Dynamic sorption of nitrophenols from aqueous solutions by polymers based on N-Vinylpyrrolidone

Sorption properties of a polymer based on N-vinylpyrrolidone and ethylene glycol dimethacrylate were studied for the example of sorption of nitrophenols from aqueous solutions under dynamic conditions. The conditions providing a 180–480-fold concentration in dynamic sorption and desorption of nitrophenols from aqueous solution were substantiated.     

FAAS determination of palladium after its selective recovery by silica modified with hydrazone derivative

Amino propyl silica (APS) gel reacts immediately with benzyl monopyridyl hydrazone (BMPH) to produce a new effective and selective derivative (BMPH-APS) for the separation and preconcentration of traces of Pd(II) in aqueous solution. Factors affecting the sorption and desorption of Pd ions have been investigated. Acidic aqueous solution of 0.5% thiourea in 0.5 mol L^?1 HCl has been used as eluent for the desorption of Pd(II). The stripped metal ion was determined by flame AAS. The modified silica quantitatively sorbed Pd(II) at pH 2–4 with a sorption capacity of 0.65 mmol g^?1 and preconcentration factor of 250 fold in less than one minute (t_1/2). Common other ions did not interfere except Co(II) which was eliminated by EDTA . The limit of detection (LOD) is 0.1 ng mL^?1 and the relative standard deviation (R. S. D.) for 10 replicate measurements at 20 ng mL^?1 Pd level was 1.51%. The method was successfully applied for Pd preconcentration in highly concentrated salt solutions and in spiked clay, road dust, scrap and water samples.     

Application of silica gel organofunctionalized with 3(1-imidazolyl)propyl in an on-line preconcentration system for the determination of copper by FAAS

This study presents a new procedure for the determination of trace levels of copper(II) in an aqueous matrix, through flow injection (FI) on-line preconcentration with a minicolumn packed with silica gel modified with 3(1-imidazolyl)propyl groups. After the preconcentration stage, the analyte was eluted with a HNO₃ solution and determined by flame atomic absorption spectrometry (FAAS). The measurements of the analytical signals were carried out as peak area and peak height with the objective of evaluating the most appropriate absorption measurement for the proposed method. Four procedures to calculate the experimental enrichment factor (EF) were also studied. For a preconcentration time of 90 s the enrichment factors found in this study varied between 19.5-25.8 and 36.2-42.2 for peak area and peak height, respectively. The precision of the proposed method was calculated for a solution containing 20 μg l⁻¹ of Cu(II), when 11.2 ml of solution was preconcentrated (n=7), and their respective relative standard deviation (R.S.D.) values were 1.2 and 1.4% for peak area and peak height, respectively. The detection limits obtained were 0.4 and 0.2 μg l⁻¹ of Cu(II) for peak area and peak height, respectively, with a preconcentration time of 90 s. The on-line preconcentration system accuracy was evaluated through a recovery test on the aqueous samples and analysis of a certified material.     

Rapid magnetic solid‐phase extraction of Congo Red and Basic Red 2 from aqueous solution by ZIF‐8@CoFe2O4 hybrid composites

Core–shell metal–organic framework materials have attracted considerable attention mainly due to their enhanced or new physicochemical properties compared with their single‐component counterparts. In this work, a core–shell heterostructure of CoFe₂O₄‐Zeolitic Imidazolate Framework‐8 (ZIF‐8@CoFe₂O₄) is successfully fabricated and used as an solid‐phase extraction adsorbent to efficiently extract Congo Red and Basic Red 2 dyes from contaminated aqueous solution. Vibrating sample magnetometry indicates that the saturated magnetization of ZIF‐8@CoFe₂O₄ is 3.3 emu/g, which is large enough for magnetic separation. The obtained hybrid magnetic metal‐organic framework based material ZIF‐8@CoFe₂O₄ can remove the investigated dyes very fast within 1 min of the contact time. The adsorbent ZIF‐8@CoFe₂O₄ also shows a good reusability. After regeneration, the adsorbent can still exhibit high removal efficiency (～97%) toward Congo Red for five cycles of desorption–adsorption. This work reveals the great potential of core–shell ZIF‐8@CoFe₂O₄ sorbents for the fast separation and preconcentration of organic pollutants in aqueous solution before high‐performance liquid chromatography analysis.     

