Study on the thin-film composite nanofiltration membrane for the removal of sulfate from concentrated salt aqueous: Preparation and performance

Thin-film composite (TFC) nanofiltration (NF) membrane was prepared through the interfacial polymerization between piperazine (PIP) and trimesoyl chloride (TMC) on the polysulphone support membrane. The chemical structure of membrane surface was studied by attenuated total reflectance infrared (ATR-IR) and X-ray photoelectronic spectroscopy (XPS). Parametric studies were conducted by varying reaction time, curing temperature, curing time and additives in PIP solution for obtaining the optimum polymerization conditions. Systematic performance studies were conducted with different feed solutions, feed concentrations, feed pHs, operating temperatures and pressures. Continuous and comparative tests were also conducted to determine the performance stability and separation efficiency of the thin-film composite NF membrane prepared. High performance thin-film composite NF membrane for the selective sulfate removal from concentrated sodium chloride aqueous with the water permeability coefficient of 75 L/(m² h MPa) could be prepared under specific conditions. Experimental results on concentrated mixed solution of NaCl and Na₂SO₄ demonstrated that the NF membrane developed could be successfully used for the removal of sodium sulfate from the concentrated brine of chloralkali industry with high permeate flux, selectivity and performance stability.     

Surface and Interface Engineering for Advanced Nanofiltration Membranes

Nanofiltration has been attracting great attention in alleviating the global water crisis because of its high efficiency,mild operation,and strong adaptability.Over decades,it remains a challenge to break the upper limit of performance and establish the formation-structureproperty relationship for nanofiltration membranes.This feature article summarizes our recent progress in the preparation of high-performance thin-film composite(TFC)nanofiltration membranes,focusing on the mussel-inspired deposition method and the optimized interfacial polymerization(IP).By accelerating the oxidation of polydopamine and equilibrating the rate of aggregation and deposition processes,the mussel-inspired deposition method realizes the rapid and uniform formation of selective coatings or nanofilms.Diverse deposition systems endow the selective layer with rich chemical structures and easy post-functionalization,highlighting its potential in water treatment.As for optimizing the conventional IP,the rapid polycondensation of amine and acid chloride groups is slowed down to enable the controllability of IP at the water-organic interface.The homogeneity and integrity of the TFC membranes are improved by constructing a uniform reaction platform and introducing a viscous medium to control the amine diffusion,which facilitates the water permeability and promotes the separation efficiency.We have proposed a series of practical strategies for improving TFC membranes and might provide more inspiration for other nanofiltration techniques.     

Study on a novel polyester composite nanofiltration membrane by interfacial polymerization of triethanolamine (TEOA) and trimesoyl chloride (TMC): I. Preparation, characterization and nanofiltration properties test of membrane

A novel thin-film composite (TFC) membrane for nanofiltration (NF) was developed by the interfacial polymerization of triethanolamine (TEOA) and trimesoyl chloride (TMC) on the polysulfone (PSf) supporting membrane. The active surface of the membrane was characterized by using FT-IR, XPS and SEM. The performance of TFC membrane was optimized by studying the preparation parameters, such as the reaction time of polymerization, pH of aqueous phase and the concentration of reactive monomers. It is found that the membrane performance is related to the changes of the monomer content in the aqueous phase rather than in the organic phase. Furthermore, the nanofiltration properties of the TFC membrane were tested by examining the separating performance of various salts at 0.6 MPa operating pressure. The rejection to different salt solutions decreased as per the order of Na₂SO₄ (82.2%), MgSO₄ (76.5%), NaCl (42.2%) and MgCl₂ (23%). Also, streaming potential tests indicated that isoelectric point of the TFC membrane is between pH 4 and 5. Moreover, the investigation of the flux for NaCl solution at different pH showed that the polyester NF composite membrane is also particularly suitable for treating acidic feeds: the flux increased from 8.4 to 11.5 L/m² h when pH of the feed decreased from 9 to 3. Additionally, the TFC membrane exhibits good long-term stability.     

