Determination of Cadmium in Seawater by Vapor Generation Atomic Fluorescence Spectrometry After Online Preconcentration with a Novel Alkyl Phosphinic Acid Resin

Abstract

Vapor generation atomic fluorescence spectrometry (VG‐AFS) coupled with online preconcentration on a short column (4.6 mm×50‐mm length) packed with a newly synthesized alkyl phosphinic acid resin (APAR) was developed for the determination of trace Cd in seawater. During the online preconcentration process, Cd in seawater was concentrated on the column while the matrix of seawater was separated flowing out of the column. Cd concentrated on the column was then eluted effectively from the column with 0.1 mol L^?1 tartaric acid within 40 s. When the sample volume was 200 mL, an enrichment factor 189 was achieved. The detection limit of this proposed method for Cd is 2.67 ng L^?1. The recovery of Cd is 96.6% obtained by spiking the correspondence standard, and the precision (RSD) is 4.34% (n=6). The established APAR/VG‐AFS was applied to the determination of soluble Cd in the seawater around Xiamen Island, China.     

Dispersive liquid–liquid microextraction based on solidification of floating organic drop for separation and preconcentration of malachite green before its determination by flow injection spectrophotometry

ABSTRACT

A simple and fast dispersive liquid–liquid microextraction based on solidification of floating organic drop has been developed for the separation and preconcentration of malachite green in water samples prior to its determination by flow injection spectrophotometry. Sodium lauryl sulfate, an anionic surfactant, was used for the ion-pair formation with malachite green. The factors affecting the ion-pair formation and extraction were optimized. Under the optimized conditions (volume of 1-undecanol as the extraction solvent, 40 μL; the volume of ethanol as the disperser solvent, 100 μL; sodium lauryl sulfate concentration, 7.5 × 10^?7 mol L^?1, and the pH of the sample, ～3.0), the calibration graph was linear over the range of 0.8–25 µg L^?1 with the detection limit of 0.3 µg L^?1 and the preconcentration factor of 750. The relative standard deviation at 7 µg L^?1 (n = 6) was found to be 2.1%. The developed method was successfully applied to the determination of malachite green in river water and fish farming water samples.     

Electrochemical detection of trace cadmium in soil using a Nafion/stannum film-modified molecular wire carbon paste electrodes

In this paper, a novel Nafion polymer-coated stannum film-modified carbon paste electrode was developed for the analysis of trace cadmium by square wave anodic stripping voltammetry. The electronic conductive material—molecular wire (diphenylacetylene)—was employed as the binder instead of traditional mineral oil for fabricating this electrode. It was found that the prepared electrode possessed excellent electrochemical performance and increased electron transfer rate due to the introduction of molecular wire as a binder, and exhibited a better sensitivity and stability as well as high resistance to surfactants due to the synergistic effect of Nafion and stannum film. Under the optimal conditions, the stripping peak currents showed a good linear relationship with the Cd(II) concentration in the range from 1.0 to 80.0 μg L^?1 with a detection limit of 0.13 μg L^?1 (S/N?=?3). The developed electrode was further applied to the determination of Cd(II) in soil extracts with satisfactory results.     

Preconcentration and Determination of Manganese and Nickel from Various Water Samples by Nano Zirconium Oxide/Boron Oxide

ABSTRACT

This work assesses the potential of the adsorptive material nano zirconium oxide/boron oxide (ZrO₂/B₂O₃) for removal of trace Mn(II) and Ni(II) from environmental samples. This method is based on the sorption of Mn(II) and Ni(II) ions directly onto nanosorbent, followed by the elution and determination by flame atomic absorption spectrometry (FAAS). Experimental parameters, including pH of sample solution, volume and concentration of eluent, sample volume, and flow rate of sample solution, that affect the recovery of the Mn(II) and Ni(II) ions from model solutions have been optimized. Under the optimum conditions, adsorption isotherms and adsorption capacities have been examined. The recoveries of Mn(II) and Ni(II) were 96% ± 2% and 95% ± 3% at 95% confidence level, respectively. The analytical detection limits for Mn(II) and Ni(II) were 1.9 and 4.9 µ g L^?1, respectively. Adsorption capacities of the nano ZrO₂/B₂O₃ were found as 92.8 mg g^?1 for Mn and 168.4 mg g^?1 for Ni. The accuracy of the method was checked by analyzing certified reference material (SPS-WW1 wastewater) and spiked real samples. The method was applied for the determination of analytes in water samples.     

