Solid-phase Extraction Membranes Research Articles

Room-temperature fabrication of fluorinated covalent organic polymer @ Attapulgite composite for in-syringe membrane solid-phase extraction and analysis of domoic acid in aquatic products

A novel fluorinated covalent organic polymer @ attapulgite composite (F-COP@ATP) was prepared at room temperature for in-syringe membrane solid-phase extraction (SM-SPE) of domoic acid (DA) in aquatic products. Natural ore ATP has the advantages of low cost, good mechanical strength and abundant hydroxyl group on its surface, and in-situ modified F-COP layer can provide abundant adsorption sites. F-COP@ATP combining the advantages of F-COP and ATP, becomes an ideal adsorbent for DA extracting. Moreover, a high-throughput sample preparation strategy was carried out by using the F-COP@ATP membrane as syringe filter and assembling syringes with a ten-channel injection pump. In addition, the experimental factors were optimized, such as pH of extract, amount of adsorbent, velocity of extraction and desorption, type and volume of desorption solvent. The DA analytical method was established by SM-SPE-HPLC/tandem mass spectrometry. The method had a wide linear range with low limit of detection (0.344 ng/kg) and low limit of quantification (1.14 ng/kg). F-COP@ATP membrane can be reused more than five times. The method realized the analysis of DA in scallop and razor clam samples, which shows its application prospect in practical analysis. This study provided an efficient, low-energy and mild idea for preparing other reusable natural mineral ATP-based composite materials for separation and enrichment, which reduces the experimental cost and is closer to environmental protection and green chemistry to a certain extent.

Preparation of MIL-101(Cr)–NH2@TAPB-DVA-COF based membrane solid-phase extraction for efficient enrichment and sensitive determination of trace aromatic disinfection by-products in juice drinks

Aromatic disinfection by-products (DBPs) have garnered considerable interest in recent years for their potential carcinogenicity. However, efficient separation and enrichment of DBPs in complex samples is a challenge due to the extremely low content of aromatic DBPs and the complexity of sample matrices. In this study, a MIL-101(Cr)–NH2@TAPB-DVA-COF hybrid material was prepared as the enrichment medium of membrane solid-phase extraction (M-SPE) to efficiently determine trace emerging aromatic DBPs. This medium exhibited excellent enrichment capacity and selectivity for aromatic DBPs because of the strong hydrogen bonding, π-π stacking and hydrophobic interactions. An efficient analytical method for five aromatic DBPs in juice drinks was successfully established by use of this hybrid material as the enrichment medium for M-SPE in combination with liquid chromatography tandem mass spectrometry (LC-MS/MS). The limits of detection of the established method were from 0.50 to 3.00 ng/L. Moreover, the method had been successfully used in real juice drinks to determine trace five aromatic DBPs with the spiked recoveries ranging from 84.1% to 125%. The method possessed high analytical sensitivity and accuracy for these five aromatic DBPs in juice drinks with the aid of the efficient M-SPE technology proposed.

Preparation of imidazole-modified paper membrane for selective extraction of gallic acid and its structural and functional analogues from Pomegranate Peel.

In the search for pharmaceutically active compounds from natural products, it is crucial and challenging to develop separation methods that target not only structurally similar compounds but also a class of compounds with desired pharmaceutical functions. To achieve both structure-oriented and function-oriented selectivity, the choice of functional monomers with broad interactions or even biomimetic roles towards targeted compounds is essential. In this work, an imidazole (IM)-functionalized paper membrane was synthesized to realize selectivity. The IM was selected based on its capability to provide multiple interactions, participation in several bioprocesses, and experimental verification of adsorption performance. Using gallic acid as a representative component of Pomegranate Peel, the preparation conditions and extraction parameters were systematically investigated. The optimal membrane solid-phase extraction (MSPE) method allowed for enrichment of gallic acid from the complex matrix of Pomegranate Peel, enabling facile quantitative analysis with a limit of detection (LOD) of 0.1 ng mL-1. Furthermore, with the aid of cheminformatics, the extracted compounds were found to be similar in both their structures and pharmaceutical functions. This work offers a novel approach to preparing a readily synthesized extraction membrane capable of isolating compounds with similar structures and pharmaceutical effects, and provides an MSPE-based analytical method for natural products.

Preparation of COPs Mixed Matrix Membrane for Sensitive Determination of Six Sulfonamides in Human Urine.

