Development of an automated on-line solid-phase extraction-high-performance liquid chromatographic method for the analysis of aniline, phenol, caffeine and various selected substituted aniline and phenol compounds in aqueous matrices

A fully automated solid-phase extraction (SPE)-high-performance liquid chromatographic method has been developed for the simultaneous analysis of substituted anilines and phenols in aqueous matrices at the low- to sub-microg/l level. Diode array and electrochemical detection operated in tandem mode were used for analyte detection. Two new polymeric sorbent materials (Hysphere-GP and Hysphere-SH) were evaluated for the on-line SPE of substituted anilines and phenols from aqueous matrices and their performance was compared with the PRP-1 and PLRP-S sorbents. Hysphere-GP sorbent packed in 10 x 2 mm cartridges was found to give better results in terms of sensitivity and selectivity of the overall analytical method. The proposed analytical method was validated for the analysis of these compounds in Axios river water that receives industrial, communal and agricultural wastes. The detection limits for all the compounds range between 0.05 and 0.2 microg/l, except for aniline and phenol which have detection limits of 0.5 and 1 microg/l, respectively (aniline detected by electrochemical detection). The recoveries for all the compounds are higher than 75% except for aniline (6%), phenol (50%) and 3-chlorophenol (67%). Finally, in order to evaluate the efficiency of the Hysphere-GP (10 x 2 mm) cartridges for sample stabilization and storage, the stability of the compounds of interest at the sorbed state onto these cartridges has been evaluated under three different temperature regimes (deep freeze, refrigeration, 20 degrees C).     

New cation-exchange resins with high reversed-phase character for solid-phase extraction of phenols

High capacity carboxylic acid functionalized resins, prepared by ring-opening metathesis polymerization, were used for solid-phase extraction (SPE) of phenols. Two resins, based on cross-linked poly-(endo,endo-norborn-2-ene-5,6-dicarboxylic acid) exhibited a capacity of 3.5 and 5.1 mequiv. COOH/g, respectively. Particle-loaded PTFE membranes were prepared from a 3.1 mequiv. COOH/g resin. The extraction behavior of the new materials versus two different EPA priority pollutant phenol standards was investigated. For most compounds, a quantitative recovery was observed. The extraction efficiency of the new resins was compared to those of other, commercially available materials such as silica C₁₈ or carboxypropylsilica. The general advantages of the new materials, the mechanism of extraction, the influence of polarity and acidity of the compounds investigated as well as differences between membranes and columns containing the new particles are discussed. Finally, the extraction efficiency of the new resins for phenols from spiked soil samples using both standard SPE as well as batch-techniques was investigated.     

Evaluation of a new hypercrosslinked polymer as a sorbent for solid-phase extraction of polar compounds

A new hypercrosslinked polymer (HXLGp) with hydrophilic character due to the presence of hydroxyl moieties has been tested as a sorbent for the solid-phase extraction (SPE) of several polar compounds from water samples. This new sorbent enables the on-line extraction of 300 ml of sample with recoveries higher than 80% for polar compounds such as oxamyl, methomyl or desisopropylatrazine (DIA). The HXLGp has also been compared to other commercially available sorbents such as Oasis HLB (hydrophilic macroporous), to hydrophobic hypercrosslinked resins and to a previously synthesized sorbent based on N-vinylimidazole-divinylbenzene. The results are consistently better with the new synthesized sorbent. The method was successfully applied to the on-line SPE-HPLC of tap and river water samples. The validation with river water samples provided good linearity range and detection limits between 0.03 for methomyl and 4-nitrophenol (4NP) to 0.2 microg l(-1) for phenol (Ph).     

Gas chromatographic profiling and screening for phenols as isobutoxycarbonyl derivatives in aqueous samples