Liquid chromatographic determination of trace levels of nitrophenols in water samples after dispersive magnetic solid phase extraction

An efficient and fast dispersive magnetic solid phase extraction method was developed using MIL‐101(Cr)/poly (mercaptobenzothiazole)@magnetite nanoparticles for the preconcentration and determination of nitrophenols in river and rain water samples. High‐performance liquid chromatography‐Ultraviolet instrument was applied for the analysis of target nitrophenols. The effect of several variables on the extraction performance was explored via design of experiment approach. Limits of detection and linear dynamic ranges were attained in the range of 0.05–0.10 µg/L and 0.2–250 µg/L, respectively. The enrichment factors were in the range of 317–363. The precision (n = 3) of dispersive magnetic solid phase extraction method was in the range of 5.3–6.8%. Eventually, the method was utilized for the analysis of target nitrophenols in river and rain water samples.     

Detection of haemoglobin using an adsorption approach at a liquid–liquid microinterface array

The behaviour of haemoglobin (Hb) at the interface between two immiscible electrolyte solutions (ITIES) has been examined for analytical purposes. When Hb is fully protonated under acidic conditions (pH <pI) in the aqueous phase, it undergoes a potential-dependent adsorption and complexation, at the interface, with the anions of the organic phase electrolyte. When utilised as a simple and fast preconcentration step, consisting of adsorbing the protein at the interface, in conjunction with voltammetric desorption, this opens up the ITIES to the adsorptive stripping voltammetry approach. Utilising a 60 s adsorption step and linear sweep voltammetry, a linear response to Hb concentration in aqueous solution over the range 0.01–0.5 μM was achieved. The equation of the best-fit straight line was I _p ? =?7.46 C???0.109, R?=?0.996, where I _p is the peak current (in nanoampere) and C is haemoglobin concentration (in micromolar). The calculated detection limit (3σ) was 48 nM for a 60 s preconcentration period, while the relative standard deviation was 13.3 % for six successive measurements at 0.1 μM Hb. These results illustrate the prospects for simple, portable and rapid label-free detection of biomacromolecules offered by electrochemistry at arrays of liquid–liquid microinterfaces.     

Adsorption–photometric determination of lead in cattle liver

A styrene–maleic anhydride copolymer is synthesized, modified in the presence of p-sulfoaniline and formaldehyde, and a new polymer adsorbent is obtained and identified by IR spectroscopy. The ionization constants of ionogenic groups in the adsorbent are determined by the potentiometric method. The adsorption and desorption of lead(II) on the obtained adsorbent are investigated, and optimal conditions of preconcentration are determined. An adsorption–photometric procedure for the determination of lead is proposed, including the adsorption preconcentration of lead(II) from a buffer solution with pH 6 and desorption with a solution of HCl (with the desorption rate of up to 99%). The procedure was used to determine lead in the cattle liver.     

Magnetic solid‐phase extraction for determination of sulpiride in human urine and blood using high‐performance liquid chromatography

A novel and efficient sample preconcentration technique based on the Fe₃O₄ magnetic nanoparticles (Fe₃O₄ MNPs) coated with silica (SiO₂) has been developed for extraction and determination of sulpiride. The functionalized MNPs showed excellent dispersibility in aqueous solution and were applied to magnetic solid‐phase extraction of sulpiride from human urine and blood prior to high‐performance liquid chromatography analysis. The separation, preconcentration and desorption procedure was completed in 10 min. Optimal experimental conditions, including sample pH, the amount of the MNPs, eluent type and volume, and the ultrasonication time were studied and established. The method showed good linearity for the determination of sulpiride in the concentration range of 10–1000 ng/mL in urine and blood. The recovery of the method was in the range between 91.2 and 97.5%, and the limit of detection was 2 ng/mL for sulpiride in human blood and urine. The results indicated that the present procedure is a suitable pretreatment method for biological samples. Copyright © 2015 John Wiley & Sons, Ltd.     

