Flow-Injection Determination of Iron Based on Its Catalysis on the Oxidation Reaction of Xylenol Orange by Potassium Bromate

A flow injection system is proposed for catalytic kinetic spectrophotometric determination of trace iron(II + III). The involved reaction is based on the catalytic effect of iron(III) on oxidation reaction of xylenol orange by potassium bromate to form a blue-violet complex. Iron(II) is also determined, being oxidized to iron(III) by potassium bromate. The calibration graph is linear in the range of 0.02–10.0 µg l^?1 and 10.0–1100 µg l^?1. The relative standard deviation is 1.5% for 4.0 µg l^?1 iron(III) and 2.3% for 60.0µg l^?1 iron(III) (n = 11). The presented system was applied successfully to the determination of iron in natural waters.     

Separation of zinc from aqueous samples using a molecular imprinting technique

In this article, the separation of zinc from aqueous samples by solid-phase extraction based on a molecular imprinting technique is described. Zn-imprinted polymer was prepared by free radical solution polymerisation in a glass tube containing ZnSO₄, morin, 4-vinylpyridine as a functional monomer, ethyleneglycoldimethacrylate as a cross-linking monomer, and 2,2′-azobisisobutyronitrile as an initiator. The obtained polymer block was ground and sieved (55–75 µm) and the Zn–morin complex was separated from polymer particles by leaching with 2M HCl. The synthesised polymer particles have been characterised by IR and differential scanning calorimetric studies either before or after leaching. The effects of different parameters, such as pH, adsorption and desorption time, type and minimum amount of the eluent for elution of the complex from polymer were evaluated. Extraction efficiency more than 99% was obtained by elution of the polymers with 10 mL of CH₂Cl₂–dimethyl sulfoxide (1 : 1, v/v). The detection limit of the proposed method was 2.9 µg L^?1. A dynamic linear range in the range of 25–200 µg L^?1 was obtained. The relative standard deviation was found to be below 9.2%. In addition, the influence of various cationic and anionic interferences on the complex recovery was studied. The method was applied to the recovery and determination of Zn in a few different real samples.     

Selective and Sensitive Determination of Uranyl Ions in Complex Matrices by Ion Imprinted Polymers‐Based Electrochemical Sensor

We report on the design of a UO₂²⁺‐selective electrode based on the use of UO₂²⁺ imprinted polymer nanoparticles (IP‐NPs), and its application for the differential pulse adsorptive cathodic stripping voltammetry determination of uranyl ions. A carbon paste electrode was modified with the IP‐NPs, and differential pulse adsorptive cathodic stripping voltammetry was applied as the detection technique after open‐circuit sorption of UO₂²⁺ ions. The modified electrode responses to UO₂²⁺ was linear in the 0.1 µg L^?1 to 10 µg L^?1 and in the 0.01 mg L^?1 to 10 mg L^?1. The method detection limit of the sensor was 0.03 µg L^?1.     

Rapid and selective determination of osmium(IV) by UV-visible spectrophotometry using o-methylphenyl thiourea as a chromogenic chelating ligand: sequential separation of osmium(IV), rhodium(III) and platinum(IV)

The objective of this research work was to develop a simple, highly sensitive and precise method for spectrophotometric determination of osmium(IV). O-Methylphenyl thiourea (OMPT) coordinates with osmium(IV) as a 1:1 (osmium(IV)–OMPT) complex in hydrochloric acid media (0.8 mol l^?1). The novelty of the investigated method is instant complex formation at room temperature with no need of heating or standing. The complex is stable for more than 8 days. The method is applicable over a wide linearity range (up to 110 µg ml^?1). A low reagent concentration is required (2 ml, 0.009 mol l^?1 in ethanol). The complex exhibits maximum absorption in the range of wavelength 510–522 nm and 514 nm was selected for further study. The molar absorptivity was 1.864 × 10³ l mol^?1 cm^?1, Sandell’s sensitivity was 0.102 µg of osmium(IV) cm^?2. Proposed method was successfully applied for separation and determination of osmium(IV) from binary and ternary synthetic mixtures containing associated metal ions. A scheme for mutual separation of osmium(IV), rhodium(III) and platinum(IV) is developed.     