An efficient method is described for the simultaneous determination of phenol and 49 substituted phenols present in aqueous samples. The method is based on the extractive two-phase isobutoxycarbonyl (isoBOC) derivatization with subsequent solid-phase extraction (SPE) for the direct analysis by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). Phenolic hydroxyl groups in acidic aqueous solutions were allowed to react with isobutyl chloroformate present in the dichloromethane phase containing triethylamine. The resulting isoBOC derivatives were then recovered by SPE using Chromosorb P in normal-phase partition mode, followed by direct GC and GC-MS analysis. Using this combined procedure, linear detector responses were obtained in the concentration range of 0.5-8 microg ml(-1), with correlation coefficients varying from 0.925 to 0.999 for most of the phenols studied except for 2,4-dinitorphenol (0.789). The temperature-programmed retention index (I) sets as measured on DB-5 and DB-17 dual-capillary columns of different polarity were characteristic of each isoBOC phenol derivative and thus, useful in the screening for isomeric phenols by I matching only. The mass spectral patterns, exhibiting characteristic [M-100]+, [M-200]+ and [M-300]+ ions for the mono-, di- and trihydroxybezenes, respectively with common ions at m/z 57, facilitated their rapid structural confirmation. The present method allowed rapid screening for phenols when applied to water samples spiked with phenols.     

Solid-phase trapping of solutes for further chromatographic or electrophoretic analysis

Because of its simplicity, speed and effectiveness, solid-phase extraction (SPE) has become the preferred technique for concentration of selected analytes prior to chromatographic or electrophoretic analysis. In this review the historical development of SPE is briefly traced. Then the principles of SPE are reviewed in some detail. Numerous references are given on the format, sorbents, elution conditions, online techniques and automation with special emphasis on relatively recent developments. The principles and recent advances in solid-phase microextraction (SPME) are also reviewed. The final section on selected recent applications includes an extensive list of references to work published within the last three years. Future trends and developments are discussed briefly.     

Use of polymeric sorbents for the off-line preconcentration of priority pollutant phenols from water for high-performance liquid chromatographic analysis

The use of porous polymeric minicolumns for the determination of phenols from the U.S. Environmental Priority Pollutant List was studied. For the off-line preconcentration of priority pollutant phenols from water by solid-phase extraction, minicolumns packed with 1,4-di(methacryloyloxymethyl)naphthalene-divinylbenzene copolymer and Amberlite XAD-4 were used. In order to compare the sorption properties of these polymeric sorbents, the recoveries and breakthrough volumes of phenol, p-nitrophenol, 2,4-dinitrophenol, o-chlorophenol, o-nitrophenol, 2,4-dimethylphenol, 4-chloro-m-cresol, 4,6-dinitro-o-cresol, 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol were studied.     

Solid-phase extraction of polar compounds with a hydrophilic copolymeric sorbent

A new synthesized copolymer based on N-vinylimidazole-divinylbenzene (VIm-DVB) was tested as a sorbent for the solid-phase extraction (SPE) of polar analytes. In the on-line SPE, this synthesized sorbent enabled 100 ml of sample to be preconcentrated with recoveries as high as 80% for oxamyl, phenol (Ph) and derivates, bentazone and (4-chloro-2-methylphenoxy)acetic acid (MCPA). For the off-line SPE, 1000 ml of sample was extracted and recoveries were higher than 92% for all compounds with the exception of oxamyl (83%) and methomyl (78%). The VIm-DVB sorbent gives better recoveries than the previously synthesized 4-vinylpyridine-divinylbenzene (VP-DVB) resin and similar to such highly crosslinked commercial sorbents as LiChrolut EN or Oasis HLB. Real water samples were used to validate the on-line SPE method. Linearity was good and detection limits were between 0.1 and 0.2 microg l(-1).     

Sensitive determination of phenols in environmental water samples with SPE packed with bamboo carbon prior to HPLC

Bamboo carbon, an inexpensive, readily available material, has attracted great attention in recent years because of adsorptive properties. In this paper, the potential of bamboo carbon as a SPE adsorbent for the determination of phenols, was investigated. Phenols are important environmental contaminants that may adversely affect human health. Parameters influencing extraction efficiency, including type of eluent, eluent volume, amount of adsorbent, as well as sample pH, volume, and flow rate were investigated and optimized. The optimized results exhibited excellent linear relationships between peak area and phenol concentrations over the range of 2.0–100 ng/mL, with precision between 2.2–7.2%. The LODs were 0.06–0.4 ng/mL for the eight phenols tested. The proposed method has been successfully applied to the analysis of several real‐world environmental water samples. These results indicate that bamboo carbon may be used as a novel SPE adsorbent for the concentration and determination of phenols in real environmental water samples.     