Highly Selective and Stable Florescent Sensor for Cd(II) Based on Poly(azomethine-urethane)

In this study a kind of poly(azomethine-urethane); (E)-4-((2 hydroxyphenylimino) methyl)-2-methoxyphenyl 6-acetamidohexylcarbamate (HDI-co-3-DHB-2-AP) was prepared as in the literature and employed as a new fluorescent probe for detection of Cd(II) concentration. The photoluminescence (PL) measurements were carried out in the presence of several kinds of heavy metals. HDI-co-3-DHB-2-AP gave a linearly and highly stable response against Cd(II) as decreasing a new emission peak at 562 nm. Possible interferences of other ions were found too low. Detection limit of the sensor was found as 8.86?×?10^?4?mol?L^?1. Resultantly, HDI-co-3- DHB-2-AP could be effectively used as an optical Cd(II) sensor.     

Graphene nanocomposites of CdS and ZnS in effective water purification

The present work deals with syntheses of CdS/graphene and ZnS/graphene nanocomposites by hydrothermal reaction of graphene oxide and morpholine-4-carbodithioate complex of Cd and Zn, respectively. The corresponding nanocomposites has been investigated separately as photocatalyst in the decomposition of methylene blue in the presence of UV light and also as adsorbents in the removal of Cd(II) and Pb(II) ions in contaminated water. These studies have established that CdS/graphene and ZnS/graphene are effective photocatalyst as well as effective adsorbents in the removal of Cd(II) and Pb(II) ions to an extent of 97 and 99 % by ZnS/graphene and CdS/graphene nanocomposite, respectively, under 1 g L^?1 of adsorption dose and at pH ~7. Further studies also established Langmuir model befitting for the adsorption of Pb(II) and Cd(II) ions on CdS/graphene and ZnS/graphene, respectively. The presence of interfering ions on extent of Cd(II) and Pb(II) removal has also been reported.     

A selective sensor for nanolevel detection of lead (II) in hazardous wastes using ionic-liquid/Schiff base/MWCNTs/nanosilica as a highly sensitive composite

An effective potentiometric sensor had been fabricated for the rapid determination of Pb²⁺ based on carbon paste electrode consisting of room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF₆), multiwalled carbon nanotubes (MWCNTs), nanosilica, synthesized Schiff base, as an ionophore, and graphite powder. The constructed nanocomposite electrode showed better sensitivity, selectivity, response time, response stability, and lifetime in comparison with typical Pb²⁺ carbon paste electrode for the successfully determination of Pb²⁺ ions in water and in waste water samples. The best response for nanocomposite electrode was obtained with electrode composition of 18% ionophore, 20% BMIM-PF₆, 49% graphite powder, 10% MWCNT, and 3% nanosilica. The new electrode exhibited a Nernstian response (29.76?±?0.10 mV decade^?1) toward Pb²⁺ ions in the range of 5?×?10^?9?C1.0?×?10^?1 mol L^?1 with a detection limit of 2.51?×?10^?9 mol L^?1. The potentiometric response of prepared sensor is independent of the pH of test solution in the pH range of 4.5?C8.0. It has quick response with response time of about 6 s. The proposed electrode show fairly good selectivity over some alkali, alkaline earth, transition, and heavy metal ions.     

Preconcentration and Separation of Gold(III) from Ore Samples by Solid-Phase Extraction Prior to Its Catalytic Fluorescent Determination

ABSTRACT

A new catalytic kinetic fluorescent quenching method for the determination of trace gold(III) was investigated. The method was based on the catalytic effect of gold on oxidation of 3-(3′-methylphenyl)-5- (2′-arsenoxylphenylazo) rhodanine by hydrogen peroxide in potassium hydrogen phthalate–hydrochloric acid (pH = 3.4). Under the optimum conditions, the great decrease of fluorescence intensity has a linear relationship against the concentration of gold in the range of 0 to 12.0 µg·L^?1 with a detection limit of 6.0 × 10^?10g·L^?1. The coexistent metal ions can be separated, and gold can be enriched by TBP resin of solid-phase extraction, which greatly improves the selectivity and sensitivity of the system. The method can be used to determine trace amounts of gold in ore samples successfully with satisfactory results.     

