Solid-phase microextraction of N-nitrosamines

A method was developed for the extraction of seven N-nitrosamine compounds from water by solid-phase microextraction (SPME). The method developed requires a total analysis time of only 1.25 h for both extraction and detection (versus 3-20 h for other isolation techniques). Three gas chromatography (GC) detection systems were tested with the SPME method, nitrogen chemiluminesence detection (NCD), nitrogen-phosphorus detection (NPD) and chemical ionization mass spectrometry (CI-MS), with method detection limits (MDLs) found in the ng/L range. This method was used to analyze wastewater samples and showed excellent selectivity of extraction. The detection limits of this method for N-nitrosodimethylamine (NDMA) range from 30 to 890 ng/L as a function of detector type. The excellent selectivity of SPME in addition to the fast analysis time would make this method ideal for general surveys, wastewater analysis and laboratory studies (e.g. degradation kinetics or formation potential).     

Fiber-in-tube solid-phase microextraction: a fibrous rigid-rod heterocyclic polymer as the extraction medium

A novel "fiber-in-tube" configuration has been applied to the extraction tube of solid phase microextraction (SPME), and the direct coupling of the extraction process to liquid chromatography (LC) has been accomplished for the analysis of n-butylphthalate in wastewater. By using this fiber-in-tube SPME/LC system the preconcentration factor for the phthalate was about 160 with 20 min extraction and no interference peak was observed in the chromatogram. The results also showed the potential applications of this fiber-in-tube SPME/LC for the analysis of sub-ppb level (i.e., lower than 1 ng/mL) of various organic analytes in aqueous sample matrix without a large solvent consumption during the preconcentration process.     

Rapid wide-scope screening of drugs of abuse, prescription drugs with potential for abuse and their metabolites in influent and effluent urban wastewater by ultrahigh pressure liquid chromatography-quadrupole-time-of-flight-mass spectrometry

In the present work, a rapid method with little sample handling has been developed for determination of 23 selected volatile organic compounds in environmental and wastewater samples. The method is based on headspace solid-phase microextraction (SPME) followed by gas chromatography coupled to tandem mass spectrometry (GC-MS/MS) determination using triple quadrupole analyzer (QqQ) in electron ionization mode. The best conditions for extraction were optimised with a factorial design taking into account the interaction between different parameters and not only individual effects of variables. In the optimized procedure, 4 mL of water sample were extracted using a 10 mL vial and adding 0.4 g NaCl (final NaCl content of 10%). An SPME extraction with carboxen/polydimethylsiloxane 75 μm fiber for 30 min at 50°C (with 5 min of previous equilibration time) with magnetic stirring was applied. Chromatographic determination was carried out by GC-MS/MS working in Selected Reaction Monitoring (SRM) mode. For most analytes, two MS/MS transitions were acquired, although for a few compounds it was difficult to obtain characteristic abundant fragments. In those cases, a pseudo selected reaction monitoring (pseudo-SRM) with three ions was used instead. The intensity ratio between quantitation (Q) and confirmation (q) signals was used as a confirmatory parameter. The method was validated by means of recovery experiments (n=6) spiking mineral water samples at three concentration levels (0.1, 5 and 50 μg L(-1)). Recoveries between 70% and 120% were generally obtained with relative standard deviations (RSDs) lower than 20%. The developed method was applied to surface water and wastewater from a wastewater treatment plant and from a municipal solid-waste treatment plant. Several compounds, like chloroform, benzene, trichloroethylene, toluene, tetrachloroethylene, dibromochloromethane, xylenes and bromoform were detected and confirmed in all the samples analyzed.     