In this study, TpDMB-COPs, a specific class of covalent organic polymers (COPs), was synthesized using Schiff-base chemistry and incorporated into a polyvinylidene fluoride (PVDF) polymer for the first time to prepare COPs mixed matrix membranes (TpDMB-COPs-MMM). A membrane solid-phase extraction (ME) method based on the TpDMB-COPs-MMM was developed to extract trace levels of six sulfonamides from human urine identified by high-performance liquid chromatography (HPLC). The key factors affecting the extraction efficiency were investigated. Under the optimum conditions, the proposed method demonstrated an excellent linear relationship in the range of 3.5-25 ng/mL (r2 ≥ 0.9991), with the low limits of detection (LOD) between 1.25 ng/mL and 2.50 ng/mL and the limit of quantification (LOQ) between 3.50 ng/mL and 7.00 ng/mL. Intra-day and inter-day accuracies were below 5.0%. The method's accuracy was assessed by recovery experiments using human urine spiked at three levels (7-14 ng/mL, 10-15 ng/mL, and 16-20 ng/mL). The recoveries ranged from 87.4 to 112.2% with relative standard deviations (RSD) ≤ 8.7%, confirming the applicability of the proposed method. The developed ME method based on TpDMB-COPs-MMM offered advantages, including simple operation, superior extraction affinity, excellent recycling performance, and easy removal and separation from the solution. The prepared TpDMB-COPs-MMM was demonstrated to be a promising adsorbent for ME in the pre-concentration of trace organic compounds from complex matrices, expanding the application of COPs and providing references for other porous materials in sample pre-treatment.

Calix[4]arene-based covalent organic frameworks with host-guest recognition for selective adsorption of six per- and polyfluoroalkyl substances in food followed by UHPLC-MS/MS detection

Long-term ingestion or exposure to food contaminated with per- and polyfluoroalkyl substances (PFASs) may cause potential harm to human health. Due to the low contents of PFASs in complex food matrices, it is of great significance to develop adsorbents with excellent properties to enrich PFASs before analysis. Herein, calix[4]arene (CX4) was used as building block to prepare ordered crystalline covalent organic frameworks (COFs). The perfect combination of the host-guest recognition ability of CX4 and the porosity of COFs makes the CX4-COFs selective and high adsorption capacity for linear molecular PFASs (261–1055 mg/g). The adsorption behavior and mechanism were verified by isotherm adsorption experiments and simulation calculations. The CX4-COFs were then used as adsorbents for membrane solid-phase extraction (M-SPE), combined with ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) to determine PFASs in food. The method has low detection limits (0.11–0.28 ng/kg) and good precision (1.3%−9.8%), and has been successfully applied to the simultaneous enrichment and determination of six PFASs in fish, shrimp and shellfish. Satisfactory recoveries (79.9%−118%) were obtained. This study provides a new strategy for preparing CX4-COFs containing macrocyclic molecules with different morphologies and expands the application of COFs as attractive enrichment media for sample pretreatment.

Fluorescent sensor based on solid-phase extraction with negligible depletion: A proof-of-concept study with amines as analytes

This paper describes the development and proof-of-concept testing of an easy-to-use trace analysis technique, namely F-SPE, by coupling fluorescent sensor with solid phase extraction (SPE). F-SPE is a two-step methodology that concentrates an analyte from a liquid sample onto a fluorophore-modified membrane and measures the amount of analyte from the extent the extracted analyte quenches the emission of the fluorophore. By applying the principle of negligible depletion (ND) intrinsic to SPE, the procedure of F-SPE for analyzing a sample can be markedly simplified while maintaining the ability to detect analytes at low limits of detection (LOD). The merits of this approach are demonstrated by impregnating a SPE membrane with a perylene diimide (PDI) fluorophore, N,N′-di(nonyldecyl)-perylene-3,4,9,10-tetracarboxylic diimide (C9/9-PDI), for the low-level detection of organic amines (e.g., aniline) and amine-containing drugs (e.g., Kanamycin). The sensing mechanism is based on the donor-acceptor quenching of PDI by amines, which, when coupled with the concentrative nature of SPE, yields LODs for aniline and Kanamycin of 67 nM (∼6 ppb) and 32 nM (∼16 ppb), respectively.

A membrane solid-phase extraction method based on MIL-53-mixed-matrix membrane for the determination of estrogens and parabens: Polyvinylidene difluoride membrane versus polystyrene-block-polybutadiene membrane.