Comparison of the acute toxicity of tributyltin and copper to veliger larvae of Nassarius reticulatus (L.)

The ban on the use of tributyltin (TBT) is promoting an increasing use of copper as an active biocide in antifouling paints, with consequent rising levels of this metal in the environment. This study assesses the acute toxicity of copper and tributyltin to the larvae of the mollusc gastropod Nassarius reticulatus. Recently hatched veligers were exposed to nominal TBT‐Sn concentrations of 0.9, 1.4, 1.9, 2.8, 3.8, 4.7 and 5.6 µg l^?1 and nominal copper concentrations of 9.4, 23.4, 46.9, 70.3, 93.8, 117.2, 140.6 and 164.1 µg l^?1 for up to 96 h, under static conditions (17 ± 1 °C and 33 ± 1 psu). The percentage of larval mortality was determined for each organometal/metal concentration and exposure time (1, 24, 48, 72 and 96 h). Both TBT and copper had a highly significant effect on larvae survival (p < 0.001) for all times of exposure, except for the first hour in the particular case of TBT. The lowest observed effect concentration for TBT‐Sn decreased over time from 3.8 µg l^?1 at 24 h to 1.9 µg l^?1 at 96 h, whereas for copper it remained constant over time (46.9 µg l^?1). The median lethal concentration (LC₅₀) for TBT‐Sn decreased from 4.87 µg l^?1 at 24 h to 1.78 µg l^?1 at 96 h, and the LC₅₀ for copper decreased from 83.08 µg l^?1 at 24 h to 58.84 µg l^?1 at 96 h. TBT is far more toxic to N. reticulatus larvae than copper. However, owing to the higher copper environmental concentrations, the risk factors of the two biocides may approach each other. This stresses the need to find adequate substitutes for organotin biocides in future antifouling paints. Copyright © 2005 John Wiley & Sons, Ltd.     

Enhanced Specificity and Sensitivity for the Determination of Nickel(II) by Square-wave Adsorptive Cathodic Stripping Voltammetry at Disposable Graphene-modified Pencil Graphite Electrodes

Chemical sensors relying on graphene-based materials have been widely used for electrochemical determination of metal ions and have demonstrated excellent signal amplification. This study reports an electrochemically reduced graphene oxide (ERGO)/mercury film (HgF) nanocomposite-modified pencil graphite electrode (PGE) prepared through successive electrochemical reduction of graphene oxide (GO) sheets and an in situ plated HgF. The ERGO-PG-HgFE, in combination with dimethylglyoxime (DMG) and square-wave adsorptive cathodic stripping voltammetry (SW-AdCSV), was evaluated for the determination of Ni²⁺ in tap and natural river water samples. A single-step electrode pre-concentration approach was employed for the in situ Hg-film electroplating, metal-chelate complex formation, and non-electrolytic adsorption at –0.7 V. The current response due to nickel-dimethylglyoxime [Ni(II)-DMG₂] complex reduction was studied as a function of experimental paratmeters including the accumulation potential, accumulation time, rotation speed, frequency and amplitude, and carefully optimized for the determination of Ni²⁺ at low concentration levels (μg?L^?1) in pH 9.4 of 0.1 M NH₃–NH₄Cl buffer. The reduction peak currents were linear with the Ni²⁺ concentration between 2 and 16?μg?L^?1. The limits of detection and quantitation were 0.120?±?0.002?µg?L^?1 and 0.401?±?0.007?µg?L^?1 respectively, for the determination of Ni²⁺ at an accumulation time of 120?s. The ERGO-PG-HgFE further demonstrated a highly selective stripping response toward Ni²⁺ determination compared to Co²⁺. The electrode was found to be sufficiently sensitive to determine metal ions in water samples at 0.1?µg?L^?1, well below the World Health Organization standards.     

A Multicommuted Flow‐based System for Hydrogen Peroxide Determination by Chemiluminescence Detection Using a Photodiode

Abstract

A simple, rapid, and automated assay for hydrogen peroxide in pharmaceutical samples was developed by combining the multicommutation system with a chemiluminescence (CL) detector. The detection was performed using a spiral flow‐cell reactor made from polyethylene tubing that was positioned in front of a photodiode. It allows the rapid mixing of CL reagent and analyte and simultaneous detection of the emitted light. The chemiluminescence was based on the reaction of luminol with hydrogen peroxide catalyzed by hexacyanoferrate(III).