Comparison of Hydrophilic Polymeric Sorbents for On-Line Solid-Phase Extraction of Polar Compounds from Aqueous Samples

Two 4-vinylimidazole-divinylbenzene (4VIm-DVB) polymers were synthesized and applied as sorbents for on-line solid-phase extraction (SPE) followed by liquid chromatography for analyzing polar compounds in aqueous samples. The new sorbents (4VIm-DVB) were compared to another sorbent that had been previously synthesized by our group (N-vinylimidazole-divinylbenzene (NVIm-DVB)) and to the commercial OASIS^® HLB and Strata^TM X. All the sorbents enabled 100 mL of sample to be on-line concentrated with good recoveries for the studied polar compounds. Real water samples were analyzed using NVIm-DVB and OASIS^® HLB as SPE sorbent, for which the best results were obtained.     

Monodisperse, hypercrosslinked polymer microspheres as tailor-made sorbents for highly efficient solid-phase extractions of polar pollutants from water samples

In this detailed analytical study, we have evaluated in-house synthesised polymeric solid-phase extraction (SPE) sorbents in the form of monodisperse, hypercrosslinked polymer microspheres with diameters in the low micrometre range (approximately 4 microm). More specifically, their performance in the on-line SPE of a group of polar pollutants has been investigated thoroughly. The novel hypercrosslinked materials were compared with satisfactory results to commercial SPE sorbents with similar chemical and morphological properties, albeit that the commercial materials had higher particle sizes and broader particle size distributions. The on-line SPE method developed using these novel particles as packing material was applied successfully to ultrapure, mineral, tap and Ebre river water samples, with near total recoveries of all the analytes studied when 500 ml samples were percolated through the sorbents. Method validation with river water samples demonstrated good linearity, low detection limits as well as satisfactory precision in terms of repeatability and reproducibility, with values of relative standard deviation (%RSD) lower than 6.7 and 8.7%, respectively.     

Retention behaviour of some high-intensity sweeteners on different SPE sorbents

The objective of this paper is to provide information about application of solid-phase extraction (SPE) for isolation of nine high-intensity sweeteners (acesulfame-K, alitame, aspartame, cyclamate, dulcin, neotame, saccharin, sucralose and neohesperidin dihydrochalcone) from aqueous solutions. The influence of several types of LC-MS compatible buffers (different pH values and compositions) on their recovery has been studied and discussed. A number of commercially available SPE cartridges, such as Chromabond C18ec, Strata-X RP, Bakerbond Octadecyl, Bakerbond SDB-1, Bakerbond SPE Phenyl, Oasis HLB, LiChrolut RP-18, Supelclean LC-18, Discovery DSC-18 and Zorbax C18 were tested in order to evaluate their applicability for the isolation of analytes. Very high recoveries (better than 92%) of all studied compounds were obtained using formic acid-N,N-diisopropylethylamine buffer adjusted to pH 4.5 and C₁₈-bonded silica sorbents. Behaviour of polymeric sorbents strongly depends on their structure. Strata-X RP behaves much like a C₁₈-bonded silica sorbent. Recoveries obtained using Oasis HLB were comparable with those observed for silica-based sorbents. The only compound less efficiently (83%) retained by this sorbent was cyclamate. Bakerbond SDB-1 shows unusual selectivity towards aspartame and alitame. Recoveries of these two sweeteners were very low (26 and 42%, respectively). It was also found that aspartame and alitame can be selectively separated from the mixture of sweeteners using formic acid-triethylamine buffer at pH 3.5.     

Determination of phenolic compounds in waste water by solid-phase micro extraction

The solid-phase micro extraction technique (SPME) using a polyacrylate coated fibre has been examined with the aim to determine phenolic components in strong contaminated waste water. Considering the high contents and the great variety of accompanying organic material, the feasibility of SPME-GC-MS analysis has been tested. In this connection the influence of matrix components on the SPME results are discussed. EPA-604 phenols and some other phenolic components have been sampled by a polar fibre under standard conditions and in original waste water. The effects of defined concentrations of humic acids and surfactants on the recovery of phenols have been studied. The influence of other organics, e.g. hexachlorocyclohexane isomers, on the recoveries of phenols are discussed. Finally, a comparison between results of a liquid-liquid extraction and SPME describes the performance of SPME regarding the phenol analysis of strong-loaded water.     

