Automated Online Preconcentration System for the Determination of Trace Amounts of Lead Using Pb‐Selective Resin and Inductively Coupled Plasma–Atomic Emission Spectrometry

Abstract

An automated sequential‐injection online preconcentration system was developed for the determination of lead by inductively coupled plasma–atomic emission spectrometry (ICP‐AES). The preconcentration of lead was performed with a minicolumn containing a lead‐selective resin, Analig Pb‐01, which was installed between a selection and a switching valve. In an acidic condition (pH 1), lead could be adsorbed on the resin. The concentrated lead was afterward eluted with 25 µL of 0.06 M nitrilotriacetic acid (NTA) solution (pH 9) and was subsequently transported into the nebulizer of ICP‐AES for quantification. The selectivity of the resin toward lead was examined using a solution containing a mixture of 61 elements. When a sample volume of 5 mL was used, the quantitative collection of lead (≥97%) was achieved, along with an enrichment factor of 19, a sampling frequency of 12 samples hr^?1, a detection limit of 70 pg mL^?1, and a lowest quantification limit of 100 pg mL^?1. The linear dynamic range was 0.1 to 5 ng mL^?1, and the relative standard deviation (n=9) was 0.5% at a 5 ng mL^?1 Pb level. The detection limit of 30 pg mL^?1 and lowest quantification limit of 50 pg mL^?1 could be achieved when 10 mL of sample volume was used. The accuracy of the proposed method was validated by determining lead in the standard reference material of river water (SLRS‐4), and its applicability to the determination of lead in environmental river water samples was demonstrated.     

Determination of Enoxacin Using Tb Composite Nanoparticles Sensitized Luminescence Method

In our study, terbium-acetylacetone (Tb-acac) composite nanoparticles have been prepared under vigorous ultrasonic irradiation. The nanoparticles are water soluble, stable and have extremely narrow emission bands and high internal quantum efficiencies. They were used as fluorescence probes in the determination of enoxacin (Enox) based on the fluorescence enhancement of nanoparticles through fluorescence resonance energy transfer (FRET). The influence of buffer solution on the fluorescence intensity was investigated. Under the optimum conditions, the fluorescence intensity of the Tb-acac-Enox system is linearly proportional to the Enox concentration in the Enox concentration range of 2 × 10⁻⁷–1 × 10⁻⁴ M. The correlation coefficient for the calibration curve was 0.9976. The limit of detection as defined by IUPAC, C _LOD = 3S _b/m (where S _b is the standard deviation of the blank signals and m is the slope of the calibration graph) was found to be 3 × 10⁻⁸ M. The relative standard deviation (RSD) for six repeated measurements of 1 × 10⁻⁴ M Enox was 1.35%. The method was applied to the determination of Enox in pharmaceutical formulation and recovery results were obtained from urine samples.     

Step-addition Method for Enhancing the Yield of Gold Nanoparticles in Block Copolymer Solution

Triblock copolymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) has been used to synthesize gold nanoparticles from hydrogen tetrachloroaureate (III) hydrate (HAuCl₄·3H₂O) salt in aqueous solution at room temperature. Measurements were performed using the triblock copolymer Pluronic P85 (EO₂₆PO₃₉EO₂₆) at a fixed concentration (1 wt%) mixed with varying HAuCl₄·3H₂O concentration in the range of 0.001 to 0.1 wt%. The surface plasmon resonance (SPR) band in UV-visible absorption spectra confirmed the formation of the gold nanoparticles. The maximum yield of the nanoparticles was found at 0.005 wt% of the salt solution. Small-angle neutron scattering (SANS) does not show any significant change in the scattering profile in these suspensions of the nanoparticles. A similar behavior was also observed in dynamic light scattering (DLS) experiments where autocorrelation function was found to be independent of the salt concentration. This can be understood since a high-block copolymer-to-gold ion ratio (r ～ 22) is required in the reduction reaction to produce gold particles. As a result, a very small fraction of the block copolymers were associated with the gold nanoparticles, and hence lead to a very low yield. Both SANS and DLS basically see the micelles of most of these block copolymers, which are not associated with nanoparticles. Based on this explanation, a step-addition method was used to enhance the yield of gold nanoparticles by manifold, where the gold salt is added in small steps to maintain higher value of r (>22), and therefore continuous formation of nanoparticles.     