The feasibility of the flow system was ascertained by analyzing a set of pharmaceutical samples. A linear response within the range of 2.2–210 µmol l^?1 H₂O₂ with a LD of 1.8 µmol l^?1 H₂O₂ and coefficient of variations smaller than 0.8% for 1.0×10^?5 mol l^?1 and 6.8×10^?5 mol l^?1 hydrogen peroxide solutions (n=10) were obtained. Reagents consumption of 90 µg of luminol and 0.7 mg of hexacyanoferrate(III) per determination and sampling rate of 200 samples per hour were also achieved.     

Flow‐Injection Spectrophotometric Determination of N‐acetylcysteine in Pharmaceutical Formulations with On‐Line Solid‐Phase Reactor Containing Zn(II) Phosphate Immobilized in a Polyester Resin

Abstract

A flow‐injection spectrophotometric procedure was developed for determining N‐acetylcysteine in pharmaceutical formulations. The sample was dissolved in deionized water and 400 µl of the solution was injected into a carrier stream of 1.0×10^?2 mol l^?1 sodium borate solution. The sample flowed through a column (70 mm length×2.0 mm i.d.) packed with Zn₃(PO₄)₂ immobilized in a polymeric matrix of polyester resin and Zn(II) ions were released from the solid‐phase reactor because of the formation of the Zn(II) (N‐acetylcysteine)₂ complex. The mixture merged with a stream of borate buffer solution (pH 9.0) containing 5.0×10^?4 mol l^?1 Alizarin red S and the Zn(II)Alizarin red complex formed was measured spectrophotometrically at 540 nm. The analytical curve was linear in the N‐acetylcysteine concentration range from 3.0×10^?5 to 1.5×10^?4 mol l^?1 (4.9 to 24.5 µg ml^?1) with a detections limit of 8.0×10^?6 mol l^?1 (1.3 µg ml^?1). The relative standard deviations (RSDs) were smaller than 0.5% (n=10) for solutions containing 5.0×10^?5 mol l^?1 (8.0 µg ml^?1) and 8.0×10^?5 mol l^?1 (13.0 µg ml^?1) of N‐acetylcysteine, and the analytical frequency was 60 determinations per hour. A paired t‐test showed that all results obtained for N‐acetylcysteine in commercial formulations using the proposed flow‐injection procedure and a comparative procedure agreed at the 95% confidence level.     

Flow-Injection Analysis Based on Extraction and Spectrophotometric Determination of Penicillins with Thiazine Dyes

Abstract

A new method for flow-injection analysis (FIA) for the determination of penicillins based on the extraction and spectrophotometric determination of ion associates with selected thiazine dyes (methylene blue, azure A, and azure B) is proposed. The reaction conditions (c_dye = 2 × 10^?4 mol l^?1, c_KCl = 1 mol l^?1, pH ? 6, λ = 635 nm) were found. The factorial design has been carried out to determine the optimum flow conditions. A wide linear dynamic range of calibration curves (5.1–700 µg ml^?1 for penicillin V with all dyes, R = 0.9985) and good repeatability (e.g., relative standard deviation [RSD] = 4.6–0.6% in this concentration range for the reaction with azure B) were found. The detection limit for penicillin V is 1.5 µg ml^?1, and the determination limit is 5.1 µg ml^?1. The maximum analysis rate is 35 samples per h. The practical samples of pharmaceutics were tested. There are no interferences from the additives in pharmaceutics.     

Continuous sonoassisted digestion coupled to flow injection minicolumn separation for the determination of total and labile Cu and Fe in fresh waters by flame atomic absorption spectrometry

