Development of an SPME/ATR-IR chemical sensor for detection of phenol type compounds in aqueous solutions.

A new method, based on a combination of solid phase micro-extraction (SPME) and attenuated total reflection infrared (ATR-IR) spectroscopy, was developed for the detection of phenols in aqueous solutions. Several types of phenols were studied including phenols attached to methyl, hydroxyl, chlorine and nitro groups, which are environmentally toxic. Because of the polarity of the phenol-type compounds, the performance of six polymers in attracting phenols was investigated. Results indicated that poly(acrylonitrile-co-butadiene) was the most suitable SPME phase among the investigated polymers. To further increase the sensitivity in phenol detection, factors, such as the pH effect, salt effect and thickness of the SPME phase, were investigated. Results indicated that pH values affected the neutral form percentage of the analytes strongly and, hence, affected the detected signals. Due to the acid nature of phenols, phenol detection occurs best in solutions with a low pH value. A two- to three-fold increase in signals was observed after the addition of salt into the solution. The results on the examination of standard curve linearity indicated that the regression coefficients (R2) were higher than 0.996 for four types of phenols. The obtained detection limits for phenols were lower than 200 micrograms L-1 for most of the compounds.     

Determination of liposome/water partition coefficients of organic acids and bases by solid-phase microextraction

The extraction of two methylated anilines and three chlorinated phenols by solid-phase microextraction (SPME) fibers coated with polyacrylate was investigated as a function of pH. Only the neutral species of the acids and bases partitioned into the polymer. Extraction kinetics were accelerated for the hydrophobic phenols at pH values around their acidity constant. This is presumably due to a reconstitution of the neutral species in the unstirred aqueous layer adjacent to the polymer surface by the charged species through the fast acid-base equilibrium. Although the charged species is not taken up into the polymer, liposome/water distribution ratios could be measured up to a pH value, where 99% of the compounds were present as charged species. The partition coefficients of the neutral and charged species were extrapolated from the pH profiles of the liposome/water distribution ratios. The resulting values were slightly lower than those measured with equilibrium dialysis. The discrepancies are discussed with respect to differences in the experimental conditions and the possibility of matrix effects during SPME measurements.     

Surfactant‐based ionic liquids for extraction of phenolic compounds combined with rapid quantification using capillary electrophoresis

A rapid liquid phase extraction employing a novel hydrophobic surfactant‐based room temperature ionic liquid (RTIL), tetrabutylphosphonium dioctyl sulfosuccinate ([4C₄P][AOT]), coupled with capillary electrophoretic‐UV (CE‐UV) detection is developed for removal and determination of phenolic compounds. The long‐carbon‐chain RTIL used is sparingly soluble in most solvents and can be used to replace volatile organic solvents. This fact, in combination with functional‐surfactant‐anions, is proposed to reduce the interfacial energy of the two immiscible liquid phases, resulting in highly efficient extraction of analytes. Several parameters that influence the extraction efficiencies, such as extraction time, RTIL type, pH value, and ionic strength of aqueous solutions, were investigated. It was found that, under acidic conditions, most of the investigated phenols were extracted from aqueous solution into the RTIL phase within 12 min. Good linearity was observed over the concentration range of 0.1–80.0 μg/mL for all phenols investigated. The precision of this method, expressed as RSD, was determined to be within 3.4–5.3% range. The LODs (S/N = 3) of the method were in the range of 0.047–0.257 μg/mL. The proposed methodology was successfully applied to determination of phenols in real water samples.     