Effect of chemical structures of amines on physicochemical properties of active layers and dehydration of isopropanol through interfacially polymerized thin-film composite membranes

Effect of chemical structures of amines on the performance of isopropanol dehydration by pervaporation through the polyamide thin-film composite membranes prepared by various amines reacting with TMC on the surfaces of the modified asymmetric polyacrylonitrile (mPAN) membranes was investigated. ATR-FTIR, SEM, AFM and water contact angle were used to characterize the chemical structures, morphologies and hydrophilicity of the polyamide active layers of the composite membranes. To investigate the correlation between the free volume of polyamide active layer and pervaporation performance, the free volume variation of the polyamide active layers was probed by positron annihilation spectroscopy (PAS) experiments performed using the slow positron beam. It was found that the pervaporation performance for separating 90 wt.% aqueous isopropanol solutions at 25 °C decreased in the order of EDA–TMC/mPAN membrane > MPDA–TMC/mPAN membrane > PIP–TMC/mPAN and HDA–TMC/mPAN membranes. The relationship between the performance of isopropanol dehydration and the physicochemical properties of the polyamide layers, that is, the free volume, surface roughness and hydrophilicity seemed very well.     

Fabrication and Performance of a Low Operating Pressure Nanofiltration Poly（vinyl chloride） Hollow Fiber Membrane

A low operating pressure nanofiltration membrane is prepared by interfacial polymerization between m-phenylenediamine(MPDA) and trimesoyl chloride(TMC) using PVC hollow fiber membrane as supporting.A series of PVC nanofiltration membranes with different molecular weight cutoff(MWCO) can be obtained by controlling preparation conditions.Chemical and morphological characterization of the membrane surface was carried out by FTIR-ATR and SEM.MWCO was characterized by filtration experiments.The preparation conditions were investigated in detail.At the optimized conditions(40 min air-dried time,aqueous phase containing 0.5% MPDA,0.05% SDS and 0.6% acid absorbent,oil phase containing 0.3% TMC,and 1 min reaction time),under 0.3 MPa,water flux of the gained nanofiltration membrane reaches 17.8 L/m2·h,and the rejection rates of methyl orange and MgSO4 are more than 90% and 60%,respectively.     

Characterization, transport and sorption properties of poly(thiol ester amide) thin-film composite pervaporation membranes

The effect of acyl chloride chemical structure on the ethanol aqueous solution dehydration through the poly(thiol ester amide) thin-film composite membrane prepared by reacting 2-aminoethanethiol (AETH) with trimesoyl chloride (TMC) or succinyl chloride (SCC) on the surface of the modified asymmetric polyacrylonitrile (mPAN) membrane was investigated. SEM/EDX, ATR-FTIR and water contact angle were applied to analyze the S element, chemical structure, and hydrophilicity of the poly(thiol ester amide) active layer of the composite membrane. In order to estimate the variation in the free volume of the poly(thiol ester amide) active layer and correlate that with the pervaporation performance, positron annihilation spectroscopy (PAS) experiments were conducted, in which a variable monoenergy slow positron beam was used. Doppler broadening S parameters of annihilation radiation energy spectra showed a significant variation with the acyl chloride chemical structures of the poly(thiol ester amide) active layers. The S parameters of the AETH–TMC/mPAN thin-film composite membrane were found to be lower than those of the AETH–SCC/mPAN thin-film composite membrane. In the ethanol aqueous solution dehydration, the AETH–TMC/mPAN thin-film composite membrane exhibited a lower permeation rate and a higher water concentration in the permeate than the AETH–SCC/mPAN. This is in good agreement with the analysis by positron annihilation spectroscopy. The solution effect dominated the pervaporation separation behavior of the poly(thiol ester amide) thin-film composite membrane with TMC substituting for SCC in the poly(thiol ester amide) active layer. The AETH–TMC/mPAN membrane was found to exhibit superior performance compared with some membranes discussed in the literature.     

Theoretical analysis of the performance of composite membrane consisting of the catalytic and nanofiltration layers

A model of the composite membrane consisting of the catalytic layer (CL) and the nanofiltration layer (NFL) is presented. It has been found that applying NFL on the permeate side of CL it is possible to enhance substantially the conversion of substrate into the product. The best performance is obtained for high retention of substrate and low of product. At higher values of volume flow and/or longer catalytic path the retention degree of product becomes negligible. The presence of NFL enhances the influence of distribution of the reaction rate constant, k, on the conversion ratio. Comparing to k = constant the positive effect is obtained if k increases along the catalytic pore, whereas negative—if k decreases.     