An automatic on-line system is developed for the trace determination of copper and iron species in fresh waters by flame atomic absorption spectrometry using only 5 and 2?mL of sample, for copper and iron determination, respectively. This system, which includes a home-made minicolumn of commercially available resin containing aminomethylphosphonic acid functional groups (Chelite P), comprises two operational modes. The first, used for the determination of the dissolved labile fraction (free copper and iron ions and their weak complexes) is based on the elution of this fraction from a minicolumn containing the chelating resin loaded in-situ with the sample. The second mode is used for the determination of total trace copper and iron concentrations. This last mode is based on the retention/preconcentration of total metals on the Chelite P resin after on-line sonoassisted digestion of water samples acidified with nitric acid (0.5?mol?L^?1 final concentration) to break down metal organic complexes present in fresh waters as river waters. The figures of merit for copper and iron determination in both fractions are given and the obtained values are discussed. The analytical method was characterized and the limit of detection and limit of quantification for the two metals were 0.5 and 1.6?µg?L^?1 for Cu and 2.3 and 6.1?µg?L^?1 for Fe, respectively. The repeatability, expressed as relative standard deviation, was in the range 1.0–2.1%. The speciation scheme was applied to the analysis of river surface water samples collected in Galicia (Northwest, Spain).     

Solid Phase Extraction and Determination of Lead in Water Samples Using Silica Gel Homogeneously Modified by Thiosalicylic Acid

Abstract

Silica gel was modified by thiosalicylic acid via homogeneous routes to obtain immobilized silica gel sorbent (TSA‐immobilized silica gel). This new sorbent was characterized using variety of physical chemistry techniques including, high resolution solid state ¹³C and ²⁹Si 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). New support was used for the selective extraction and concentration of lead ions by silica gel modified with thiosalicylic acid, as a highly selective and stable reagent, from aquatic samples and its determination with FAAS. Lead ions can be desorbed with 4 mol dm^?3 HNO₃. The sorption capacity for lead ions are found in the range of 64.40 to 69.90 µmol g^?1 of chelating matrix. Tolerance limits for electrolytes and some trace metals in the sorption of lead is reported. Preconcentration factor was found as 150 for Pb(II). The lead in drinking water, mineral water, tap water, and fruit juice was quantitatively recovered with a relative standard deviation lower than 1.50%. A detection limit of the method for lead ions was found as 3.7 µg l^?1.     

Novel Imprinted Polymer for the Preconcentration of Cadmium with Determination by Inductively Coupled Plasma Mass Spectrometry

A novel Cd(II)-imprinted polymer was prepared with chemical immobilization using N-methacryloyl-L-Histidine as a vinylated chelating agent for online solid-phase extraction of Cd(II) for determination by inductively coupled plasma mass spectrometry. The Cd(II)–monomer complex was synthesized and copolymerized through bulk polymerization method in the presence of ethyleneglycoldimethacrylate cross-linker. The resulting polymer was leached with 1.0?mol?L^?1 HNO₃ to generate the cavities in the polymer for Cd(II) ions. The experimental conditions, including load pH, solution flow rate, and eluent concentration for effective sorption of Cd(II), were optimized using a minicolumn of the imprinted polymer. A volume of 5.0?mL sample 5?µg?L^?1 Cd(II) solution at pH 6.5 was loaded on the column at 2.0?mL?min^?1 using a sequential injection system followed by elution with 1.0?mL of 0.75?mol?L^?1 HNO₃. The relative selectivity coefficients of the imprinted polymer for Cd(II) were 38.5, 3.5, 3.0, 2.5, and 6.0 in the presence of Cu(II), Ni(II), Zn(II), Co(II), and Pb(II), respectively. Computational calculations revealed that the selectivity of the imprinted polymer was mediated by the stability of Cd(II)–N-methacryloyl-L-Histidine complex which was more stable than commonly used monomers including 4-vinyl pyridine, methacrylic acid, and vinylimidazole. The detection limit and relative standard deviation were 0.004?µg?L^?1 and 3.2%, respectively. The method was validated by the analysis of seawater certified reference material (CASS-4) and successfully used for the determination of Cd(II) in coastal seawater and estuarine water.     

