Quantitation of Atmospheric Suspended Polystyrene Nanoplastics by Active Sampling Prior to Pyrolysis-Gas Chromatography-Mass Spectrometry.

Plastic has been demonstrated to release nanoplastics (NPs) into the atmosphere under sunlight irradiation, posing a continuous health risk to the respiratory system. However, due to lack of reliable quantification methods, the occurrence and distribution of NPs in the atmosphere remain unclear. Polystyrene (PS) micro- and nanoplastics (MNPs) represent a crucial component of atmospheric MNPs. In this study, we proposed a simple and robust method for determining the concentration of atmospheric PS NPs using pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS). Following active sampling, the filter membrane is directly ground and introduced into the Py-GC/MS system to quantify PS NPs. The proposed method demonstrates excellent reproducibility and high sensitivity, with a detection limit as low as down to 15 pg/m3 for PS NPs. By using this method, the occurrence of PS NPs in both indoor and outdoor atmospheres has been confirmed. Furthermore, the results showed that the abundance of outdoor PS NPs was significantly higher than that of indoor samples, and there was no significant difference in NP vertical distribution within a height of 28.6 m. This method can be applied for the routine monitoring of atmospheric PS NPs and for evaluating their risk to human health.

Removal of iodide anions in water by silver nanoparticles supported on polystyrene anion exchanger.

The removal of iodide (I-) from source waters is an effective strategy to minimize the formation of iodinated disinfection by-products (DBPs), which are more toxic than their brominated and chlorinated analogues. In this work, a nanocomposite Ag-D201 was synthesized by multiple in situ reduction of Ag-complex in D201 polymer matrix, to achieve highly efficient removal of iodide from water. Scanning electron microscope /energy dispersive spectrometer characterization showed that uniform cubic silver nanoparticles (AgNPs) evenly dispersed in the D201 pores. The equilibrium isotherms data for iodide adsorption onto Ag-D201 was well fitted with Langmuir isotherm with the adsorption capacity of 533 mg/g at neutral pH. The adsorption capacity of Ag-D201 increased with the decrease of pH in acidic aqueous solution, and reached the maximum value of 802 mg/g at pH 2. This was attributed to the oxidization of I-, by dissolved oxygen under the catalysis of AgNPs, to I2 which was finally adsorbed as AgI3. However, the aqueous solutions at pH 7 - 11 could hardly affect the iodide adsorption. The adsorption of I- was barely affected by real water matrixes such as competitive anions (SO42-, NO3-, HCO3-, Cl-) and natural organic matter, of which interference of NOM was offset by the presence of Ca2+. The proposed synergistic mechanism for the excellent performance of iodide adsorption by the absorbent was ascribed to the Donnan membrane effect caused by the D201 resin, the chemisorption of I- by AgNPs, and the catalytic effect of AgNPs.

Sequential Isolation of Microplastics and Nanoplastics in Environmental Waters by Membrane Filtration, Followed by Cloud-Point Extraction.

Respective detection of microplastics (MPs) and nanoplastics (NPs) is of great importance for their different environmental behaviors and toxicities. Using spherical polystyrene (PS) and poly(methyl methacrylate) (PMMA) plastics as models, the efficiency for sequential isolation of MPs and NPs by membrane filtration and cloud-point extraction was evaluated. After filtering through a glass membrane (1 µm pore size), over 90.7% of MPs were trapped on the membrane, whereas above 93.0% of NPs remained in the filtrate. The collected MPs together with the glass membrane were frozen in liquid nitrogen, ground, and suspended in water (1 mL) and subjected to pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) determination. The NPs in the filtrate were concentrated by cloud-point extraction, heated at 190 °C to degrade the extractant, and then determined by Py-GC/MS. For MPs and NPs spiked in pure water, the method detection limits are in the range of 0.05-1.9 µg/L. The proposed method is applied to analyze four real water samples, with the detection of 1.6-7.6 µg/L PS MPs and 0.6 µg/L PMMA MPs in three samples, and spiked recoveries of 75.0-102% for MPs and 67.8-87.2% for NPs. Our method offers a novel sample pretreatment approach for the respective determination of MPs and NPs.

Cloud-Point Extraction Combined with Thermal Degradation for Nanoplastic Analysis Using Pyrolysis Gas Chromatography-Mass Spectrometry.

