Infrared Chemical Sensor for Detection of Chlorinated Phenols in Aqueous Solutions Based on a ATR Waveguide Coated with Structural Designed Polymers

A combination of solid phase micro‐extraction (SPME) with attenuated total reflection (ATR) infrared spectrometry provides a fast and sensitive way to detect organic compounds in aqueous solutions. It is especially useful for detection of chlorinated organic compounds in environmental samples. Currently, analyses of organic compounds in aqueous solutions are limited to low‐polarity compounds by the SPME/ATR‐IR sensing method. This limitation was mainly caused by the low polarity nature of the SPME phase. To increase the capability of this method to detect more polar compounds and also to increase the sensitivity in detection of organic compounds, the principle of “like‐dissolve‐like” was used to design a specific SPME phase for a certain class of chlorinated compounds. To demonstrate this concept, chlorinated phenols were used as probe molecules and polyvinyl chloride was chemically modified with phenol, ‐naphthol and ‐naphthol to provide SPME phases with a similar chemical structure to chlorinated phenols. These polymers were used as SPME phases and their performance were compared with the commonly used SPME phases (i.e., polystyrene and polyisobutylene). Results indicated that naphthols attached to PVCs provided much lower compactness, which allows fast speed in absorption of phenols. Meanwhile, due to the structural similarity between naphthols attached to PVCs and phenols, much higher partition coefficients were found for these chemically modified PVCs than conventionally used polymers. To further increase the sensitivity for analysis of chlorinated phenols, the common influencing factors, such as pH values and salt effect were also investigated. Apparently, pH values of the solutions did not influence the structure of the modified PVCs significantly. In absorption of chlorinated phenols in aqueous solutions with different pH values, the observed IR signals were decreased greatly in pH higher than 6 due to the charged form of chlorinated phenols that were presented. Results of the salt effect indicated that three times stronger of IR signals can be obtained if 20% (w/vol) of NaCl was added.     

Reflection–absorption infrared sensing device for detection of semivolatile aromatic compounds in soils

In this article, a new IR-sensing device is described for the examination of chlorinated aromatic compounds in soils. To prepare this sensing device, a 20-mL glass vial was modified for use in the analysis of soil samples by conventional Fourier-transform infrared (FT-IR) spectroscopy. In this sampling device, an aluminium plate coated with a hydrophobic film was placed on top of the cap of the sample vial to absorb the analytes that evaporated from the soil matrix. After this absorption process was complete, the cap was placed in an FT-IR spectrometer, and the absorbed analytes were detected in the reflection–absorption (RA) mode. To accelerate the rate of evaporation of the analytes, the soil samples were heated to various temperatures. Meanwhile, other factors, such as the moisture content, sampling time, thickness of the hydrophobic film, and the volatilities and concentrations of the analytes, were also examined to optimize the analytical conditions. The results indicated that the time required to reach equilibrium conditions was short, and evaporation/absorption could be achieved within 10?min. With a water content of 10% (v/w) or less, the intensities of the analytical signals were increased greatly when compared with those of dry samples; when the water content was above 10% (v/w), these intensities decreased, partially as a result of the heating efficiency. After examining the compounds that had different vapour pressures, the analytical results indicated that this method was applicable to the examination of compounds that had vapour pressures below 1.0?Torr. Using the optimal conditions determined in this study, the detection limits for semivolatile aromatic compounds were lower than 100?ng/g, and the regression coefficients of the standard curves for compounds that had a vapour pressure lower than 1.0?Torr were larger than 0.99 in the concentration range of 1–100?µg/g.     

Cooled internal reflection element for infrared chemical sensing of volatile to semi-volatile organic compounds in the headspace of aqueous solutions