Preconcentration of trace amounts of cobalt (II) ions in water and agricultural products samples using of 5-(4-dimethylaminobenzylidene) rhodanin modified SBA-15 sorbent prior to FAAS determination

In the present study, the ?5-(4-dimethylaminobenzylidene)rhodanin-modified SBA-15? was applied as stable solid sorbent for the separation and preconcentration of trace amounts of cobalt ions in aqueous solution. SBA-15 was modified by ?5-(4-dimethylaminobenzylidene)rhodanin reagent. The sorption of Co²⁺ ions was done onto modified sorbent in the pH range of 6.8–7.9 and desorption occurred in 5.0 mL of 3.0 mol L^?1 HNO₃. The results exhibit a linear dynamic range from 0.01 to 6.0 mg L^?1 for cobalt. Intra-day (repeatability) and inter-day (reproducibility) for 10 replicated determination of 0.06 mg L^?1 of cobalt was ±1.82% and ?±1.97%?. Detection limit was 4.2 µg L^?1 (3S_b, n = 5) and preconcentration factor was 80. The effects of the experimental parameters, including the sample pH, flow rates of sample and eluent solution, eluent type and interference ions were studied for the preconcentration of Co²⁺. The proposed method was applied for the determination of cobalt in standard samples, water samples and agricultural products.     

Solid phase extraction and preconcentration of trace mercury(II) from aqueous solution using magnetic nanoparticles doped with 1,5-diphenylcarbazide

A new method for solid-phase extraction and preconcentration of trace mercury(II) from aqueous solution was developed using 1,5-diphenylcarbazide doped magnetic Fe₃O₄ nanoparticles as extractant. The surface treatment did not result in the phase change of Fe₃O₄. Various factors which influenced the recovery of the analyte were investigated using model solutions and batch equilibrium technique. The maximum adsorption occurred at pH?>?6, and equilibrium was achieved within 5 min. Without filtration or centrifugation, these mercury loaded nanoparticles could be separated easily from the aqueous solution by simply applying an external magnetic field. At optimal conditions, the maximum adsorption capacity was 220 μmol g^?1. The mercury ions can be eluted from the composite magnetic particles using 0.5 mol L^?1 HNO₃ as a desorption reagent. The detection limit of the method (3σ) was 0.16 μg L^?1 for cold vapor atomic absorption spectrometry, and the relative standard deviation was 2.2%. The method was validated by the analysis of a certified reference material with the results being in agreement with those quoted by manufactures. The method was applied to the preconcentration and determination of trace inorganic mercury(II) in natural water and plant samples with satisfactory results.     

Determination of partition coefficient and analysis of nitrophenols by three‐phase liquid‐phase microextraction coupled with capillary electrophoresis

A three‐phase hollow fiber liquid‐phase microextraction method coupled with CE was developed and used for the determination of partition coefficients and analysis of selected nitrophenols in water samples. The selected nitrophenols were extracted from 14 mL of aqueous solution (donor solution) with the pH adjusted to pH 3 into an organic phase (1‐octanol) immobilized in the pores of the hollow fiber and finally backextracted into 40.0 μL of the acceptor phase (NaOH) at pH 12.0 located inside the lumen of the hollow fiber. The extractions were carried out under the following optimum conditions: donor solution, 0.05 M H₃PO₄, pH 3.0; organic solvent, 1‐octanol; acceptor solution, 40 μL of 0.1 M NaOH, pH 12.0; agitation rate, 1050 rpm; extraction time, 15 min. Under optimized conditions, the calibration curves for the analytes were linear in the range of 0.05–0.30 mg/L with r²>0.9900 and LODs were in the range of 0.01–0.04 mg/L with RSDs of 1.25–2.32%. Excellent enrichment factors of up to 398‐folds were obtained. It was found that the partition coefficient (K_a/d) values were high for 2‐nitrophenol, 3‐nitrophenol, 4‐nitrophenol, 2,4‐dinitrophenol and 2,6‐dinitrophenol and that the individual partition coefficients (K_org/d and K_a/org) promoted efficient simultaneous extraction from the donor through the organic phase and further into the acceptor phase. The developed method was successfully applied for the analysis of water samples.     