Histidine‐modified organic‐silica hybrid monolithic column for mixed‐mode per aqueous and ion‐exchange capillary electrochromatography

A novel organic‐silica hybrid monolith was prepared through the binding of histidine onto the surface of monolithic matrix for mixed‐mode per aqueous and ion‐exchange capillary electrochromatography. The imidazolium and amino groups on the surface of the monolithic stationary phase were used to generate an anodic electro‐osmotic flow as well as to provide electrostatic interaction sites for the charged compounds at low pH. Typical per aqueous chromatographic behavior was observed in water‐rich mobile phases. Various polar and hydrophilic analytes were selected to evaluate the characteristics and chromatographic performance of the obtained monolith. Under per aqueous conditions, the mixed‐mode mechanism of hydrophobic and ion‐exchange interactions was observed and the resultant monolithic column proved to be very versatile for the efficient separations of these polar and hydrophilic compounds (including amides, nucleosides and nucleotide bases, benzoic acid derivatives, and amino acids) in highly aqueous mobile phases. The successful applications suggested that the histidine‐modified organic‐silica hybrid monolithic column could offer a wide range of retention behaviors and flexible selectivities toward polar and hydrophilic compounds.     

Development of a solid-phase microextraction/reflection-absorption infrared spectroscopic method for the detection of chlorinated aromatic amines in aqueous solutions.

In this paper, the reflection-absorption infrared (IR) spectroscopic method combined with the principle of solid-phase micro-extraction (SPME) is proposed to detect chlorinated aromatic amines in aqueous solutions. This proposed method provides simplicity in both the optical system and equipment setup. Compared to the SPME/attenuated total reflection-IR method, this method reduces the cost for internal-reflection elements and optical systems. Meanwhile, it has no SPME/transmission IR method problems, which require high polymer film preparation techniques to obtain a standing film that has no physical/chemical property changes when immersed in an aqueous solution. The typical linear coefficients obtained using this method for chloroanilines in aqueous solutions are around 0.995 and the detection can be lower than 100 ppb. The thickness of the hydrophobic film is relatively important in the SPME/ATR-IR method, but the uncertainty caused by the film thickness can be partially eliminated in the proposed method. This is because the IR signals are proportional to the film thickness and can be corrected using hydrophobic film signals. The low detection limits have also indicated that this proposed method can compete with the currently existing IR methods, but allowing much simpler detection.     

Development of the Headspace SPME/ATR‐IR Method for Detection of Chlorinated Aromatic Compounds in Soils

In this paper, a new method based on attenuated total reflection infrared (ATR‐IR) spectroscopy was developed to detect chlorinated aromatic compounds in soil. To eliminate the problems associated in inspection of soil samples by the ATR‐IR method, chlorinated compounds were evaporated from soil matrices and detected in the headspace. The sensing device was constructed by an internal reflection element (IRE) coated with a hydrophobic film to attract and concentrate chlorinated compounds evaporated to the headspace. Factors that influence the analytical signals were studied such as the moisture content, volatilities of analytes, and effect of heating temperature. Results indicated that the addition of thermal energy to the soil sample resulted in an increase of IR signal. However, the IRE was also warmed up and caused a slight decrease of the IR signals after a long detection time. The studies of the influence of moisture indicated that a small amount of water present in soils could tremendously increase the intensity of detected IR signals. The further increase of moisture contents resulted in a decrease of the analytical signals, and the optimal signal was found when soil samples contained 5% (v/w) water. Results in analyses of compounds with different volatilities indicated that even with vapor pressure lower than 0.017 Torrs, quality IR spectra could still be obtained. Using the optimal conditions found in this work, the results in determination of five compounds in soil samples indicated that the linear regression coefficients (R‐square) were higher than 0.992 with detection limits around a few hundreds of ppb.     

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.     

Study of influence of additives of tyloxapol on the chromatographic characteristics of the model compounds: the comparative characterization of micellar mobile phases of tyloxapol and Triton X‐100

The chromatographic behavior of model compounds of biomedical significance (organic acids, amino acids, drugs) was investigated using mobile phases modified with tyloxapol. The influence of factors such as concentration of tyloxapol, content of organic modifier and pH of mobile phase on the retention factor of solutes was studied. The results were compared with the data obtained by elution with mobile phases containing Triton X‐100 additives, since units of Triton X‐100 are repeated in the structure of tyloxapol. Divergence in chromatographic behavior of model compounds was explained by the difference in physico‐chemical characteristics (microviscosity, polarity, critical micelle concentration, shape of micelles, etc.) of tyloxapol and Triton X‐100 micelles. Copyright © 2009 John Wiley & Sons, Ltd.     