Preparation,structure characteristics and separation properties of thin-film composite polyamide-urethane seawater reverse osmosis membrane

A novel thin-film composite (TFC) seawater reverse osmosis membrane was developed by the interfacial polymerization of 5-chloroformyloxyisophthaloyl chloride (CFIC) and metaphenylenediamine (MPD) on the polysulphone supporting membrane. The performance of the TFC membrane was optimized by studying the preparation parameters, which included the reaction time, pH of the aqueous-MPD solution, monomer CFIC concentration, additive isopropyl alcohol content in aqueous solution, curing temperature and time. The reverse osmosis performance of the resulting membrane was evaluated through permeation experiment with synthetic seawater, and the structure of the novel membrane was characterized by using SEM, AFM and XPS. Furthermore, the separation properties of the TFC membrane were tested by examining the reverse osmosis performances of various conditions, the boron rejection performance and the long-term stability. The results show that the desired TFC seawater reverse osmosis membrane has a typical salt rejection of 99.4% and a flux of about 35 L/m² h for a feed aqueous solution containing 3.5 wt.% NaCl at 5.5 MPa, and an attractive boron rejection of more than 92% at natural pH of 7–8; that the novel seawater reverse osmosis membrane appears to comprise a thicker, smoother and less cross-linking film structure. Additionally, the TFC membrane exhibits good long-term stability.     

Preparation,characterization and application of a novel thermal stable composite nanofiltration membrane

A thermal stable composite membrane was prepared by interfacial polymerization of piperazine (PIP) and trimesoyl chloride (TMC) on poly(phthalazinone ether amide) (PPEA) ultrafiltration membrane. The effect of reaction parameters on the performance of composite membranes was studied and optimized. The surface morphologies of the composite membrane and the substrate were observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The rejection of optimized composite membrane for dyes Congo red (CGR) and Acid chrome blue K (ACBK), the molecular weight (MW) of which is over 400, was over 99.2%, with a flux at about 180 L m⁻² h⁻¹. While the rejection for NaCl was only 18.2% with a flux over 270 L m⁻² h⁻¹, when tested at 1.0 MPa 60 °C. The composite membrane was applied in the desalination-purification experiment of dye ACBK and NaCl mixed solution. The flux of the membrane increased obviously as the operation pressure and/or temperature increased, while the rejection for dye was constant and kept over 99.3%. The purification experiments were accomplished effectively at 1.0 MPa, 80 °C. Only after five rounds of desalination-concentration experiment, about 160 min, the salt mixed in dye solution was fully removed. The initial flux of the eighth cycle was about 254 L m⁻² h⁻¹, which was only 20 L m⁻² h⁻¹ lower than that of the first round. The rejection of the membrane was constant and kept over 99.3% through out the eight cycles of purification experiment.     

Effect of aqueous and organic solutions on the performance of polyamide thin‐film‐composite nanofiltration membranes

Polyamide/polyacrylonitrile thin‐film‐composite (TFC) nanofiltration (NF) membranes for the separation of oleic acid dissolved in organic solvents (methanol and acetone) were interfacially prepared by the reaction of trimesoyl chloride in an organic phase with an aqueous phase containing piperazine and m‐phenylene diamine. The interfacial reaction was confirmed by an investigation of the attenuated total reflection infrared spectrum. The surface morphology of the polyamide TFC membranes was examined with scanning electron microscopy. The hydrophilic properties of the membrane surfaces were conjectured on the basis of the ζ potential and contact angle. The effects of the monomer concentrations of the monomer blends (aliphatic and aromatic diamines) and drying times on various aspects of membrane performance, such as the solvents (water, alcohols, ketones, and hexane), permeation rates, and organic solute [poly(ethylene glycol) 200 and oleic acid] rejection rates, were investigated. All the membranes showed good solvent resistance. The polar solvent flux for water and methanol was higher than that for a nonpolar solvent (hexane). The membranes gave good rejection rates of oleic acid dissolved in methanol and acetone. The NF membranes were compared with various commercial membranes. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2151–2163, 2002     

