Sorption and Desorption of Lead on 5-Amino-1,3,4-Thiadiazole-2-Thiol Immobilized Silica Gel by Flame Atomic Absorption Spectrometry (FAAS)

Abstract

Silica gel was modified by 5-amino-1,3,4-thiadiazole-2-thiol via homogeneous routes to obtain immobilized silica gel sorbent (ATT-immobilized silica gel). This sorbent was characterized using a variety of physical chemical techniques including, high resolution solid state ¹³C CP/MAS NMR, X-ray photoelectron spectroscopy (XPS), thermal analysis (TGA and DTA), elemental analysis, and BET surface analysis, as well as infrared spectroscopy (FTIR). The support was used for sorption and desorption of leadions by silica gel modified with 5-amino-1,3,4-thiadiazole-2-thiol from aquatic samples and their determination with FAAS. Lead ions can be desorbed with 0.001 mol dm^?3 EDTA. The sorption capacity for lead ions is found to be in the range of 48.20–49.50 µmol g^?1(about 10.14 mg L^?1) of chelating matrix. Tolerance limits for electrolytes in the sorption of lead are reported. Experimental data obtained from batch equilibrium tests have also been analyzed by Langmuir isotherm and the Freundlich equation. Theoretically, maximum monolayer adsorption capacity was obtained to be 14.28 for ATT-immobilized silica gel. Pb(II) sorption on ATT-immobilized silica gel was found favorable according to the Langmuir isotherm and the Freundlich equation.     

Determination of copper in industrial water by innovative flow injection flame atomic absorption spectrometry

An online flow injection procedure for the preconcentration of copper at µg L^?1 levels was developed using a novel chelating resin and flame atomic absorption spectrometry for the analysis of industrial water. Amberlite XAD-2 functionalized with dithizone resin was packed in a minicolumn for flow injection. The pH, sample and eluent flow rates, and eluent concentration were optimized to ensure maximum recovery of Cu(II). The effect of concomittant ions on Cu (II) sorption was also investigated. The limit of detection and enrichment factor for a 180 s preconcentration time were 76 and 0.6 µg L^?1, respectively. The resin offered precision of 1.0% for seven successive determinations of 100 µg L^?1 Cu(II). The resin was used for more than 300 sorption and desorption cycles without appreciable loss of efficiency. The accuracy of the preconcentration procedure was confirmed by fortified recovery studies in industrial water with NIST certified copper nitrate with recovery exceeding 96%. Validation was performed by the analysis of a standard reference material.     

Sorption and Preconcentration of Vanadium,Chromium, Manganese,and Lead on Silica Gel Modified with (3‐Mercaptopropyl) Trimethoxysilane

Abstract

3‐mercaptopropyltrimethoxysilane, (CH₃O)₃SiCH₂CH₂CH₂SH, loaded on silica gel was used as a preconcentration sorbent for V, Cr, Mn and Pb prior to their determination by graphite furnace atomic absorption spetrometry (GFAAS). Surface characteristics and surface area of the silica gel before and after chemical modification were determined by elemental analysis. The retention and recovery of the analyte elements were studied by applying batch and column techniques. The experimental parameters, such as the effect of pH of the sample, shaking time in batch technique, flow rate of the eluent, the concentration of acid solution in the column section, and the amount of silica on retention and elution have been investigated. All elements were quantitatively (≥90%) recovered in the batch technique with R.S.D. values of 3.0 for vanadium, 1.8 for chromium, 1.7 for manganese, and 0.4 for lead. The same recoveries were obtained in the column techniques for all elements, while manganese in sea water could not be succesfully recovered. Detection limits of the method for vanadium, chromium, manganese, and lead are 1.1, 1.4, 1.3, and 0.8 ng, respectively.     

改性纳米TiO2分离富集-ICP—AES法测定环境样品中痕量铬、铜、镍和铅

提出了改性纳米TiO2分离富集电感耦合等离子体原子发射光谱（ICP—AES）法测定环境样品中痕量Cr3＋、Cu2＋、Ni2＋和Pb2＋的新方法。系统地研究了溶液pH值、吸附剂用量、洗脱条件、流速、静态吸附容量和干扰离子等因素对分析物分离富集的影响。结果表明,在pH4．0,Cr3＋、Cu2＋、Ni2＋和Pb2＋可被改性纳米TiO2定量富集,吸附的金属离子可用2．0mL2．5mol·L^-1 HCl溶液完全洗脱。在优化的实验条件下,吸附剂对Cr3＋、Cu2＋、Ni2＋和Pb2＋的吸附容量分别为18．1,17．6,23．2和26．8mg·g-1。本法对Cr3＋、Cu2＋、Ni2＋和Pb2＋的检出限（30）分别为：0．25,0．43,0．62,0．39ng·mL-1,相对标准偏差（RSD）分别为2．3％,3．1％,2．5％,3．8％（n=11）。方法用于环境样品中痕量Cr3＋、Cu2＋、Ni2＋和Pb2＋的测定,结果令人满意。     