Fiber-in-tube solid-phase microextraction: a fibrous rigid-rod heterocyclic polymer as the extraction medium

A novel “fiber-in-tube” configuration has been applied to the extraction tube of solid phase microextraction (SPME), and the direct coupling of the extraction process to liquid chromatography (LC) has been accomplished for the analysis of n-butylphthalate in wastewater. By using this fiber-in-tube SPME/LC system the preconcentration factor for the phthalate was about 160 with 20 min extraction and no interference peak was observed in the chromatogram. The results also showed the potential applications of this fiber-in-tube SPME/LC for the analysis of sub-ppb level (i.e., lower than 1 ng/mL) of various organic analytes in aqueous sample matrix without a large solvent consumption during the preconcentration process.     

Application of on-site solid-phase microextraction in aquatic dissipation studies of profoxydim in rice

The application of a manual operated solid-phase microextraction (SPME)-HPLC interface is discussed for the analysis of thermally labile analytes in aqueous matrices. The technique has been applied on-site at a flooded rice field to demonstrate its potential for real time extraction of the herbicide profoxydim. Thus, compounds which would otherwise easily degrade in the aqueous matrices within hours or days could be determined more accurately. The fibers were shipped back to the laboratory with express delivery where the target analyte was desorbed from the fiber and determined by HPLC-UV analysis. The SPME method was characterized by significant ruggedness where conventional techniques such as liquid-liquid extraction and solid-phase extraction require additional shipping and handling costs and time-consuming multiple sample preparation steps. In general, any delay in shipping the aqueous samples to the laboratory has the potential for sample degradation and a loss in accuracy when using non on-site extraction techniques. Fifty microm Carbowax-templated resin coatings were most suitable for coupling SPME to HPLC in order to achieve a high sensitivity for polar analytes. The SPME technique was characterized by a good sensitivity and a precision less than 10% RSD. The SPME-LC-UV method was linear over at least three orders of magnitude while achieving a limit of detection in the lower microg/l range. The on-site SPME method has shown significantly increased accuracy. Profoxydim was determined at concentrations of ca. 180 microg/l 3 h after an application on a flooded bare soil field.     

Determination of the plasticizer N-butylbenzenesulfonamide and the pharmaceutical Ibuprofen in wastewater using solid phase microextraction (SPME)

A rapid, inexpensive and solvent-free method for the simultaneous determination of the polyamide plasticizer N-butylbenzenesulfonamide (NBBS) and the widely used pharmaceutical Ibuprofen by solid phase microextraction (SPME) combined with gas chromatography/mass spectrometry (GC/MSD) in wastewater samples was developed. Besides the optimized analytical conditions, results of investigations with varying analytical parameters are reported. Problems, which may occur during the analytical procedure (e.g. salt deposits, adsorption phenomena, carry-over), are discussed. For the determination of Ibuprofen, it is important to carry out the extraction under acidic conditions with sufficiently buffered samples; the GC/MSD system must be very clean and well maintained. SPME allows an extraction of Ibuprofen without derivatization of its carboxylic group. For quantification in complex matrices, the standard addition technique is necessary. Limit of detection and limit of determination are 0.1 μg/L for both analytes. NBBS and Ibuprofen were detected in several raw and treated wastewater samples from municipal wastewater treatment plants in the range from < 0.1 to 3.5 μg/L.     

On-line solid-phase microextraction of triclosan, bisphenol A, chlorophenols, and selected pharmaceuticals in environmental water samples by high-performance liquid chromatography–ultraviolet detection

A method using on-line solid-phase microextraction (SPME) on a carbowax-templated fiber followed by liquid chromatography (LC) with ultraviolet (UV) detection was developed for the determination of triclosan in environmental water samples. Along with triclosan, other selected phenolic compounds, bisphenol A, and acidic pharmaceuticals were studied. Previous SPME/LC or stir-bar sorptive extraction/LC-UV for polar analytes showed lack of sensitivity. In this study, the calculated octanol–water distribution coefficient (log D) values of the target analytes at different pH values were used to estimate polarity of the analytes. The lack of sensitivity observed in earlier studies is identified as a lack of desorption by strong polar–polar interactions between analyte and solid-phase. Calculated log D values were useful to understand or predict the interaction between analyte and solid phase. Under the optimized conditions, the method detection limit of selected analytes by using on-line SPME-LC-UV method ranged from 5 to 33 ng?L^?1, except for very polar 3-chlorophenol and 2,4-dichlorophenol which was obscured in wastewater samples by an interfering substance. This level of detection represented a remarkable improvement over the conventional existing methods. The on-line SPME-LC-UV method, which did not require derivatization of analytes, was applied to the determination of TCS including phenolic compounds and acidic pharmaceuticals in tap water and river water and municipal wastewater samples.