Effects of surfactants on the morphology of composite polymer particles produced by two‐stage seeded emulsion polymerization

Poly(methyl methacrylate) (PMMA)–polystyrene (PS) composite polymer particles were synthesized in the presence of a surfactant by two‐stage seeded emulsion polymerization. The first stage was the synthesis of PMMA particles by soapless emulsion polymerization; the second stage was the synthesis of the PMMA–PS composite polymer particles with the PMMA particles as seeds. In the second stage of the reaction, three kinds of surfactants—sodium laurate sulfate (SLS), polyoxyethylene (POE) sorbitan monolaurate (Tween 20), and sorbitan monolaurate (Span 20)—were used to synthesize the PMMA–PS composite particles. Both the properties and concentrations of the surfactants influenced the morphology of the composite particles significantly. Core–shell composite particles, with PS as the shell and PMMA as the core, were synthesized in the presence of a low concentration of the hydrophilic surfactant SLS. This result was the same as that in the absence of the surfactant. However, a low concentration of Tween 20 led to composite particles with a core/strawberry‐like shell morphology; the core region was a PS phase, and the strawberry‐like shell was a PS phase dispersed in a PMMA phase. With an increase in the concentration of SLS, the morphology of the composite particles changed from core (PMMA)–shell (PS) to core (PS)–shell (PMMA). Moreover, the effects of a high concentration of Tween 20 or Span 20 on the morphology of the PMMA–PS composite particles were investigated in this study. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2224–2236, 2005     

Fabrication and evaluation of molecularly imprinted regenerated cellulose composite membranes via atom transfer radical polymerization

A simple and effective method for surface molecularly imprinted composite membranes （MICMs） for artemisinin （Ars） based on regenerated cellulose membranes was first prepared through surface- initiated atom transfer radical polymerization （ATRP）, and the as-prepared MICMs were then evaluated as adsorbents for selective recognition and separation of Ars molecules. Batch rebinding studies were conducted to determine the specific adsorption equilibrium, kinetics and selective permeation performance. The adsorption capacity of MICMs toward Ars by the Langmuir isotherm model was 2.008 mgg-1, which was nearly 5.0 times higher than non-molecularly imprinted composite membranes （NICMs）. The kinetic property of MICMs was well-fitted by the pseudo-second-order rate equation. The selective permeation experiments were successfully investigated to prove the excellent selective permeation performance for Ars than the competitive analog （artemether）.     

Influence of the polyacyl chloride structure on the reverse osmosis performance,surface properties and chlorine stability of the thin-film composite polyamide membranes

This paper aims to study the structure–property relationship and make several reasonable suggestions for tailoring special separation performance and surface properties of thin-film composite polyamide membranes. In the experiments, composite membranes of different thin films with small structural differences were prepared through interfacial polymerization of trimesoyl chloride (TMC), 5-isocyanato-isophthaloyl chloride (ICIC), and 5-chloroformyloxy-isophthaloyl chloride (CFIC) with m-phenylenediamine (MPD) separately, after which their reverse osmosis performances were evaluated by permeation experiment with salt aqueous solution, and film properties were characterized by AFM, SEM, XPS, ATR-IR, contact angle and streaming potential measurements. Chlorine stability was also studied through the evaluation of membrane performance before and after hypochlorite exposure. The results show that the polyacyl chloride structure strongly influences the reverse osmosis performance, surface properties and chlorine stability of the composite membranes; that the introduction of isocyanato group into polyacyl chloride improves the hydrophilicity, water permeability and surface smoothness of the thin-film composite membrane, and increases the absolute value of zeta potential at both low and high pH, but reduces the chlorine stability; and that the introduction of chloroformyloxy group increases the salt rejection rate and the surface roughness of the composite membrane, but lowers the water permeability.     