Analyses of the surfaces of concrete by Raman and FT‐IR spectroscopies: comparative study of hardened samples after demoulding and after organic post‐treatment

Concrete surfaces were studied by two spectroscopic techniques, FT‐IR (in ATR mode) and Raman, to establish a nondestructive method to analyze the distribution of hydrated and organic phases. The surface composition of ordinary clinker, polished concrete, concrete after demoulding, and coated concrete as used in building construction was studied. The clinker's mineral phases and the polished concrete were first analyzed by Raman spectroscopy to determine a spectrum database of the specific phases located on the surface of the concrete. Then, both spectroscopic techniques were used to analyze, directly, the surface of hardened concrete after demoulding. No impact of roughness or porosity was highlighted using Raman spectroscopy; many cementitious, or hydrated phases (alite, belite, tricalcium aluminate, ferrite, portlandite and ettringite) were clearly identified. FT‐IR in ATR mode only identified some hydrated phases: portlandite and CaO? SiO₂? H₂O (C? S? H), but organic residues from the demoulding oil were characterized by this technique. Furthermore, the convenience of using these techniques together was tested by analyzing the composition of concrete surfaces coated by different organic post‐treatments. FT‐IR spectroscopy was useful to identify the main organic groups at the concrete surface, whereas Raman spectroscopy was especially able to characterize the mineral/hydrated phases under a thick post‐treatment layer (constituted of polyester varnish). Due to their own specificities, these complementary techniques should be used together to easily identify all the mineral phases and organic residues/coatings on concrete surfaces. Copyright © 2010 John Wiley & Sons, Ltd.     

Combined Extraction and Electrochemical Detection of Amines and Phenols Using Microelectrodes in Organic Solvents

A straightforward approach for liquid‐liquid extractive detection of aromatic amines and phenols is described based on the spontaneous transfer of the molecule from the aqueous to an organic phase and subsequent electrochemical detection in the latter phase using a microelectrode. It is demonstrated that the extent of the transfer can be modified by altering the pH of the aqueous solution and the organic solvent. It is also concluded that the presence of an ion‐pair formation agent does not increase the transfer yield for 4‐chloroaniline and phenol. The present approach combines liquid‐liquid sample clean‐up and quantification into a single step which significantly facilitates determinations of aromatic amines and phenols present in complex samples.     

Optimization of headspace sampling using solid-phase microextraction for volatile components in tobacco

Solid-phase microextraction (SPME) was evaluated as a tool for headspace sampling of tobacco samples. Several experimental parameters (e.g. sampling temperature, pH, moisture, and the type of SPME fibers) were optimized to improve sampling efficiency in two aspects; maximum adsorption and selective adsorption of volatile components onto SPME fibers. The effect of these parameters was often dominated by the physical and chemical nature (e.g. volatility, polarity) of target compounds, thus, SPME sampling conditions can be adjusted to favor a selected group of compounds, such as organic acids in tobacco.     

Radiolytic transformations of chlorinated phenols and chlorinated phenoxyacetic acids