In this work, MIL-53(Al), as an inorganic "filler" component, was embedded in polyvinylidene difluoride (PVDF) and polystyrene-block-polybutadiene (SBS) matrices to prepare two mixed-matrix membranes (MMMs), using a simpler method than that previously reported. The PVDF and SBS membranes retained much of the properties of PVDF, SBS, and native MIL-53(Al). The prepared MMMs were then placed in a vortex-stirred sample solution to develop a membrane solid-phase extraction method to extract estrogens and parabens, which were determined by high-performance liquid chromatography with fluorescence detection. The extraction efficiencies of the two membranes were compared, with the PVDF membrane exhibiting superior performance. In addition, the PVDF membrane was more freestanding and flexible, and its preparation method was also more facile and simple. The extraction conditions were optimized, and the analytical method showed low limits of detection (0.005-0.18 ng/mL), good linearity, and high accuracy, with recoveries ranging from 90.7% to 102.5%. As a result, this membrane solid-phase extraction method indicated its potential for application in aqueous sample pretreatment. For metal-organic framework-based MMM used in this method, in addition to being durable, freestanding, mechanically stable, and possessing a large area, it should also exhibit high metal-organic framework incorporation, good flexibility, and appropriate thickness and weight.

Esterified-sawdust decorated with AgNPs as solid-phase extraction membranes for enrichment and high-sensitivity detection of polychlorinated biphenyls

Polychlorinated biphenyls (PCBs) are a class of persistent organic pollutants, which cause serious harm to human health and ecological environment. Thus, a low-cost membrane was developed for highly effective removal and rapid surface-enhanced Raman scattering (SERS) detection of PCBs by filling esterified-sawdust (CA-SD) modified with silver nanoparticles (AgNPs) into solid phase extraction (SPE) column. SD was first modified by an esterification cross-linking strategy and then AgNPs were anchored on the CA-SD to prepare highly sensitive and reproducible SERS substrates (AgNPs/CA-SD). Due to the contraction of the surface area of the CA-SD caused by drying, the gap between the AgNPs could be reduced, thereby generating a large number of hot spots and driving more target molecules into them to obtain the enhanced SERS signals. The AgNPs/CA-SD-based SPE membrane showed excellent SERS activity with an enhancement factor of 5.98 × 108 for the R6G analysis. The proposed SERS-active SPE membrane with functionalization of mercapto-β-cyclodextrin was further developed for the determination of PCB-77 and PCB-1 with the LODs of 1.43 × 10−9 M and 2.12 × 10−8 M, respectively. In addition, each PCB in the mixed sample could be quickly distinguished based on the characteristic peaks. The current research exhibits great potential for the simultaneous detection of multiple environmental contaminants and can meet the needs of on-site emergency detection.

Ultrasensitive SERS detection of exhaled biomarkers of lung cancer using a multifunctional solid phase extraction membrane.

The construction and clinical application of a surface-enhanced Raman scattering (SERS) platform for the early diagnosis of lung cancer could improve the survival rate of patients and would be of great significance. Nevertheless, a sensitive and reusable method for the detection of aldehydes, as biomarkers of lung cancer, in exhaled breath is still an enormous challenge. Aldehydes generally have a low cross section in Raman scattering and have a weak specific affinity to plasmonic nanoparticle surfaces, meaning that sensing them at low concentrations is incredibly difficult. Herein, an ultrasensitive SERS strategy, that can be recycled for further use, for the detection of lung cancer biomarkers in the form of aldehydes was realized by fabrication of a multifunctional Ag NPs@ZIF-67/g-C3N4 solid phase extraction (SPE) membrane. Based on the change in the vibrational fingerprints of 4-ATP before and after reaction with the aldehydes, the SPE membrane was successfully used for the ultrasensitive detection of aldehydes with a detection limit of 1.35 nM. The excellent SERS performance was attributed to the synergistic effect of the densely and closely distributed Ag NPs (providing SERS "hot spots"), ZIF-67 (concentrating the analyte molecules) and g-C3N4 (forming a membrane to prolong the contact time between the aldehydes and the substrate). In addition, recycling of the SPE membrane was achieved by utilizing the self-cleaning ability of the Ag NPs@ZIF-67/g-C3N4 membrane originating from the photocatalytic properties of g-C3N4. The proposed SERS membrane was easy to operate, rapid and portable, thus providing a potential tool for a point-of-care test in clinical and diagnostic practice.