Simultaneous Determination of Six Trace Elements in Plant Medicines by Derivative Adsorption Waves in Conjunction with a Microwave Technique

Abstract

Complex adsorption waves of Cu(II), Pb(II), Cd(II), Ni(II), Co(II), and Zn(II) in substrate solution (pH=9.26) of diacetyldioxime‐ammonia‐ammonium chloride‐sodium citrate‐gelatin‐sodium sulfite were studied and a new method for determination of the six trace elements in aqueous solutions was developed. The results show that there are sensitive adsorption waves of Cu(II), Pb(II), Cd(II), Ni(II), Co(II), and Zn(II) complexes at about ?0.45, ?0.61,?0.78, ?1.07, ?1.23, and ?1.38 V, respectively. The method is easy to operate and is able to determine these trace elements in aqueous solutions rapidly and simultaneously. When the signal‐to‐noise ratio equals 3, the detection limits of copper, lead, cadmium, nickel, cobalt, and zinc are 3.2×10^?4, 4.8×10^?3, 1.9×10^?3, 1.7×10^?5, 2.1×10^?6, and 1.0×10^?3 µg/cm³. Good linear relationships exist between the concentrations and the current peaks when copper, lead, cadmium, nickel, cobalt, and zinc concentrations are within 6.5×10^?4～10⁰, 9.3×10^?3～10, 4.1×10^?3～10, 3.2×10^?5～10^?1, 4.0×10^?6～10^?2, and 2.1×10^?3～10 µg/cm³, respectively. In conjunction with a microwave assimilation technique, the method has been used in the rapid and simultaneous determination of these trace elements in some plant medicines with satisfactory results.     

On‐Line Preconcentration System for Cobalt Determination in Bee Honey Using Flow Injection‐Flame AAS

Abstract

A methodology for the on‐line preconcentration and determination of cobalt by flame atomic absorption spectrometry (FAAS) coupled with flow injection (FI) in bee honey samples is proposed. For the retention of cobalt, 2‐(5‐bromo‐2‐pyridylazo)‐5‐diethylaminophenol (5‐Br‐PADAP) complexing reagent, and Amberlite XAD‐7 resin were used, at pH 9.5. The Co‐(5‐Br‐PADAP) complexes were completely removed from the column with ethanol. An enrichment factor (EF) of 50‐fold for a sample volume of 50 mL was obtained. The detection limit (DL) for the preconcentration of 50 mL of aqueous solution was 0.18 µg L^?1. The precision for 10 replicate determinations at the 10 µg L^?1 cobalt levels was 3.6% relative standard deviation (RSD), calculated with peak heights obtained. The calibration graph using the preconcentration system for cobalt was linear with a correlation coefficient of 0.9997 at levels near the DL, up to at least 300 µg L^?1. The method was successfully applied to determination of total cobalt in honey samples.     

DETERMINATION OF COPPER(II) IN NATURAL WATERS BY EXTRACTION USING N-O-VANILLIDINE-2-AMINO-P-CRESOL AND FLAME ATOMIC ABSORPTION SPECTROMETRY

A simple and accurate solvent extraction method was developed for the separation and preconcentration of trace levels of copper(II) in water using N-o-vanillidine-2-amino-p-cresol prior to its determination using flame atomic absorption spectrometry. Analytical parameters such as the pH of the aqueous phase, extraction time, concentration of the reagent, concentration of the nitric acid back extraction agent, volumes of aqueous phase and back extraction agent, and concomitant ions on the extraction yield of the copper(II) were investigated and optimized. Under the optimal conditions, the detection limit (3σ) was 0.61 µ g L^?1 for a 25 mL blank solution, yielding a preconcentration factor of 12.5. The method was succesfully applied to the determination of copper(II) in tap water, river water, and seawater. The accuracy of the method was verified by analyzing two certified reference materials and spiked water samples. The results obtained were in agreement with the certified values and the recoveries for spiked water samples were between 98 and 112%.     