A Highly Selective Turn-On Fluorescent Chemosensor for Zinc Ion in Aqueous Media

In the paper, a novel rhodamine6G based fluorescent chemosensor bearing 3-carbaldehyde chromone was designed and synthesized. According to the fluorescence behavior toward several metal ions, it showed highly selectivity and sensitivity to Zn(II) over other commonly coexistent metal ions (Cu(II), Cd(II), Hg(II), Mg(II), K(I), Pb(II), Fe(III) and Cr(III)) in aqueous environment (pH?=?7.4). Meanwhile the binding constant between Zn(II) and chemosensor achieved 6.21?×?10¹¹ M^?1 in aqueous media. Moreover, according to the Job plot, 1:1 stoichiometry between Zn(II) and sensor was deduced in aqueous media (pH?=?7.4). The good selectivity and sensitivity in aqueous media effectively enhanced the application value of the fluorescent chemosensor for Zn(II).     

Hydrodynamic Sequential Injection Spectrophotometric System for Determination of Manganese in Soil

ABSTRACT

A novel hydrodynamic sequential injection (HSI) spectrophotometric system for determination of manganese was developed. It is based on the complexation of Mn(II) with formaldoxime in basic solution (pH ≥ 10) to produce product that could be monitored spectrophotometrically at 450 nm. Based on the HSI concept, both sample and reagents were aspirated through solenoid valves to fill a defined volumes conduit between 3-way connectors connected in series, forming stacked zones of solutions similar to those in normal SI. The concept was successfully demonstrated for manganese determination. A linear calibration graph over a range of 0.5 to 30 mg L^?1 Mn(II) with a detection limit of 0.2 mg L^?1 was obtained. Relative standard deviations for 11 replicated injections of 5 and 20 mg Mn L^?1 were 5.6% and 2.4%, respectively. A sample throughput of 45 h^?1 was achieved. The results from investigation of exchangeable manganese in soil samples by the developed method were found to be in good agreement with the results obtained by a batch spectrophotometric method, despite the proposed system employed simpler and more cost-effective devices/instruments, had higher degrees of automation with full microcontroller control of the operation, and consumed smaller amounts of chemicals (250 µL each of hydroxylamine, sample, and formaldoxime solutions and 2.5 mL of buffer carrier solution per operation cycle).     

Spectrofluorimetric Determination of Nickel (ΙΙ) with Murexide

A very sensitive and selective spectrofluorimetric method has been developed for nickel (ΙΙ) determination in environmental samples. The method is based on measuring the decrease in fluorescence intensity of murexide after nickel (ΙΙ) binding. The intensity of the fluorescence emission peak was measured at ex/em 345/431 nm in several solutions with pH interval 3.0–7.0. The fluorescence intensity decrease was found to be linear in the concentration range of 0.007 mg.L^?1 to 0.1 mg.L^?1 and 0.1 mg.L^?1 to 20 mg.L^?1 of nickel (ΙΙ) by using 10^?4 M murexide at pH 3. The detection limit was found 0.004 mg.L^?1. Relatively large excesses of over 20 cations and anions do not interfere. The method was successfully applied to the analysis of nickel (ΙΙ) in sea, rain and ground water. This method is very precise and accurate (R.S.D.?=?0.42 % for the determination of 0.05 mg.L?¹ nickel in 10 replicates).     

Synthesis of Tapioca Cellulose-based Poly(amidoxime) Ligand for Removal of Heavy Metal Ions

Poly(acrylonitrile)/cellulose block copolymer (PAN-b-cell) was prepared by using a free radical initiating process and then the nitrile functional groups of the PAN blocks of the copolymers were transformed into amidoxime ligands. The resulting poly(amidoxime) ligands could complex with heavy metal ions; for example, the reflectance spectra of the [Cu -ligand]ⁿ⁺ was found to be at the highest absorbance, about 94%, at pH 6. The pH was the key parameter for metal ions sensing by the ligand. The adsorption capacity for copper was very good, 272 mg g^?1, with a fast adsorption rate (t_1/2 = 10 min). The adsorption capacities for other heavy metal ions such as Fe³⁺, Cr³⁺, Co³⁺ and Ni²⁺ were also good, being 242, 219, 201 and 195 mg g^?1, respectively, at pH 6. The heavy metal ions removal efficiency from water was 98% at low concentration. The data proved that the heavy metal ions adsorption onto the polymer ligands were well fitted with the Langmuir isotherm model (R²>0.99), which suggests that the cellulose-based adsorbent surface namely the poly(amidoxime) ligand, was homogenous and a monolayer. The reusability was examined by a sorption/desorption process for six cycles and the extraction efficiency was determined. This new adsorbent could be reused for 6 cycles without any significant loss in its original removal function.     