Hydroxyl radical reactions of selected chlorinated aromatic phenols (2,4-dichlorophenol, 2,4,6-trichlorophenol, and pentachlorophenol) and chlorinated phenoxyacetic acids [2,4-dichlorophenoxyacetic acid (2,4-D), 2,4-D methyl ester, 2-(2,4-dichlorophenoxy)propionic acid (2,4-DP)] were studied using the radiolysis techniques of pulse radiolysis and gamma radiolysis. Hydroxyl radical addition was the prominent reaction pathway for the chlorinated phenoxyacetic acids and also for the chlorinated phenols at pH values below the pK(a) of the compounds. A very prominent change in (*)OH reactivity was observed with the chlorinated phenoxide ions in high pH solutions. Two different reaction pathways were clearly present between the hydroxyl radical and the chlorinated phenoxide ions. One of the reaction pathways was suppressed when the concentration of chlorinated phenoxide ions was increased 10-fold. Amid a greater electron-withdrawing presence on the aromatic ring (higher chlorinated phenoxide ions), the hydroxyl radical reacted preferably by way of addition to the aromatic ring. Steady-state experiments utilizing gamma radiolysis also showed a substantial decrease in oxidation with an increase in pH of substrate.     

Zeolitic imidazolate framework 8 (ZIF‐8) reinforced macroporous resin D101 for selective solid‐phase extraction of 1‐naphthol and 2‐naphthol from phenol compounds

Macroporous resin has been attracting intensive attention due to its critical role in separation and purification of natural products. Herein, a zeolitic imidazolate framework 8 reinforced macroporous resin D101 was prepared via a room temperature growth method and used for dispersive SPE of 1‐naphthol and 2‐naphthol. The parameters affecting the adsorption and desorption efficiency such as the sample pH, adsorbent amount, extraction time, desorption solvent, and desorption time were investigated. The as‐prepared adsorbent showed selectivity for 1‐naphthol and 2‐naphthol compared to other phenols. Under the optimum dispersive SPE conditions, the detection of 1‐naphthol and 2‐naphthol coupled with a CZE method was conducted and the LODs for 1‐naphthol and 2‐naphthol were 1.37 and 1.43 ng/mL, respectively. Moreover, the results of urine sample analysis showed the spiked recoveries to be in the range of 96.2–106.9%. This study indicated that D101@ZIF‐8 (where ZIF is zeolitic imidazolate framework) is a promising selective adsorbent for the analysis of 1‐naphthol and 2‐naphthol in urine samples.     

An electronic spectral study of the coupled effect on the tautomeric equilibria of some α-hydroxy azo compounds

The spectral behaviour of six a-hydroxy azo compounds has been investigated in solution. The bands appearing in the u.v. and visible regions are assigned to possible electronic transitions. Azo compounds containing pyrazolone and acetyl or ester moieties are found to exist mainly in the hydrazo form in solution, while those containing the naphthol moiety exist in the azo-hydrazone tautomeric equilibrium. The solvatochromic behaviour of the compounds is investigated by studying their spectra in organic solvents of different polarities. The acidity constants are determined from the spectra of the compounds in aqueous ethanolic solutions of varying pH values.     

Electrochemical Detection of 2‐Naphthol at a Glassy Carbon Electrode Modified with Tosflex Film

In this study, a Tosflex (a perfluoro‐anion‐exchange membrane) modified glassy carbon electrode has been used to detect 2‐naphthalenol (2‐naphthol) in aqueous solutions in order to demonstrate the electroanalytical application of Tosflex. 2‐naphthol polymerizes upon electrochemical oxidation at a glassy carbon electrode; however, the current related to this oxidation is too small for analytical purpose at low concentration level. A Tosflex polymer modified glassy carbon electrode (TFGCE) was found of having capability to improve the detection limit because 2‐naphthol molecules deprotonated in basic solutions to form 2‐naphtholate anions that were accumulated to TFGCE by the anion‐exchange characteristic of Tosflex. The accumulated 2‐naphtholate anions were determined with the following differential pulse voltammetry. With 3 minutes accumulation at +0.05 V, the dependence of oxidation current versus concentration was linear from 8×10^?7 M to 1×10^?5 M with a regression coefficient of 0.999 and a detection limit of 2×10^?7 M. Unlike many other anion‐exchange polymer modified electrodes, the TFGCE is stable at highly basic condition.     

