Accurate and sensitive determination of lead in black tea samples using cobalt magnetic particles based dispersive solid-phase microextraction prior to slotted quartz tube-flame atomic absorption spectrometry

Novel paper-based potentiometric combined sensors using coumarin derivatives modified with vanadium pentoxide nanoparticles for the selective determination of trace levels of lead ions

Novel miniaturized Pb(II) paper-based potentiometric sensors are described using coumarin derivatives I and II as electroactive ionophores and nano vanadium pentoxide as a solid contact material for the sensitive and selective monitoring of trace lead ions. Density functional theory (DFT) confirms optimum geometries, electronic properties, and charge transfer behaviors of 1:2 Pb(II): coumarin complexes. The sensors are prepared by using two strips of 20 × 5 mm filter paper with two circular orifices. One orifice is coated with vanadium pentoxide (V2O5) nanoparticles in colloidal conductive carbon as a solid-contact, covered by a PVC membrane containing coumarin ionophore to act as a sensing probe. The other orifice is treated with Ag/AgCl in a polyvinyl butyral (PVB) film, to act as a reference electrode. Sensors with ionophores (I) and (II) exhibit Nernstian slopes of 27.7 ± 0.2 and 30.2 ± 0.2 mV/decade over the linear concentration range 4.5 × 10-7 to 6.2 × 10-3 M and 8.5 × 10-8 to 6.2 × 10-3 M, with detection limits of 1.3 × 10-7 M (26.9 ppb) and 2.1 × 10-8 M (4.4 ppb), respectively. The sensors are satisfactorily used for accurate determination of lead ions in drinking water, lead-acid battery wastewater, and electronic waste leachates. The results compare favourably well with data obtained by flameless atomic absorption spectrometry.

CNTs intercalated graphene oxide with interspersed MoS2 nanoparticles for selective preconcentration and determination of trace Hg(II) ions

The carbon nanotubes (CNT) intercalated graphene oxide (GO) nanosheets was functionalized with molybdenum disulfide nanoparticles (MSNP). Intercalation of CNT in between GO nanosheets significantly enhances porosity and avail both surfaces of GO for MSNP decoration. High porosity and densely populated MSNP led to faster Hg(II) ions diffusion and sorption. The material shows high selectivity for Hg(II) sorption due to sulfur rich sites. The GO/CNT@MSNP packed column employed for trace Hg(II) preconcentration and determination in fish, rice, mushroom, sunflower seeds and river and ground water samples. No significant hindrances by co-existing matrices in the determination of Hg(II) was found. The method shows a preconcentration factor of 540 and a preconcentration limit of 0.37 μg L^-1. The method detection limit was found to be 0.03 μg L^-1 and a good precision (RSD 4.2%). The Student's t test score was lower than critical Student's t value of 4.303 at the 95% confidence level. ENVIRONMENTAL IMPLICATION: Metal ions toxicity is a global issue and their trace level analysis from complex matrices is remains challenging. SPE of trace Hg(II) by graphene oxide is challenging due to agglomeration and less selectivity, nevertheless of its high surface area. We prepared a Hg(II) selective nanocomposite of MoS₂ quantum dots grows onto GO surface. The hybrid nanocomposite selectively adsorbed Hg(II) ions from complex sample matrices. Compared to a nascent GO membrane, it were more efficient to preconcentrate and determine Hg(II) from real samples and provide more accurate data for environmental monitoring and assessment of action plan to control the Hg(II) pollution.

Simultaneous determination of Co and Pb in P. polyphylla var. yunnanensis by ICP-OES after GO-TiO2-DES-based dispersive micro solid phase extraction

In this work, deep eutectic solvent (DES) was used to modify GO-TiO₂ to synthesize new adsorption material GO-TiO₂-DES nanocomposites. It was first used for dispersive micro solid phase extraction (DMSPE) and combined with inductively coupled plasma optical emission spectrometry (ICP-OES) for simultaneous determination of trace cobalt (Co) and lead (Pb) in natural medicine P. polyphylla var. yunnanensis. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), and the Brunauer-Emmett-Teller (BET) specific surface area were used to characterize. The results showed that GO-TiO₂-DES nanocomposites were successfully prepared and had better adsorption effect on metal ions. The factors affecting the extraction and elution of Co and Pb were optimized, including the type of DES, pH, adsorption time, amount of adsorbent, adsorption temperature, and elution time. Under the optimum conditions, the enhancement factors (EFs) of Co and Pb were 31 and 28, the limits of detection (LODs) were 0.11 and 0.24 μg L^-1, and the limits of quantification (LOQs) were 0.36 and 0.82 μg L^-1, respectively. The results of Co and Pb determined by the established method were in good agreement with those of inductively coupled plasma mass spectrometry (ICP-MS), which verified the accuracy and reliability of the method.

Chiral Graphene Hybrid Materials: Structures, Properties, and Chiral Applications

Chirality has become an important research subject. The research areas associated with chirality are under substantial development. Meanwhile, graphene is a rapidly growing star material and has hard-wired into diverse disciplines. Rational combination of graphene and chirality undoubtedly creates unprecedented functional materials and may also lead to great findings. This hypothesis has been clearly justified by the sizable number of studies. Unfortunately, there has not been any previous review paper summarizing the scattered studies and advancements on this topic so far. This overview paper attempts to review the progress made in chiral materials developed from graphene and their derivatives, with the hope of providing a systemic knowledge about the construction of chiral graphenes and chiral applications thereof. Recently emerging directions, existing challenges, and future perspectives are also presented. It is hoped this paper will arouse more interest and promote further faster progress in these significant research areas.

Nano-sized magnetic Ni particles based dispersive solid-phase extraction of trace Cd before the determination by flame atomic absorption spectrometry with slotted quartz tube: a new, accurate, and sensitive quantification method

In this study, a new analytical strategy was developed to determine trace cadmium in aqueous samples with high sensitivity and accuracy. A combination of magnetic nickel nanoparticles (Ni-MNPs) based dispersive solid-phase extraction (DSPE) and flame atomic absorption spectrometry fitted with a slotted quartz tube (SQT-FAAS) lowered the detection limit of cadmium. The magnetic Ni nanoparticles were synthesized, characterized, and thoroughly optimized in a stepwise approach. The quartz tube was custom cut in the laboratory to suit the specifics of the flame burner. Using the optimized conditions, a limit of detection value of 0.58 μg/L and limit of quantification value of 1.93 μg/L were obtained. To demonstrate accuracy and applicability of the developed method, well water samples were analyzed for their Cd content, and matrix effect on the extraction yield was investigated. The percent recovery results calculated ranged from 93.8 to 108.2%, with corresponding standard deviation values ranging from 1.7 to 7.7. These results established the developed method as sensitive, accurate, and precise for determination of cadmium at trace levels.