Solid-phase Microextraction Efficiency Research Articles

Preparation of sulfonic acid functionalized covalent organic framework solid phase microextraction fibers and their application in the analysis of neurotransmitters in the mouse brain

Neurotransmitters (NTs) are essential for intercellular communication and primarily include monoamine, amino acid, and cholinergic NTs. These molecules play important roles in the body's stress response, motor coordination, neuronal communication, and homeostatic functions. Previous studies have shown that abnormal changes in NT levels are associated with various neurological disorders. Therefore, the development of accurate analytical methods for NT detection will enhance the current understanding on complex neuropathophysiology by providing functional knowledge and techniques for early diagnosis, thereby facilitating the development of new therapeutic options for the related diseases. The solid phase microextraction (SPME) technique combines sample preparation, separation, and enrichment in a single step and is minimally invasive, low cost, solvent free, and high throughput. SPME has been successfully applied to the in vivo analysis of target analytes in animal, human, and plant tissues. The coating material plays a significant role in the development of in vivo SPME methods and must meet various analytical requirements, including a suitable geometry for the SPME device, high extraction capacity, excellent selectivity, and wide extraction coverage for the target analytes. Covalent organic frameworks (COFs) are porous crystalline polymers constructed from organic framework units through strong covalent bonds; these materials are characterized with a low density, large specific surface area, permanent porosity, excellent chemical/thermal stability, and easy functionalization.In this study, a sulfonic acid-functionalized COF material (COF-SO3H) with good crystallinity, excellent chemical/thermal stability, strong hydrophobicity, a uniform mesoporous structure, and narrow pore size distribution was prepared using 2,4,6-triformylphloroglucinol and 1,4-diamino-2-nitrobenzene as monomers. Then, the COF-SO3H was coated onto the surface of stainless-steel fibers and used for in vivo enrichment of NTs. The structural properties of COF-SO3H were characterized using various techniques, such as scanning electron microscopy (SEM), Fourier transform-infrared spectroscopy (FT-IR), and X-ray diffraction (XRD), all of which showed that COF-SO3H had a good crystalline structure and uniform mesopore distribution with a specific surface area of 46.17 m2/g. Compared with the SPME fibers of HLB, C18, MCX, amino, and PXC columns, the prepared COF-SO3H fibers showed better extraction efficiency for the target NTs. Next, the factors affecting SPME efficiency were optimized. The optimal desorption solvent was formic acid-methanol-water (0.5∶49.5∶50, v/v/v), and the optimal extraction and desorption times were 15 min. A method for the in vivo analysis of NTs in the brains of mice was established by combining the COF-SO3H fibers with ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) under optimal conditions. The NTs were separated on an Acquity UPLC BEH-C18 analytical column (100 mm×2.1 mm, 1.7 μm) with 0.1% formic acid aqueous solution (A) and acetonitrile (B) as the mobile phases. The flow rate was set to 0.2 mL/min, and the gradient elution procedure was as follows: 0-4 min, 5%B-6%B; 4-7 min, 6%B-5%B; 7-11 min, 5%B. Under optimal conditions, the method showed good linearity (r2>0.99). The limits of quantification (S/N≥5) were in the range of 0.003-0.005 μg/mL and 3-5 μg/mL for monoamine and amino acid NTs, respectively, with RSDs of less than 20%. The method showed good precision (0.80%-9.70%) and accuracy (2.08%-17.72%), with absolute matrix effects in the range of 82.22%-117.92%. These values reflect the good purification and enrichment abilities of the proposed fibers for the target analytes. Finally, the established SPME method was combined with UPLC-MS/MS and successfully applied to quantify target NTs in the brains of mice. The proposed strategy provides a practical method for the in vivo detection and quantitative analysis of NTs and expands the applications of functionalized COF materials for the analysis of various targets.

Purge-assisted solid phase microextraction based on activated carbon as a new technique for determination of odorous compounds in drinking water samples

The purge and trap method is widely used to extract volatile organic compounds from aqueous samples, but this method is time-consuming and analytes are difficult to desorb. Compared to purge and trap, solid phase microextraction (SPME) can desorbs analytes easily and quickly by inserting the fiber into the injection site of a gas chromatograph. However, other studies have demonstrated that the purge and trap method has a lower detection limits than SPME. This research aims to improve the efficiency of SPME by coupling it with purging by N2, named purge assisted SPME or PSPME as a novel technique for determination and quantification of trace amounts of odorous compounds (geosmin and 2-methylisoborneol) from water samples. The results showed that the extraction efficiency of PSPME has increased more than five times compared to normal SPME. Also, the optimal extraction time has decreased from 30 min to about 10 min.