A new experimental approach for liquid-liquid extractive spectrophotometric determination of chromium(VI) in tannery wastewater and alloy samples

In this research work, a new approach is developed for the extractive determination of chromium. The principle of this approach is based on the complexation reaction between 4-(4?-chlorobenzylideneimino)-3-methyl-5-mercapto-1,2,4-triazole (CBIMMT) in dichloromethane as a complexing reagent and chromium(III) in presence of potassium iodide to form a yellow coloured complex at room temperature. The 1:2:2 [Cr(III)-CBIMMT-iodide] ternary complex was quantitatively extracted in dichloromethane from 2.5 mol L^?1 of hydrochloric acid medium which showed maximum absorption intensity at λ_max 411 nm and was stable for more than 72 h. The values of molar absorption coefficient and Sandell’s sensitivity of the complex were found to be 0.7019 × 10⁴ L mol^?1 cm^?1 and 0.00748 µg cm^?2, respectively. The system adheres to Beer’s law from 1.5 to 6.0 µg mL^?1; however, Ringbom’s plot suggests optimal concentration range was 1.8–5.8 µg mL^?1. The limit of detection and limit of quantification of the approach is 0.26 and 0.79 µg mL^?1. This approach was successfully used for the determination of chromium from wastewater effluents from the tannery industries (Kolhapur, MS, India), alloy samples and for separation of it from synthetic mixtures. The present experimental approach is apparently much simpler than the conventional method comprising multistep processes.     

HPLC determination of domoic acid in shellfish based on magnetic molecularly imprinting polymers

A magnetic molecularly imprinting polymer for domoic acid was fabricated. Synthesis conditions were optimized. The polymer particles have high magnetization for rapid magnetic separation. The apparent maximum absorption amount and dissociation constant of the polymer were 1,600?µg?g^?1 and 20.6?µg?mL^?1, respectively. The polymer retained 90% of adsorption amount after 5 times of repeated use. It was used as an adsorbent for purification and HPLC detection of domoic acid in shellfish with a detection limit of 0.050?µg?g^?1. Thus, the polymer could be applied to the sample pretreatment of aquatic products.     

Elemental Analysis of Tarhana by Microwave Induced Plasma Atomic Emission Spectrometry

Elemental analysis of tarhana, a traditional Turkish cereal soup, has been conducted. A new method was developed for the determination of calcium, iron, magnesium, manganese, potassium, and sodium, in tarhana by microwave induced plasma atomic emission spectrometry. A sample of 0.1?g were mineralized by microwave digestion in 10?mL of 65% HNO₃. A wheat flour standard reference material (GBW 08503) was used for validation. Linear calibration using standards prepared in acid was conducted for all determinations. The limits of detection were 1.21?µg?g^?1 for Ca at 393.366?nm, 0.43?µg?g^?1 for Fe at 259.940?nm, 11.5?µg?g^?1 for K at 766.491?nm, 0.12?µg?g^?1 for Mg at 285.213?nm, 0.04?µg?g^?1 for Mn at 403.076?nm, and 0.04?µg?g^?1 for Na at 588.995?nm. Ca, K, Fe, Mg, Mn, and Na were determined in tarhana with values from 0.73 to 1.61, 0.016 to 0.061, 2.02 to 4.09, 0.473 to 1.414, 0.019 to 0.043, and 0.26 to 1.83?mg?g^?1, respectively.     

Imprinted Polymer Particles for Aluminum Uptake: Synthesis and Analytical Applications

This work reports the preparation of molecularly imprinted polymer (MIP) particles for selective extraction and determination of aluminum ion from aqueous media. Polymerization was achieved in a glass tube containing AlCl₃, morin, 4-vinylpyridine, ethyleneglycoldimethacrylate, 2,2′ - azobisisobutyronitrile. The polymer block obtained was ground and sieved (55–75 μ m) and the Al (III)-morin complex was removed from polymer particles by leaching with 2 M of HCl, which leaves a cavity in the polymer particles. The polymer particles, both prior to and after leaching, have been characterized by IR and differential scanning calorimetry (DSC) studies. The effect of different parameters, such as pH, adsorption and desorption time, type and least amount of eluent for elution of complex from polymer were evaluated. Extraction efficiencies more than 99% were obtained by elution of the polymers with 15 mL of methanol-acetonitrile mixture (1:2) followed by ICP-OES. The limit of detection of the proposed method was 3.5 μ g L^?1. A dynamic linear range (DLR) in the range of 20 to 200 μ g L^?1 was obtained. The relative standard deviation (RSD) was less than 6.5%. The influence of various cationic and anionic interferences on percent recovery of complex was studied. The method was applied to the recovery and determination of aluminum in different real samples.     

