Dongyan Deng

Organic Solvent-Free Cloud Point Extraction-like Methodology Using Aggregation of Graphene Oxide

Because of its unique properties and capability of formation of well-dispersed aqueous colloids in aqueous phase, graphene oxide can be used for the efficient preconcentration of heavy metal ions prior to their determination. The complete collection of graphene oxide colloids from water has generally been considered to be insurmountable. Here, graphene oxide aggregation triggered by introducing NaCl was used to develop a novel organic solvent-free cloud point extraction-like method for the determination of trace toxic metals. The graphene oxide sheets were uniformly dispersed in aqueous samples or standard solutions for a fast and efficient adsorption of Pb(II), Cd(II), Bi(III), and Sb(III) owing to its hydrophilic character and the electrostatic repulsion among the graphene oxide sheets, and its aggregation immediately occurred when the electrostatic repulsion was eliminated via adding NaCl to neutralize the excessive negative charges on the surface of graphene oxide sheets. The aggregates of graphene oxide and analytes ions were separated and treated with hydrochloric acid to form a slurry solution. The slurry solution was pumped to mix with KBH4 solution to generate hydrides, which were subsequently separated from the liquid phase and directed to an atomic fluorescence spectrometer or directly introduced to an inductively coupled plasma optical emission spectrometer for detection. On the basis of a 50 mL sample volume, the limits of detection of 0.01, 0.002, 0.01, and 0.006 ng mL(-1) were obtained for Pb, Cd, Bi, and Sb, respectively, when using atomic fluorescence spectrometry, providing 35-, 8-, 36-, and 37-fold improvements over the conventional method. Detection limits of 0.6, 0.15, 0.1, and 1.0 ng mL(-1) were obtained with the use of slurry sampling inductively coupled plasma optical emission spectrometry. The method was applied for analysis of two Certified Reference Materials and three water samples for these elements.

Ultrasensitive determination of selenium by atomic fluorescence spectrometry using nano-TiO2 pre-concentration and in situhydride generation

An ultrasensitive, simple and interference-free method using nano-TiO2 preconcentration and in situ slurry hydride generation (HG) coupled with atomic fluorescence spectrometry (AFS) was developed for the determination of trace selenium. Total Se reduced in Se(IV) form can be selectively adsorbed on TiO2 at pH < 8 for pre-concentration, and then separated and slurried/released by a mixture containing 3% (m/v) KBH4 and 1% (m/v) KOH. The slurry solution was mixed with 25% (v/v) HCl to generate selenium hydrides, which was subsequently separated from the liquid phase for subsequent AFS detection. Optimum conditions for adsorption, disadsorption and hydride generation of selenium as well as potential interferences from concomitant ions were investigated. Due to the repulsive force between the positively charged TiO2 and metal cationic ions, this approach permits 1000 mg L−1 for Fe3+, Ni2+ and Co2+, 500 mg L−1 for Cu2+ or 100 mg L−1 for Ag+ and Au3+ present in a 5 μg L−1Se(IV) solution without any significant interferences. A limit of detection of 0.0006 μg L−1 was obtained by sampling a 40 mL sample solution. Compared to the conventional HG method, the sensitivity and the limit of detection were improved 17- and 16-fold by the present method, respectively. The proposed method was successfully applied for the determination of trace selenium in several real samples.

Amino-Functionalized Metal-Organic Frameworks Nanoplates-Based Energy Transfer Probe for Highly Selective Fluorescence Detection of Free Chlorine.