A New Spectrophotometric Method with Di-2-Pyridyl Ketone Benzoylhydrazone for Determination of Nickel(II)

Abstract

Nitrogen-containing heterocyclic hydrazones have been used as analytical reagents, mainly to metallic ion spectrophotometric determinations in natural water samples. Using the reagent di-2-pyridil ketone benzoilhydrazone (DPKBH) we have developed a spectrophotometric method for the determination of Ni(II) in samples of several sources. DPKBH was used in excess in order to coordinate Ni(II) and the highest sensitivity was obtained in 50% v/v ethanol solutions when ammonium acetate buffer was added to maintain pH?6.

Analysis for Ni(II) in natural water is frequently performed by EAAS following preconcentration involving solvent extraction. While these methods are sensitive, they also require relatively expensive instrumentation and are generally time-consuming. In contrast, the advantages of the proposed method are the use of simple instrumentation and the possibility of its application in the field. The method is fast, shows high sensitivity, good precision and several samples can be prepared and measured until 10 hours later .

The best order for the addition of reagents, stability of the complex, effect of the reagents excess and foreign ions besides composition of the complex are here reported. A linear behavior was observed between absorbance and nickel concentration. The favorable range is 8.50×10^?7 to 1.72×10^?5 mol.L^?1. The correlation coefficient is 0.997. The intercept of the linear curve is 3.55×10^?3 and the slope is 4.00×10⁴cm^?1.moI^?1.L. The standard error of the intercept and slope is 3.73×10^?3 and 4.48×10^?4, respectively.     

Simultaneous Determination of Ritodrine and Isoxsuprine Using Coupling Technique of Synchronous Fluorimetry and H-Point Standard Addition Method

Simultaneous determination of two structurally related ß₂ adrenergic receptor agonists namely, Ritodrine HCl (RTH) and Isoxsuprine HCl (ISP) was performed using coupling technique of synchronous fluorimetry and H-point standard addition method. Under optimum conditions, linear determination ranges were 1.48 – 14.80?×?10^?6 mol L^?1 and 1.54 – 15.44?×?10^?6 mol L^?1 for ISP and RTH respectively. RTH and ISP could be determined simultaneously without interference from each other when their concentration ratio varies from 5:1 to 1:5 in the mixed sample. The proposed method was applied to the determination of RTH and ISP in synthetic mixture of pharmaceutical samples, the accuracy and precision of the results were satisfactory.     

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.     

Study on the Cofluorescence Effect of Europium (III)–Yttrium (III)–Balofloxacin–Sodium Dodecyl Sulfate System and Its Analytical Application

A new fluorescence enhancement phenomenon in the europium(III)–balofloxacin–sodium dodecyl sulfate system was observed when yttrium(III) was added. Based on this, a sensitive cofluorescence assay for the estimation of balofloxacin was established. Under the optimized conditions, the enhanced fluorescence signal was linear over the concentration of balofloxacin ranging from 3.0 × 10^?9 to 7.0 × 10^?6 mol L^?1 with a correlation coefficient of 0.9993. The detection limit (3 σ) was determined as 8.3 × 10^?10 mol L^?1. The presented method was successfully applied to determination of balofloxacin in pharmaceutical preparations, human serum, and urine. The possible fluorescence enhancement mechanism was also discussed.     

Flow‐Injection Online Reduction Atomic Fluorescence Spectrometry Determination of Se(IV) and Se(VI) with Electrochemical Hydride Generation

Abstract

A new flow‐injection online reduction electrochemical hydride generation system for the determination of Se(IV) and Se(VI) by atomic fluorescence spectrometry (AFS) was developed. In the system, an electromagnetic induction oven was used as heating resource to reduce Se(VI) to Se(IV) and a homemade tubular electrolytic cell as hydride generator. All analytical procedures were automatically controlled by a computer. The conditions of online reduction, including temperature, HCl concentration, and reduction time, have been studied in detail. The detection limits (3σ) of Se(IV) and Se(VI) in aqueous solution were 0.26 µg L^?1 and 0.23 µg L^?1, respectively. The precision for 11 replicate measurements of 50 µg L^?1 Se(IV) and Se(VI) was 2.2% and 2.5%. This proposed method has been applied to the determination of Se(IV) and Se(VI) in springwater samples.     