ON-LINE MINI-COLUMN SOLID-PHASE EXTRACTION COUPLED WITH SEQUENTIAL INJECTION FOR THE DETERMINATION OF CADMIUM IN ENVIRONMENTAL SAMPLES

□Trace cadmium(II) in environmental samples was separated and enriched in an automated fashion using a diphenylcarbazone-functionalized silica gel mini-column coupling with sequential injection. Cadmium was determined using a multicomponent system involving the analyte, potassium iodide, ethyl violet, and polyvinyl alcohol. Under the optimum conditions, the linear range for cadmium(II) was 0.015–0.50 µ g mL^?1, and the detection limit was 0.012 µ g mL^?1. The relative standard deviation of 11 determinations for 0.1 and 0.2 µ g mL^?1 standard solutions was smaller than 3.5%. This method was applied for the determination of cadmium(II) in water, plant, soil, and electroplating wastewater. No statistically significant differences in the results were observed between the reported method and those obtained by atomic absorption spectrometry. The analysis was performed within 13 min and a total reagent volume of only 0.14 mL (0.07 mL of eluent and 0.07 mL of reagents) was consumed in each determination of cadmium(II).     

Development of a 635 nm-Laser Diode Spectrometer for Continuous Monitoring of Amino Nitrogen in the Beet Sugar Industry

Abstract

The quality of sugar beet is affected by harmful nitrogen compounds. Although nitrogen is one of the essential elements for plants, introduction of excess nitrogen as fertilizer to the soil increases the nitrogen containing compounds in beet which deteriorates the quality of sugar production. Hence, the concentration of soluble nitrogen in beets was monitored as a routine process in the sugar industry. In this work, a low cost, but very long life time laser diode spectrometer, was developed for continuous monitoring of amino nitrogen compounds in sugar beets. A laser diode source emits monochromatic light at 635 nm which is the maximum of absorption spectrum of Cu(II)-glutamine complex. A standard solution of Cu(II) ion and glutamine was prepared at pH = 6.0 to calibrate the laser diode spectrometer. The formation of Cu(II)-glutamine complex was examined at pH = 5.0, 6.0, and 7.0 by a continuous variations method and we found a monovalent complex, Cu(II)(glutamine) at pH = 6.0, and a divalent complex, Cu(II)(glutamine)₂ at pH = 7.0. A continuous mixing system with a peristaltic pump and tubing was set for monitoring of harmful nitrogen in beets, besides sugar determination with a polarimeter and Na and K measurement with a flame photometer, synchronously. The calibration of the laser diode spectrometer yielded a linear correlation coefficient of R² = 0.999. A negative correlation between sugar digestion and amino nitrogen content of sugar beets was found, with a correlation coefficient of R² = 0.807.     

Inductively Coupled Plasma Optical Emission Spectrometric Determination of Gadolinium in Urine Using Flow Injection On‐Line Sorption Preconcentration in a Knotted Reactor

Abstract

An on‐line gadolinium preconcentration and determination system, implemented with ultrasonic nebulization coupled to inductively coupled plasma optical emission spectrometry (ICP‐OES), associated with flow injection (FI) was studied. Gadolinium was retained as Gd‐2‐(5‐bromo‐2‐pyridilazo)‐5‐diethylaminophenol complex (Gd‐5‐Br‐PADAP) at pH 9.0, on the inner walls of the knotted reactor (KR). The collected analyte complexes were quantitatively eluted from the 200 cm KR with 30% (v/v) nitric acid. An enhancement factor of 255‐fold was obtained (17 for KR and 15 for USN). The detection limit (DL) value for the preconcentration of 15 mL of sample was 4.0 ng L^?1. The relative standard deviation (RSD) was 3.5%, calculated from the peak heights obtained. The calibration graph using the preconcentration system for gadolinium was linear, with a correlation coefficient of 0.9996 at levels near the detection limit up to at least 200 µg L^?1. The method was successfully applied to the determination of gadolinium in urine samples.     

Determination of Lead in Spiked Seawater Samples by Electrothermal Atomic Absorption Spectrometry using Chemical Modifiers

Abstract

The determination of lead in spiked sodium chloride solution with 3.4% salinity and natural sea‐water samples by electrothermal atomic absorption spectrometry (ETAAS) with Zeeman‐effect background correction was investigated using neodymium, samarium, and erbium salts as modifiers with the addition of citric acid (CA) as a reducing agent. In order to demonstrate the high potential of rare earth metals in combination with citric acid, optimum pyrolysis temperature, atomization temperature, and optimum masses of neodymium, samarium, and erbium were found for the determination of lead. These modifiers were used for the determination of lead in sodium chloride solution with 3.4% salinity and in natural sea water samples by means of the calibration graphs prepared with pure analyte solutions.