Determination of the plasticizer N-butylbenzenesulfonamide and the pharmaceutical Ibuprofen in wastewater using solid phase microextraction (SPME)

A rapid, inexpensive and solvent-free method for the simultaneous determination of the polyamide plasticizer N-butylbenzenesulfonamide (NBBS) and the widely used pharmaceutical Ibuprofen by solid phase microextraction (SPME) combined with gas chromatography/mass spectrometry (GC/MSD) in wastewater samples was developed. Besides the optimized analytical conditions, results of investigations with varying analytical parameters are reported. Problems, which may occur during the analytical procedure (e.g. salt deposits, adsorption phenomena, carry-over), are discussed. For the determination of Ibuprofen, it is important to carry out the extraction under acidic conditions with sufficiently buffered samples; the GC/MSD system must be very clean and well maintained. SPME allows an extraction of Ibuprofen without derivatization of its carboxylic group. For quantification in complex matrices, the standard addition technique is necessary. Limit of detection and limit of determination are 0.1 μg/L for both analytes. NBBS and Ibuprofen were detected in several raw and treated wastewater samples from municipal wastewater treatment plants in the range from < 0.1 to 3.5 μg/L. Received: 13 March 1998 / Revised: 16 June 1998 / Accepted: 19 June 1998     

Determination of the fungicides vinclozolin and dicloran in soils using ultrasonic extraction coupled with solid-phase microextraction

Solid-phase microextraction (SPME) coupled to ultrasonic extraction was evaluated for extracting trace amounts of two agrochemical fungicides, vinclozolin and dicloran, in soil samples. Extraction was performed following two experimental approaches prior to the submission of the aqueous extracts to SPME-GC analysis. In the first approach, extraction involved sample homogenization with a water solution containing 5% (v/v) acetone and centrifugation prior to fiber extraction. In the second approach, the extraction of the fungicides from the soil samples was conducted using acetone as organic solvent which was then diluted with water to give a 5% (v/v) content. The pesticides were isolated with fused silica fiber coating with 85 μm polyacrylate. Parameters that affect both the extraction of the fungicides by the soil samples and the trapping of the analytes by the fiber were investigated and their impact on the SPME-GC-MS was studied. The procedures with respect to repeatability and limits of detection were evaluated by soil spiked with both analytes. Repeatability was between 5.6 and 14.2% and the limits of detection were 2-13 ng g⁻¹. The efficiency of acetone/SPME was generally better than that for water/SPME procedure showing good linearity (R²>0.99) with coefficient variations below 9%, recoveries higher than 91% and limits of detection between 2 and 3 ng g⁻¹. Finally, the recoveries obtained with acetone/SPME procedure were compared with the conventional liquid-liquid extraction using real soil samples. The acetone/SPME method was shown to be an inexpensive, fast and simple preparation method for the determination of target analytes at low nanogram per gram levels in soils.     