Use of polymethine dyes for the extraction separation and spectrophotometric determination of nitrophenols

The extraction of nitrophenols with polymethine dyes of the common formula R₁-(CH=CH)₃-R₂, indolium and benzothiazolium derivatives was studied. The effect of the acidity of the solution, the nature and the concentration of the dye, and the nature of the organic solvent on the formation and extraction of ion pairs of nitrophenols was examined; the optimum conditions were found. The most important chemical analytical characteristics of the ion pairs were determined. Molar absorptivities of extracts are 11.9 × 10⁴–14.3 × 10⁴ for ion pairs of trinitrophenol and 6.8 × 10⁴–10.1 × 10⁴ for ion pairs of dinitrophenol. A new procedure was developed for the extraction-photometric determination of nitrophenols in a mixture.     

Preconcentration and determination of Sn- and Pb-organic species in environmental samples by SPME and GC-AED

A new sample preparation and preconcentration technique – solid phase microextraction (SPME) – is reported for the application of several tinorganic compounds and tetrabutyllead in aqueous samples. The solvent-free procedure is rapid in comparison with liquid-liquid extraction or SFE but also sensitive. Analytical variables of the extraction such as adsorption and desorption time, stirring rate and temperature has been investigated. The determination has been performed by GC coupled with atomic emission detection (AED). After optimization of the conditions of SPME a calibration was realized on the basis of a multicomponent standard solution, prepared by ethylation of organotin salts directly in the sample using sodium tetraethylborate (NaBEt₄) without prior separation of the analytes from the matrix. The method permits preconcentration. Values of about 10 can be reached. A detection limit of 0.09 pg Sn and 0.08 pg Pb can be achieved under optimized conditions. The proposed procedure has been successfully applied to the analysis of organotin compounds in various slurry samples.     

Cross‐linked starch‐based polymer as an SPE material for the determination of nitrophenols at trace levels in environmental water

SPE using a cross‐linked starch‐based polymer (CSMDI) as an adsorbent for the determination of four nitrophenols at trace levels from aqueous solution was investigated. The CSMDI was synthesized from native starch using 4,4′‐methylenebisphenyldiisocyanate as a cross‐linking agent in dry DMF. Parameters affecting the extraction efficiency including the pH of the water sample, type of eluent and its volume, flow rate, sample volume, and methanol content were investigated and optimized. The optimized results exhibited excellent linear relationships (R² > 0.995) for all the nitrophenols over the range of 2.0–200 ng/mL, with the RSD values in the range of 2.9–5.7% (n = 5). The LODs ranged from 0.08–0.34 ng/mL (S/N = 3) for the four nitrophenols tested under optimum conditions. The developed method has been successfully applied for the analysis of several real environmental water samples including tap, river, and reservoir water. These results indicated that the CSMDI had a tremendous potential for the enrichment and determination of nitrophenols at trace levels in environmental water samples.     