The contamination of micro- and nanoplastics in marine systems and freshwater is a global issue. Determination of micro- and nanoplastics in the aqueous environment is of high priority to fully assess the risk that plastic particles will pose. Although microplastics have been detected in a variety of aquatic ecosystems, the analysis of nanoplastics remains an unsolved challenge. Herein, for the first time, a Triton X-45 (TX-45)-based cloud-point extraction (CPE) was proposed to preconcentrate trace nanoplastics in environmental waters. Under the optimum extraction conditions, an enrichment factor of 500 was obtained for two types of nanoplastics with different compositions, polystyrene (PS) and poly(methyl methacrylate) (PMMA), without disturbing their original morphology and sizes. Additionally, following thermal treatment at 190 °C for 3 h, the CPE-obtained extract could be submitted to pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) analysis for mass quantification of nanoplastics. Taking 66.2 nm PS nanoplastics and 86.2 nm PMMA nanoplastics as examples, the proposed method showed excellent reproducibility, and high sensitivity with respective detection limits of 11.5 and 2.5 fM. Feasibility of the proposed approach was verified by application of the optimized procedure to four real water samples. Recoveries of 84.6-96.6% at a spiked level of 88.6 fM for PS nanoplastics and 76.5-96.6% at a spiked level of 50.4 fM for PMMA nanoplastics were obtained. Consequently, this work provides an efficient approach for nanoplastic analysis in environmental waters.

Polyvinylidene Fluoride Micropore Membranes as Solid-Phase Extraction Disk for Preconcentration of Nanoparticulate Silver in Environmental Waters.

Efficient separation and preconcentration of trace nanoparticulate silver (NAg) from large-volume environmental waters is a prerequisite for reliable analysis and therefore understanding the environmental processes of silver nanoparticles (AgNPs). Herein, we report the novel use of polyvinylidene fluoride (PVDF) filter membrane for disk-based solid phase extraction (SPE) of NAg in 1 L of water samples with the disk-based SPE system, which consists of a syringe pump and a syringe filter holder to embed the filter membrane. While the PVDF membrane can selectively adsorb NAg in the presence of Ag+, aqueous solution of 2% (m/v) FL-70 is found to efficiently elute NAg. Analysis of NAg is performed following optimization of filter membrane and elution conditions with an enrichment factor of 1000. Additionally, transmission electron microscopy (TEM), UV-vis spectroscopy, and size-exclusion chromatography coupled with ICP-MS (SEC-ICP-MS) analysis showed that the extraction gives rise to no change in NAg size or shape, making this method attractive for practical applications. Furthermore, feasibility of the protocol is verified by applying it to extract NAg in four real waters with recoveries of 62.2-80.2% at 0.056-0.58 µg/L spiked levels. This work will facilitate robust studies of trace NAg transformation and their hazard assessments in the environment.

Speciation Analysis of Labile and Total Silver(I) in Nanosilver Dispersions and Environmental Waters by Hollow Fiber Supported Liquid Membrane Extraction.

Hollow fiber supported liquid membrane (HFSLM) extraction was coupled with ICP-MS for speciation analysis of labile Ag(I) and total Ag(I) in dispersions of silver nanoparticles (AgNPs) and environmental waters. Ag(I) in aqueous samples was extracted into the HFSLM of 5%(m/v) tri-n-octylphosphine oxide in n-undecane, and stripped in the acceptor of 10 mM Na2S2O3 and 1 mM Cu(NO3)2 prepared in 5 mM NaH2PO4-Na2HPO4 buffer (pH 7.5). Negligible depletion and exhaustive extraction were conducted under static and 250 rpm shaking to extract the labile Ag(I) and total Ag(I), respectively. The extraction equilibration was reached in 8 h for both extraction modes. The extraction efficiency and detection limit were (2.97 ± 0.25)% and 0.1 µg/L for labile Ag(I), and (82.3 ± 2.0)% and 0.5 µg/L for total Ag(I) detection, respectively. The proposed method was applied to determine labile Ag(I) and total Ag(I) in different sized AgNP dispersions and real environmental waters, with spiked recoveries of total Ag(I) in the range of 74.0-98.1%. With the capability of distinguishing labile and total Ag(I), our method offers a new approach for evaluating the bioavailability and understanding the fate and toxicity of AgNPs in aquatic systems.

Highly dynamic PVP-coated silver nanoparticles in aquatic environments: chemical and morphology change induced by oxidation of Ag(0) and reduction of Ag(+).