The detection limits for lead spiked sample matrices were calculated with the 2σ criterion between 2.0 to 2.1 ng mL^?1 for neodymium and citric acid, between 5.3 to 7.4 ng mL^?1 for samarium and citric acid, and between 1.7 to 2.1 ng mL^?1 for erbium and citric acid and for a sample volume of 10 µL. The recoveries for lead spiked sea water samples were 97–102%, with neodymium and citric acid modifier and erbium and citric acid modifier. They were only 66–68% without modifier.     

VIRTUAL INSTRUMENTATION FOR STRIPPING VOLTAMMETRY ON THE ROTATING DISK ELECTRODE

ABSTRACT

This paper describes a dedicated virtual instrumentation system constructed for stripping voltammetry on a rotating disk electrode (RDE) covered with a thin film of mercury. The experimental configuration consisted of a purpose-built potentiostat, a rotating disk electrode assembly and a peristaltic pump. The sequence of operations (plating of the mercury film, preconcentration of the analyte, potential scan and data acquisition, cleaning of the electrode) was under full computer control. The software programme that was selected for interfacing and control was LabVIEW 4.0. The system was configured in such a way as to perform either single measurements, a series of consecutive measurements (i.e., standard additions) or even multi-scan experiments. The analytical utility of the apparatus was assessed for the determination of Cu(II), Cd(II) and Pb(II) by anodic stripping voltammetry (ASV) and for the detection of Co(II) by multi-scan adsorptive cathodic stripping voltammetry (AdCSV).     

Modernization of the proton spin decoupling unit of the pulse fourier transform NMR spectrometer

The modernization of the proton spin decoupling unit in the NMR spectrometer is described. It consists in designing a pulsed modulator and including it in the circuit of the spin decoupling unit. The modified unit ensures a thermal stability of the sample at a level of ±2°C and an ±10% accuracy in measuring factors of the nuclear Overhauser effect for ¹³C nuclei. The unit was tested by measuring the factors of the nuclear Overhauser effect for ¹³C nuclei in a solution of deuterated acetone (10%) in ethylbenzene (90%).     

Nanotribology of a Silica Nanoparticle-Textured Surface

Tribological properties of a silica nanoparticle-textured (SNPT) surface were investigated at the nanoscale using a nanoindenter. The sample was fabricated by spin coating chemically synthesized silica nanoparticle solution onto a silicon substrate and then annealing the substrate in an N₂ environment. Environmental scanning electron microscopy (ESEM) and scanning probe microscopy (SPM) were used to characterize the morphology of the SNPT surface. Adhesion and friction experiments were performed with a diamond tip of nominal radius of curvature of 5 μ m, under contact forces of 750-1500 μ N, and with sliding speed of 0.1-2 μ m/s. The nanotribological properties of the SNPT sample were compared to those of a smooth silicon oxide film (SOF)-coated sample. The adhesion performance of the SNPT surface was found to be much better than that of the SOF surface. The coefficient of friction (COF) reduced up to 26%.

     

Construction of an Optical Sensor for Cobalt Determination Based on Methyltrioctylammonium Chloride Immobilized on a Polymer Membrane

Abstract

An optical sensor has been designed for the determination of cobalt by spectrophotometry. The sensing membrane is made by immobilizing methyltrioctylammonium chloride on a triacetylcellulose membrane. In the presence of Co(II) and thiocyanate ions, the colorless membrane changes to blue. The response time of the optode was about 7 min. The sensor can readily be regenerated with 0.02 mol L^?1 sodium oxalate solution. This optode is stable and can be stored under water for more than a month without reagent leaching. The calibration curve was linear in the range of 8.5×10^?6–1.3×10^?4 mol L^?1 of Co(II) ion with a limit of detection 5.9×10^?6 mol L^?1. The relative standard deviations for seven replicate measurements of 3.4×10^?5 and 1×10^?4 mol L^?1 of Co(II) were 1.58 and 1.10%, respectively. The sensor was successfully applied to the determination of cobalt in food samples and vitamin B₁₂ ampoule.     