On‐line photodecomposition for the determination of antimony species

On‐line UV photooxidation by peroxodisulfate was coupled to ion chromatography hydride generation atomic fluorescence spectroscopy (IC‐UV‐HG‐AFS) for the speciation of inorganic antimony [Sb(III) and Sb(V)] and methylated species. Several parameters (UV lamp, irradiation time and peroxodisulfate concentration) that greatly influence the sensitivity of these three antimony species were investigated in depth. Under optimized conditions, photodecomposition resulted in an improvement in methylantimony species sensitivity. Dilution in di‐ammonium tartrate medium was necessary in order to ensure short‐term stability of Sb(III) at the µg l^?1 concentration level. Furthermore, the efficiency of irradiation was strongly dependent on the chemical composition of the measured solution. Detection limits of 0.04 µg l^?1 for Sb(V), 0.03 µg l^?1 for Me₃SbCl₂ and 0.03 µg l^?1 for Sb(III) as well as repeatability and reproducibility better than 4 and 8% RSD, respectively, were obtained. The proposed methodology was applied for antimony speciation in terrestrial plant sample extracts. Copyright © 2005 John Wiley & Sons, Ltd.     

The Use of Ultrasound for the Analytical Determination of Nitrite on Diamond Electrodes by Square Wave Voltammetry

Abstract

This work describes an analytical methodology for the determination of nitrite ions in aqueous solutions using boron‐doped diamond electrodes and square wave voltammetry associated with ultrasound radiation. The nitrite ions were oxidized to nitrate ions in Britton‐Robinson buffer solutions 0.1 M, pH 2.0 at 1.0 V versus Ag/AgCl. The voltammetric response of nitrite in the presence of ultrasound showed a peak current five times higher than the obtained in silent conditions. Thus, the detection limit obtained in the presence of radiation was 17 nM (0.782 µg l^?1), a small value if compared with that obtained in the absence of ultrasound: 140 nM (6.44 µg l^?1).     

Synthesis of Molecularly Imprinted Polymer for Sensitive Penicillin Determination in Milk

Abstract

Penicillin G (PG) in milk is unsafe for human and is a big problem for the foods industry. Hence, the better analytical and eliminative techniques are demanded. We investigated a PG molecular imprinted polymer (MIP), which can sensitively detect and extract the PG from milk and other samples. The MIP synthesis involved a β-lactam antibiotics PG, methacrylic acid (MAA) and dimethyl formamide (DMF). Its properties were analyzed with Scatchard plot, which showed that there were two affinity sites of the PG polymer. The first equilibrium dissociation constant of the high-affinity binding sites Kd₁ was 1.14 × 10^?4 mol/L and the binding capacity Q_max1 was 46.01 µmol/g; the second equilibrium dissociation constant of the low-affinity binding sites Kd₂ was 1.35 × 10^?3 mol/L and the binding capacity Q_max2 was 72.55 µmol/g. Furthermore, two PG determination methods using the polymer were developed. The first was carried out quantitatively with a spectrophotometer and the detection limit was 1 ppm. The other one was the combination of the MIP particles with milk fermentation for PG analysis and the sensitivity was 10 ppb.     

Determination of Manganese(II) with Preconcentration on Almond Skin and Determination by Flame Atomic Absorption Spectrometry

Almond skin was used as a biosorbent by solid-phase extraction for the preconcentration of manganese(II) before the determination by flame atomic absorption spectrometry. Characterization of almond skin was performed by infrared spectroscopy. The functional groups of the almond skin surface were shown to be beneficial for the adsorption of manganese(II). At pH 6.0, the manganese(II) ions were retained on the almond skin and afterward quantitatively eluted using 1.5?mol?L^?1 nitric acid. The pH, flow rate and volume of sample, concentration, and flow rate of eluent and interfering ions were characterized. Using a sample size of 30?mL, a linear dynamic range of 1–120?µg?L^?1 was obtained. A detection limit of 0.24?µg?L^?1 manganese(II) and a relative standard deviation of 1.6% at 30?µg?L^?1 were achieved. The accuracy of the present procedure was evaluated by the determination of manganese(II) in a certified reference material (GSB07-1189-2000). The protocol was also used for the determination of manganese(II) in wastewater. The fortified recoveries were from 99.0 to 99.4%.