Solid phase microextraction of polycyclic aromatic hydrocarbons by using an etched stainless-steel fiber coated with a covalent organic framework.

A new covalent organic framework (COF) was synthesized by the amide coupling between 1,3,5-tris(4-aminophenyl)benzene and trimesoyl chloride at room temperature. The COF was applied as a steelfiber coating for the solid phase microextraction of polycyclic aromatic hydrocarbons (PAHs) from water samples. The effect of extraction time, salt concentration, and extraction temperature on the efficiency of SPME was optimized by a Box-Behnken design. The PAHs were quantified by gas chromatography with mass spectrometric detection. Figures of merit include (a) a wide linear range (typically from 0.2ngL-1 to 2μgL-1), (b) low limits of detection (0.29 to 0.94ngL-1 at S/N= 3), and (c) high enrichment factors (EFs; 819-2420). Density functional theory was employed to study the interaction between the COF cluster and the PAHs. The results demonstrated that the EFs increase with the enhancement of π stacking interaction. The repeatability (one fiber; n= 5) and reproducibility (fiber to fiber; n= 5), expressed as the relative standard deviations were in the range of 4.3%-8.4% and 8.5-11.0%, respectively. The recoveries of the PAHs from water samples spiked at levels of 20.0 and 100ngL-1 ranged from 79.0% to 105.0%. Graphical abstract A covalent organic framework prepared from1,3,5-tris(4-aminophenyl)benzene and trimesoyl chloride(TAPB-TMC-COF) was synthesized and employed as solid phase microextraction (SPME) fiber coating for the extraction of polycyclic aromatic hydrocarbons from water samples prior to gas chromatography (GC) - mass spectrometric (MS) detection.

Assessing bioaccessibility and bioavailability of chlorinated organophosphorus flame retardants in sediments

The distribution of chlorinated organophosphate flame retardants (OPFRs) in sediments has been well documented, but the study about their bioavailability remains lacking. This study investigated the applicability of solid phase microextraction (SPME) fiber and Tenax extraction to predict the bioavailability of two chlorinated OPFRs: tri(2-chloroisopropyl) phosphate and tri(1,3-dichloro-2-isopropyl) phosphate, in sediments. Our results showed that both SPME fiber and Tenax extracted concentrations correlated significantly with the measured concentrations in the aquatic worm (Lumbriculus variegatus). We also measured the Tenax extracted concentrations at 6 and 24 h, and a strong linear relationship between these two time durations was found. In addition, the 6-h Tenax extracted concentrations also significantly correlated with the SPME fiber extracted concentrations, and the Tenax extracted concentrations were much higher than the SPME fiber extracted concentrations. These results demonstrate the efficiency of SPME and Tenax extraction methods to predict the bioavailability of chlorinated OPFRs in sediments, and it was found that the Tenax extraction is more promising than the SPME extraction.

Ordered mesoporous carbon film as an effective solid-phase microextraction coating for determination of benzene series from aqueous media

The present work reports preparation of ordered mesoporous carbon (OMC) film supported on a graphite fiber as a new type of solid-phase microextraction (SPME) fiber for determination of benzene series from aqueous media. The strategy for the supported OMC film preparation was combined dip-coating technology with solvent evaporation-induced self-assembly (EISA) approach. A graphite fiber was immersed in an ethanol solution containing phenolic resin and Pluronic triblock copolymer. Upon solvent evaporation and subsequent pyrolysis under 700 °C, the phenolic resin and the surfactant self-assembled on the surface of the graphite fiber to form smooth OMC film. X-ray diffraction (XRD), transmission electron microscopy (TEM) and nitrogen isothermal adsorption results indicate that the resultant OMC film possesses well-ordered two dimensional hexagonal mesostructure with pore diameters of 4.5 nm and BET surfaces of 630 m2/g. Scanning electron microscopy (SEM) studies show the supported OMC film with thickness at 8.5 μm is continuous and defect-free. The SPME efficiency of the OMC fiber was evaluated by analysis of five benzene series (benzene, toluene, ethylbenzene, p-xylene and m-xylene) from water samples by gas chromatography-flame ionization detection (GC-FID). The analysis results indicate that the prepared OMC fiber has wide linear ranges (0.5–500 μg/L), low detection limits (0.01–0.05 μg/L) and good repeatabilities (4.0–5.8% for one fiber, 2.9–8.7% for fiber-to-fiber). Compared with commercial counterparts, the OMC fiber exhibits improved extraction efficiency for benzene series and PAHs.