Rapid detection of sulfamethoxazole in plasma and food samples with in-syringe membrane SPE coupled with solid-phase fluorescence spectrometry

In this work, in-syringe membrane solid-phase extraction (MSPE) device was fabricated for the on-site sampling of sulfamethoxazole (SMX) in food samples followed by solid-phase fluorescence spectra analysis. The samples and fluorescamine (FA) were added to a syringe for derivation. Then, the derivative of SMX was extracted by a membrane in the syringe SPE device. Subsequently, the derivative on the membrane was measured immediately without additional elution procedure. The method was successfully applied in plasma, milk, and egg samples for the trace SMX detection, with the recovery of 98%–102%, RSDs from 1% to 6%. Compared with liquid chromatography, direct detection of the concentrated analyte significantly improved the sensitivity. Moreover, fluorescamine made it unnecessary to separate SMX from the interference. Consequently, it was a time-saving, low-cost, and easy-operation method, which demonstrated the potential of in-syringe SPE as a promising candidate for on-site analysis.

Determination of polychlorinated biphenyls in water by stable isotope dilution through automatic solid-phase extraction membrane coupled to gas chromatography-mass spectrometry

The method for analyzing of 20 polychlorinated biphenyls(PCBs) in water by stable isotope internal standard-automatic solid-phase extraction membrane(auto SPEM) coupled to gas chromatography-mass spectrometer(GC-MS) was established, and applied to the analysis of trace PCBs in water samples. The sample backgrounds of bottled mineral water production in Fuzhou(groundwater), inland water in Fuzhou university city(surface water), tap water(pipe tip water) and stream water in Xiyuan Gong(water source of life) were analyzed by GC-MS. Surrogate solution(SS)internal standards including ~(13)C_(12 )PCBs stable isotope was used for quantification. The method was confirmed by calculating recovery rate(RR) and relative standard deviation(RSD) of spiked water samples(20, 40 and 80 ng/L, n=7). And recovery rates of SS were used to evaluate the effect of the pretreatment. And the method was used to determine PCBs of a total of 17 cross-sectiona river water in minjiang river tributaries upstream to the downstream estuary. The method detection limits(MDL) were 1. 9-6. 6 ng/L, and RRs were 70. 9%-127%, and RSDs were 0. 5%-13%. The RRs of SS were 40%-90%. Positive sample was not detected. The method of auto SPEM is less solvent, more automatic than traditional manual SPE. And the method is more accurate and reliable by stable isotope internal standard coupled to GC-MS. Therefore, it is useful for the trace PCBs determination of waters.

Research on the distribution of neonicotinoid and fipronil pollution in the Yangtze River by high-performance liquid chromatography.

Neonicotinoid and fipronil insecticides have been consumed worldwide, particularly in China. There is growing interest in the environmental research community about the occurrence, sources, and risks of neonicotinoids and fipronil. A new method based on high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) and disc solid phase extraction (SPE) techniques were developed for the determination of neonicotinoids and fipronil in seawater in this research. The effects of the styrene divinyl benzene-reverse phase sulfonated (SDB-RPS) membrane-based solid phase extraction optimization process and the HPLC separation parameters on the detection results of the target compounds were studied. Under the optimized conditions, the detection limit of this method for 12 target compounds ranged from 0.05 ng L-1 to 0.50 ng L-1 and absolute recovery was achieved from 58.9-106.5%. The results proved that this method can effectively detect neonicotinoid and fipronil pesticides in seawater. At the same time, dinotefuran, nitenpyram, thiamethoxam, imidacloprid, thiacloprid, fipronil and its metabolites were found in seawater samples from the Yangtze River Estuary and the adjacent sea area. Among them, the total concentration of neonicotinoid insecticides ranged from ND-12.45 ng L-1 and the average total concentration was 3.5 ng L-1; the total concentration of fipronil and its metabolites ranged from ND-2.45 ng L-1, and the average total concentration was 0.79 ng L-1. The results showed that there was contamination of neonicotinoids and fipronil in the Yangtze River Estuary and its adjacent area.

Octadecylsilyl-bonded silica based novel solid phase extraction membranes

Octadecylsilyl-bonded silica based novel solid phase extraction membranes were fabricated by non-solvent vapor induced phase separation method for the first time, and employed for extraction trace phenol as a model. The effects of membrane fabrication conditions and extraction parameters on the recoveries were explored. Under the optimized fabrication conditions, the extraction recovery of phenol (0.02 mg/L, 100 mL) attains 100% with enrichment factor of 10. The spike recovery of real water samples reaches 97.67%–99.40% with standard deviation of 1.16%–1.42%, demonstrating great potential in solid phase extraction.

Determination of four main components of gentamicin in animal tissues after solid-phase extraction by high-performance liquid chromatography/tandem mass spectrometry.

