Search

Abstract Heteroatom doping can endow graphene quantum dots (GQDs) with various new or improved structural, optical and physicochemical properties. In contrast to the widely reported oxygen, nitrogen or sulfur doping in GQDs, simple and scalable synthesis of boron-doped GQDs (B-GQDs) with high yield and quantum yields remains challenge. In this work, B-GQDs are one-step synthesized and serve as the fluorescence probes for the fabrication of sensors towards Fe3+ ion or phosphate (Pi) as well as biosensor towards cytochrome C (Cyt C). The B-GQDs are facile synthesized using one-step bottom-up molecular fusion between 1,3,6-trinitropyrene and borax in sodium hydroxide under hydrothermal process. The synthesis can be performed using large volume autoclave (500 ml) with a high yield of 71%, indicating possibility for gram-scale production of B-GQDs. The as-prepared B-GQDs exhibit single or bilayer graphene structure, high crystallinity, uniform size, bright (absolute photoluminescence quantum yield of 16.8%) and excitation-independent green fluorescence (maximum excitation wavelength and emission wavelength of 480 nm and 520 nm, respectively). Successful doping of B atoms in the lattice of GQDs enables high selectivity towards Fe3+. Based on quenching of fluorescence of B-GQDs by Fe3+ (turn-off model), detection of Fe3+ (with limit of detection-LOD of 31.2 nM) and Fe3+-rich Cyt C (with LOD of 5.9 μg/ml) are demonstrated. As Pi can recover Fe3+-quenched fluorescence of B-GQDs (turn-off-on model), indirect fluorescent detection of Pi is also achieved with LOD of 340 nM. In addition, detection of Fe3+, Cyt C and Pi in real samples is achieved. Graphic abstract fx1 Highlights • B doped GQDs (B-GQDs) are facile prepared using one-step hydrothermal process. • Fluorescence sensor for sensitive detection of Fe3+ is achieved with B-GQDs as probe. • Fluorescence biosensor for detection of cytochrome C using B-GQDs is demonstrated. • Indirect detection of phosphate is achieved by recovery of Fe3+-quenched fluorescence. [ABSTRACT FROM AUTHOR]

The presence of heavy metals in crude oil can create different problems on the oil processing and devices as well as pollution of the environment. Establishment of sample preparation methods for the extraction of metals from crude oil is the bottleneck of a successful determination method due to high hydrophobicity and complexity of crude oil matrix. In this study, a dispersive solid phase extraction procedure was developed for the simultaneous extraction of sixteen metal ions based on in-situ formation of an adsorbent in the sample solution. For this purpose, a suitable amount of dithiooxamide was dissolved in an organic solvent and was injected into the sample solution. By this action, dithiooxamide was re-precipitated in the sample solution and adsorbed the ions. The solid particles were separated and then the ions were eluted by a few microliters of choline chloride: 5-amino-8-hydroxyquinoline deep eutectic solvent under sonication. The presented method was validated and broad linear ranges (7.56–50000 ng g−1) were obtained for calibration curves with coefficient of determination ≥0.992. Acceptable limits of detection (0.003–2.32 ng g−1) and quantification (0.009–7.56 ng g−1) were achieved. Good precision (relative standard deviation less than or equal to 4.3% for intra and inter-day precisions) and acceptable extraction recoveries (66–91%) were also obtained. Seven crude oil samples were analyzed and ten metal ions were determined successfully. The method was compared with the methods reported in literature and it was found that the data obtained by this method were reliable and accurate. [Display omitted] • In-situ formation of a solid adsorbent was used for the extraction of some metal ions from crude oil. • Microflow nebulizer inductively coupled plasma-mass spectrometry was used for determination of the analytes. • Choline chloride: 5-amino-8-hydroxyquinoline deep eutectic solvent was used during extraction procedure. • Greenness, low cost, and effective sample preparation are advantages of the method. [ABSTRACT FROM AUTHOR]

A new rhodamine functionalized fluorogenic Schiff base CS was synthesized and its colorimetric and fluorescence responses toward various metal ions were explored. The sensor exhibited highly selective and sensitive colorimetric and “off–on” fluorescence response towards Al 3+ in the presence of other competing metal ions. These spectral changes are large enough in the visible region of the spectrum and thus enable naked-eye detection. Studies proved that the formation of CS –Al 3+ complex is fully reversible and can sense to AcO − /F − via dissociation. The results revealed that the sensor provides fluorescence “off–on–off” strategy for the sequential detection of Al 3+ and AcO − /F − . [ABSTRACT FROM AUTHOR]

Abstract: Near-infrared spectroscopy (NIRS) has been proved to be a powerful analytical tool and used in various fields, it is seldom, however, used in the analysis of metal ions in solutions. A method for quantitative determination of metal ions in solution is developed by using resin adsorption and near-infrared diffuse reflectance spectroscopy (NIRDRS). The method makes use of the resin adsorption for gathering the analytes from a dilute solution, and then NIRDRS of the adsorbate is measured. Because both the information of the metal ions and their interaction with the functional group of resin can be reflected in the spectrum, quantitative determination is achieved by using multivariate calibration technique. Taking copper (Cu2+), cobalt (Co2+) and nickel (Ni2+) as the analyzing targets and D401 resin as the adsorbent, partial least squares (PLS) model is built from the NIRDRS of the adsorbates. The results show that the concentrations that can be quantitatively detected are as low as 1.00, 1.98 and 1.00mgL−1 for Cu2+, Co2+ and Ni2+, respectively, and the coexistent ions do not influence the determination. [Copyright &y& Elsevier]