Optimisation of a headspace solid-phase microextraction with on-fiber derivatisation method for the direct determination of haloanisoles and halophenols in wine

A solid-phase microextraction (SPME) procedure for the determination of four haloanisoles (2,4,6-trichloroanisole, 2,3,4,6-tetrachloroanisole, pentachloroanisole and 2,4,6-tribromoanisole), as well as their precursor halophenols (2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol, pentachlorophenol and 2,4,6-tribromophenol), involved in the presence of cork taint in wine, was developed. Firstly, analytes were concentrated on a SPME fiber, and then halophenols were derivatised using N-methyl-N-trimethylsilyltrifluoroacetamide (MSTFA). The compounds were desorbed for 5 min in the gas chromatography injector port and then determined with an electron capture detector. The influence of different parameters on the efficiency of extraction (volume of sample, type of fibre coating and time) and derivatisation (time, temperature and volume of MSTFA) steps was evaluated. Polyacrylate (PA) was selected as the extraction fiber, optimised parameters for SPME were 10 ml of wine, temperature 70 degrees C and extraction time 60 min. The optimal conditions identified for the derivatisation step were temperature 25 degrees C, reagent volume 50 microl and extraction time 25 min. Under optimal conditions, the proposed method showed satisfactory linearity, precision and detection limits. The method was applied successfully to the analysis of red wine samples. To our knowledge, this is the first time that headspace (HS) SPME combined with on-fiber derivatisation has been applied to determine cork taint responsible compounds in wine.     

Preparation and application of solid-phase microextraction fiber based on molecularly imprinted polymer for determination of anabolic steroids in complicated samples

A relatively selective, chemically and physically robust SPME fiber was developed in a simple way with testosterone-imprinted polymer, and then directly coupled with gas chromatography-mass spectrometry (GC-MS) for selective extraction and analysis of anabolic steroids. The factors influencing polymerization (i.e., cross-linker, polymerization solvent, polymerization time) were optimized in detail and the polymer was characterized by scanning electron microscope, infrared spectrometer and thermogravimetric analyzer. Furthermore, the extraction performance of the MIP-coated SPME fibers such as extraction ability and selectivity was evaluated. Moreover, the interaction mode between target analytes and fiber coating was deducted. Finally, the method for extraction and determination of androsterone, stanolone, androstenedione and methyltestosterone by the homemade MIP-coated SPME fibers with GC-MS was obtained. It was applied to the simultaneous analysis of four anabolic steroids in the spiked human urine with the satisfactory recoveries.     

Application of solid-phase microextraction for determination of pyrethroids in groundwater using liquid chromatography with post-column photochemically induced fluorimetry derivatization and fluorescence detection

Solid-phase microextraction (SPME) is a rapid and simple analytical technique which uses coated fused-silica fibers to extract analytes from aqueous samples. This study develops a method of SPME analysis for seven pyrethroids, including fenpropathrin, lambda-cyhalothrin, deltamethrin, fenvalerate, permethrin, tau-fluvalinate and bifenthrin in groundwater samples using high performance liquid chromatography combined with post-column photochemically induced fluorimetry derivatization and fluorescence detection (SPME-LC-PIF-FD). To perform the SPME, a 60 microm polydimethylsiloxane/divinylbenzene (PDMS/DVB) fiber was used for the extraction of the pesticides from groundwater samples. The main factors affecting the SPME process, such as extraction time, stirring rate, extraction temperature, pH and the desorption process were studied. The use of photochemically induced fluorescence for detection improved sensitivity and selectivity. The limits of quantification (LOQs) obtained in the matrix, with respect to EURACHEM Guidance, varied between 0.03 and 0.075 microgL(-1). Relative recoveries ranged from 92 to 109% and relative standard deviations values ranged from 2 to 9%.     

Determination of major compounds in sweet wines by headspace solid-phase microextraction and gas chromatography

Headspace solid-phase microextraction (HS-SPME) was studied by high resolution gas chromatographic analysis of major compounds (ethyl acetate, methanol, 1-butanol, 2-butanol, 1-propanol, isobutanol, 2-methyl-1-butanol and 3-methyl-1-butanol) in sweet wines. Five different SPME fibres were tested and the influence of different factors such as temperature and time of desorption, extraction time, stirring, sample and vial volume, sugar and ethanol content were studied and optimized using model solutions. The SPME method was validated with the direct injection method. The proposed HS-SPME-GC method is an appropriate technique for the quantitative analysis of the mentioned analytes in real sweet wines.     