In this study, the cooling effect was applied to an evanescent wave type infrared (IR) chemical sensing method to effectively trap volatile organic compounds (VOCs), which have been absorbed in the hydrophobic film coated around the internal reflection element (IRE). The detection of VOCs in aqueous solutions was taken in the headspace of the aqueous solution. This method eliminates the long-term instability of hydrophobic film soaked in an aqueous solution and the potential spectral interference caused by the matrix of the aqueous solution. Thermal energy has been applied to the aqueous solution to assist in the evaporation of VOCs out of the aqueous matrix. By applying a cooling system to the IRE, the excess thermal energy can be removed leading to more stable IR signals. After examination of organic compounds with vapour pressure (P_v) ranging from 0.017 to 150 Torr, significant differences were found between IR signals from cooled and un-cooled systems. Because the thermal conductivity of the IRE used in IR detection is typically low; the efficiency in removing the thermal energy is limited. By heating the aqueous solutions to different temperatures, the IR signals showed that the sample temperature was limited to around 80 °C. The IR signal determination results for five different volatility organic compounds indicated that the optimal heating temperature was not necessary to match with the volatilities of organic compounds in cooling system. The linear regression coefficient (R²) of the standard curve for sample concentrations in the range 5-200 μg ml⁻¹ was generally higher than 0.991 and the detection limit was around a few hundred ng ml⁻¹, which was two to three times lower than that of un-cooled system.     

An infrared evanescent wave sensing system coupled with a hollow fiber membrane for detection of volatile organic compounds in aqueous solutions.

We have developed an on-line sensing method for the detection of volatile organic compounds (VOCs) in contaminated aqueous solutions by combining a microporous hollow fiber membrane with an infrared (IR) sensing system. Polypropylene microporous hollow fibers were used to separate the VOCs from the aqueous solution into the hollow fibers, which were purged countercurrently for detection by the IR sensing systems. An evanescent-wave-type IR sensing system was used to detect the VOCs that were purged from the hollow fibers. The sensing element was coated with polyisobutylene (PIB) to concentrate the VOCs for their detection. To study the performance of this system, we examined a number of factors, such as the purging flow rate, the sample flow rate, and the volatilities of the VOCs. The results indicate that an increase in the purging flow rate reduces the analytical signal significantly, especially for purging flow rates >2 mL/min. The pumping flow rate for the aqueous sample also influenced the analytical signals, but far less sensitively. The volatilities of the examined compounds also affected the analytical signals: the higher the volatility of the compound, the lower the intensity of the analytical signals and the shorter the time required to reach the equilibrium signal. From an examination of the dynamic range of this proposed method, a regression coefficient >0.994 was obtained for concentrations below 250 mg/L, even under non-equilibrium conditions. The response time of the system was studied in an effort to examine the suitability of using this sensing method for automatic detection. The results indicate that new equilibrium conditions were established within 3 min for highly volatile compounds, which suggests that on-line monitoring of the levels of VOCs can be performed in the field.     

Membrane-introduced infrared spectroscopic chemical sensing method for the detection of volatile organic compounds in aqueous solutions

A novel membrane-introduced infrared (IR) chemical sensing method has been developed for the detection of volatile organic compounds (VOCs) in aqueous solutions. In this method, a porous Teflon membrane was used to eliminate the problems associated with conventional IR spectroscopic sensing methods. The porous Teflon membrane was sealed below an IR spectroscopic sensing element pre-coated with a hydrophobic film and a two-channel flow cell configuration was established. In this configuration, the aqueous sample was allowed to pass through the lower channel and the VOCs that penetrated through the membrane to the upper channel were detected by the IR sensor. In this manner, the performance of the sampling at the headspace was improved while the problems caused by the presence of water were eliminated. Meanwhile, using a purging channel allowed the sensing element to be regenerated rapidly and enabled automation of the detection process. The parameters that influenced the analytical signals were studied, such as the sampling flow rate, the pH and ionic strength of the sample solutions, the effect of the volatilities of the VOCs, and the regeneration efficiency of the sensing element. The results indicated that the analytical signals were insensitive to the sampling flow rate and to the pH and ionic strength of the sample solutions. The results obtained from the detection of seven different volatile compounds indicated that this method is highly suitable for the detection of organic compounds that have vapor pressures >1 Torr and that it is potentially usable for organic compounds that have vapor pressures between 20 mTorr and 1 Torr. The regression analysis of the standard curves indicated that a regression coefficient (R(2)) > 0.99 was obtainable in the concentration range from 1 to 100 microg mL(-1). The detection limits for the tested compounds were around a few hundred ng mL(-1).     