Determination of lead at physiological level in human biological materials using the total reflection X‐ray fluorescence analysis

Total reflection X‐ray fluorescence (TXRF) analysis was applied in determination of low concentration of lead in samples of human biological materials. The determination of lead in human serum and hair samples is presented as an example. In serum samples, lead concentration was in the range from 0.013 to 0.051 μg/g (median 0.024 μg/g). The reference ranges of lead content in hair are from 1.41 to 4.08 μg/g for men and from 1.18 to 3.29 μg/g for women groups, respectively. Because of Pb concentration range close to the detection limit of the TXRF method, the measurement needed evaluation of the best analytical conditions. This paper presents the results of this evaluation, namely internal standard selection, measurement conditions, and quantitative calibration of the spectrometer. Finally, as a result of evaluation, the detection limit was found on the level 0.001 μg/g (water solution) and about 0.005 μg/g for human hair samples and 0.007 μg/g for serum samples. The obtained values reach nearly the physiological lead level. The presented results are of practical importance for lead concentration studies in human biological materials using the TXRF method. Copyright © 2016 John Wiley & Sons, Ltd.     

A total reflection X‐ray fluorescence method for the determination of chlorine at trace levels in nuclear materials without sample dissolution

A total reflection X‐ray fluorescence (TXRF) method for the determination of chlorine at trace levels in nuclear fuel samples is described. Chlorine present in trace concentrations in nuclear fuel materials such as U₃O₈, (U,Pu)C, PuO₂ and Pu‐alloys was first separated from the solid matrix by pyrohydrolysis as HCl and was collected in 5 mM NaOH solution. This solution was analyzed for chlorine by TXRF spectrometry using Cl Kα analytical line excited by W Lα. Cobalt was used as internal standard. The precision for such chlorine determination was found to be within 27% (n = 4) when the analysis was carried out in air atmosphere. This could be improved to 8% by making TXRF measurement in flowing helium atmosphere. The results obtained from TXRF determinations were also compared with those obtained from ion chromatography (IC) and were in good agreement. The collection of distillate during pyrohydrolysis in NaOH helped in counterchecking loss of chlorine during TXRF sample preparation. The average deviation of TXRF‐determined values in helium‐purged TXRF measurements with IC determined values (as chloride) was 15% at a chlorine concentration level in the range of 1–70 µg/mL. Copyright © 2012 John Wiley & Sons, Ltd.     

Confocal Fluorescence Recovery After Photobleaching of Green Fluorescent Protein in Solution

Fluorescence recovery after photobleaching (FRAP) is one of the most widely used approaches to quantitatively estimate diffusion characteristics of molecules in solution and cellular systems. In general, comparison of the diffusion times (t _1/2) from a FRAP experiment provides qualitative estimates of diffusion rates. However, obtaining consistent and reliable quantitative estimates of mobility of molecules using FRAP is hindered by the lack of appropriate standards for calibrating the FRAP set-up (microscope configuration and data fitting algorithms) used in a given experiment. In comparison with other fluorescent markers, the green fluorescent proteins (GFP) possess characteristics that are ideal for use in such experiments. We have monitored the mobility of pure enhanced green fluorescent protein (EGFP) in a viscous solution by confocal FRAP experiments. Our experimentally determined diffusion coefficient of EGFP in a glycerol–water mixture is in excellent agreement with the value predicted for GFP in a solution of comparable viscosity, calculated using the Stokes–Einstein equation. The agreement in the experimentally determined diffusion coefficient and that predicted from theoretical framework improves significantly when one takes into account the effective size of the bleached spot in such experiments. Our results therefore validate the use of GFP as a convenient standard for FRAP experiments. Importantly, we present a simple method to correct for artifacts in the accurate determination of diffusion coefficient of molecules measured using FRAP arising due to the underestimation in the effective size of the bleached spot.     