Recent advances in sample preparation techniques for effective bioanalytical methods

This paper reviews the recent developments in bioanalysis sample preparation techniques and gives an update on basic principles, theory, applications and possibilities for automation, and a comparative discussion on the advantages and limitation of each technique. Conventional liquid-liquid extraction (LLE), protein precipitation (PP) and solid-phase extraction (SPE) techniques are now been considered as methods of the past. The last decade has witnessed a rapid development of novel sample preparation techniques in bioanalysis. Developments in SPE techniques such as selective sorbents and in the overall approach to SPE, such as hybrid SPE and molecularly imprinted polymer SPE, have been addressed. Considerable literature has been published in the area of solid-phase micro-extraction and its different versions, e.g. stir bar sorptive extraction, and their application in the development of selective and sensitive bioanalytical methods. Techniques such as dispersive solid-phase extraction, disposable pipette extraction and micro-extraction by packed sorbent offer a variety of extraction phases and provide unique advantages to bioanalytical methods. On-line SPE utilizing column-switching techniques is rapidly gaining acceptance in bioanalytical applications. PP sample preparation techniques such as PP filter plates/tubes offer many advantages like removal of phospholipids and proteins in plasma/serum. Newer approaches to conventional LLE techniques (salting-out LLE) are also covered in this review article.     

On-line trace enrichment of phenolic compounds from water using a pyrrole-based polymer as the solid-phase extraction sorbent coupled with high-performance liquid chromatography

A pyrrole-based conductive polymer was prepared and applied as new sorbent for on-line solid-phase extraction (SPE) of phenol and chlorophenols from water samples. Polypyrrole (PPy) was synthesized by chemical oxidation of the monomer in non-aqueous solution. The efficiency of this polymer for extraction of phenol and chlorophenols was evaluated using 35 mg of PPy as the sorbent in an on-line SPE system coupled to reversed-phase liquid chromatography with UV detection. The mobile phase were mixture of phosphate buffer-acetonitrile and compounds were eluted by the mobile phase using a six-port switching valve. High volumes of water, up to 160 ml, could be preconcentrated without the loss of phenols, except for the more polar ones. The R.S.D. for a river water sample spiked with phenol and chlorophenols at sub-ppb level was lower than 7% (n=5) and detection limits of 15-100 and 35-150 ng l⁻¹ for tap and river water were obtained, respectively.     

Determination of phenolic compounds in waste water by solid-phase micro extraction

The solid-phase micro extraction technique (SPME) using a polyacrylate coated fibre has been examined with the aim to determine phenolic components in strong contaminated waste water. Considering the high contents and the great variety of accompanying organic material, the feasibility of SPME-GC-MS analysis has been tested. In this connection the influence of matrix components on the SPME results are discussed. EPA-604 phenols and some other phenolic components have been sampled by a polar fibre under standard conditions and in original waste water. The effects of defined concentrations of humic acids and surfactants on the recovery of phenols have been studied. The influence of other organics, e.g. hexachlorocyclohexane isomers, on the recoveries of phenols are discussed. Finally, a comparison between results of a liquid-liquid extraction and SPME describes the performance of SPME regarding the phenol analysis of strong-loaded water. Received: 13 October 1995 / Revised: 6 March 1996 / Accepted: 9 March 1996     

Solid-phase extraction of polycyclic aromatic compounds

Solid-phase extraction (SPE) for two groups of polyaromatic compounds--polycyclic aromatic hydrocarbons and naphthalenesulfonates--with completely different problems in the extraction process are reviewed. The sorbents used in each case and the different steps of SPE are studied. Particular problems encountered in the SPE of each group are described. Adsorption problems of PAHs which require an organic solvent or a surfactant to be added to the sample are explained. The need of ion-pair solid-phase extraction for extracting naphthalenesulfonates and the influence of the inorganic species in the extraction are discussed. The on-line systems are described for both group of compounds.     

Solid-phase extraction clean-up of soil and sediment extracts for the determination of various types of pollutants in a single run

A new sample clean-up procedure based on solid-phase extraction (SPE) sorbents was proposed for the determination of pesticides, polycyclic aromatic hydrocarbons and polychlorinated biphenyls in soils and sediments. The main purpose of the research was to find a combination of sorbents for the SPE method that would permit the determination of many types of analytes (polycyclic aromatic hydrocarbons, polychlorinated biphenyls, N-, P- and Cl-containing pesticides) in a single run. Elution profiles for both the analytes and the interfering components were determined for several types of SPE sorbents (alumina, silica and surface-modified silica) and combinations of them. The efficiency of the clean-up method developed was evaluated using real soil samples.     

