Structural and spectrophotometric characterization of 2-[4-(dimethylamino)styryl]-1-ethylquinolinium iodide as a reagent for sequential injection determination of tungsten

An Innovative Vortex-Assisted Liquid-Liquid Microextraction Approach Using Deep Eutectic Solvent: Application for the Spectrofluorometric Determination of Rhodamine B in Water, Food and Cosmetic Samples

A new green and highly sensitive method for the determination of rhodamine B (RhB) by deep eutectic solvent-based vortex-assisted liquid-liquid microextraction with fluorescence detection (DES-VALLME-FLD) was developed. The extraction efficiency of conventional solvents and different deep eutectic solvent (DES) systems composed of tetrabutylammonium bromide (TBAB) and an alcohol (hexanol, octanol, or decanol) in different ratios were compared. DFT calculations of intermolecular electrostatic and non-covalent interactions of the most stable RhB forms with DES and water explain the experimental DESs' extraction efficiency. Semiempirical PM7 computations were used to obtain Hansen solubility parameters, which supported the good solubility of the monocationic RhB form in selected DESs. The dependence of the linear calibration of microextraction into 100 µL DES was observed in the RhB calibration range from 0.2 to 10.0 µg L-1 with a correlation coefficient of R2 = 0.9991. The LOD value was calculated to be 0.023 µg L-1. The accuracy and precision of the proposed method were verified over two days with RSD values of 2.9 to 4.1% and recovery of 94.6 to 103.7%. The developed method was applied to the determination of RhB in real samples (tap water, energy drink, and lipstick).

Chemical vapor generation of tungsten for atomic spectrometric determination: Homogeneous sensitizer and mechanism study

BACKGROUND

Inductively coupled plasma-mass spectrometry (ICP-MS) is one of the most powerful instrumental techniques for the determination of tungsten for its low detection limit and wide linear range, while it remains challenging since the analytical performance can be affected by complicated sample matrix. Chemical vapor generation (CVG) harbors the potential to be an alternative to conventional solution nebulization for sample introduction to reduce matrix effect. However, the CVG of tungsten was low in efficiency. It is clear that green and homogeneous enhancement for CVG of tungsten is desired and the mechanism is worth in-depth investigation.

RESULTS

Two green and homogeneous enhancement systems for CVG of tungsten were studied, including photochemical vapor generation (PVG) and hydride generation (HG) with sensitizers, Fe3+ and DDTC, respectively. Under optimal conditions, the limits of detection (LODs) were 0.02 μg L-1 for the PVG and 0.003 μg L-1 for the HG, respectively. For PVG, the Fe3+/Fe2+ cycling, free radical species, gaseous product, and the chemical speciation evolution of W in the PVG process were studied in detail. Photo-Fenton effect, generated reductive radical ·CO2-, gaseous product Fe(CO)5, and the mixed valence of W5+/W6+ in the PVG process were found to be crucial for the enhancement. As for HG, the complexation between W(VI) and DDTC might be conducive to the enhanced HG efficiency.

SIGNIFICANCE

This work not only in-depth expands the element scope of CVG, but also investigates the enhancement mechanisms experimentally, which might render a deep insight into the CVG processes and foreshadow new guidelines for screening green and efficient homogeneous sensitizers for CVGs of more elements in the future.

Recovery of W(VI) from Wolframite Ore Using New Synthetic Schiff Base Derivative

A new synthetic material, namely, (3-(((4-((5-(((S)-hydroxyhydrophosphoryl)oxy)-2-nitrobenzylidene) amino) phenyl) imino) methyl)-4-nitrophenyl hydrogen (R)-phosphonate)), was subjected to a quaternary ammonium salt and named (HNAP/QA). Several characterizations, such as FTIR spectrometry, ¹H-NMR analysis, ¹³C-NMR analysis, ³¹P-NMR Analysis, TGA analysis, and GC-MS analysis, were performed to ensure its felicitous preparation. HNAP/QA is capable of the selective adsorption of W(VI) ions from its solutions and from its rock leachate. The optimum factors controlling the adsorption of W(VI) ions on the new adsorbent were studied in detail. Furthermore, kinetics and thermodynamics were studied. The adsorption reaction fits the Langmuir model. The sorption process of the W(VI) ions is spontaneous due to the negative value of ∆G° calculated for all temperatures, while the positive value of ∆H° proves that the adsorption of the W(VI) ions adsorption on HNAP/QA is endothermic. The positive value of ∆S° suggests that the adsorption occurs randomly. Ultimately, the recovery of W(IV) from wolframite ore was conducted successfully.