Effects of pressure and temperature on the solubility of monosodium L-glutamate monohydrate in water

Abstract

The solubility of monosodium L-glutamate monohydrate (MSG.H₂O) in water was measured at pressures in the range of 0.10-300MPa and 298.15K. The density of MSG solution at high concentrations and heat of solution at saturated concentration were also measured at atmospheric pressure. The solubility, m_s, increased with increasing pressure and the pressure coefficient, Θ_p, [?(? In m_s,? p)_T] at 0.10 MPa was (2.0 ± 0.1) × 10-¹⁰Pa-1. It agrees well with (2.1 ±0.2)× 10-¹⁰ Pa-¹ thermodynamically estimated using the partial molar volume, the activity coefficient of the solute in solution, and the molar volume of the crystal. The excellent agreement at 0.10MPa gives us confidence in the solubility data at higher pressures. The heat of solution data and other pertinent values were used to calculate the temperature coefficient of solubility, Θ_T [? (? In m_s/?(1/T))_p], by a thermodynamic equality. The resulting Θ_T compares well with the data directly measured by Ogawa.     

Graphene oxide‐based solid phase extraction of vitamin B12 from pharmaceutical formulations and its determination by X‐ray fluorescence

In the present study, a novel quantitative method, namely solid phase extraction, was applied to extract vitamin B₁₂ from pharmaceutical formulations. The technique involves the use of graphene oxide (GO) as an efficient adsorbent for solid‐phase extraction of vitamin B₁₂. Collection of GO from aqueous solution was simply achieved by applying filtration assembly. The extracted analyte was directly analyzed by using X‐ray fluorescence (XRF) spectroscopy. Factors affecting the extraction efficiency were investigated and optimized. Under the optimum conditions, enhancement factor of 46, linear dynamic range of 25–1000 µg l^?1 with correlation of determination (R² = 0.998) and limit of detection of 20 µg l^?1 were obtained for vitamin B₁₂. The percent relative standard deviation based on three‐replicate determination was less than 8.1%. The method was successfully applied for extraction and determination of vitamin B₁₂ in different types of pharmaceutical samples such as multivitamin tablet, effervescent tablet and injection sample. The results showed that the proposed method based on GO was a simple, accurate, and highly efficient approach for analysis of vitamin B₁₂. Copyright © 2014 John Wiley & Sons, Ltd.     

Ab Initio Investigation of the Microspecies and Energy in Hydrated Strontium Ion Clusters

Quantum chemistry calculations were used to study the structure and energy of strontium (Sr) ion hydrated clusters [Sr(H₂O)_1?25]²⁺. The saturated hydration number of the first hydration layer of Sr²⁺ was 8, and the hydration distance was 2.58 Å. The second hydration layer had 1–9 hydration numbers, and the hydration distance was in the range of 4.4–4.6 Å. This work also developed the relationship between the thermodynamic data (average water binding energy E_n and successive water binding energy ΔE_n,n?1, etc.) of the aforementioned low-energy structure and the hydration structures. The first hydration layer was formed by the strong electrostatic interaction between Sr²⁺ and water molecules, and the decrease in ΔE_n,n?1 was relatively large. Hydrogen bonds were formed between water molecules of the second hydration layer and water molecules of the inner layer, and the decrease in ΔE_n,n?1 was relatively small. When one water molecule was added beyond the second hydration layer, ΔE_n,n?1 was close to the hydrogen bond energy 8.88 kcal/mol (37.1 kJ/mol) of dimer water molecule, indicating that there was very weak interaction between Sr²⁺ and the water molecules beyond the second hydration layer.     

Incoherent quasielastic neutron scattering from H2O and aqueous ZnCl2 solutions

A study of the diffusive motions of the protons in pure water and ZnCl₂ aqueous solutions has been performed, using incoherent quasielastic neutron scattering. It is shown that it is essential to take into account the rotational motion of the water molecules. The translational linewidth is conveniently fitted over the whole Q-range, using the Random Jump Diffusion model for which the jump length turns out to be roughly the same for pure H₂O and the saturated solution, fairly close to the distance between protons in the water molecule.     

Fluorescence of a Benzothienopyridopyrimidone in Solution and in Lipid Vesicles

Fluorescence properties of a biologically active benzothienopyridopyrimidone in solution and in lipid vesicles are reported. Assays at different pH values (0.5–10) allowed the determination of pK _a = 2.0, showing that this compound may be useful as a pH indicator for pH ≤ 4. In lipid vesicles, benzothienopyridopyrimidone locates in a water-rich environment, indicating that it can be carried in the hydrophilic region of liposomes for drug delivery applications.     