The fast growing and abundant use of silver nanoparticles (AgNPs) in commercial products alerts us to be cautious of their unknown health and environmental risks. Because of the inherent redox instability of silver, AgNPs are highly dynamic in the aquatic system, and the cycle of chemical oxidation of AgNPs to release Ag(+) and reconstitution to form AgNPs is expected to occur in aquatic environments. This study investigated how inevitable environmentally relevant factors like sunlight, dissolved organic matter (DOM), pH, Ca(2+)/Mg(2+), Cl(-), and S(2-) individually or in combination affect the chemical transformation of AgNPs. It was demonstrated that simulated sunlight induced the aggregation of AgNPs, causing particle fusion or self-assembly to form larger structures and aggregates. Meanwhile, AgNPs were significantly stabilized by DOM, indicating that AgNPs may exist as single particles and be suspended in natural water for a long time or delivered far distances. Dissolution (ion release) kinetics of AgNPs in sunlit DOM-rich water showed that dissolved Ag concentration increased gradually first and then suddenly decreased with external light irradiation, along with the regeneration of new tiny AgNPs. pH variation and addition of Ca(2+) and Mg(2+) within environmental levels did not affect the tendency, showing that this phenomenon was general in real aquatic systems. Given that a great number of studies have proven the toxicity of dissolved Ag (commonly regarded as the source of AgNP toxicity) to many aquatic organisms, our finding that the effect of DOM and sunlight on AgNP dissolution can regulate AgNP toxicity under these conditions is important. The fact that the release of Ag(+) and regeneration of AgNPs could both happen in sunlit DOM-rich water implies that previous results of toxicity studies gained by focusing on the original nature of AgNPs should be reconsidered and highlights the necessity to monitor the fate and toxicity of AgNPs under more environmentally relevant conditions.

Quantification of the uptake of silver nanoparticles and ions to HepG2 cells.

The toxic mechanism of silver nanoparticles (AgNPs) is still debating, partially because of the common co-occurrence and the lack of methods for separation of AgNPs and Ag(+) in biological matrices. For the first time, Triton-X 114-based cloud point extraction (CPE) was proposed to separate AgNPs and Ag(+) in the cell lysates of exposed HepG2 cells. Cell lysates were subjected to CPE after adding Na2S2O3, which facilitated the transfer of AgNPs into the nether Triton X-114-rich phase by salt effect and the preserve of Ag(+) in the upper aqueous phase through the formation of hydrophilic complex. Then the AgNP and Ag(+) contents in the exposed cells were determined by ICP-MS after microwave digestion of the two phases, respectively. Under the optimized conditions, over 67% of AgNPs in cell lysates were extracted into the Triton X-114-rich phase while 94% of Ag(+) remained in the aqueous phase, and the limits of detection for AgNPs and Ag(+) were 2.94 µg/L and 2.40 µg/L, respectively. This developed analytical method was applied to quantify the uptake of AgNPs to the HepG2 cells. After exposure to 10 mg/L AgNPs for 24 h, about 67.8 ng Ag were assimilated per 10(4) cells, in which about 10.3% silver existed as Ag(+). Compared to the pristine AgNPs (with 5.2% Ag(+)) for exposure, the higher ratio of Ag(+) to AgNPs in the exposed cells (10.3% Ag(+)) suggests the transformation of AgNPs into Ag(+) in the cells and/or the higher uptake rate of Ag(+) than that of AgNPs. Given that the toxicity of Ag(+) is much higher than that of AgNPs, the substantial content of Ag(+) in the exposed cells suggests that the contribution of Ag(+) should be taken into account in evaluating the toxicity of AgNPs to organisms, and previous results obtained by regarding the total Ag content in organisms as AgNPs should be reconsidered.

Speciation analysis of silver nanoparticles and silver ions in antibacterial products and environmental waters via cloud point extraction-based separation.

The rapid growth in commercial use of silver nanoparticles (AgNPs) will inevitably increase silver exposure in the environment and the general population. As the fate and toxic effects of AgNPs is related to the Ag(+) released from AgNPs and the transformation of Ag(+) into AgNPs, it is of great importance to develop methods for speciation analysis of AgNPs and Ag(+). This study reports the use of Triton X-114-based cloud point extraction as an efficient separation approach for the speciation analysis of AgNPs and Ag(+) in antibacterial products and environmental waters. AgNPs were quantified by determining the Ag content in the Triton X-114-rich phase with inductively coupled plasma mass spectrometry (ICPMS) after microwave digestion. The concentration of total Ag(+), which consists of the AgNP adsorbed, the matrix associated, and the freely dissolved, was obtained by subtracting the AgNP content from the total silver content that was determined by ICPMS after digestion. The limits of quantification (S/N = 10) for antibacterial products were 0.4 µg/kg and 0.2 µg/kg for AgNPs and total silver, respectively. The reliable quantification limit was 3 µg/kg for total Ag(+). The presence of Ag(+) at concentrations up to 2-fold that of AgNPs caused no effects on the determination of AgNPs. In the cloud point extraction of AgNPs in antibacterial products, the spiked recoveries of AgNPs were in the range of 71.7-103% while the extraction efficiencies of Ag(+) were in the range of 1.2-10%. The possible coextracted other silver containing nanoparticles in the cloud point extraction of AgNPs were distinguished by transmission electron microscopy (TEM), scanning electron microscopy (SEM)- energy dispersive spectroscopy (EDS), and UV-vis spectrum. Real sample analysis indicated that even though the manufacturers claimed nanosilver products, AgNPs were detected only in three of the six tested antibacterial products.