A solid phase microextraction fiber coated with graphene–poly(ethylene glycol) composite for the extraction of volatile aromatic compounds from water samples

Poly(ethylene glycol)-grafted graphene (PEG-g-G) was prepared and used as the solid phase microextraction (SPME) fiber coating for the extraction of seven volatile aromatic compounds (VACs) from water samples followed by the determination with gas chromatography-flame ionization detection. The PEG-g-G coating was characterized by both the thermal gravimetric analysis and scanning electron microscopy. The results verified that the PEG was successfully grafted onto the surface of graphene and the coating had a highly porous structure. Several important experimental parameters that could influence the SPME efficiency were investigated and optimized. Under the optimized conditions, the limits of detection were in the range from 1.0 to 6.0 ng L(-1). The relative standard deviations for intraday and interday variations were in the range of 1.8-5.8% and 5.1-8.3%, and for fiber-to-fiber variations, were between 6.5 and 11.9%, respectively. The results indicated that the PEG-g-G fiber had the advantages of high extraction efficiency and good thermal stability and durability. It can be reused more than 200 times without a significant loss of extraction efficiency. The method was successfully applied to the analysis of seven VACs in tap, river and mineral water samples.

Determination of organochlorine pesticides in textiles using solid-phase microextraction with gas chromatography–mass spectrometry

Abstract A method based on solid-phase microextraction (SPME) and gas chromatography with mass spectrometry (GC/MS) for the determination of 10 organochlorine pesticides (OCPs) in ecological textiles was described. Commercially available SPME fibers, 100 μm PDMS, 85 μm PA, 65 μm PDMS–DVB, 75 μm CAR/PDMS and 30 μm PDMS were compared and 100 μm PDMS exhibited the best performance to the OCPs. Various parameters affecting the extraction efficiency of SPME were optimized, including extraction time, desorption time, extraction temperature, salinity and pH. The optimized conditions were 40 min extraction at room temperature, 2% NaCl content, pH 6.0, and 4.0 min desorption in GC injector port at 250 °C. Under the optimized conditions, the limits of detections ranged from 0.04 μg L− 1 (dieldrin) to 0.41 μg L− 1 (aldrin) and the RSDs were between 3.2% and 11.3%. The optimized method was then used to analyze 10 OCPs in textile samples, and good relative recoveries were obtained (from 70.0 to 112.6%). This study illustrated the potential applicability of SPME for routine analysis of OCPs in textiles.

Determination of distribution coefficients of polycyclic aromatic nitrogen heterocycles using solid-phase microextraction

The possibility and the efficiency of solid-phase microextraction (SPME) for determination of distribution coefficients of polycyclic aromatic nitrogen heterocycles (PANHs) in aqueous samples are presented in this study. Influence of sample extraction conditions, extraction time, stirring rate, pH, salinity and temperature were tested to optimize extraction efficiency. Three types of fibre sorbent layers, PDMS, PDMS/DVB and PA, were tested and fibre/water distribution coefficients, Kf s , were calculated. The extraction efficiency for PANHs increased in the order PDMS < PA < PDMS/DVB. Values of log Kfs ranged from 0.2 to 2.7 for PDMS, from 0.4 to 3.6 for PA and from 1.4 to 4.4 for PDMS/DVB. The values of log Kfs were correlated with octanol/water distribution coefficients log Kow . The relationship between log Kfs and log Kow shows linear response with regression coefficient in the range of 0.985 and 0.997.

Rapid and simultaneous determination of twenty amino acids in complex biological and food samples by solid-phase microextraction and gas chromatography–mass spectrometry with the aid of experimental design after ethyl chloroformate derivatization

Amino acids play a vital role as intermediates in many important metabolic pathways such as the biosynthesis of nucleotides, vitamins and secondary metabolites. A sensitive and rapid analytical method has been proposed for the first time for the simultaneous determination of twenty amino acids using solid-phase microextraction (SPME). The protein samples were hydrolyzed by 6M HCl under microwave radiation for 120min. Then the amino acids were derivatized by ethyl chloroformate (ECF) and the ethoxy carbonyl ethyl esters of amino acids formed were extracted using SPME by direct immersion. Finally the extracted analytes on the SPME fiber were desorbed at 260°C and analyzed by gas chromatography–mass spectrometer (GC–MS) in electron ionization mode. Factors which affect the SPME efficiency were screened by Plackett–Burmann design; most significant factors were optimized with response surface methodology. The optimum conditions for SPME are as follows: pH of 1.7, ionic strength of 733mg, extraction time of 30min and fiber of divinyl benzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS). The recovery of all the amino acids was found to be in the range of 89.17–100.98%. The limit of detection (LOD) of all derivatized amino acids in urine, hair and soybean was found to be in the range of 0.20–7.52μgL−1, 0.21–8.40μgL−1 and 0.18–5.62μgL−1, respectively. Finally, the proposed technique was successfully applied for the determination of amino acids in complex biological (hair, urine) and food samples (soybean). The method can find wide applications in the routine analysis of amino acids in any biological as well as food samples.