Modified Activated Carbon as Solid Phase Extraction Adsorbent for the Preconcentration and Determination of Trace As(III) in Environmental Samples by Graphite Furnace Atomic Absorption Spectrometry

A simple and selective method was developed for the preconcentration, separation, and determination of trace amounts of As(III) in an aqueous solution by solid phase extraction combined with graphite furnace atomic absorption spectrometry. Activated carbon (AC) was modified by sodium diethyldithiocarbamate (NaDDTC) and then used as a new, stable and easily prepared solid sorbent in a mini column for the extraction of As(III) in aqueous solution. Factors influencing the sorption and desorption of As(III), such as volume and concentration of eluent, sample pH, flow rate and effect of interfering ions on the recovery of As(III) have been systemically investigated. At pH 2.0 As(III) could be adsorbed quantitatively by NaDDTC‐AC, and then eluted completely with 2 mL of 3.0 mol·L^?1 HNO₃. The amount of eluted As(III) was measured using graphite furnace atomic absorption spectrometry. The detection limit of As(III) was 0.04 ng·mL^?1 with enrichment factor of 100 and the relative standard deviation (RSD, n=8) was 1.58% at 10 ng·mL^?1 level.     

Speciation analysis of chromium by separation on a 5-palmitoyl oxine-functionalized XAD-2 resin and spectrophotometric determination with diphenylcarbazide

The method developed in this work for the separation and preconcentration of Cr(III) is based on its retention by an Amberlite XAD-2 copolymer resin functionalized with 5-palmitoyl-8-hydroxyquinoline (oxine), abbreviated XAD-POx, with the ligand covalently bound to the copolymer. Cr(III) sorption was quantitative within the pH range 4.5–7.0 and Cr(VI) was not retained. The Cr(III) held by the resin column was eluted with a hot solution of H₂O₂ in pH9.0 aqueous NH₃–NH₄Cl buffer, and Cr oxidized to CrO₄^2– was rejected by the chelating cation-exchanger column. Any Cr(VI) originally present with Cr(III) could be reduced with an acidic solution of H₂O₂, and retained by the column yielding total Cr results, Cr(VI) being determined from the difference. The resin showed a maximal preconcentration factor of 60 for Cr(III), the LOD and LOQ being 9.3 and 30.1 nmol L^–1, respectively. The developed preconcentration-speciation analysis was finished with a diphenylcarbazide (DPC) spectrophotometric procedure suitable for conventional laboratories. The resin showed excellent salt tolerance, enabling Cr analysis in seawater, and was stable over extended use. All the interferents of this procedure that normally occur in an electroplating effluent, a blended coal CRM, and a standard steel sample could be removed by the recommended procedure, by use of partial and total selectivity at the adsorption and desorption stages, respectively, enabling preconcentration and colorimetric determination of chromium in various complex matrices.     

Magnetic solid‐phase extraction method for extraction of some pesticides in vegetable and fruit juices

A new version of magnetic solid‐phase extraction performed in a narrow‐bore tube has been proposed for the extraction and preconcentration of different pesticides from various vegetable and fruit juices followed by gas chromatography. A few milligrams of C₈@SiO₂@Fe₃O₄ nanoparticles are added into an aqueous sample solution placed in a narrow‐bore tube. The sorbent particles move down through the tube under gravity and are collected at the end of the tube by applying an external magnetic field. The end of the tube is narrower and it is connected to a stopcock. After a predetermined time, the stopcock is opened and the solution is passed through the bed of the sorbent maintained by the magnet. Then the adsorbed analytes are desorbed using an elution solvent. To achieve high enrichment factors, a dispersive liquid–liquid microextraction method is carried out. The nanoparticles were characterized by scanning electron microscopy, X‐ray diffraction, and FTIR spectroscopy. Under the optimum extraction conditions, limits of detection and quantification were in the ranges of 0.1–0.3 and 0.3–0.9 μg/L, respectively. High enrichment factors (1166–1605) and good extraction recoveries (58–80%) were obtained.     