The evaluation of different sorbents for the preconcentration of phenoxyacetic acid herbicides and their metabolites from soils

A procedure using alkaline extraction, solid-phase extraction (SPE) and HPLC is developed to analyze the polar herbicides 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-chloro-2-methylphenoxyacetic acid (MCPA) together with their main metabolites in soils. An ion-pairing HPLC method is used for the determination as it permits the baseline separation of these highly polar herbicides and their main metabolites. The use of a highly cross-linked polystyrene-divinylbenzene sorbent (PS-DVB) gives the best results for the analysis of these compounds. This sorbent allows the direct preconcentration of the analytes at the high pH values obtained after quantitative alkaline extraction of the herbicides from soil samples. Different parameters are evaluated for the SPE preconcentration step. The high polarity of the main analytes of interest (2,4-D and MCPA) makes it necessary to work at low flow rates (< or =0.5 mL min(-1)) in order for these compounds to be retained by the PS-DVB sorbent. A two stage desorption from the SPE sorbent is required to obtain the analytes in solvents that are appropriate for HPLC determination. A first desorption with a 50:50 methanol:water mixture elutes the most polar analytes (2,4-D, MCPA and 2CP). The second elution step with methanol permits the analysis of the other phenol derivatives. The humic and fulvic substances present in the soil are not efficiently retained by PS-DVB sorbents at alkaline pH's and so do not interfere in the analysis. This method has been successfully applied in the analysis of soil samples from a golf course treated with a commercial product containing esters of 2,4-D and MCPA as the active components.     

Hydrophilic hypercrosslinked polymeric sorbents for the solid-phase extraction of polar contaminants from water

Three new hypercrosslinked polymers with hydrophilic character arising from hydroxyl moieties in their skeletons have been prepared in microsphere format and applied to the off-line solid-phase extraction (SPE) of polar compounds from water samples. For sample volumes of 1000 ml, the recoveries of various polar pesticides, such as oxamyl, methomyl, selected phenolic compounds, as well as some pharmaceuticals, were close to 90%. The HXLPP-polar polymer with the best performance characteristics was applied to real samples. Its performance was also compared to commercially available sorbents, such as LiChrolut EN (hydrophobic, hypercrosslinked), Oasis HLB (hydrophilic, macroporous) and Isolute ENV+ (hydrophilic, hypercrosslinked); the new sorbent out-performed the commercially available sorbents. The polymer was applied successfully in off-line SPE of river water samples followed by liquid chromatography and ultraviolet detection, providing a good linear range and detection limits of 0.2 μg l⁻¹ for the majority of the compounds, with the exception of oxamyl, methomyl, guaiacol and salicylic acid where the detection limit was 0.5 μg l⁻¹.     

Preparation of phenothiazine bonded silica gel as sorbents of solid phase extraction and their application for determination of nitrobenzene compounds in environmental water by gas chromatography-mass spectrometry

In this paper, two phenothiazine bonded silica (PTZ-Si) sorbents were prepared and used as sorbents of solid-phase extraction (SPE) for the determination of nitrobenzene compounds in environmental water samples by gas chromatography-mass spectrometry (GC-MS). Different synthesis routes were proposed to obtain high bonded amount of PTZ on the surface of silica gel. PTZ molecule was derived to its amino or acyl chloride derivatives for reacting with isocyanate or amino silane coupling agent, which was further reacted with the surface silanol groups of silica gel to obtain the PTZ-Si sorbents. The resultant PTZ-Si sorbents were characterized by nitrogen sorption porosimetry (NSP), Fourier transform infrared spectroscopy (FT-IR) and elemental analysis (EA) to assure the successful bonding of PTZ on the surface of silica gel. Then the PTZ-Si sorbents were served as SPE sorbents for the enrichment of nitrobenzene compounds. Several parameters affecting the extraction performance were investigated. Under the optimized conditions, the proposed method was applied to the analysis of six nitrobenzene compounds in environmental water samples. Good linearities were obtained for all nitrobenzene compounds with R(2) larger than 0.9958. The limits of detection were found to be in the range of 0.06-0.3 ng/mL. The method recoveries of nitrobenzene compounds spiked in water samples were from 71.4% to 124.3%, with relative standard deviations (RSDs) less than 10.1%.