重金属离子的场增强富集装置构建及应用研究

基于场增强效应,结合固相萃取技术设计一种新型富集装置富集水中微量重金属离子;并采用电感耦合等离子体原子发射光谱(ICP-AES)对富集的金属离子进行检测,实现微量金属离子的高倍富集。通过考察背景离子溶液浓度、富集时间、pH值、树脂用量等参数对富集的影响,优化富集装置设计与富集条件。采用此装置,水中Cu(Ⅱ)、Zn(Ⅱ)、Pb(Ⅱ)的富集倍数分别达到904倍,692倍,556倍,回收率在62.6%-84.2%之间,相对标准偏差为5.2%-9.4%。     

Aggregation of Dye on Polymer: Naphthochrome Green/PVP/Cu(II) Interaction and Determination of Cu Traces

Abstract

The interaction of naphthochrome green (NCG) with polyvinylpyrrolidone (PVP) and the complexation of NCG with Cu on PVP chain were investigated in basic medium by the spectral correction technique. The binding of NCG on PVP by the electrostatic attraction obeys the Langmuir isothermal adsorption in aqueous solution. Both the NCG–PVP aggregate and Cu–NCG–PVP ternary complex was characterized at 20°C, 40°C, and 60°C. The presence of PVP sensitized the complexation between Cu and NCG. This novel approach is sensitive and selective in the presence of citrate and has been applied to the quantitative detection of Cu traces in samples with satisfactory recovery.     

Modified nanoporous carbon as a novel sorbent before solvent-based de-emulsification dispersive liquid–liquid microextraction for ultra-trace detection of cadmium by flame atomic absorption spectrophotometry

Combination of different extraction methods is an interesting work in the field of sample pretreatment. In the current study, for the first time, solid phase extraction combined with solvent-based de-emulsification dispersive liquid–liquid microextraction (SPE-SD-DLLME) was developed for preconcentration and trace detection of cadmium in water samples using flame atomic absorption spectrophotometry (FAAS). The adsorbed cadmium ions on prepared SPE (75 mL of aqueous solution) were eluted by optimized elution solvent and introduced to the second microextraction step. The effective variables of SPE including the pH of sample, flow rates, type, concentration and volume of the eluent and the effect of potentially interfering ions of the separation of cadmium were evaluated and optimized. Also, several factors that influence the SD-DLLME step such as pH, neocuproine concentration (the cadmium binding ligand), type of dispersed/de-emulsifier solvent, volume of disperser/de-emulsifier solvent and type and volume of extraction solvents were investigated. SPE-SD-DLLME provides a preconcentration factor of 165 for cadmium ions. Calibration plot was linear in the range of 0.1–50 μg L⁻¹ with correlation of determination (r²) of 0.988. The precision and limit of detection of proposed method were 5.1% (RSD%, n = 8) and 0.03 μg L⁻¹, respectively.     

Influence of BN and B4C particulates on wear and corrosion resistance of electroplated nickel matrix composite coatings

Abstract

Electrodeposition of nickel–boron nitride–boron carbide (Ni–BN–B₄C) composites was carried out from a Watt's solution containing 50 and 10?g L of dispersed boron nitride and boron carbide particles respectively. The corrosion behaviour for both Ni and Ni–BN–B₄C deposits was evaluated by polarisation curves in a 3·5% NaCl solution at room temperature. Wear resistance of the composites was also studied using pin on disc technique. Scanning electron microscopy was extensively used to understand the effect of different electroplating conditions on the concentration and distribution of particles. The results showed that BN and B₄C particle concentration in the Ni–BN–B₄C composite film was sensitively dependent on the electroplating current density and bath temperature. Meanwhile, the Ni–BN–B₄C composite films were much more resistant to corrosion and wear than pure Ni coatings.     

DETERMINATION OF TRACE CADMIUM BY FLOW INJECTION ON-LINE MICROCOLUMN PRECONCENTRATION COUPLED WITH FLAME ATOMIC ABSORPTION SPECTROMETRY USING HUMAN HAIR AS A SORBENT

A novel method using a cone-shaped pipette tip packed with human hair as an adsorption material has been developed for the on-line flow injection preconcentration of trace Cd(II) ions based on its complex formation with the ammonium pyrrolidine dithiocarbamate (APDC) prior to flame atomic absorption spectrometric (FAAS) determination. Cd-PDC complex sorbed on the human hair was eluted by 4.0 mol L^?1 HNO₃. The enhancement factor is 19, and the detection limit (3σ) is 0.77 μg L^?1. The proposed method was successfully applied to the determination of trace cadmium in drinking water, beverage samples, and the certified reference materials.