Effect of the pore surface modification of an inorganic substrate on the plasma‐grafting behavior of pore‐filling‐type organic/inorganic composite membranes

We have investigated the effect of the surface state and surface treatment of the pores of an inorganic substrate on the plasma‐grafting behavior of pore‐filling‐type organic/inorganic composite membranes. Shirasu porous glass (SPG) was used as the inorganic substrate, and methyl acrylate was used as the grafting monomer. The grafting rate increased as the density of silanol on the SPG substrate increased. This result suggests that radicals are generated mainly at the silanol groups on the pore surface by plasma irradiation. The SPG substrates were treated with silane coupling agents used to control the mass of organic material bonded to the pore surface. The thickness of the grafted layer became thinner as the mass of organic material bonded to the pore surface of SPG increased. This decrease in the thickness of the grafted layer could be explained by the decrease in the penetration depth of vacuum ultraviolet rays contained in plasma having a wavelength of less than 160 nm that generated radicals in the pores of the substrate. The thickness of the grafted layer inside the SPG substrates could be controlled through the control of the mass of organic material bonded to the pore surface of the SPG substrate. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 846–856, 2006     

Effects of additives and post‐treatment on the thermoelectric performance of vapor‐phase polymerized PEDOT films

Vapor‐phase polymerization (VPP) is an important method for the fabrication of high‐quality conducting polymers, especially poly(3,4‐ethylenedioxythiophene) (PEDOT). In this work, the effects of additives and post‐treatment solvents on the thermoelectric (TE) performance of VPP‐PEDOT films were systematically investigated. The use of 1‐butyl‐3‐menthylinidazolium tetrafluoroborate ([BMIm][BF₄], an ionic liquid) was shown to significantly enhance the electrical conductivity of VPP‐PEDOT films compared with other additives. The VPP‐PEDOT film post‐treated with mixed ethylene glycol (EG)/[BMIm][BF₄] solvent displayed the high power factor of 45.3 μW m^?1 K^?2 which is 122% higher than that prepared without any additive or post‐treatment solvent, along with enhanced electrical conductivity and Seebeck coefficient. This work highlighted the superior effect of the [BMIm][BF₄] additive and the EG/[BMIm][BF₄] solvent post‐treatment on the TE performance of the VPP‐PEDOT film. These results should help with developing the VPP method to fabricate high‐performance PEDOT films. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 1738–1744     

Synthesis and morphology of Fe3O4/polystyrene/poly(isopropylacrylamide‐co‐methyl acrylate acid) magnetic composite latex – 2,2′‐azobis (2‐methylpropionamidine) dihydrochloride as initiator

In this work, Fe₃O₄/polystyrene/poly(N‐isopropylacryl amide‐co‐methylacrylate acid) (Fe₃O₄/PS/P(NIPAAM‐co‐MAA)) magnetic composite latex was synthesized by the method of two stage emulsion polymerization. In this reaction system, 2,2′‐azobis(2‐methyl propionamidine) dihydrochloride (AIBA) was used as initiator to initiate the first stage reaction and second stage reaction. The Fe₃O₄ particles were prepared by a traditional coprecipitation method. Fe₃O₄ particles were surface treated by either PAA oligomer or lauric acid to form the stable ferrofluid. The first stage for the synthesis of magnetic composite latex was to synthesize PS in the presence of ferrofluid by soapless emulsion polymerization to form the Fe₃O₄/PS composite latex particles. Following the first stage of reaction, the second stage of polymerization was carried out by the method of soapless emulsion polymerization with NIPAAM and MAA as monomers and Fe₃O₄/PS latex as seeds. The magnetic composite particles, Fe₃O₄/PS/P(NIPAAM‐co‐MAA), were thus obtained. The mechanism of the first stage reaction and second stage reaction were investigated. Moreover, the effects of PAA and lauric acid on the reaction kinetics, morphology, and particle size distribution were studied. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3912–3921, 2007     

Crosslinking‐induced morphology change of latex nanoparticles: A study of RAFT‐mediated polymerization in aqueous dispersed media using amphiphilic double‐brush copolymers as reactive surfactants

Amphiphilic double‐brush copolymers (DBCs) with each graft site quantitatively carrying both a hydrophilic poly(ethylene oxide) (PEO) graft and a hydrophobic polystyrene (PSt) graft are synthesized by sequential reversible addition‐fragmentation chain transfer (RAFT) polymerization and ring‐opening metathesis polymerization (ROMP). These DBCs are used as both surfactants and polyfunctional RAFT agents in the radical polymerization of St in aqueous dispersed media. Miniemulsions with narrowly dispersed St‐based nanodroplets are readily obtained after ultrasonication of the reaction mixtures. Without the presence of crosslinker, chain‐extension polymerization of St from the DBCs yields well‐defined polymeric latexes with narrow size distributions. However, with the presence of divinylbenzene (DVB) as the crosslinker, vesicular polymeric nanoparticles are formed as the major product. Such crosslinking‐induced change in morphology of the resulting latex nanomaterials may be ascribed to the increase of interfacial curvature in the heterophase systems during crosslinking polymerization. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3250–3259     

