Dongxia Zhang

Ultrasound-assisted liquid–liquid microextraction based on an ionic liquid for preconcentration and determination of UV filters in environmental water samples

In the present study, a dispersive liquid–liquid microextraction with ionic liquids (ILs) as extraction solvents was developed for the preconcentration and determination of four ultraviolet (UV) filters from different environmental water samples. Ultrasound-assisted dispersion of the ILs in the water phase was employed. The UV filters were easily concentrated into the ionic liquid phase. This technique combined the process of extraction and concentration of the analytes into one step and avoided the use of more toxic halogenated solvents. Affecting factors including the type and volume of the ILs and disperser solvents, ultrasonic time, centrifugation time, ionic strength and pH of aqueous samples were optimized. The extracts were directly analyzed by high-performance liquid chromatography coupled with a diode array detector. Under the optimized conditions, the current method provided good repeatability (RSDs < 7.6%, n = 5) and high enrichment factors in the range of 492–834. The limits of detection (LOD) for the UV filters were in the range of 0.06–0.16 ng mL−1. The linearities were between 0.2 and 500 ng mL−1 for 2-hydroxy-4-methoxybenzophenone, 0.5 and 500 ng mL−1 for 2-ethylhexyl 4-(N,N-dimethylamino) benzoate, 0.4 and 500 ng mL−1 for 2-ethylhexyl-4-methoxycinnamate, and 0.5 and 500 ng mL−1 for 2-ethylhexyl salicylate, respectively. The current procedure was successfully applied to simultaneous analyses of four UV filters in environmental water samples. For all analyzed samples, the established method has allowed fast and reliable preconcentration and determination of these UV filters with simple sample pre-treatment requirements.

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.

Au-Pt bimetallic nanoparticles supported on functionalized nitrogen-doped graphene for sensitive detection of nitrite.

In this work, we report a novel Au-Pt bimetallic nanoparticles (Au-PtNPs) decorated on the surface of nitrogen-doped graphene (NG) functionalized with 1, 3, 6, 8-pyrene tetra sulfonic acid sodium salt (PyTS) by direct electrodeposition method. The results of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and electrochemical impendence spectrum (EIS) reveal that the Au-PtNPs were successfully anchored on the surface of NG sheets with a diameter of 20-40nm. Further, the prepared Au-PtNPs/PyTS-NG nanocomposite exhibits superior catalytic activity for the oxidation of nitrite. Under optimal experimental conditions, an amperometric sensor with a linear range of 0.5-1621μM and a detection limit of 0.19μM (S/N=3) for the detection of nitrite was set up and applied to real samples.

Au-Pt bimetallic nanoparticles decorated on sulfonated nitrogen sulfur co-doped graphene for simultaneous determination of dopamine and uric acid

In this work, a novel nanohybrid (AuPtNPs/S-NS-GR) of well-defined Au-Pt bimetallic nanoparticles (Au-PtNPs) decorated on sulfonated nitrogen sulfur co-doped graphene (S-NS-GR) was developed. Firstly, nitrogen sulfur co-doped graphene (NS-GR) was synthesized by one-step thermal annealing method. Secondly, phenyl SO3H- group was introduced onto the surface of NS-GR via diazotization reaction, which could provide more binding sites for the formation of metal nanoparticles. Finally, Au-Pt bimetallic nanoparticles were anchored on the surface of S-NS-GR by using electrochemical deposition. The prepared material was characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), Raman spectroscopy and electrochemical impedance spectra (EIS). In addition, the electrocatalytic activity towards dopamine (DA) and uric acid (UA) was systematically studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. Under optimum conditions, the linear ranges for the detection of DA and UA were 1.0×10-8 - 4.0×10-4 M and 1.0×10-6 - 1.0×10-3 M with the limits of detection (LOD, S/N = 3) of 0.006μM and 0.038μM, respectively. Furthermore, the modified electrode was applied to real sample analysis.

A Novel Sensitive Electrochemical Sensor for the Simultaneous Determination of Hydroquinone and Catechol using Tryptophan-Functionalized Graphene

A novel tryptophan-functionalized graphene nanocomposite was employed for the simultaneous determination of hydroquinone and catechol. The analyte electrochemical behavior on the surface of tryptophan-functionalized graphene was investigated by cyclic voltammetry and differential pulse voltammetry. Compared to conventional graphene, enhanced peak currents were obtained that were attributed to the large number of defects on tryptophan-functionalized graphene that accelerated electron transfer between the electrode and analytes. The peak potential difference between hydroquinone and catechol at the tryptophan-functionalized graphene modified glassy carbon electrode was 104 millivolt, which was sufficiently wide to simultaneously determine hydroquinone and catechol. This method was used for the analysis of tap water.

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.