Triton X-114 based cloud point extraction: a thermoreversible approach for separation/concentration and dispersion of nanomaterials in the aqueous phase.

Capable of preserving the sizes and shapes of nanomaterials during the phase transferring, Triton X-114 based cloud point extraction provides a general, simple, and cost-effective route for reversible concentration/separation or dispersion of various nanomaterials in the aqueous phase.

Simultaneous conduction of two- and three-phase hollow-fiber-based liquid-phase microextraction for the determination of aromatic amines in environmental water samples.

This paper describes a simultaneously performed two-/three-phase hollow-fiber-based liquid-phase microextraction (HF-LPME) method for the determination of aromatic amines with a wide range of pK(a) (-4.25 to 4.6) and logK(OW) (0.9-2.8) values in environmental water samples. Analytes including aniline, 4-nitroaniline, 2,4-dinitroaniline and dicloran were extracted from basic aqueous samples (donor phase, DP) into the microliter volume of organic membrane phase impregnated into the pores of the polypropylene hollow fiber wall, then back extracted into the acidified aqueous solution (acceptor phase, AP) filling in the lumen of the hollow fiber. The mass transfer of the analytes from the donor phase through the organic membrane phase into acceptor phase was driven by both the counter-coupled transport of hydrogen ions and the pH gradient. Afterwards, the hollow fiber was eluted with 50 microL methanol to capture the analytes from both the organic membrane and the acceptor phase. Factors relevant to the enrichment factors (EFs) were investigated. Under the optimized condition (DP: 100 mL of 0.1 M NaOH with 2 M Na(2)SO(4); organic phase: di-n-hexyl with 8% trioctylphosphine oxide (TOPO); AP: 10 microL of 8 M HCl; extraction time of 80 min), the obtained EFs were 405-2000, dynamic linear ranges were 5-200 microg/L (R>0.9976), and limits of detection were 0.5-1.5 microg/L. The presence of humic acid (0-25 mg/L dissolved organic carbon) had no significant effect on the extraction efficiency. The proposed procedure worked very well for real environmental water samples with microgram per liter level of analytes, and good spike recoveries (80-103%) were obtained.

Passive extraction and clean-up of phenoxy acid herbicides in samples from a groundwater plume using hollow fiber supported liquid membranes.

Hollow fiber supported liquid membranes were applied for the passive extraction of phenoxy acid herbicides from water samples. Polypropylene hollow fiber membranes (240 microm i.d., 30 microm wall thickness, 0.05 microm pore size, 30 cm length) were impregnated with 2.0% tri-n-octylphosphine oxide (TOPO) in di-n-hexyl ether in the pores of the fiber wall to form a liquid membrane. They were then filled with basic solution in the lumen as acceptor and finally placed into the sample (donor). Complete extraction of phenoxy acid herbicides including 2,4-D, MCPA, dichlorprop, and mecoprop from an acidified sample (4 mL, adjusted to pH 1.5 with HCl) into basic acceptor (10 microL of 0.2M NaOH) was achieved after 4 h of shaking (100 rpm) resulting in an enrichment factor of 400 times. The acceptor was then neutralized by addition of HCl and injected into a HPLC system for the determination of the phenoxy acid herbicides. Environmentally relevant salinity (0-3.5% NaCl) and dissolved organic matter (0-25 mg/L of dissolved organic carbon) had no significant effect on the extraction. The method provided extraction efficiencies of more than 91%, detection limits of 0.3-0.6 microg/L, and combined extraction and clean up in one single step. This procedure was applied to determine aqueous concentrations of phenoxy acid herbicides in groundwater samples collected from an old dumping site (Cheminova, Denmark) with detected concentrations up to 5800 microg/L. Although the samples were very dirty with large amounts of suspended particles, non-aqueous phase liquids (NAPLs) and dissolved organic matters, good spike recoveries (80-126%) were obtained for 10 of the 11 samples.