Insights into the surface property and blood compatibility of polyethersulfone/polyvinylpyrrolidone composite membranes: toward high‐performance hemodialyzer

Applications of blood purification membranes are fuelled by diverse clinical needs, such as hemodialysis, hemodiafiltration, hemofiltration, plasmapheresis, and plasma collection. For clinical usage, the adding of polyvinylpyrrolidone (PVP) is the general protocol for the design of antifouling and antithrombotic properties integrated artificial membranes. In the present work, to insight into the detailed surface properties and blood compatibilities of the PVP blended composite membranes, we synthesized a series of PVP polymers with different molecular weights using reversible addition fragmentation chain transfer polymerization and designed a series of polyethersulfone (PES)/PVP composite membranes by a physically blending method. The effects of PVP molecular weights and blending ratios on the surface properties and the blood compatibilities of the composite membranes were investigated in detail. The surface attenuated total reflection Fourier transform infrared spectra and scanning electron microscopy pictures indicated that the PVP was successfully immobilized into the membranes, and the composite membranes exhibited morphology transformation from finger‐like structure to sponge‐like structure, which indicated that the composite membrane had tunable porosity and permeability by adding PVP. The blood compatible tests revealed that the composite membranes showed increased hydrophilicity, decreased plasma protein adsorption, suppressed platelet adhesion, and prolonged blood clotting time compared with pristine PES membrane. These results indicated that the PES/PVP composite membranes exhibited enhanced antifouling and antithrombotic properties than the pristine PES membrane. Meanwhile, the results also suggested that the composite membranes with larger molecular weight PVP and higher blending ratios might show better blood compatibility. Copyright © 2014 John Wiley & Sons, Ltd.     

Fabrication and performance of microencapsulated phase change materials with hybrid shell by in situ polymerization in Pickering emulsion

Microencapsulated phase change materials (MePCMs) using melamine–formaldehyde resin/SiO₂ as shell were investigated in this paper. Organically modified SiO₂ particles were employed to stabilize Pickering emulsion, and in situ polymerization of melamine and formaldehyde was carried out to form hybrid shell. The performances of resultant MePCMs with hybrid shell were investigated comparatively with the MePCMs with polymer shell. SiO₂ particles raise the microencapsulation efficiency by improving the stability of emulsion and providing a precipitation site for melamine–formaldehyde resin. Also, the mechanical strength, thermal reliability, and anti‐osmosis performance of MePCMs were improved significantly by SiO₂ particles in the shell. Our study shows that Pickering emulsion is a simple and robust template for MePCMs with polymer‐inorganic hybrid shell. Copyright © 2015 John Wiley & Sons, Ltd.     

Improved in‐tube electro‐membrane extraction followed by high‐performance liquid chromatography for simple and selective determination of ionic compounds: Optimization by central composite design

In this work, an efficient sample clean‐up method, named in‐tube electro‐membrane extraction, is modified to resolve the formation of bubbles in the extraction process. This modified method is applied for the extraction of two model analytes including tartrazine and sunset yellow from food samples. The method is based on the electro‐kinetic migration of ionized compounds by the application of an electrical potential difference, and on this basis the analytes under investigation, as anionic compounds, simply migrate from the donor phase and concentrate in the acceptor phase. A thin polypropylene sheet placed in the tube acts as a support for the membrane solvent, and it separates 30 μL of the aqueous acceptor from 1.2 mL of the aqueous donor. This setup can be used to solve the problem of extracting highly hydrophilic analytes. Response surface methodology is used for optimization of the experimental parameters so that under the optimized conditions, the method provides a good linearity in the range of 50–1000 ng/mL, low limits of detection (15–25 ng/mL), good extraction repeatabilities (relative standard deviations below 8.1%, n  = 5), and high extraction recoveries (54–76%).