Carbon-13 Kinetic Isotope Effects in the Decarbonylation Of Liquid Formic Acid in Water Solution

Abstract

Carbon-13 kinetic isotope effects (¹³C KIEs) in the decarbonylation of formic acid diluted with water 1:1 (V:V) has been studied in the 130–181°C temperature interval in sealed vacuum all glass reactions vessels. The experimental ¹³C KIEs are higher than the ¹³C KIEs values extrapolated from low 50–100°C temperature interval ¹³C KIEs observed in the decarbonylation of water free liquid formic acid but less than ¹³C KIEs expected theoretically assuming the complete carbon—oxygen (¹³C[sbnd]¹⁶O) bond rupture in the transition state. For instance the (k₁₂/k₁₃) KIE found in this study is 1.0375 at 170.2°C while the “full” ¹³C KIE is expected to be 1.0429 at this temperature. The ¹³C KIE extrapolated to 170.2°C from the low temperature data published earlier is 1.0299. - The Arrhenius activation energy for the decarbonylation of formic acid in 1:1 water solution E = 31.3 kcal/mol is by 6 kcal/mol higher than that which was obtained with 99,9% pure formic acid (E = 25,660 kcal/mol). The entropy of activation ΔS ^≠ increased from -21.4 e.u. (pure formic acid) to -15.3 e.u. in the decarbonylation of formic acid diluted with water 1:1. The increases of the enthalpy of activation, of the entropy of activation and partly of the carbon-13 kinetic isotope effect observed in the decarbonylation of formic acid in water solution have been rationalized by suggesting isotopic equilibria interfering the pure kinetic fractionation of ¹³C and intervention of the water molecules into the process of transfer of protons to the formic acid molecules lowering the absolute rate of their decomposition.     

Distribution and speciation of lead in model plant Arabidopsis thaliana by synchrotron radiation X‐ray fluorescence and absorption near edge structure spectrometry

To obtain reliable in situ information on the distribution and speciation of Pb in plants with low Pb content, special attention needs to be paid to the synchrotron radiation based micro‐X‐ray fluorescence and micro‐X‐ray absorption near edge structure (μ‐XANES) spectrometry to avoid specious results in the chosen XRF region of interest and speciation linear combination fitting. First, an Arabidopsis thaliana shoot cultured in a Pb solution is analyzed to obtain two‐dimensional Pb distribution graphs, where an overlap of Pb, As, Se, and Br lines in synchrotron radiation based micro‐X‐ray fluorescence spectra is found. To avoid this overlap, (1)As K‐L₃ and Pb L₃‐M₅, (2)As K‐M₃, (3)Pb L₂‐M₄, (4)Se K‐L₃, and (5)Br K‐M₃ lines should be chosen in the region of interest. The Pb content in the seed coat, root, and stem are 48.2, 17.3, and 5.8 times higher, respectively, than in the leaf, while the Pb content in the seed coat, root, stem, and leaf increased 3458, 1241, 420, and 72 times, respectively, compared with the A. thaliana sample without a Pb solution soak. Second, Pb speciation of the same shoot is analyzed using μ‐XANES. It is important to define a combination fitting range because different possible Pb combinations can emerge using different ranges. Different speciations were found in the root[Pb(Ac)₂ and PbSO₄], stem[Pb(Ac)₂ and Pb₃(PO₄)₂], leaf[Pb(OH)₂ and Pb₅Cl(PO₄)₃], and seed coat[Pb₃(PO₄)₂, Pb(OH)₂, and PbCO₃] between the fitting range of E₀ ? 20eV and E₀ + 70eV. A more complete Pb XANES database with more references, especially organic Pb compounds, is needed. Copyright © 2013 John Wiley & Sons, Ltd.     

Room‐Temperature Synthesis of High Surface Area Anatase TiO2 Exhibiting a Complete Lithium Insertion Solid Solution

The synthesis of highly divided anatase TiO₂ nanoparticles displaying 300 m² g^?1 surface area is achieved by following a two‐step synthetic process at room temperature. The particles exhibit a needle‐like morphology composed of self‐assembled 4 nm nanoparticles. The crystallization process from amorphous TiO₂.1.6H₂O to oriented aggregation of anatase TiO₂ proceeds according to a slow solid dehydration process taking place in a large range of pH in deionized water (1 < pH < 12) or alternatively when including a low amount of NH₄F_(aq) in solution. Driven by their high surface area enhancing the chemical/electrochemical reactivity, it is reported in the case of the anatase TiO₂ that a modification in the lithium insertion mechanism is no longer attributable to a two‐phase reaction between the two‐end members Li_εTiO₂ and Li_0.5±αTiO₂ when downsizing the particle size, but instead through a complete solid solution all along the composition range.     