Role of precursors and coating polymers in sol–gel chemistry toward enhanced selectivity and efficiency in solid phase microextraction

To evaluate the selectivity and efficiency of solid phase microextraction (SPME) fiber coatings, synthesized by sol–gel technology, roles of precursors and coating polymers were extensively investigated. An on-line combination of capillary microextraction (CME) technique and high performance liquid chromatography (HPLC) was set up to perform the investigation. Ten different fiber coatings were synthesized in which five of them contained only the precursor and the rests were prepared using both the precursor and coating polymer. All the coatings were chemically bonded to the inner surface of copper tubes, intended to be used as the CME device and already functionalized by self-assembly monolayers of 3-(mercaptopropyl)trimethoxysilane (3MPTMOS). The selected precursors included tetramethoxysilane (TMOS), 3-(trimethoxysilyl)propylmethacrylate (TMSPMA), 3-(triethoxysilyl)-propylamine (TMSPA), 3MPTMOS, [3-(2,3-epoxypropoxy)-propyl]-trimethoxysilane (EPPTMOS) while poly(ethyleneglycol) (PEG) was chosen as the coating polymer. The effects of different precursors on the extraction efficiency and selectivity, was studied by selecting a list of compounds ranging from non-polar to polar ones, i.e. polycyclic aromatic hydrocarbon, herbicides, estrogens and triazines. The results from CME–HPLC analysis revealed that there is no significant difference between precursors, except TMOS, in which has the lowest extraction efficiency. Most of the selected precursors have rather similar interactions toward the selected analytes which include Van der Walls, dipole–dipole and hydrogen bond while TMOS has only dipole–dipole interaction and therefore the least efficiency. TMOS is silica but the other sorbents are organically modified silica (ORMOSIL). Our investigation revealed that it is rather impossible to prepare a selective coating using conventional sol–gel methodologies. The comparison study performed among the fiber coatings contained only a precursor and those synthesized by a precursor along with coating polymer proved that the extraction efficiency obtained for all coatings are the same. This is an indication that by selecting the appropriate precursor there is no need to use any coating polymer. In overall, a fiber coating in sol–gel process could be synthesize with no coating polymer which leads to faster, easier, cheaper and more controllable synthesis.

Enantioselective analysis of mirtazapine, demethylmirtazapine and 8‐hydroxy mirtazapine in human urine after solid‐phase microextraction

A selective and reproducible off-line solid-phase microextraction procedure was developed for the simultaneous enantioselective determination of mirtazapine (MRT), demethylmirtazapine and 8-hydroxymirtazapine in human urine. CE was used for optimization of the extraction procedure whereas LC-MS was used for method validation and application. The influence of important factors in the solid-phase microextraction efficiency is discussed, such as the fiber coatings, extraction time, pH, ionic strength, temperature and desorption time. Before extraction, human urine samples were submitted to enzymatic hydrolysis at 37 degrees C for 16 h. Then, the enzyme was precipitated with trichloroacetic acid and the pH was adjusted to 8 with 1 mol/L pH 11 phosphate buffer solution. In the extraction, the analytes were transferred from the aqueous solution to the polydimethylsiloxane-divinylbenzene fiber coating and then desorbed in methanol. The mean recoveries were 5.4, 1.7 and 1.0% for MRT, demethylmirtazapine and 8-hydroxymirtazapine enantiomers, respectively. The method was linear over the concentration range of 62-1250 ng/mL. The within-day and between-day assay precision and accuracy were lower than 15%. The method was successfully employed in a preliminary cumulative urinary excretion study after administration of racemic MRT to a healthy volunteer.