An analytical method for gentamicin in animal tissues was developed and validated. An alkaline mobile phase with an HPH C8 column was selected so that all the four gentamicin components were retained and eluted without using fluorinated ion-pairing reagents. The method is sufficiently sensitive and highly selective, using a strong cation-exchange solid-phase extraction cartridge (PCX) to clean up the samples. Different types of solid-phase extraction columns and membranes were considered to obtain a high recovery. The method was validated on spiking samples, recovery, inter- and intra-assay variation, to ensure its accuracy and precision. The LOQ (S/N ≥ 10) for gentamicin in goat meat, liver, kidney and adipose tissue was 25, 50, 30 and 30 ng/g, respectively; the LOD (S/N ≥ 3) was 5, 10, 10 and 10 ng/g, respectively. The recoveries were between 88% and 106%. The method in all animal tissues was calibrated from 10 to 1000 μg/L in the matrix-assisted standard solution. The novelty of this method is that the commonly used fluorinated ion-pairing reagent was not used in the mobile phase in our analysis, greatly reducing the contamination of the ESI source in negative mode. Moreover, the four gentamicin components were clearly separated via chromatographic separation.

Highly reproducible solid-phase extraction membrane for removal and surface-enhanced Raman scattering detection of antibiotics

A disposable solid-phase extraction (SPE) membrane was developed for rapid removal and sensitive surface-enhanced Raman scattering (SERS) detection of antibiotics in water samples. The membrane was fabricated on commercially available SPE column by filtration of the activated carbon modified with silver nanoparticles (Ag NPs/AC). The prepared SPE membrane exhibited outstanding preconcentration ability due to the high adsorption properties of AC, and excellent ability to enhance Raman signal resulting from “hot spots” between the embedded Ag NPs, improving the sensitivity of SERS detection. A detection limit (LOD) of 5.0 × 10−11 and 1.6 × 10−10 M was achieved for rhodamine 6G and p-aminothiophenol. In addition, the membrane exhibited high reproducibility with spot-to-spot variation in SERS spectral intensity less than 15%. Based on the membrane, the qualitative and quantitative analysis of the antibiotics in aqueous solution was accomplished with the LOD at nM level, demonstrating the feasibility of the disposable SPE membrane for in situ rapid preconcentration and detection.

Rapid determination of sulfonamide residues in pork by surface-modified hydrophilic electrospun nanofibrous membrane solid-phase extraction combined with ultra-performance liquid chromatography.

This study aimed to rapidly determine 13 representative sulfonamide (SA) residues in pork by using a surface-modified hydrophilic polystyrene sulfonic acid (PSSA) electrospun nanofibrous membrane as the solid-phase extraction (SPE) pretreatment sorbent, followed by ultra-performance liquid chromatography (UPLC) analysis. The highly hydrophilic nature of PSSA nanofibrous membrane created by vacuum plasma treatment was characterized using Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), water contact angle, and X-ray photoelectron spectroscopy (XPS) measurements. In the pretreatment procedures, 13 SA standards, which were spiked in the fatty pork samples, were extracted, enriched, and purified by the SPE procedure based on the principle of ion exchange with the sulfonic groups on the PSSA chains. Under the optimized conditions, the calibration curves of 13 SA compounds showed good linearities with correlation coefficients (r) of more than 0.99 in the range of 50.0-200μgkg(-1). The mean recoveries of 13 SAs at the spiked concentrations of 50, 100, and 200μgkg(-1) were in the range of 70.3-92.5% with average RSDs (n = 6) of less than 15% (except for sulfacetamide, 56.9-61.6%). Compared with other pretreatment methods reported previously, less organic solvent (especially without degreasing the extract with n-hexane) was used in this time-saving SPE procedure, which avoids the possibility of emulsification and therefore enhances the recoveries. The developed and validated analysis method was sensitive, accurate, rapid, convenient, environmentally friendly, and was successfully applied for the detection of 13 SA residues in commercially available pork samples.

Solid phase extraction membranes with submicron multifunctional adsorbent particles

Asymmetric polyethersulfone membranes with submicron particles comprising crosslinked poly(glycidyl methacrylate-co-2-acrylamido-2-methylpropane sulfonic acid) were prepared by a combination of a traditional liquid phase inversion process for making membranes with photopolymerization and crosslinking of functional monomers included in the casting solution. Scanning electron microscope images of the membrane cross-section revealed a hybrid structure with an interconnected network of submicron particles embedded within the porous polyethersulfone support. Permeation of toluidine blue solutions through non-functionalized membranes showed a dramatic effect of 2-acrylamido-2-methylpropane sulfonic acid concentration in the casting solution on the dynamic adsorption performance. The epoxide groups present in glycidyl methacrylate copolymer were transformed into amine functionalities by ring opening under alkaline conditions. Permeation of dilute Cu2+ solutions through functionalized membranes demonstrated that the plate height for some of these membranes was an order of magnitude smaller than for commercial particle-filled membranes used in solid phase extraction.