Determination of short-chain fatty acids in serum by hollow fiber supported liquid membrane extraction coupled with gas chromatography.

A method based on hollow fiber supported liquid membrane extraction coupled with a gas chromatograph equipped with flame ionization detector (GC-FID) was developed for the determination of six short-chain fatty acids including acetic acid, propionic acid, i-butyric acid, n-butyric acid, i-valeric acid and n-valeric acid in serum. Hollow fiber supported liquid membrane extraction was employed for preconcentration and clean-up of the samples. The fatty acids were extracted from the acidic donor (diluted serum) into a liquid membrane formed in the wall of the hollow fiber with 10% tri-n-octylphoshphine oxide (TOPO) in di-n-hexyl ether, and then extracted back into a basic acceptor solution filled in the lumen of the hollow fiber. After being acidified with HCl, the acceptor was directly analyzed by GC-FID. The acceptor concentration, donor pH, membrane liquid and extracting time were optimized giving an enrichment factor up to 155 times. The good linearity (r(2)>0.980), reasonable recovery (87.2-121%), and satisfactory intra-assay (8.2-11.5%) and inter-assay (6.1-11.6%) precision illustrated the good performance of the present method. Limits of detection (LOD) ranged from 0.04 to 0.24 microM and limits of quantification (LOQ) varied from 0.13 to 0.80 microM.

Equilibrium sampling through membrane based on a single hollow fibre for determination of drug-protein binding and free drug concentration in plasma.

The determination of drug-protein binding and free drug concentration in plasma applying the equilibrium sampling through membrane (ESTM) technique has been studied using supported liquid membrane extraction in a single hollow fibre without any membrane carrier. In the extraction setup, the donor phase (plasma or buffer) was placed in the vial, into which was immersed the hollow fibre with the acceptor phase situated in the lumen. This proposed technique was applied to study the drug-protein binding of five local anaesthetics and two antidepressants as model substances, and the influence of the total drug concentration on the drug-protein binding was investigated. The brief theoretical background for determination of the drug-protein binding under equilibrium conditions is described. The developed method shows a new, improved and simple procedure for determination of free drug concentration in plasma and extent of drug-protein binding.

Development of a solid-phase microextraction fiber by chemical binding of polymeric ionic liquid on a silica coated stainless steel wire.

A novel approach was developed for the fabrication of solid-phase microextraction (SPME) fiber by coating stainless steel fiber with a polymeric ionic liquid (PIL) through covalent bond. The stainless steel fiber was sequentially coated with a gold film by replacement reaction between Fe and Au when immerged in chloroauric acid, assembled with a monolayer of 3-(mercaptopropyl) triethoxysilane on the gold layer through the Au-S bond, and coated with a silica layer by the hydrolysis and polycondensation reaction of the surface-bonded siloxane moieties and the active silicate solution. Then, 1-vinyl-3-(3-triethoxysilylpropyl)-4,5-dihydroimidazolium chloride ionic liquid was anchored on the silica layer by covalent bond, and the PIL film was further formed by free radical copolymerization between 1-vinyl-3-(3-triethoxysilylpropyl)-4,5-dihydroimidazdium and vinyl-substituted imidazolium with azobisisobutyronitrile (AIBN) as initiator. Parameters influencing the preparation of PIL fiber were optimized, and the developed SPME fiber has a coating thickness of ~20 µm with good thermal stability and long lifetime. The performance of the PIL fiber was evaluated by analysis of polycyclic aromatic hydrocarbons (PAHs) in water samples. The developed PIL fiber showed good linearity between 0.5 and 20 µg l(-1) with regression coefficient in the range of 0.963-0.999, detection limit ranging from 0.05 to 0.25 µg l(-1), and relative standard deviation of 9.2-29% (n=7). This developed PIL fiber exhibited comparable analytical performance to commercial 7 µm thickness PDMS fiber in the extraction of PAHs. The spiked recoveries for three real water samples at 0.5-5 µg l(-1) levels were 49.6-111% for the PIL fiber and 40.8-103% for the commercial PDMS fiber.

Use of Triton X-114 as a weak capping agent for one-pot aqueous phase synthesis of ultrathin noble metal nanowires and a primary study of their electrocatalytic activity.

By using Triton X-114 as structure-director and weak binding stabilizer, ultrathin Au, Pd and Pt nanowires are synthesized in seconds by reduction of inorganic metal precursors with KBH(4) in aqueous phase. The nanowires show high catalytic activity and long-term stability toward electrooxidation of alcohols.