Single-walled carbon nanotubes as solid-phase microextraction adsorbent for the determination of low-level concentrations of butyltin compounds in seawater

Carbon nanotubes are a kind of new carbon-based nanomaterials, which have drawn great attention in many application fields. The potential of single-walled carbon nanotubes (SWCNTs) as solid-phase microextraction (SPME) adsorbent for the preconcentration of environmental pollutants has been investigated in recent years. In the present study, the feasibility of SWCNTs as SPME adsorbent for the determination of monobutyltin, dibutyltin and tributyltin in seawater samples was studied. To achieve this aim, the potential factors affecting the SPME efficiency, including extraction time, extraction temperature, desorption time, desorption temperature, and salinity were optimized. The developed method showed good performance according to the ICH (International Conference on Harmonization of Technical Requirements for Analytical Methods) criteria. The acquired calibration curves were linear ( r ≥ 0.992) over the concentration range from ≤12 to 2000 ng L −1. For all of the analytes, the limit of detection at signal-to-noise ratio of 3 was below 5 ng L −1. Furthermore, in comparison with the commercial carboxen/polydimethylsiloxane fiber, the developed SWCNT fiber showed better thermal stability (over 350 °C) and longer life span (over 150 times). The application of the proposed method in environmental analyses was shown by analyzing seawater samples from the harbors on the Persian Gulf for butyltin residues. Some of the butyltins were detected in the analyzed samples. Results of the present study demonstrate the feasibility of the SWCNTs as SPME adsorbent for the determination of butyltins in seawater samples.

Solid-phase microextraction using poly(pyrrole) film and liquid chromatography with UV detection for analysis of antidepressants in plasma samples

Poly(pyrrole) (PPY) coating was prepared on a stainless-steel (SS) wire for solid-phase microextraction (SPME) by electrochemical deposition (cyclic voltammetric). The PPY was evaluated by analyzing new-generation antidepressants (mirtazapine, citalopram, paroxetine, duloxetine, fluoxetine, and sertraline) in plasma sample by SPME and liquid chromatography with UV detection (LC-UV). The effect of electrolyte solution (lithium perchlorate or tetrabutylammonium perchlorate) and the number of cycles (50, 100 or 200) applied during the polymerization process on the SPME performance was evaluated. Important factors in the optimization of SPME efficiency such as extraction time, temperature, pH, influence of plasma proteins on sorption mechanisms, and desorption conditions are discussed. The SPME–PPY/LC method showed to be linear in concentrations ranging from the limit of quantification (LOQ) to 1200 ng mL −1. The LOQ values range from 16 to 25 ng mL −1. The inter-day precision of the SPME–PPY/LC method presented coefficient of variation (CV) lower than 15%. Based on analytical validation results, the SPME–PPY/LC methodology showed to be adequate for antidepressant analysis, from therapeutic to toxic levels. In order to evaluate the proposed method for clinical use, the SPME–PPY/LC method was applied to the analysis of plasma samples from elderly depressed patients.

Solid-phase microextraction and gas chromatography-mass spectrometry for the determination of polycyclic aromatic hydrocarbons in environmental solid matrices.

A solid-phase microextraction (SPME) and gas chromatography-mass spectrometry method for determining polycyclic aromatic hydrocarbons (PAHs) in environmental solid matrices is developed. Investigated matrices include seaweed (Undaria pinnatifida and Himanthalia elongata), humic substances (isolated from a wetland out-flow and purchased from Aldrich), and soil. Optimal conditions for a good SPME efficiency of 16 hydrocarbon compounds are obtained using a 100- micro m polydimethylsiloxane fiber directly immersed in aqueous carrier medium. The method is remarkable for presenting short extraction times and considerably high sensitivities. The SPME results obtained by using internal calibration give the total analyte concentration based on the identical partitioning behavior of native and spiked pollutants. The detection limits range from 0.001 to 0.1 mg of PAH per kilogram of dry matrix. SPME external calibration provides information regarding freely dissolved analytes. The detection limits range from 0.001 to 0.05 micro g of PAH per liter of carrier medium. The SPME with external calibration procedure can be applied to measure free concentrations of a target compound spiked into a carrier medium and onto a matrix. Based on a comparison of results obtained for the two samples, the partitioning of the target analyte between the matrix and the carrier medium is calculated.