Neuro-genetic multioptimization of the determination of polychlorinated biphenyl congeners in human milk by headspace solid phase microextraction coupled to gas chromatography with electron capture detection

Polychlorinated biphenyls (PCB) can eventually contaminate breast milk, which is a serious issue to the newborn due to their high vulnerability. Solid phase microextraction (SPME) can be a very convenient technique for their isolation and pre-concentration prior chromatographic analysis. Here, a simultaneous multioptimization strategy based on a neuro-genetic approach was applied to a headspace SPME method for determination of 12 PCB in human milk. Gas chromatography with electron capture detection (ECD) was adopted for the separation and detection of the analytes. Experiments according to a Doehlert design were carried out with varied extraction time and temperature, media ionic strength and concentration of the methanol (co-solvent). To find the best model that simultaneously correlate all PCB peak areas and SPME extraction conditions, a multivariate calibration method based on a Bayesian Neural Network (BNN) was applied. The net output from the neural network was used as input in a genetic algorithm (GA) optimization operation (neuro-genetic approach). The GA pointed out that the best values of the overall SPME operational conditions were the saturation of the media with NaCl, extraction temperature of 95 °C, extraction time of 60 min and addition of 5% (v/v) methanol to the media. These optimized parameters resulted in the decrease of the detection limits and increase on the sensitivity for all tested analytes, showing that the use of neuro-genetic approach can be a promising way for optimization of SPME methods.     

Attachment of nickel hexacyanoferrates nanoparticles on carbon nanotubes: preparation, characterization and bioapplication

Anilinemethyltriethoxysilane (AMTEOS) was first used as precursor as well as selective stationary phase to prepare the sol-gel derived anilinemethyltriethoxysilane/polydimethylsiloxane (AMTEOS/PDMS) solid-phase microextraction (SPME) fibers. The novel SPME fiber exhibits high extraction efficiency, good thermal stability and long lifetime compared with commercial SPME coatings. In addition, the phenyl groups in the porous layer can exhibit π-π interactions with aromatic compounds, such as monocyclic aromatic hydrocarbons (MAHs) and polycyclic aromatic hydrocarbons (PAHs). Therefore, SPME using the AMTEOS/PDMS sol-gel fiber coupled with GC-FID was recommended as a sensitive and selective method towards the analysis of these compounds in environmental water samples. The optimal extraction conditions were investigated by adjusting extraction time, salt addition, extraction temperature, and desorption time. The method showed linearity between 2 and 4000 μg l⁻¹ for MAHs and 1 and 1000 μg l⁻¹ for PAHs. The limit of detection (LOD) was 0.6-3.8 μg l⁻¹for MAHs and 0.2-1.5 μg l⁻¹ for PAHs. The novel AMTEOS/PDMS fiber was applied to extract small amount of aromatic compounds in wastewater and river water respectively. The recovery of the method was acceptable for quantitative analysis.     

Comparison of simultaneous distillation extraction and solid-phase microextraction for the determination of volatile flavor components

Traditional simultaneous distillation extraction (SDE) and solid-phase microextraction (SPME) techniques were compared for their effectiveness in the extraction of volatile flavor compounds from various mustard paste samples. Each method was used to evaluate the responses of some analytes from real samples and calibration standards in order to provide sensitivity comparisons between the two techniques. Experimental results showed traditional SDE lacked the sensitivity needed to evaluate certain flavor volatiles, such as 1,2-propanediol. Dramatic improvements in the extraction ability of the SPME fibers over the traditional SDE method were noted. Different SPME fibers were investigated to determine the selectivity of the various fibers to the different flavor compounds present in the mustard paste samples. Parameters that might affect the SPME, such as the duration of absorption and desorption, temperature of extraction, and the polarity and structure of the fiber were investigated. Of the various fibers investigated, the PDMS–DVB fiber proved to be the most desirable for these analytes.     