Preparation of ZnO Nanowires and Study of Surface‐adsorbate Interaction by Fourier‐Transform Infrared Spectroscopy

To study the surface‐adsorbate properties of ZnO nanowires, a hydrothermal method was modified to grow ZnO nanowires directly on ZnSe, which were then characterized by attenuated total reflection infrared (ATR‐IR) spectroscopy. To prepare ZnO nanowires directly on ATR sensing element of ZnSe, ZnO seed layers were first formed by annealing of ZnO seeds on ZnSe surfaces. The ZnO seed layers then were exposed to growth solution, forming ZnO nanowires directly on the ATR crystals. The interaction properties of the resulting surfaces were studied by an ATR‐IR method. The diameter, length and distribution of the ZnO nanowires can be tuned by adjusting the growth conditions, particularly the growing time and the concentrations of reagents. Two surfaces, namely Zn‐rich and Zn‐O ion‐pair surfaces were studied in detail for their adsorption properties toward compounds bearing different functional groups. By examination of several volatile organic compounds (VOCs), it was found that the Zn‐rich surface is less selective and interacts with compounds bearing the functional groups of amino and hydroxyl. The Zn‐O ion‐pair surface is more selective and a much stronger interaction was observed with non‐aromatic amino compounds. These results indicate that the improving of the selectivity of a ZnO‐based sensing device can be achieved by tuning the surface structure of the ZnO nanomaterials.     

Development of an environmentally friendly methodological approach to determine chlorinated hydrocarbons and chlorobenzenes in soils

A modified version of the quick, easy, cheap, efficient, rugged, and safe method is proposed for the determination of chlorinated pollutants in soil samples. Measurements were collected using a programmed temperature vaporizer coupled to a gas chromatograph and a µ-electron capture detector. The optimization and validation of this extraction technique for these compounds in soils have been performed in order to provide an alternative tool for determining these kinds of pollutants in soils. Advantages over conventional extraction techniques include the applicability to compounds of very different volatilities and polarities, the low cost of the reagents employed, and the possibility of being used by nonspecialist operators, with standard analytical tools. This method can be considered more environmentally friendly, due to the reduction of solvent and energy consumption and to the elimination of harmful organic solvents, reducing the negative impact of chemical analyses on the environment (principles of green analytical chemistry).     

Polymer mediated capillary electrophoresis with attenuated total reflectance infrared microspectroscopy detection

Polymer mediated capillary electrophoresis (CE) using poly(diallyldimethylammonium chloride) (PDDAC) in the electrolyte with end-column single reflection attenuated total internal reflectance (ATR) Fourier transform infrared (FT-IR) microspectroscopy is presented. The terminus of the capillary is placed ∼1 μm from the internal reflectance element (IRE), at the focus of the ATR infrared microscope. Electrophoretic separations of benzenesulfonate, 1-naphthalenesulfonate and 1,5-naphthalenesulfonate in a NaCl and PDDAC electrolyte using either −11 or −15 kV are demonstrated with the CE-ATR FT-IR spectra providing identification of these compounds. Running electrolyte salt concentrations in the 0.85-1.7 M range are required due to the 50-80 mg mL⁻¹ sample concentrations. Increasing the NaCl salt concentration improves peak resolution but also increases analysis time. A PDDAC concentration as low as 0.0075% can facilitate the separation of the aromatic sulfonates while maintaining reasonable electroosmotic flow. Etching of the germanium IRE by the applied current, which can affect the intensity of the infrared beam, is corrected by fabrication of a plastic mounting post for the IRE to prevent current conduction through the IR instrument.     

Characterization of cyclodextrin modified infrared chemical sensors. Part II. Selective and quantitative determination of aromatic acids

In this paper, the selectivity and sensitivity of cyclodextrin (CD) modified infrared (IR) chemical sensor in detection of aromatic acids in aqueous solutions were reported. To eliminate the interference from water, the technique of attenuated total reflection was employed. By surface treated with CD molecules on the internal reflection elements, the sensors were selective in sensing of aromatic acids compared to aromatic compounds with other functional groups. To facilitate the use of this method for the quantitative analyses of aromatic acids in aqueous solutions, analytical functions were also developed in this work and a linear relationship between analytical responses and concentrations of analytes can be obtained. To optimize the analytical conditions, the factors that influence the IR spectroscopic signals were examined. These factors included response time, CD loadings of the sensors, pH effect on response, regeneration efficiency and stability of sensors. Under the optimal conditions, the detection limits for aromatic acids at a detection time of 2 min can be <100 μg/L. Meanwhile, the dynamic linear range for detection was only ca. two orders of magnitude if direct IR signals were used. Using the analytical function developed in this work, the linearity can be extended up to a concentration of 100 mg/L.     