Further research on the photo-SPME of triclosan

In this study the photoinduced degradation of triclosan has been investigated by photo-solid-phase microextraction (photo-SPME). In photo-SPME, photodegradation is carried out on the SPME fibre containing the target compound. Triclosan was extracted from aqueous solutions by use of polydimethylsiloxane SPME fibres and these were subsequently exposed to UV irradiation (power 8 W, wavelength 254 nm) for different times (from 2 to 60 min). The photodegradation kinetics of triclosan were investigated, the photoproducts generated were tentatively identified, and the photochemical behaviour of these products was studied by use of this on-fibre approach followed by gas chromatographic–mass spectrometric analysis. Eight photoproducts were tentatively identified, including chlorinated phenols, chlorohydroxydiphenyl ethers, 2,8-dichlorodibenzo-p-dioxin, and a possible dichlorodibenzodioxin isomer or dichlorohydroxydibenzofuran. The main photodegradation mechanisms were postulated and photodegradation pathways proposed. The effect of pH on triclosan degradation and on triclosan-to-dioxin conversion was also investigated. Triclosan degradation occurred, and generation of 2,8-dichlorodibenzo-p-dioxin was confirmed, throughout the pH range studied (from 3 to 9).      

Selectivity differences between alkyl and polar‐modified alkyl phases in reversed phase high performance liquid chromatography

Compared to conventional C18 phases, polar‐modified phases have distinct differences with regards to chromatographic behavior. In the present study, ODS phases and polar‐modified phases were synthesized. The columns containing these new packings demonstrated satisfactory stability under both acidic (pH 1.5) and basic (pH 10) conditions. We evaluated the selectivity differences between alkyl and polar‐modified alkyl RP columns by using a range of neutral analytes. The polar‐modified alkyl phases showed excellent peak shapes for almost all compounds. We also compared the selectivity differences between them for separating nucleotides by using 100% aqueous mobile phase and tricyclic antidepressants in the intermediate pH mobile phases. The results demonstrated that polar‐modified phases display a significantly reduced hydrophobic nature and a significantly reduced silanol activity compared to the conventional C18 phases.     

Supported liquid membrane work-up in combination with liquid chromatography and electrochemical detection for the determination of chlorinated phenols in natural water samples

Summary A sample preparation method has been developed for the determination of chlorinated phenols in water. The method is based on a supported liquid membrane extraction system connected on-line to liquid chromatography with electrochemical detection. The supported liquid membrane technique utilizes a porous PTFE membrane. The membrane is impregnated with an organic solvent which forms a barrier between two aqueous phases and enables selective extraction. The technique can easily be coupled in a flow system. In this investigation five chlorinated phenols (1–5 chlorine atoms) were extracted from natural water samples. Extraction for 30 minutes resulted in detection limits of approximately 25 ng L^–1.     

IPC behaviour of some sulphonated naphthols and nitroso-naphthols

Summary The ion-pair chromatographic behaviour of a naphthol and some sulpho-substituted naphthols and nitroso-naphthols is studied. Formation of the ion-pair compounds is done either by pre-extraction or during elution with long-chained quaternary alkyl- or alkylarylammonium salts. Identification is based in UV/VIS absorption using a diode array detector at 229, 240, 254 or 280 nm. Special emphasis is placed on the column material, the positions of the substituents in the naphthols and the organic ion-pairing agents in the eluent.

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IPC-Verhalten einiger sulfonierter Naphthole und Nitrosonaphthole

     

Sorption of carbaryl and naphthols by polymers based on N-vinylamides from aqueous solutions

New cross-linked copolymers based on N-vinylpyrrolidone and N-vinylcaprolactam were proposed for preconcentration of carbaryl and naphthols from aqueous media. The influence of pH, nature of salting-out agent, surfactant, and temperature on the recovery of the analytes was examined. The most efficient sorption systems for recovery of carbaryl and naphthols from aqueous solutions were developed.