Evaluation of Gypsum and Calcium Oxalates in Deteriorated Mural Paintings by Quantitative FTIR Spectroscopy

This study dealt with the development of a procedure based on quantitative FTIR spectroscopy to determine the amount of some contaminants in wall paintings, mortars, and stone micro‐samples. As contaminants we selected gypsum, CaSO₄ · 2H₂O, and calcium oxalate monohydrate, CaC₂O₄ · H₂O, among the most common polluting substances present in architectural porous materials. Calibration curves of absorbance versus analyte concentration were determined by adopting both the internal and external standard methods. As internal standard we used Prussian blue, Fe₃[Fe(CN)₆]₄, that presents an unique infrared peak at 2094 cm^? 1. The correlation coefficient for a linear fit was very good for every calibration, being in each case greater than 0.9900. Furthermore, the precision of the evaluation of gypsum and calcium oxalates varied in the range 8–15% and ca. 4% respectively. In order to verify the findings, some specimens, which came from real frescoes, were analysed both by DSC calorimetry and FTIR spectroscopy: we found a satisfactory match between the quantitative analyses performed by the two techniques. For the first time, the application of this method allowed the quantitative determination of the desulphatization power of the Ferroni‐Dini method—based on the ammonium carbonate and barium hydroxide technique—in the conservation of mural paintings.     

Polymer/clay nanocomposites based on MMT/ODA intercalates

Natural Na-montmorillonite (MMT) with the formula (Na_0.67K_0.01Ca_0.02)(Al_2.90Mg_0.59 Fe³⁺ _0.49Ti_0.01)(Si_7.92Al_0.08)O₂₀(OH)₄was intercalated with octadecylamine (C₁₈H₃₉N) (ODA) with varied MMT/ODA ratios. The basal spacings d(00l) of natural and intercalated Na-MMT with ODA were determined by XRD analysis. The set of basal diffractions: d(001) = 56 Å, d(002) = 28 Å, d(003) = 18 Å, d(004) = 14 Å, d(005) = 11 Å for the saturated Na-MMT/ODA intercalate indicates existence of highly ordered periodic structure with the ODA double-layer intercalated in the silicate interlayer spacing. Molecular modeling calculations were applied to the Na-MMT/ODA saturated intercalation system. Stable structure with d-spacing 53 Å has been calculated which is in a good agreement with the experimental data. Such structure gives good conditions for the organosilicate layered structure exfoliation and nanocomposite production. Na-MMT/ODA intercalates were compounded with polypropylene. In accordance with theoretical predictions, XRD analysis applied to compounded structures have proved that a high degree of the organoclay exfoliation was achieved.     

Influence of silver on the anodic corrosion and gas evolution of Pb-Sb-As-Se alloys as positive grids in lead acid batteries

The influence of silver addition in the range 0.01-0.09 wt.% on the anodic corrosion and gas evolution of Pb-Sb-As-Se alloy in 1.28 sp.gr. H₂SO₄ solution at 25 °C was studied using linear sweep voltammetry, cyclic voltammetry, weight loss measurements and scanning electron microscopy. The results drawn from different techniques are comparable. The effect of different concentration of silver on the corrosion behavior of Pb-Sb-As-Se was investigated. The experimental results show that the silver added to Pb-Sb-As-Se alloy inhibits the growth of anodic corrosion layer. A decrease in the oxygen evolution overpotential and an increase in the hydrogen evolution overpotential with the addition of Ag were also observed during the experiments. Cyclic voltammetric measurements provided information on the effect of Ag on the oxidation of PbSO₄ to PbO₂.     