A novel ATR FT-IR microspectroscopy technique for surface contamination analysis without interference of the substrate.

Surface contaminants, such as powder and thin film on various solid surfaces, were analyzed by ATR FT-IR microspectroscopy. An ATR accessory consisting of a miniature-Ge IRE with contact area smaller than 50 microm, in diameter was fabricated and employed for a non-destructive characterization. The IRE was pre-aligned and fixed onto a 15x Schwarzschild-Cassegrain infrared objective. Easy maneuvering of the microscope stage enabled an accumulative collection of the contaminant at the tip of a miniature-Ge IRE, where the contaminants were analyzed under the ATR condition. By making a gentle contact between the Ge tip and selected area on the surface, any removable contaminants were transferred onto the Ge tip where its molecular information was acquired without any interference from the solid substrate. A thin organic film (i.e., mineral oil or fluorolube) was coated at the tip of the IRE in order to enhance the collecting efficiency of the removable contaminants.     

Characterisation of the surface chemistry of magnesium exposed to the ambient atmosphere

The changes in the surface chemistry of the oxidised surface of evaporated magnesium metal stored in the ambient atmosphere are studied with water contact angle (WCA) measurement, polarisation‐modulation infrared reflection‐absorption spectroscopy (PM‐IRRAS) and X‐ray photoelectron spectroscopy (XPS). Upon exposure to the ambient atmosphere, the surface picks up volatile organic compounds (VOC), which cause a significant increase in the WCA values. The PM‐IRRAS and XPS analyses indicate that the adsorbates contain hydrocarbons, carboxylates and carbonate functionalities. After long ambient storage times, the composition of the carbon‐containing functionalities on the surface changes significantly. This change could be caused by the build‐up and/or surface‐catalysed oxidation of adsorbed organic species. Thickening of the air‐formed oxide/hydroxide layer was also noted, ascribed to the reaction of adsorbed atmospheric moisture with the magnesium surface. Copyright © 2006 John Wiley & Sons, Ltd.     

Irrelevance of Carbon Monoxide Poisoning in the Methanol Oxidation Reaction on a PtRu Electrocatalyst

Based on detailed in situ attenuated total‐reflection–surface‐enhanced IR reflection absorption spectroscopy (ATR‐SEIRAS) studies of the methanol oxidation reaction (MOR) on Ru/Pt thin film and commercial Johnson–Matthey PtRu/C, a revised MOR enhancement mechanism is proposed in which CO on Pt sites is irrelevant but instead Pt‐Ru boundary sites catalyze the oxygen insertion reaction that leads to the formation of formate and enhances the direct reaction pathway.     

ATR-FTIR spectroscopy reveals bond formation during bacterial adhesion to iron oxide

The contribution of various bacterial surface functional groups to adhesion at hematite and ZnSe surfaces was examined using attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy. When live Shewanella oneidensis, Pseudomonas aeruginosa, and Bacillus subtilis cells were introduced to a horizontal hematite (alpha-Fe(2)O(3))-coated internal reflection element (IRE), FTIR peaks emerged corresponding to bacterial phosphate group binding. These IR peaks were not observed when bacteria were introduced to the uncoated ZnSe IRE. When cells were added to colloidal suspensions of alpha-Fe(2)O(3) at pH 7, spectra included peaks corresponding to P-OFe and nu(COOH), the latter being attributed to bridging of carboxylate at mineral surface OH groups. Selected model organic compounds with P-containing functionalities (phenylphosphonic acid [PPA], adenosine 5'-monophosphate [AMP], 2'-deoxyadenyl(3'-->5')-2'-deoxyadenosine [DADA], and deoxyribonucleic acid [DNA]) produce spectra with similar peaks corresponding to P-OFe when adsorbed to alpha-Fe(2)O(3). The data indicate that both terminal phosphate/phosphonate and phosphodiester groups, either exuded from the cell or present as surface biomolecules, are involved in bacterial adhesion to Fe-oxides through formation of innersphere Fe-phosphate/phosphonate complexes.     