Abstract: New chromogenic diazophenylcalix[4]arenes 1 and 2 were synthesized in cone conformation. Compound 1 with the ortho-carboxyl groups in CH3CN solution preferentially binds with alkaline earth and transition metal ions, whereas no significant changes in absorption spectra are observed in the presence of alkali metal ions. While 2 with the ortho-ester groups shows selective complexation properties towards transition metal ions over alkali and alkaline earth metal ions. The detection of metal ions gives rise to bathochromic shifts in the absorption spectra (from orange/yellow to red), which is clearly visible even to the naked eye. According to the selective color changes using both receptors upon cation complexation, one can set up a qualitative analytical routine to screen alkali, alkaline earth, and transition metal ions. [Copyright &y& Elsevier]

Macrocyclic polyethers are ligands with selectivity for metal ions. In order to understand the interactions between ligand, ion and solvent we resorting to study of magnetic field effect on ion-macrocyclic complexes. Therefore, we studied the complexation between 18-crown-6 and potassium ion in water through the conductometry technique (in 25+0.05 °C) by a nonlinear least-square program (Genplot) under magnetic field.We observed that stability constants of complexes in the presence of the magnetic field, were decreased. Like-wise, we observed that, magnetic field influenced on ion, solvent and ligand one by one. [Copyright &y& Elsevier]

In the earlier parts of this series of reviews , the most relevant flowing stream techniques (namely, segmented flow analysis, continuous flow analysis, flow injection (FI) analysis, sequential injection (SI) analysis, multicommuted flow injection analysis and multisyringe flow injection analysis) applied to the determination of several core inorganic parameters for water quality assessment, such as nutrients and anionic species including nitrogen, sulfur and halogen compounds, were described.In the present paper, flow techniques are presented as powerful analytical tools for the environmental monitoring of metal ions (alkaline and alkaline-earth metals, and elemental and harmful transition metals) as well as to perform both multielemental and speciation analysis in water samples. The potentials of flow techniques for automated sample treatment involving on-line analyte separation and/or pre-concentration are also discussed in the body of the text, and demonstrated for each individual ion with a variety of strategies successfully applied to trace analysis. In this context, the coupling of flow methodologies with atomic spectrometric techniques such as flame atomic absorption spectrometry (FAAS), electrothermal atomic absorption spectrometry (ETAAS), inductively coupled plasma mass spectrometry (ICPMS) or hydride-generation (HG)/cold-vapor (CV) approaches, launching the so-called hyphenated techniques, is specially worth mentioning. [Copyright &y& Elsevier]

Pyrocatechol is immobilized on cellulose via &z.sbnd;NH&z.sbnd;CH2&z.sbnd;CH2&z.sbnd;NH&z.sbnd;SO2&z.sbnd;C6H4&z.sbnd;N&z.dbnd6;N&z.sbnd; linker and the resulting macromolecular chelator characterized by IR, TGA, CPMAS 13C NMR and elemental analyses. It has been used for enrichment of Cu(II), Zn(II), Fe(III), Ni(II), Co(II), Cd(II) and Pb(II) prior to their determination by flame atomic absorption spectrometry (FAAS). The pH ranges for quantitative sorption (98.0–99.4%) are 4.0–7.0, 5.0–6.0, 3.0–4.0, 5.0–7.0, 5.0–8.0, 7.0–8.0 and 4.0–5.0, respectively. The desorption was found quantitative with 0.5 mol dm−3 HCl/HNO3 (for Pb). The sorption capacity of the matrix for the seven metal ions has been found in the range 85.3–186.2 μmol g−1. The optimum flow rate of metal ion solution for quantitative sorption of metal onto pyrocatechol functionalized cellulose as determined by column method, is 2–6 cm3 min−1, whereas for desorption it is 2–4 cm3 min−1. The tolerance limits for NaCl, NaBr, NaI, NaNO3, Na2SO4, Na3PO4, humic acid, EDTA, ascorbic acid, citric acid, sodium tartrate, Ca(II) and Mg(II) in the sorption of all the seven metal ions are reported. Ascorbic acid is tolerable up to 0.8 mmol dm−3 with Cu and Pb where as sodium tartrate does not interfere up to 0.6 mmol dm−3 with Pb. There is no interference of NaBr, NaCl and NaNO3 up to a concentration of 0.5 mol dm−3, in the sorption of Cu(II), Cd(II) and Fe(III) on to the chelating cellulose matrix The preconcentration factors are between 75 and 300 and t1/2 values ≤5 min for all the metal ions. Simultaneous sorption of Cu, Zn, Ni and Co is possible at pH 5.0 if their total concentration does not exceed lowest sorption capacity. The present matrix coupled with FAAS has been used to enrich and determine the seven metal ions in river and tap water samples (relative standard deviation (R.S.D.) 1.05–7.20%) and synthetic certified water sample SLRS-4 (NRC, Canada) with R.S.D. ∼2.03%. The cobalt present in pharmaceutical vitamin tablets was also preconcentrated on the modified cellulose and determined by FAAS (R.S.D. ∼1.87%). [Copyright &y& Elsevier]