Automated multiple solid phase micro extraction. An approach to enhance the limit of detection for the determination of pesticides in water

A method was developed to decrease the limit of detection (LOD) for pesticide residue analysis in water using multiple SPME. To enhance the absolute amount transferred to the GC column an enrichment step is integrated in the SPME/GC-analysis. A series of several extraction and desorption steps are performed and the analytes are trapped at the front of the cold GC column before the GC analysis is started. The parameters mainly influencing this enrichment are the equilibrium time, the slope of the adsorption time/peak area profile at its start, the number and the duration of the extraction steps. The role of these parameters was investigated.     

Automated multiple solid phase micro extraction. An approach to enhance the limit of detection for the determination of pesticides in water

A method was developed to decrease the limit of detection (LOD) for pesticide residue analysis in water using multiple SPME. To enhance the absolute amount transferred to the GC column an enrichment step is integrated in the SPME/GC-analysis. A series of several extraction and desorption steps are performed and the analytes are trapped at the front of the cold GC column before the GC analysis is started. The parameters mainly influencing this enrichment are the equilibrium time, the slope of the adsorption time/peak area profile at its start, the number and the duration of the extraction steps. The role of these parameters was investigated.     

Analysis of volatile contaminants in vegetable oils by headspace solid-phase microextraction with carboxen-based fibres

The headspace solid-phase microextraction (HS-SPME) efficiencies from vegetable oil of the recently available Carboxen-poly(dimethylsiloxane) (PDMS) and divinylbenzene-Carboxen-PDMS fibres were found to be much greater than those of the PDMS fibre for a number of volatile contaminants. Using these Carboxen-based fibres, the commonly used HS-SPME equilibration times for aqueous matrices of 30-45 min at room temperature for a number of halogenated and aromatic analytes with volatilities ranging from 1,1-dichloroethylene to hexachlorobenzene were found to be insufficient for the effective extraction of the less volatile analytes from vegetable oil. HS-SPME at 100 degrees C for 45 min, followed by rapid cooling to 0 degrees C with a 10 min continuing extraction, however, significantly increased the SPME efficiencies for the less volatile analytes. Spiking solutions were prepared in vegetable oil instead of methanol as the latter was found to displace analytes from the Carboxen material. Using either of the Carboxen-based fibres and SPME at 100 degrees C, all the target analytes could be determined at low or sub-microg kg(-1) with repeatability < or =10%, even though an equilibrium SPME of the less volatile analytes was not achieved.     

A highly thermal-resistant electrospun-based polyetherimide nanofibers coating for solid-phase microextraction

A high-temperature-resistant solid-phase microextraction (SPME) fiber was prepared based on polyetherimide (PEI) by the electrospinning method. The PEI polymeric solution was converted to nanofibers using high voltages and directly coated on a stainless steel SPME needle. The scanning electron microscopy images of PEI coating showed fibers with diameter range of 500–650 nm with a homogeneous and smooth surface morphology. The SPME nanofibers coating was optimized for PEI percentage, electrospinning voltage, and time. The extraction efficiency of the coating was investigated for headspace SPME of some environmentally important polycyclic aromatic hydrocarbons from aqueous samples followed by gas chromatography–mass spectrometry measurement. In addition, the important extraction parameters including extraction temperature, extraction time, ionic strength, as well as desorption temperature and time were investigated and optimized. The detection limits of the method under optimized conditions ranged from 1 to 5 ng L^?1 using time-scheduled selected ion monitoring mode. The relative standard deviations of the method were between 1.1 and 7.1 %, at a concentration level of 500 ng L^?1. The calibration curves of polycyclic aromatic hydrocarbons showed linearity in the range of 5–1000 ng L^?1. The developed method was successfully applied to real water samples and the relative recovery percentages obtained from the spiked water samples were from 84 to 98 % for all the selected analytes except for acenaphthene which was from 75 to 106 %.