Development of an infrared hollow waveguide sampler for the detection of organic compounds in aqueous solutions with limited sample volumes.

In this study, an infrared (IR) hollow waveguide sampler was developed to detect organic compounds in aqueous samples with sample volumes less than 50 microL. This sampler was prepared by coating a thin hydrophobic film inside the IR hollow waveguide. After injecting a certain amount of aqueous solution, organic compounds could be absorbed into the hydrophobic film by partitions. By removing the residual water in the hollow waveguide sampler with a nitrogen purging gas, the absorbed organic compounds could be sensed using IR radiation. To investigate the applicability of this hollow waveguide sampler in the detection of small amounts of aqueous samples, an analytical working function was developed following an examination of the parameters which influence the analytical signals. Such factors as the volume of the aqueous solution, the sample concentration, the length of the hollow waveguide, and the sensitivity of this method were investigated. Excellent agreement between the analytical and theoretical predicted values was observed. Upon examining the linear relationship between the analyte signals and the concentration, the regression coefficients were generally higher than 0.998 in the examined concentration range of 1 to 100 ppm. Under the condition that the sample volume was 300 microL and based on three-times the spectra noise level, the calculated detection limits for this method were found at around 1 ppm for the examined analytes.     

A New Infrared Spectroelectrochemical Cell for the Detection of Species Generated by Platinum and Screen‐Printed Carbon Electrodes

In this paper, we describe a simple and effective infrared (IR) spectroelectrochemical cell for detecting species generated from an electrochemical system featuring low‐IR‐reflectivity electrodes. The IR detection mode of attenuated total reflection (ATR) was employed to construct the spectroelectrochemical cell. Two kinds of electrodes, platinum (Pt) and screen‐printed carbon (SPC), were used to examine the performance of this new cell in detection of electroactive species generated by cyclic voltammetry. Because data generated from highly reflective electrodes are available in the literature, Pt electrode was used to characterize the performances of the developed spectroelectrochemical cell. Results indicated that species generated electrochemically can be observed readily and their responses were comparable to those described in the literature. The cell volume could be lower than 300 μL, which suggests that this approach may be very useful to obtain chemical information during electrochemistry for biological fluids with limited sample volumes. By examining the electrochemical behavior of several amino acids using both Pt and SPC electrodes, the redox behaviors can be readily observed indicating a new spectroelectrochemical cell was successfully developed for the purpose of using of SPC electrode.     

High resolution field desorption mass spectrometry—I: Nucleosides and nucleotides

The first complete high resolution (HR) field desorption (FD) mass spectra (MS) are presented and constitute a helpful tool in the structure elucidation of biologically significant compounds. This is especially relevant for the determination of the molecular weight of substances with very low volatilities which suffer from thermal decomposition when evaporated into the ion source. An additional advantage is the very small sample consumption (in the submicrogram range). Further improvements in the ion production method are the introduction of high temperature activated emitters and a specially designed micromanipulator for optimal adjustment of the field anodes. These enabled values of mass resolution between 15000 and 25000 (10% valley definition) to be achieved when vacuum evaporated Ag Br plates were used for photographic recording.     

Investigation of patinas formed on Chinese bronzes using modern multianalytical techniques

This paper presents an integrated study on nine natural Chinese bronze patinas without causing any damage to the bronze substrates, employing five modern analytical techniques including X‐ray diffraction (XRD), Fourier transform infrared (FT‐IR) and Raman spectroscopy, inductively coupled plasma atomic emission spectroscopy (ICP‐AES), and inductively coupled plasma mass spectrometry (ICP‐MS). Two artificial Chinese bronze patinas were also investigated by the same techniques for comparative purposes. As a result, XRD determined the chemical compositions of all selected samples and showed that the primary compound was malachite in natural soil environment under the general situation. Meanwhile, some interesting corrosion products such as gerhardtite and free copper were also observed. Three groups were classified according to the XRD results in order to provide a deeper insight into their spectroscopic characterization. Spectroscopic data of these patinas from FT‐IR and Raman spectroscopy are shown and interpreted in detail. ICP‐AES and ICP‐MS analyses provided valuable quantitative information, and made the study of the patinas more profound. Furthermore, all analytical results indicated that bronze patinas are extremely complex by virtue of the storage environment and their substrate alloys. The natural samples were rather heterogeneous and the artificial samples, especially the sample formed in the laboratory, were rather homogeneous of which the chemical constituents could be well defined. Copyright © 2007 John Wiley & Sons, Ltd.     

