Xinzhen Du

Electrodeposition of gold nanoparticles onto an etched stainless steel wire followed by a self-assembled monolayer of octanedithiol as a fiber coating for selective solid-phase microextraction

In the present study, a novel approach for rapid electrodeposition on an etched stainless steel (SS) wire followed by self-assembled monolayer (SAM) was proposed for the fabrication of solid-phase microextraction (SPME) fiber. The etched SS wire offers a rough surface structure for subsequent electrochemical deposition of gold nanoparticles (AuNPs). As a result, uniform AuNPs coating was tightly attached to the etched SS wire substrate. After SAM of 1,8-octanedithiol onto AuNPs coating via Au-S bonding, a unique floccular structure with extremely large surface area was obtained for the fabricated fiber. The mercaptooctyl groups modified AuNPs coated etched SS fiber (C8-S-AuNPs/SS) was then assessed for SPME of phthalate esters (PAEs), polychlorinated biphenyls (PCBs), chlorophenols (CPs), ultraviolet (UV) filters, polycyclic aromatic hydrocarbons (PAHs) and substituted anilines coupled to high-performance liquid chromatography with UV detection. This fiber exhibits higher extraction capability and better selectivity for some PCBs, CPs, UV filters and PAHs. Extraction conditions were investigated and optimized for SPME performance of UV filters. Under the optimized conditions, the developed method showed good linearity between 0.10 and 400μgL-1 with corresponding coefficients in the range of 0.9989-0.9998. The limits of detection ranged from 0.025 to 0.056μgL-1. The relative standard deviation for fiber-to-fiber reproducibility of five fabricated fibers was less than 9.4%. The developed method was successfully applied to the preconcentration and determination of trace UV filters from environmental water samples. Furthermore the fabrication of the C8-S-AuNPs/SS fiber can be performed in a highly reproducible manner. This fabricated fiber exhibits good stability and long lifetime, and could be a potential alternative for the conventional fused silica fiber.

Fabrication of a novel Ti–TiO2–ZrO2 fiber for solid-phase microextraction followed by high-performance liquid chromatography for sensitive determination of UV filters in environmental water samples

A novel Ti–TiO2–ZrO2 fiber for solid-phase microextraction (SPME) was fabricated by chemical oxidization of a Ti wire substrate and subsequent electrodeposition of ZrO2 nanoparticle coating. The chemically oxidized procedure afforded in situ fabrication of porous TiO2 nanostructures on a Ti wire and provided a desirable substrate for further deposition of ZrO2 nanoparticle coating. The best extraction capability was obtained by ZrO2 nanoparticles with a size distribution of 20–30 nm and a coating thickness of about 4.5 μm after 10 cyclic voltammetry scans. The main parameters affecting the Ti–TiO2–ZrO2 fiber for SPME of ultraviolet (UV) filters were investigated coupled to high-performance liquid chromatography with UV detection. A good linearity was achieved in the range of 0.5–500 μg L−1 with correlation coefficients higher than 0.996. Limits of detection were 0.032–0.082 μg L−1 (S/N = 3). The single fiber repeatability ranged from 4.3% to 12% and the fiber-to-fiber reproducibility ranged from 4.3% to 11% for SPME of spiked water with 50 μg L−1 UV filters (n = 5). Furthermore this fiber has high stability, long service time and high extraction capability for UV filters compared to the commercially available polymeric fibers.

A Novel Fiber with Phenyl-Functionalized MSU (Michigan State University) Coating for Solid-Phase Microextraction Combined with High Performance Liquid Chromatography for Preconcentration and Determination of Trace Polychlorinated Biphenyls in Environmental Water Samples

A novel and robust phenyl-functionalized MSU-1 (Ph-MSU) coated fiber for solid-phase microextraction (SPME) coupled to high performance liquid chromatography (HPLC) was developed for the preconcentration and the determination of 2,4,4′-trichlorobiphenyl (PCB 28), 2,4′,5-trichlorobiphenyl (PCB 31), 2,2′,5,5′-tetrachlorobiphenyl (PCB 52), 2,2′,4,5,5′-pentachlorobiphenyl (PCB 101), 2,3′,4,4′,5-pentachlorobiphenyl (PCB 118), 2,2′,3,4,4′,5′-hexachlorobiphenyl (PCB 138), 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB 153), and 2,2′,3,4,4′,5,5′-heptachlorobiphenyl (PCB 180) in environmental water samples. Experimental conditions affecting SPME were examined in detail. The Ph-MSU coating provided large porosity and short-range mesostructures necessary for high extraction capacity and rapid mass transfer of PCBs. The Ph-MSU coated fiber exhibited selectivity for PCB 28, PCB 31, PCB 118, and PCB 138 in a limited extraction time. Good linearity for all PCBs was obtained with correlation coefficients from 0.9987 to 0.9994. The recoveries were within 94.3% to 103% for the spiked water with 300 ng · L−1 per PCB. The relative standard deviations (RSDs) ranged from 3.10% to 6.23% and the limits of detection (LODs) were between 8.73 ng · L−1 and 13.8 ng · L−1. The proposed method was applied for the determination of PCBs in real river water and rainwater samples. The median recoveries ranged from 85.6% to 118% with RSDs between 4.23% and 8.78%. The experimental results demonstrated that the Ph-MSU fiber coating could be reused for over 250 times without loss of the extraction efficiency. These results clearly indicate that the Ph-MSU coated fiber was rapid, sensitive, and suitable for the preconcentration and determination of trace PCBs in environmental water samples.