Novel highly fluorescent NH2-MIL-53(Al) was controllably synthesized by a facile one-step hydrothermal treatment of AlCl3·6H2O and NH2-H2BDC in water with urea as a modulator. The as-synthesized NH2-MIL-53(Al) nanoplates exhibited excellent water solubility and stability. In the present work, it can be found that strong fluorescence of NH2-MIL-53(Al) nanoplates was significantly suppressed after the addition of free chlorine, and a simple sensing system for fast, highly selective direct detection of free chlorine in water was established. Compared with other fluorescent sensors for free chlorine, the present methodology has a comparable detection limit of 0.04 μM (S/N = 3) and a wide detection range of 0.05 to 15 μM. On the other hand, the traditional redox-based fluorescent probes sharply suffered from the interference of MnO4(-), Cr2O7(2-), and other oxidants with stronger oxidation capability than free chlorine while ours overcame this disadvantage. Further research suggests that it is more likely the energy transfer through N-H···O-Cl hydrogen bonding interaction between amino group and ClO(-) ions plays the key role in our system, providing a new and promising platform for free chlorine determination in water quality monitoring.

Online solid sampling platform using multi-wall carbon nanotube assisted matrix solid phase dispersion for mercury speciation in fish by HPLC-ICP-MS

The integrity of chemical species throughout the analytical procedure and sample throughput are usually two serious impediments in elemental speciation. In this work, a simple solid sampling platform using multi-wall carbon nanotubes (MWCNTs) assisted matrix solid phase dispersion (MSPD) was constructed for online coupling to high performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC-ICP-MS) for the high accuracy and sample throughput mercury speciation in fish samples. Owing to the large surface area and excellent mechanical strength of MWCNTs, which facilitate a sufficient dispersion of a sample matrix and diffusion of the eluent into the mixture of solid support and fish samples, a fast, efficient and online extraction of mercury species was achieved. Compared to the conventional MSPD and other sample pretreatment methods, the proposed method has several advantages including the integration of extraction, clean-up, separation and determination into one single step to achieve a high sample throughput, eliminating the need for derivatization of the Hg species and/or subsequent purification steps, reduced usage of solid supports, minimized contamination and mild operation conditions. The limits of detection of 9.9 ng g−1 and 8.4 ng g−1 were obtained for Hg2+ and CH3Hg+, respectively, based on 1 mg of fish sample. The accuracy of the proposed method was validated by analyzing two certified reference materials. The proposed method was applied for two fresh fish samples for Hg speciation.

Application of Preconcentration and Separation Techniques in Atomic Fluorescence Spectrometry

Abstract With 135 references, this review presents the recent application of various preconcentration and separation techniques in atomic fluorescence spectrometry for the sensitive determination and speciation of various elements and their species. It focuses on sample pretreatment, separation, and enrichment-related techniques, including liquid–liquid extraction, solid-phase (micro)extraction, microwave/ultrasound-assisted extraction, pressurized liquid extraction, as well as chemical vapor generation. In this review, the historical development and overview of these preconcentration and separation methodologies are briefly discussed, together with a comprehensive collection of application of these methods in combination with atomic fluorescence spectrometry for determination of ultratrace amounts of elements and their species in various sample matrices (liquids and solids).

A compact electrothermal-flame tandem atomizer for highly sensitive atomic fluorescence spectrometry

A novel compact tandem atomizer is described and evaluated for its analytical performance using atomic fluorescence spectrometry (AFS). The atomizer simply comprises an argon–hydrogen (Ar–H2) flame atomizer and an electrothermal atomization/vaporization (ETV) sampling device, which utilizes a tungsten coil (W-coil) onto which a liquid sample is pipetted, and subsequently the analyte is electrothermally atomized/vaporized and swept directly into the highly reducing environment of the Ar–H2 flame atomizer for further atomization and detection. The flame sits directly on top of the W-coil without any interface tubing. Improvements in elemental coverage, sensitivity and minimization of analyte loss as well as reduction of reagent consumption were simultaneously achieved by the use of this technique. The absolute limits of detection (LODs) are comparable to those obtained by GF-AAS but provide significant improvements over FAAS and ICP-OES. Its application example was demonstrated by analyzing several Certified Reference Materials and environmental water samples for ultratrace Cd, Pb, Au and Ag.

