTS display two strong bands at 1566 cm−1 and 1485 cm−1 which result from amino groups strongly hydrogen bonded to free silanols. The deformation modes of the amino groups in chemisorbed layers can be found at 1609 cm−1 and 1512 cm−1, which is due to the deformation modes of the free amino groups. A controlled chemisorption is important for the development of chemical IR-sensors [15].

Infrared fiber optic gas sensor for chlorofluorohydrocarbons

Abstract In this paper the detection of several gaseous species of chlorofluorohydrocarbons such as 1,2-dichlorotetrafluoroethane (R 114) or trifluoromethane (R 23) using the fiber optic evanescent field absorption spectroscopy is presented. By coupling mid-infrared transparent silver halide fibers to a conventional Fourier transform infrared spectrometer reasonable results could be obtained in the concentration range of 1–15% of the gas species diluted in synthetic air using a gas sensing device exploiting uncoated fibers. As shown for the example R 114 the enrichment of the analyte in a polymer layer (low-density polyethylene, polyisobutylene) coating the fiber lowered the detection limit to 0.1%.

FTIR-ATR spectroscopic analysis of bis-crown-ether based PVC-membrane surfaces

ZusammenfassungZum besseren Verständnis der Komplexbildungsreaktionen an der Oberfläche von K+-selektiven Elektrodenmembranen aus PVC, Dioctylsebacat und dem Kronenether BME-44, sowie nachfolgender Diffusionsvorgänge wurden Modellmembranen hergestellt und mit der molekülspezifischen IR-ATR-Spektrometrie im Oberflächenbereich untersucht. Mit der verwendeten Meßanordnung war die Erfassung von chemischen Veränderungen als Folge der Wechselwirkung der Membran mit wäßrigen Alkalisalzlösungen (NaCl, KCl, KSCN, NH4SCN, c= 0,1–2mol/l) im Schichttiefenbereich zwischen 0,1–3 μm möglich. Ausgehend von reproduzierbar hergestellten Membranen (65 mg PVC, 120 mg DOS, 4 mg BME-44 in 2 ml THF) wurde Komplexbildung und -diffusion ins Innere nur bei KSCN und — schwächer — bei NH4SCN festgestellt, während KCl und vor allem NaCl keine ähnlich stark ausgeprägte Komplexbildung geschweige denn Diffusion des Kronenetherkomplexes ins Membraninnere ergibt. Dies wird auf Lipophilie des SCN−-Ions bzw. die Lipophobie des Cl−-Ions zurückgeführt. Durch Variation des Einfallswinkels konnte weiterhin bei den Versuchen mit KSCN eine bevorzugte Auswaschung des Komplexes durch Spülen mit H2O in oberflächennahen Bereichen festgestellt werden. Da das elektrochemische Ansprechverhalten der genannten Elektrodenmembranen im Bereich niedriger Konzentrationen für KCl und KSCN nahezu gleich ist (−58,5 mV/Dekade) und sie bei höheren KSCN-Konzentrationen ihre Empfindlichkeit für K+ verlieren (nicht bei KCl), unterstützen die vorliegenden IR-spektroskopischen Resultate das „space charge effect“-Modell zur Erklärung der Potentialausbildung.SummaryModel membranes have been prepared from PVC (65 mg), dioctyl sebacate (120 mg) and the crown ether BME-44 (4 mg) in 2 ml THF solution and analyzed by the molecular-specific surface technique Attenuated Total Reflectance (ATR) in the infrared region in order to better understand the complexation reactions at the interface between the membrane and aqueous solutions of NaCl, KCl, KSCN and NH4SCN. The information depth provided by this method was between 0.1 and 3 μm and could be changed by variation of the angle of incidence of the IR-radiation. The study of the reactions was carried out ex-situ (at the dried membrane surfaces) after contact times of 1 h with 0,1–2 M aqueous solutions and subsequent rinsing with H2O for 0–100 s. It was found that KSCN- and NH4SCN-contact results in significant complex formation with the membrane, whereas KCl and of course NaCl do not react in such a way (under diffusion of the complex into the bulk of the membrane). Through rinsing with H2O and variation of the angle of incidence experimental evidence was found that KCl forms a complex only in the outmost surface region of the membrane. This complex cannot penetrate into the membrane because of the lipophobic nature of Cl−. These findings support the “space-charge effect” model for the explanation of the potential generation since the electrochemical behaviour of the electrode membrane described is nearly equal for KCl and KSCN in low concentrations (−58.5 mV/decade) while it loses its sensitivity for KSCN (not for KCl) at higher concentrations.