Chemically Modified Mesoporous Silica as a Coating Layer of Solid‐Phase Microextraction for Determination of Benzo[a]pyrene in Water Samples

Abstract Phenyl‐functionalized mesoporous silica was synthesized and employed as the coating layer of solid‐phase microextraction (SPME) for the determination of trace amount of benzo[a]pyrene (B[a]P) in water samples coupling to high‐performance liquid chromatography (HPLC) for the first time. The performance of the fiber coating was examined by the effect of extraction time, desorption time, temperature, stirring rate, and ionic strength. Under the experimental conditions, the chromatographic peak area is proportional to the concentration of B[a]P in the range 1.00u2009×u200910−9 to 1.00u2009×u200910−6 molu2009·u2009L−1. The limit of detection is 1.10u2009×u200910−10 molu2009·u2009L−1 (S/Nu2009=u20093). The analytical results of water samples show that the recovery was 86.50u2009∼u2009106.67% and relative standard deviation was 1.80u2009∼u20092.45%. As compared with conventional loop injection of HPLC, SPME with mesoporous silica coating is convenient, sensitive, and suitable for the determination of B[a]P in water samples. It also indicates that chemically modified mesoporous silica is a novel alternative coating of SPME. The authors are grateful to the Key Laboratory of Polymer Materials of Gansu Province and the National Natural Science Foundation of China for its financial support (No. 20735031).

Enantiomeric Separation Using Erythromycin as a New Capillary Zone Electrophoresis Chiral Selector

Abstract The chiral selectivity of erythromycin was examined in capillary zone electrophoresis using a fused silica capillary column. Excellent chiral separations of four derivatives of biphenyldimethylester for antihepatitis drugs (A1–A4) have been achieved, respectively. The effects of various experimental factors such as chiral selector concentration and pH value, voltage and temperature, organic modifiers on enantiomeric resolution were investigated. Enatioresolution was found to significantly improve with increasing chiral selector concentration while the migration time of the analytes showed slight increase. Enantioselectivities of the chiral solutes were considerable influenced by the content of organic modifieres in running buffer. For chiral separation of the above racemates, the optimal run-buffer consisting of 20 mM erythromycin, 50 mM phosphate and 50% methanol (pH = 6) was obtained by experiment.

Rapid preparation of robust polyaniline coating on an etched stainless steel wire for solid-phase microextraction of dissolved bisphenol A in drinking water and beverages

A new approach for rapid preparation of porous polyaniline (PANI) coating on a stainless steel (SS) wire was developed in nitric acid containing aniline. The SS wire was first etched in hydrofluoric acid and then used as a working electrode for electrodeposition of PANI coating. The etching procedure on a SS wire provides porosity necessary for higher extraction capability of PANI coating and for the extraction phase to hold firmly onto the SS fiber. The porous structure of the PANI coating prepared in nitric acid (PANI–NO3) was more uniform than that prepared in sulfuric acid (PANI–SO4). These PANI coatings were applied to solid-phase microextraction (SPME) of bisphenol A (BPA) coupled with high performance liquid chromatography with ultraviolet detection (HPLC-UV). Their SPME performance was compared and SPME conditions based on the PANI–NO3 coating were further optimized. The linear range was 0.01–100 ng mL−1 with a correlation coefficient of 0.9996. The relative standard deviation was 2.36% for a spiked sample with BPA of 10 ng mL−1 (n = 5) and the limit of detection was 0.005 ng mL−1. The fiber-to-fiber reproducibility of 6.41% was achieved for three PANI–NO3 coated fibers prepared under the same conditions. Finally, the porous PANI–NO3 coating was used for the selective and efficient preconcentration of dissolved BPA in drinking water and beverages. The recoveries of spiked BPA in the real samples ranged from 90.56% to 108.2%. The prepared PANI–NO3 coated fibers have high mechanical strength and chemical stability, long lifetime, high extraction efficiency and good selectivity for the extraction of BPA in complex matrices.