Silicon carbon nanoparticles-based chemiluminescence probe for hydroxyl radical in PM2.5

A new SiC nanoparticles (SiC NPs)-based chemiluminescence (CL) probe for selective and sensitive detecting of ˙OH has been developed. The radiative recombination of ˙OH-injected holes and electrons in the SiC NPs accounts for the CL phenomenon. Furthermore, the as-developed CL probe has been successfully applied to detect ˙OH in PM2.5.

Carbon nitride quantum dot-based chemiluminescence resonance energy transfer for iodide ion sensing

In this study, a dramatically enhanced chemiluminescence (CL) was observed in Ce(IV) and sulfite system in the presence of graphitic carbon nitride quantum dots (g-CNQDs). On the basis of CL spectra, UV-vis absorption, fluorescence (FL), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) and the effect of various free radical scavengers, a possible CL mechanism of radiative recombination of the holes-injected and electrons-injected g-CNQDs was suggested to account for the surprising g-CNQD CL behavior. Meanwhile, the excited sulfur dioxide molecules , produced from the interaction between Ce(IV) and sulfite under acidic conditions, could transfer energy to g-CNQDs and further enhance the CL emission. In addition, the CL was dependent on the FL quantum yields of g-CNQDs with different surface states, since the chemiluminescence resonance energy transfer (CRET) efficiency was affected by the FL quantum yields of the g-CNQDs. The designed CL system was successfully applied to determine I− in urine samples with good recoveries. It is anticipated that g-CNQDs could be a new class of CRET receptors for fabricating CL sensors. These findings would provide new insight into the optical properties of g-CNQDs and further broaden their applications in CL fields.

A cataluminescence gas sensor based on mesoporous Mg-doped SnO2 structures for detection of gaseous acetone

In this work, the fabrication of mesoporous magnesium doped tin oxide (Mg-doped SnO2) materials with various doping levels has been achieved through a facile one pot and low cost hydrothermal method without the use of a surfactant. The structure, morphology, chemical states and specific surface area were analyzed in detail. By tuning the amount of Mg doping concentration, a series of Mg-doped SnO2 structures with various morphologies including flower-shaped, nanopolyhedrons, nanocubes, and microcubes were successfully synthesized. It was found that the concentration of the Mg dopant has a significant effect on the crystal structure, surface area and morphology. Moreover, the 1 : 3 Mg-doped SnO2 had a specific surface area as high as 138.6 m2 g−1 with a pore size of ca. 3.8 nm. The as-synthesized Mg-doped SnO2 materials and commercial SnO2 powders were used to fabricate cataluminescence gas sensor devices for acetone. It was noted that the CTL sensor based on 1 : 3 Mg-doped SnO2 nanomaterials displayed excellent acetone gas sensing performances such as a fast response time (2 s)/recovery time (25 s), high sensitivity, and good repeatability and selectivity, which indicated that 1 : 3 Mg-doped SnO2 materials would have very promising applications in high performance acetone sensors.

Single nanoparticle analysis by ICPMS: a potential tool for bioassay

Inductively coupled plasma mass spectrometry (ICPMS) has already been demonstrated as a promising technique for metallic nanoparticle tagged bioassays due to its high sensitivity, wide dynamic linear range, and more importantly multiplex and absolute quantification ability. Besides, single nanoparticle analysis by ICPMS has also recently been applied for many metal nanoparticles. Moreover, its short data acquisition dwell times (serval hundred microseconds) lead to an extremely high signal to noise ratio for metal nanoparticles (i.e., low detection limits). This perspective focuses on single nanoparticle analysis-based ICPMS bioassays, which provide high sensitivity without any sophisticated signal amplification procedures. Herein, the recent development of single nanoparticle analysis, ICPMS instrument design, and single molecule analysis is discussed. Considering the vast types of metallic nanoparticles currently available and simultaneous multiplex detection capability of TOF-ICPMS, single nanoparticle analysis-based bioassays may open a new avenue for multiplex single molecule analysis.