Tungsten coil atomic emission spectrometry combined with dispersive liquid–liquid microextraction: A synergistic association for chromium determination in water samples

Tip-porous microneedle: A highly stable sensing platform for direct determination of labile metals in natural seawater

Nanomaterial-functionalized voltammetric microsensors are promising tools for detecting trace metals at low concentrations in the complex environment of natural seawater. However, the sensitivity reduction caused by the loss of modified nanomaterials in the detection process has always been a major problem. Herein, to fabricate a highly stable sensing platform, a microneedle electrode with a hierarchical porous tip was prepared through electrochemical etching technology to firmly embed nanoparticles. Using copper (Cu) as a model trace metal, a micro-cluster needle sensor based on a gold nanoparticle (AuNP)-embedded tip-porous microneedle electrode (P-MNE) was fabricated for the direct voltammetric determination of labile Cu in natural seawater. The porous structure of P-MNE not only provided a larger specific surface area and active sites for AuNPs which had excellent electrocatalytic performance for Cu²⁺ determination, but also protected from their loss during the detection process in seawater. Therefore, this novel micro-cluster needle sensor exhibited significantly improved stability with a relative standard deviation (RSD) of 1.5% for 30 detections. The linear range of Cu²⁺ on this micro-cluster needle sensor was from 0.1 to 1000 nM with a detection limit of 0.03 nM. More importantly, this micro-cluster needle sensor was successfully used for directly detecting labile Cu in natural seawater samples without any preaccumulation treatment or reagent addition to obtain the contribution proportions of the labile fraction in total dissolved Cu. Furthermore, this sensing platform might also be extended to the reliable determination of other labile metals in seawater by changing the functional nanoparticles embedded in the nanopores.

Landing microextraction sediment phase onto surface enhanced Raman scattering to enhance sensitivity and selectivity for chromium speciation in food and environmental samples

The current study explores the first full mode liquid microextraction technique coupled with surface-enhanced Raman spectroscopy (SERS), and has been successfully applied for chromium speciation in food and environmental matrices. Herein, chromium as chlorochromate anion [CrO3Cl]- and the cationic rhodamine 6G [RG]+ dye has been extracted in organic phase as a complex ion associate [RG+.CrO3Cl-.nS]org at pH ≤ 1.0. Afterwards, the extracted phase was deposited on the surface of the nano-flower shaped silver nanoparticles substrate and the SERS response was monitored against the reagent blank at 1505 cm-1. Substrate characterizations, reaction mechanism assignment, stoichiometry, speciation, analytical applications, selectivity and validation were performed. The analytical procedure exhibits a detection limit of 0.03 µg L-1 under the optimized experimental conditions. The accuracy of the proposed strategy was validated by inductively coupled plasma optical emission spectrometry method using student's t- and F tests at 95% confidence.

State-of-the-art on the technique of dispersive liquid-liquid microextraction

Dispersive liquid-liquid microextraction is a new sample pretreatment technology based on traditional liquid liquid extraction. In this paper, the application of low-toxicity extractants such as low-density extractants, auxiliary extractants, stripping agents and ionic liquids in this technology and the extraction modes such as solvent de-emulsification, suspension extractant curing, auxiliary extraction, back extraction, and ionic liquid-dispersion liquid microextraction, are summarized. In addition, the synergism of this technique with other sample preparation techniques, such as liquid-liquid extraction, solid-phase extraction, solid-phase microextraction, dispersive solid phase extraction, matrix solid-phase dispersion extraction, supercritical fluid extraction and ultrasound-assisted dispersive liquid-liquid microextraction is discussed.

Simultaneous Speciation Analysis of Trace Heavy Metals (Cu, Pb, Cd and Zn) in Seawater from Sishili Bay, North Yellow Sea, China

Different species of trace heavy metals (HMs) in seawater samples were simultaneously analyzed by anodic stripping voltammetric method, an analytical technique that does not require sample pre-concentration or the addition of reagents. The effects of the crucial parameters, deposition potential and time, on the determination of HMs were investigated. Concentrations of the total dissolved, dissolved active, and dissolved inert HMs were obtained through different analysis processes. The three species of Cu, Pb, Cd and Zn in seawater samples collected in different locations across Sishili Bay, North Yellow Sea, China were studied. The relative concentration of the dissolved active Cu, Pb, Cd and Zn in the total dissolved concentrations is 59.0%, 69.6%, 87.3% and 84.1%, respectively. The concentrations of different HMs species in Sishili Bay could be affected by the discharged effluent, sea current, and uptake of marine organism.

Determination of Trace Elements in Cow Placenta by Tungsten Coil Atomic Emission Spectrometry

Tungsten coil atomic emission spectrometry (WCAES) is used to determine trace levels of Mn (403.1 nm) and Cr (425.5 nm) in cow placenta. All samples were collected in Ilha Solteira, SP, Brazil. The instrumental setup is based on a tungsten filament extracted from 150 W, 15 V microscope light bulbs, a solid state power supply, fused silica lens, crossed Czerny-Turner spectrograph, and a thermoelectrically cooled charge-coupled device detector. The limits of detection (LOD) and quantification (LOQ) for Cr are 2 and 8 μg L^-1, and 20 and 60 μg L^-1 for Mn, respectively. Recoveries for 0.30 mg L^-1 spikes of each analyte were in the range 93.0-103.0%, and relative standard deviation (RSD) was between 6.50 and 7.20% for both elements. Placenta samples were microwave-assisted digested with diluted HNO₃ and H₂O₂ and analyzed by WCAES. The results for Cr and Mn were compared with values obtained by tandem inductively coupled plasma mass spectrometry (ICP-MS/MS). No statistically significant difference was observed between the different methods by applying a paired t test at a 95% confidence level. The average concentrations of Cr and Mn in the placentas evaluated were 0.95 ± 0.22 and 2.64 ± 0.39 μg g^-1, respectively. By using a short integration time, LODs for Cr and Mn were lower than values reported by recent works using a similar WCAES system.