Complexation-association-extraction spectrophotometric determination of Pt cations based on a multi-reagent analytical system with I- anions and 2-[2-[4-[(2-cyanoethyl)methylamino]phenyl]vinyl]-1,3,3-trimethyl-3H-indolium cations

A new multi-reagent analytical system with 2-[2-[4-[(2-cyanoethyl)methylamino]phenyl]vinyl]-1,3,3-trimethyl-3H-indolium chloride (CPVTI), which is a styryl hemicyanine cationic dye with good photostability and a high molar absorption coefficient, as its core is first established and utilized successfully to determine the content of Pt ions via a spectrophotometric method. The process involves two treatment steps: adding CPVTI and I solutions to the Pt solution to be detected, and then using butyl acetate for vortex liquid-liquid extraction. A Pt cation can be incorporated into the CPVTI cation with the help of an I^- anion, initially converting the Pt cation into a [PtI₆]^2- complex anion. After forming a [PtI₆^2-·2CPVTI⁺]_(aq) ion associate in the aqueous phase, the Pt cation can be extracted selectively by butyl acetate with maximum extraction efficiency, and exists as [PtI₆^2-·2CPVTI⁺]_(org) in the extract phase. Via the formation of the iodo-complex of Pt and its ion associate with CPVTI, and the extraction with butyl acetate, Pt is selectively partitioned into the butyl acetate extractant in a step-by-step manner with good interference resistance. In the CPVTI-Pt-I analytical system, the charge state of CPVTI is retained by adjustment with H₂SO₄; the monovalent CPVTI⁺ presents a strong spectrophotometric absorbance signal at 530 nm with long-term stability, which allows determination of the Pt content. The system shows a high molar absorption coefficient of 6.52 × 10⁴ L mol^-1 cm^-1 at 530 nm, a lower limit of detection of 0.07 mg L^-1, and a good Sandell's sensitivity of 0.0030 μg cm^-2. Mechanistic analysis of the establishment of the system, concentration optimization, standard working curve, system sensitivity and stability, resistance against interference from diverse metal ions, and practical applications are investigated and discussed.

A DFT study of fulvic acid binding with bivalent metals: Cd, Cu, Mg, Ni, Pb, Zn

3,7,8-Trihydroxy-3-methyl-10-oxo-4,10-dihydro-1H,3H-pyrano [4,3-b]chromene-9-carboxylic acid is a structurally well-characterized fulvic acid (FA) capable to act as a polyfunctional bidentate ligand in the complexes with metal ions. Investigations of the formation mechanisms and structure of the above-mentioned FA complexes with bivalent metals [Cd(II), Cu(II), Mg(II), Ni(II), Pb(II) and Zn(II)] are presently an actual and trending topic in the modern chemistry of humic and fulvic acids. Furthermore, the importance of the theoretical DFT investigations of binding of metals with fulvic acids is stipulated by the lack of the relevant experimental structural data for such complexes. The quantum chemical calculations have shown that, of the four possible FA tautomers, the two FA forms are more stable. The wavefunction analysis and computed reactivity descriptors (electrostatic potential, Hirshfeld surface analysis, natural population analysis charges, and condensed Fukui indexes) give the insight on the properties and reactive ability of these two different forms of the FA. The computed thermochemical parameters of the ion-exchange reaction explain the metal binding affinity and selectivity of the FA forms.

A quercetin based fluorescent chemical sensor for ultra-sensitive determination and speciation of tungsten species in water

The current study explores the use of quercetin for developing a highly selective spectrofluorimetric methodology for trace determination, speciation and thermodynamic characterization of tungstate (WO₄^2-) species in water. The study relies on the principle of chelate formation between WO₄^2- and quercetin with subsequent increase in the emission intensity. The developed method could be applied successfully in a wide linear range (1.0-400.0 μg L^-1) with a detection limit of 0.28 μg L^-1 and quantification limit of 0.92 μg L^-1 at λ_ex/em = 400/492 nm. The developed method was successfully applied in real tap and waste water samples. The suitability of the proposed method was further validated by inductively coupled plasma-optical emission spectrometry (ICP-OES) in terms of student's t and F tests at 95% confidence. Characterization (NMR, FTIR and electronic spectra), stoichiometry, stability constant, fluorescence mechanism and thermodynamic parameters (ΔH, ΔS, and ΔG) of the produced complex species were evaluated and properly assigned. The fluorescence quenching mechanism of tungstate quercetin complex by Triton X-100 was also evaluated for computing Stern-Volmer quenching constant and approximating quenching sphere. The method showed a clear significance over most of the reported methods for tungsten in literature in terms of good accuracy, robustness, ruggedness, short analytical time and cost-effectiveness.