Solventless Sample Preparation for Pesticides Analysis in Environmental Water Samples Using Solid‐Phase Microextraction‐High Resolution Gas Chromatography/Mass Spectrometry (SPME‐HRGC/MS)

Solid‐phase micro‐extraction (SPME) coupled on line with high resolution gas chromatography and mass spectrometric detection is described for the analysis of pesticides in environmental water samples. Experiments were performed in order to optimize the SPME extraction conditions for selected pesticides including tiomethon, trichorfon, dimethoate, diazinon, malathion, dicofol, methidathion, ethion, bromopropylate and pyrazophos from spiked water solutions. To enhance the SPME efficiency, experimental conditions including the fiber composition, stirring rate, temperature, adsorption time, desorption time and salt concentration were optimized. After validation, the SPME‐GC/MS methodology was applied to real‐world environmental water samples.

Solid phase micro-extraction (SPME) fibre performance in turbid aqueous samples

The performance of solid phase microextraction (SPME) fibres was assessed in river water samples containing suspended solids. The effects of repeated immersion and the influence of variable solids loadings were considered for a soluble (phenol) and moderately hydrophobic organic contaminant (1,2-dimethylnaphthalene). For 1,2-dimethylnaphthalene the extractive efficiency of fibres declined progressively with repeated immersion in solutions with high solids levels (1g l −1) and with increased suspended solids concentrations. However, for phenol there was no decrease in extractive efficiency with increased solids concentrations. Results suggest that SPME efficiency is not likely to be significantly reduced in typical natural waters, or effluent samples with solids concentrations concentrations <1 g l −1.

Derivatization/Solid-Phase Microextraction: New Approach to Polar Analytes

Trace analysis of fatty acids in water and/or air was enhanced by coupling solid-phase microextraction (SPME) with derivatization of the target analytes to less polar and more volatile species prior to GC analysis. Derivatization was performed in three ways: in the sample matrix, in the SPME fiber coating, and in the GC injector port. Derivatization converts polar analytes into less polar analogues, therefore increasing their coating/water or coating/gas partition coefficients and improving SPME efficiency and method sensitivity. Derivatization changes analytes with low volatilities into more volatile derivatives, thus improving their GC separations, detection, and quantitation. Pentafluorobenzyl bromide and (pentafluorophenyl)diazoethane (PFPDE) were used to derivatize short-chain fatty acids directly in sample matrices for selective and sensitive ECD detection. Diazomethane and pyrenyldiazomethane (PDAM) were used for effective in-fiber derivatization of long-chain and short-chain fatty acids, respectively, to increase their detectability. Tetramethylammonium hydroxide and tetramethylammonium hydrogen sulfate were employed to convert long-chain fatty acids into their volatile methyl esters via in-injector derivatization, for adequate and convenient GC analysis. For aqueous sample analysis, all six reagents were employed. The limits of detection (LODs) for short-chain fatty acids were in low nanogram per milliliter to the high picogram per milliliter levels. For air sample analysis, PDAM and PFPDE were employed. The LODs for short-chain fatty acids using both PFPDE and PDAM were in femtogram per milliliter to low picogram per milliliter levels. The LODs with derivatization/SPME for the analysis of short-chain fatty acids were 1−4 orders of magnitude lower than direct SPME without derivatization, therefore improving the sensitivity of SPME technique significantly.

Analysis of pesticides in environmental water samples by solid-phase micro-extraction—high-performance liquid chromatography

Solid-phase micro-extraction (SPME) followed by high-performance liquid chromatography (LC) has been applied to analyze pesticides in water samples. A device interfaces SPME to the LC injection process by solvent extracting analytes from the fiber and then introducing the solvent into the LC injector. LC analysis with UV detection was performed first with a conventional column (4.6 mm I.D.). To enhance efficiency of SPME, three extraction conditions, stirring, temperature and salt concentration, were optimized. Subsequently, semi-microcolumn LC (1.5 mm I.D.) was evaluated for this method, giving lower detection limits and less solvent consumption. Detection limits were within Japanese regulatory limits for drinking water. The SPME-LC method was applied to real-world environmental water samples.

Determination of 4-nonylphenol—part 2: Orthogonal array design as a chemometric method for the solid-phase microextraction of 4-nonylphenol in water

Orthogonal array design (OAD) using two-level OA8(27) matrix was employed for the optimization of solid-phase microextraction (SPME) conditions for the determination of 4-nonylphenol (4-NP) in water. The parameters under consideration for the optimization of SPME conditions include: injector port temperature, initial oven temperature, desorption time, and pH. The effect of dissolved humic substances on the extraction efficiency of SPME for the determination of 4-NP was also investigated. The method is capable of parts per billion detection limit with a %RSD of 6.5%. Thus, the SPME approach is suitable for analytical determination of 4-NP in environmental water samples compared to conventional liquid-liquid extraction (LLE) technique. © 1996 John Wiley & Sons, Inc.