Screen‐Printed Disposable Sensors Modified with Bismuth Precursors for Rapid Voltammetric Determination of 3 Ecotoxic Nitrophenols

This work reports the application of screen‐printed electrodes bulk‐modified with bismuth precursors to the voltammetric determination of 2‐nitrophenol (2‐NP), 4‐nitrophenol (4‐NP) and 2,4‐dinitrophenol (2,4‐DNP) in water samples. A bismuth film was formed at the electrode surface via in situ reduction of the precursor compound contained in the electrode matrix by cathodic polarization at ?1.20 V. The formation of bismuth layer at the precursor‐modified electrodes was assessed by cyclic voltammetric (CV) at different pH values and by optical techniques. The target nitrophenols were voltammetrically determined by recording their reduction peaks in the differential pulse (DP) mode. The composition and content of the precursor compounds in the printed ink and the effect of the pH of the supporting electrolyte on the DP reduction currents of the 3 target nitrophenols were studied. The limits of quantification (LOQs) in three water matrices (distilled water, tap water and surface water) were in the range 1.1–2.2 µmol L^?1_. Using a simple solid‐phase extraction (SPE) procedure with Lichrolut EN cartridges and elution with methanol, a preconcentration factor of 100 was achieved; the LOQs were 0.021, 0.027 and 0.025 µmol L^?1 for 2‐NP, 4‐NP and 2,4‐DNP, respectively. The recoveries of samples spiked with the 3 target nitrophenols at two concentration levels (0.04 and 0.1 µmol L^?1) were always >87 %.     

Loading controlled magnetic carbon dots for microwave‐assisted solid‐phase extraction: Preparation,extraction evaluation and applications in environmental aqueous samples

An adsorbent of carbon dot@poly(glycidyl methacrylate)@Fe₃O₄ nanoparticles has been developed for the microwave‐assisted magnetic solid‐phase extraction of polycyclic aromatic hydrocarbons in environmental aqueous samples prior to high‐performance liquid chromatography with UV/visible spectroscopy detection. Poly(glycidyl methacrylate) was synthesized by atom transfer radical polymerization. The chain length and amount of carbon dots attached on them can be easily controlled through changing polymerization conditions, which contributes to tunable extraction performance. The successful fabrication of the nano‐adsorbent was confirmed by transmission electronic microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and vibrating sample magnetometry. The extraction performance of the adsorbent was evaluated by using polycyclic aromatic hydrocarbons as model analytes. The key factors influencing the extraction, such as microwave power, adsorption time, desorption time and desorption solvents were investigated in detail. Under the optimal conditions, the microwave‐assisted method afforded magnetic solid‐phase extraction with short extraction time, wide dynamic linear range (0.02–200 μg/L), good linearity (R² ≥ 98.57%) and low detection limits (20–90 ng/L) for model analytes. The adsorbent was successfully applied for analyzing polycyclic aromatic hydrocarbons in environmental aqueous samples and the recoveries were in the range of 86.0–124.2%. Thus, the proposed method is a promising candidate for fast and reliable preconcentration of trace polycyclic aromatic hydrocarbons in real water samples.     

Solid-phase Microextraction of Volatile Polar Compounds in Water

A method was developed for the analysis of volatile polar compounds in a water matrix using open cap vials Solid Phase Micro-Extraction (SPME) and Capillary Gas Chromatography (CGC). Both SPME techniques – direct sampling and headspace – were tested. Optimization of experimental conditions – exposure time, desorption time, with headspace SPME in addition the influence of the temperature and ionic strength of the sample solution on compound sorption, and finally GC response – were investigated. The analytes were extracted by directly immersing the 85 μm polyacrylate fiber in the aqueous sample or in the headspace. The linear range of the preconcentration process and the precision were examined. The amount of polar analytes sorbed on the fiber was determined and was found to be concentration dependent; it amounted to 0.014–0.64% in the concentration range of 0.00425–425 ppm studied in aqueous solution for direct sampling SPME and to 0.011–2.76% for solutions of concentration 0.0425–255 ppm for headspace SPME. The limits of determination were ascertained. Headspace SPME was applied to the analysis of real-life samples.