Optical Flow-Through Sensor for the Determination of Norfloxacin Based on Emission of KMnO<Subscript>4</Subscript>–Na<Subscript>2</Subscript>SO<Subscript>3</Subscript>–Tb<Superscript>3+</Superscript> System

A simple and selective method to determine norfloxacin using an optical flow-through sensor has been developed. The present sensor was prepared by packing anionic ion exchange resin in a glass tube, followed by introducing KMnO₄ solution to the glass tube for immobilization on resin. The optical sensor is based on the emission intensity from the Tb(III) solution sensitized by norfloxacin. The excitation of norfloxacin occurred by the chemiluminescence from the reaction of KMnO₄ and Na₂SO₄ solutions. The effects of pH, concentration of Tb(III) ion, KMnO₄ and Na₂SO₄ solutions and flow rate of the norfloxacin solution on the chemiluminescence intensity were studied to find the optimum experimental conditions. The emission intensity increased linearly with increasing norfloxacin concentration from 1.0 × 10⁻³ to 1.0 × 10⁻⁸ M and the detection limit (3σ) was 8.7 × 10⁻⁹. The applicability of the present method was demonstrated by determination of norfloxacin in various pharmaceutical preparations and serum sample.     

IR absorption spectrum (4200–3100 cm) of H2O and (H2O)2 in CCl4. Estimates of the equilibrium constant and evidence that the atmospheric water absorption continuum is due to the water dimer

IR absorption spectra, 4200–3100 cm⁻¹, of water in CCl₄ solutions are presented. It is shown that for saturated solutions significant amounts of water are present as dimer (ca. 2%). The IR spectra of the monomer and dimer are retrieved. The integrated absorption coefficients of the monomer absorption are significantly enhanced relative to the gas phase values. The dimer spectrum consists of 5 bands, of which 4 were expected from data from cold beams and cold matrices. The origin of the “extra” band is discussed. In addition it is argued that the dimer absorption bands intensities must be enhanced relative to the gas phase values. Based on recent calculations of band strengths, and observed frequency shifts relative to the gas phase, the intensity enhancement factors are estimated as well as the monomer/dimer equilibrium constant in CCl₄ solution at T=296 K (K_c=1.29 mol⁻¹ L). It is noted that the observed dimer spectrum has a striking resemblance with the water vapour continuum determined by Burch in 1985 which was recently remeasured by Paynter et al. and it is concluded that the atmospheric water absorption continuum in the investigated spectral region must be due to water dimer. Based on the newly published spectral data a revised value of the gas phase equilibrium constant is suggested (K_p=0.035 atm⁻¹ at T=296 K) as well as a value for the standard enthalpy of formation, ΔH⁰=15.4 kJ mol⁻¹.     

Effects of Monomer Feed Amounts on Solution Properties and Solution Morphologies for a Comb-like Ter-polymer

An acrylamide(AM)-based ter-polymer (PAAB) containing sodium 2-acrylamido-2-methylpropane sulphonate (NaAMPS) and p-vinylbenzyl-terminated octylphenoxy poly(ethylene oxide) (VBE, polymerization degree: 24) was synthesized by an aqueous free-radical copolymerization. In order to obtain a PAAB polymer with both good thickening properties and surface and interfacial properties in brine solutions for enhanced oil recovery (EOR), the influences of the NaAMPS and VBE feed amounts on the intrinsic and apparent viscosities and the surface and interfacial tensions of the PAAB polymer in aqueous solutions were investigated. The optimum NaAMPS feed amount was 9 mol%; an excessive feed amount interfered with the aggregations of the PAAB macro-molecules in aqueous solutions and on the surfaces of aqueous solutions and the interfaces between aqueous solutions and kerosene. In addition, for this NaAMPS feed concentration, the PAAB polymer showed the highest apparent viscosities and the lowest surface and interfacial tensions in 5 g L^?1 NaCl for a VBE feed amount of 1.1 mol%. The mechanism giving rise to the solution properties for this polymer was examined. For this purpose, the effect of the polymer concentration on the supra-molecular structures of the PAAB polymer in water and in 5 g/L NaCl, were investigated by ultraviolet spectral analysis using pyrene as a probe. A transmission electron microscope (TEM) was also used to observe the morphologies of the associated structures in aqueous solutions to explore the correlation between the solution properties and solution structures for PAAB; expanded polymer chain bundles were formed at a polymer concentration of 0. 4 g L^?1, higher than the critical micelle concentration (0. 3 g L^?1).