Density functional theory study of 13C NMR chemical shift of chlorinated compounds

The use of the standard density functional theory (DFT) leads to an overestimation of the paramagnetic contribution and underestimation of the shielding constants, especially for chlorinated carbon nuclei. For that reason, the predictions of chlorinated compounds often yield too high chemical shift values. In this study, the WC04 functional is shown to be capable of reducing the overestimation of the chemical shift of Cl‐bonded carbons in standard DFT functionals and to show a good performance in the prediction of ¹³C NMR chemical shifts of chlorinated organic compounds. The capability is attributed to the minimization of the contributions that intensively increase the chemical shift in the WC04. Extensive computations and analyses were performed to search for the optimal procedure for WC04. The B3LYP and mPW1PW91 standard functionals were also used to evaluate the performance. Through detailed comparisons between the basis set effects and the solvent effects on the results, the gas‐phase GIAO/WC04/6‐311+G(2d,p)//B3LYP/6‐31+G(d,p) was found to be specifically suitable for the prediction of ¹³C NMR chemical shifts of chlorides in both chlorinated and non‐chlorinated carbons. Further tests with eight molecules in the probe set sufficiently confirmed that WC04 was undoubtedly effective for accurately predicting ¹³C NMR chemical shifts of chlorinated organic compounds. Copyright © 2012 John Wiley & Sons, Ltd.     

Effects of variation in modulator temperature during cryogenic modulation in comprehensive two‐dimensional gas chromatography

Many modulation systems in comprehensive 2D GC (GC×GC) are based on cryogenic methods. High trapping temperatures in these systems can result in ineffective trapping of the more volatile compounds, whilst temperatures that are too low can prevent efficient remobilisation of some compounds. To better understand the trapping and release of compounds over a wide range of volatilities, we have investigated a number of different constant temperature modulator settings, and have also examined a constant temperature differential between the cryo‐trap and the chromatographic oven. These investigations have led us to modify the temperature regulation capabilities of the longitudinally modulated cryogenic system (LMCS). In contrast to the current system, where the user sets a constant temperature for the cooling chamber, the user now sets the temperature difference between the cryo‐trap and the chromatographic oven. In this configuration, the cooling chamber temperature increases during the chromatographic run, tracking the oven temperature ramp. This produces more efficient, volatility‐dependent modulation, and increases the range of volatile compounds that can be analysed under optimal trap‐and‐release conditions within a single analytical run. This system also reduces cryogenic fluid consumption.     

Development of an aminocarboxylic acid-modified infrared chemical sensor for selective determination of tyrosine in urine

An infrared (IR) chemical sensor based on immobilization of an acidified tris(2-aminoethyl)amine (ATAA) for the detection of tyrosine in urine is described. The sensing phase (i.e., coating) was saturated with nickel ions so that it would interact with tyrosine molecules in aqueous solution through the formation of stable ATAA-Ni²⁺-tyrosine complexes. Investigation of the signals of nine amino acids shows that only the three containing phenyl groups could be detected by this sensor system. A unique spectral feature located at 1515 cm⁻¹ allowed tyrosine to be discriminated from the other two amino acids. To examine the performance of the ATAA sensing phase in the quantitative analysis of tyrosine, the effects of several factors were examined. pH affected the ability of tyrosine to form complexes; the optimal signal occurred at ca. pH 8. The concentration of ammonia buffer also affected the analytical signals through a competition effect; lower concentrations of ammonia buffer provided higher intensity signals. It was found that nickel ions are the most useful for detection of tyrosine. Although the concentration of nickel ions had less influence on the analytical signal than did the concentration of the ammonia buffer, the signal intensity was optimal when the nickel ions and the target molecule had similar concentrations. The detected time profiles indicated that the ATAA sensor phase functioned via a surface adsorption mechanism. The linear range of signal intensities was up to 600 μM with a detection limit of 30 μM.