In situ anodic growth of rod-like TiO2 coating on a Ti wire as a selective solid-phase microextraction fiber

A novel rod-like TiO2 based solid-phase microextraction (SPME) coating was directly fabricated by in situ anodization of Ti wire substrates in ethylene glycol and aqueous solution with 5 wt% NH4F (v/v = 1:1). The compact rod-like TiO2 has much larger surface area with a diameter of about 150 nm and a length of about 1.2 µm. The SPME performance of the as-fabricated fiber was investigated for the concentration and determination of polycyclic aromatic hydrocarbons, phthalates and ultraviolet (UV) filters coupled to high performance liquid chromatography with UV detection (HPLC-UV). It was found that the rod-like TiO2 coating exhibited high extraction capability, good selectivity and rapid mass transfer for some UV filters. The main parameters affecting extraction performance were investigated and optimized. Under the optimized conditions, the calibration graphs were linear in the range of 0.05–200 µg L−1. The limits of detection of the method were 0.024–0.032 µg L−1 (S/N = 3). The single fiber repeatability varied from 5.44% to 7.81% and the fiber-to-fiber reproducibility ranged from 7.41% to 8.63% for the extraction of spiked water with 50 µg L−1 UV filters (n = 5). The SPME-HPLC-UV method was successfully applied to the selective concentration and determination of target UV filters from real environmental water samples with recoveries from 84.68% to 104.8% at the spiking level of 5 µg L−1, 25 µg L−1 and 50 µg L−1. The relative standard deviations were below 9.82%. Furthermore, the in situ growth of the rod-like TiO2 coating on a Ti wire by one-step anodization is simple, rapid and reproducible. The rod-like TiO2 coating was cross-linked and embedded into the Ti wire substrate. As a result, the as-fabricated fiber is robust and has long service time.

Dispersive liquid–liquid microextraction followed by high performance liquid chromatography for determination of phthalic esters in environmental water samples

A new method was developed for the simultaneous determination of six phthalic acid esters (PAEs) in different environmental water samples using salt-assisted dispersive liquid–liquid microextraction with carbon tetrachloride as an extraction solvent and acetonitrile as a dispersive solvent coupled with high performance liquid chromatography with UV detection. The influence of the added NaCl on the enrichment factor (EF) in DLLME was investigated. The salting-out effect causes the hydrophobicity of organic analytes to be increased and high EFs to be more pronounced than those in salt-free water. Greater EF, wider linearity, better recovery, smaller relative standard deviation (RSD) and lower limit of detection were obtained at higher concentration of NaCl. Under optimized extraction conditions, good linearity was observed for all analytes in a range of 1.00–100 μg L−1 with the correlation coefficient (r2) ≥0.9992. The limits of detection based on the signal to noise ratio of 3 were 0.01–0.03 μg L−1. The recoveries of PAEs were 97.5–105.5% for spiked water with 20 μg L−1 of PAEs. The repeatability of the proposed method expressed as RSDs ranged from 3.13 to 5.32% (n = 3). EFs are in the range of 78 to 262 fold. The method was applied to the determination of PAEs in water samples from local river, rain and urban wastewater treatment plants with the standard addition, the recoveries of PAEs were 86.2–105.0%, 93.8–107.0% and 92.4–106.3%, and the RSDs were below 6.79%. The current procedure afforded a convenient, inexpensive and reliable sample preparation with high extraction efficiency for trace PAEs in environmental water samples.

Comparative study on fluorescence enhancement and quenching of europium and terbium chelate anions in cationic micelles

Fluorescence enhancement and quenching of water soluble chelates of terbium (Tb3+) with Tiron, salicylic acid (SA), 4-sulfonyl salicylic acid (SSA) and acetylacetone (AA) and sparingly soluble chelates of europium (Eu3+) with beta-diketones were comparatively examined in the presence of cetyltrimethyl ammonium bromide (CTMAB) and cetylpyridinium chloride (CPC). By the composition of the complexes, surface tension measurements and spectral analysis, the binding mode of chelate anions to the micellar surface of cationic surfactants was discussed in terms of ion-exchange model. Quenching effect of CPC on the fluorescence of association complexes seems to arise from the charge transfer from a fluorescent ligand to pyridinium cation. In the case of the chelates of Eu3+ with beta-diketones, however, pyridinium ion is only capable of overlapping the aromatic ring of beta-diketones to less extent since the poorly soluble charged chelates have a weak affinity for the highly polar surface of pyridinium cationic micelles. Efficient charge transfer between the excited aromatic beta-diketone and pyridinium cation fails to be established. CPC also shows enhanced effect on fluorescence like CTMAB.

Solid-Liquid Extraction, Separation, and Determination of Rare Earths With Di-(2-Ethylhexyl)Phosphoric Acid

Abstract The extraction behavior of rare earths has been studied with di-(2-ethylhexyl)phosphoric acid (DEHP) in paraffin, naphthalene, and biphenyl. The group separation of rare earths with DEHP was further examined in paraffin. In the presence of 0.3 mol/L HNO3 and 2.0 mol/L DEHP, light rare earths can be separated from heavy ones in rare earth ores. Quantitative analysis of the rare earths was then done by spectrophotometry.