Synthesis of thiol-functionalized MCM-41 mesoporous silicas and its application in Cu(II), Pb(II), Ag(I), and Cr(III) removal

Thiol-functionalized MCM-41 mesoporous silicas were synthesized via evaporation-induced self-assembly. The mesoporous silicas obtained were characterized by X-ray diffraction (XRD), nitrogen adsorption–desorption analysis, Fourier transform infrared spectroscopy (FTIR), elemental analysis (EA), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The products were used as adsorbents to remove heavy metal ions from water. The mesoporous silicas (adsorbent A) with high pore diameter (centered at 5.27 nm) exhibited the largest adsorption capacity, with a BET surface area of 421.9 m² g^?1 and pore volume of 0.556 cm³ g^?1. Different anions influenced the adsorption of Cu(II) in the order NO₃ ^? < OAc^? < SO₄ ^2? < CO₃ ^2? < Cit^? < Cl^?. Analysis of adsorption isotherms showed that Cu²⁺, Pb²⁺, Ag⁺, and Cr³⁺ adsorption fit the Redlich–Peterson nonlinear model. The mesoporous silicas synthesized in the work can be used as adsorbents to remove heavy metal ions from water effectively. The removal rate was high, and the adsorbent could be regenerated by acid treatment without changing its properties.     

Synthesis,Spectral Characterization,DNA Binding Studies and Antimicrobial Activity of Co(II), Ni(II), Zn(II), Fe(III) and VO(IV) Complexes with 4-Aminoantipyrine Schiff Base of Ortho-Vanillin

A series of transition metal complexes of Co(II), Ni(II), Zn(II), Fe(III) and VO(IV) have been synthesized involving the Schiff base, 2,3-dimethyl-1-phenyl-4-(2-hydroxy-3-methoxy benzylideneamino)-pyrazol-5-one(L), obtained by condensation of 4-aminoantipyrine with 3-methoxy salicylaldehyde. Structural features were obtained from their FT-IR, UV–vis, NMR, ESI Mass, elemental analysis, magnetic moments, molar conductivity and thermal analysis studies. The Schiff base acts as a monovalent bidentate ligand, coordinating through the azomethine nitrogen and phenolic oxygen atom. Based on elemental and spectral studies six coordinated geometry is assigned to Co(II), Ni(II), Fe(III) and VO(IV) complexes and four coordinated geometry is assigned to Zn(II) complex. The interaction of metal complexes with Calf thymus DNA were carried out by UV–VIS titrations, fluorescence spectroscopy and viscosity measurements. The binding constants (K_b) of the complexes were determined as 5?×?10⁵ M^?1 for Co(II) complex, 1.33?×?10⁴ M^?1 for Ni(II) complex, 3.33?×?10⁵ M^?1 for Zn(II) complex, 1.25?×?10⁵ M^?1 for Fe(III) complex and 8?×?10⁵ M^?1 for VO(IV) complex. Quenching studies of the complexes indicate that these complexes strongly bind to DNA. Viscosity measurements indicate the binding mode of complexes with CT DNA by intercalation through groove. The ligand and it’s metal complexes were screened for their antimicrobial activity against bacteria. The results showed the metal complexes to be biologically active, while the ligand to be inactive.     

Spectrofluorometric Determination of Iron II Based on the Fluorescence Quenching of Cadmium/Tellurium Quantum Dots

Water-soluble and stable CdTe quantum dots were synthesized in aqueous solution with thioglycolic acid as the stabilizer. A spectrofluorometric method for the determination of iron (II) has been developed based on quenching of the fluorescence of CdTe quantum dots by iron (II) in aqueous solutions. It can perform an accurate and simple determination of iron (II) concentration in water samples. Under optimum conditions, the quenched fluorescence intensity increased linearly with the concentration of iron (II) ranging from 5.0 × 10^?8 to 4.0 × 10^?6 mol/L with a correlation coefficient R = 0.9969. The limit of detection for iron (II) was found to be 1.2 × 10^?8 mol/L. As an application, the proposed method was successfully applied to the analysis of iron (II) in water samples, and the results were satisfactory.