Porous membrane ultrafiltration—A novel method for enrichment of the active compounds from micro-plasma samples

To enrich the active compounds from plasma samples, a novel and simple method has been developed using a porous membrane envelope based on the ultrafiltration technique combining with high-performance liquid chromatography. The ultrafiltration device is a sealed porous membrane envelope prepared with a polypropylene sheet to effectively separate the active small molecules and large biomolecules, and a sample carrier is held inside the envelope to load plasma samples. The enrichment of hyperoside and isoquercitrin from rat plasma was used as an example. Significant factors of this method, such as membrane types, the desorption solvent, and the desorption time were optimized for the ultrafiltration method. Under the optimal conditions, correlation coefficients of 0.999 and 0.998 were obtained for hyperoside and isoquercitrin, respectively, with a linear range between 0.5 and 100μg/mL. The absolute extraction recoveries from 83.2% to 86.8% were achieved. The detection limits of the method for hyperoside and isoquercitrin were 0.22 and 0.20μg/mL, respectively. Compared with protein precipitation, solid-phase extraction and commercial ultrafiltration membrane methods, our proposed method demonstrates lower detection limits and lower cost for extraction. Also, it consumes less plasma samples and is found to be applicable to biological samples.

Development of a membrane solid-phase extraction method based on polyethyleneimine modified MWNTs for on-line extraction and preconcentration of acidic proteins in serum samples

A membrane solid-phase extraction method based on polyethyleneimine modified multi-walled carbon nanotubes (MWNTs) for the on-line separation and concentration of acidic proteins in serum sample, followed by UV-Vis spectrophotometric determination, is developed. In this study, the polyethyleneimine was noncovalently adsorbed on the outer surface of the MWNTs and then the polyethyleneimine modified MWNTs (PEI–MWNTs) were filtered through a membrane to form an adsorbent layer. The alkalescent PEI coating provided high-density homogeneous functional groups on MWNTs' sidewall and led to homogeneous dispersion of MWNTs in aqueous solutions. The PEI–MWNTs membrane was applied to on-line separation of proteins in serum and exhibited excellent extraction and concentration ability for acidic proteins. Factors, which affected the efficiency of proteins extraction and their subsequent spectrophotometric determination, were studied and optimized. Under optimized conditions, the retention and recovery efficiencies of 100% and 92% for 25 μg mL−1 of BSA solution were achieved, along with a RSD value of 1.9% at a flow rate of 30 μL s−1. The limit of method detection was 1.0 μg mL−1 with an enrichment factor of 12. The maximum adsorption capacity for BSA was 112 mg g−1 MWNTs. The method was applied to isolating acidic proteins from bovine serum sample and obtained satisfactory results.

Simultaneous liquid–liquid microextraction and polypropylene microporous membrane solid-phase extraction of organochlorine pesticides in water, tomato and strawberry samples

A procedure involving the simultaneous performance of liquid–liquid microextraction and polypropylene microporous membrane solid-phase extraction was carried out. The applicability of the proposed procedure was evaluated through extraction of several organochlorine pesticides from river water, tomato and strawberry samples. The parameters affecting the extraction efficiency were optimized by multivariable designs, and the analytical features were estimated. Under optimized conditions, analytes were concentrated onto 1.5 cm long microporous membranes placed directly into the sample containing 15 mL of water with 20 μL of 1-octanol. The best extraction conditions were achieved at 59 °C, with 60 min of extraction time and 2.91 g of sodium chloride. The desorption of the analytes was carried out using 30 μL of a mixture of toluene and hexane in the proportion of 60:40% (v/v) for 10 min. Detection limits in the range of 2.7–20.0 ng L −1, 0.50–1.15 μg kg −1, and 1.53–12.77 μg kg −1 were obtained for river water, strawberry and tomato samples, respectively. Good repeatability was obtained for all three sample types. The results suggest that the proposed procedure represents a very simple and low-cost microextraction alternative rendering adequate limits of quantification for the determination of organochlorine pesticides in environmental and food samples.