Automated online preconcentration system for the determination of trace amounts of lead using Pb-selective resin and inductively coupled plasma-atomic emission spectrometry

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 mu L 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 ( &#62;= 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.</p

An easily prepared graphene oxide-ionic liquid hybrid nanomaterial for micro-solid phase extraction and preconcentration of Hg in water samples

A preconcentration method based on the use of graphene oxide (GO) functionalized with an ionic liquid (IL) was developed for trace Hg determination in water samples. The IL-GO hybrid nanomaterial was prepared by a simple procedure to functionalize GO with the IL 1-butyl-3-dodecylimidazolium bromide ([C4C12im]Br) and its performance as a sorption material for Hg was evaluated. A microcolumn filled with the IL-GO nanomaterial was used for preconcentration and determination of Hg followed by electrothermal atomic absorption spectrometry (ETAAS) detection. Mercury was retained at pH 5.0 and 20% (v/v) HNO3 was used for the elution of Hg from the microcolumn. The effects of different variables, including the sample volume, extraction time, sample flow rate, type and concentration of eluent and eluent flow rate were carefully studied. High retention efficiency (100%) was achieved with the proposed IL-GO sorption nanomaterial without the need for additional chelating reagents or derivatization reagents, which is an important advantage compared with traditional preconcentration methods. A sensitivity enhancement factor of 100 and a low detection limit of 14 ng L-1 were obtained under optimal experimental conditions. The proposed method can be considered as a simple, cost-effective and efficient alternative for Hg determination in water samples like river, rain, mineral and tap water.Fil: Cruz Sotolongo, Annaly. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Cuyo; ArgentinaFil: Martinis, Estefanía Mabel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Cuyo; ArgentinaFil: Wuilloud, Rodolfo German. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Cuyo; Argentin

Accurate Multi-physics Numerical Analysis of Particle Preconcentration Based on Ion Concentration Polarization

This paper studies mechanism of preconcentration of charged particles in a straight micro-channel embedded with permselective membranes, by numerically solving coupled transport equations of ions, charged particles and solvent fluid without any simplifying assumptions. It is demonstrated that trapping and preconcentration of charged particles are determined by the interplay between drag force from the electroosmotic fluid flow and the electrophoretic force applied trough the electric field. Several insightful characteristics are revealed, including the diverse dynamics of co-ions and counter ions, replacement of co-ions by focused particles, lowered ion concentrations in particle enriched zone, and enhanced electroosmotic pumping effect etc. Conditions for particles that may be concentrated are identified in terms of charges, sizes and electrophoretic mobilities of particles and co-ions. Dependences of enrichment factor on cross-membrane voltage, initial particle concentration and buffer ion concentrations are analyzed and the underlying reasons are elaborated. Finally, post priori a condition for validity of decoupled simulation model is given based on charges carried by focused charge particles and that by buffer co-ions. These results provide important guidance in the design and optimization of nanofluidic preconcentration and other related devices.Comment: 18 pages, 11 firgure

Chromium speciation using an aminated amberlite XAD-4 resin column combined with microsample injection-flame atomic absorption spectrometry

Amberlite XAD-4 resin (AXAD-4) was chemically modified to an aminated Amberlite XAD-4 (AAXAD-4) resin and characterized by infrared spectroscopy. AAXAD-4 resin was used as an efficient solid phase for the preconcentration and speciation of Cr(III) and Cr(VI) ions by column technique. The concentration of chromium species was determined by microsample injection system-flame atomic absorption spectrometer (MIS-FAAS). Selective retention of Cr(III) ions was achieved at pH 8.0 and eluted using 1.0 mL of 3.0 mol L–1 HCl and 1.0 mL of 2.0 mol L–1 NaOH, successively, at the flow rate of 5.0 mL min–1. The maximal sorption capacity of AAXAD-4 resin for Cr(III) ions was found to be 67.0 mg g–1. The limit of detection (LOD) and limit of quantitation (LOQ) for Cr(III) ions were found to be 0.041 and 0.131 µg L–1, respectively, with preconcentration factor (PF) of 375 and relative standard deviation (RSD) of 3.75% (n = 11). The method was validated using certified reference materials (CRMs) and successfully applied to the real samples, spiked with Cr(III) and Cr(VI) ions. © 2018 Slovensko Kemijsko Drustvo. All rights reserved

On-line preconcentration using dual mini-columns for the speciation of chromium(III) and chromium(VI) and its application to water samples as studied by inductively coupled plasma-atomic emission spectrometry

On-line preconcentration system for the selective, sensitive and simultaneous determination of chromium species was investigated. Dual minicolumns containing chelating resin were utilized for the speciation and preconcentration of Cr(III) and Cr(VI) in water samples. In this system, Cr(III) was collected on first column packed with iminodiacetate resin. Cr(VI) in the effluent from the first column was reduced to Cr(III), which was collected on the second column packed with iminodiacetate resin. Hydroxyammonium chloride was examined as a potential reducing agent for Cr(VI) to Cr(III). The effects of pH, sample flow rate, column length, and interfering ions on the recoveries of Cr(III) were carefully studied. Five millilitres of a sample solution was introduced into the system. The collected species were then sequentially washed by 1 M ammonium acetate, eluted by 2 M nitric acid and measured by ICP-AES. The detection limit for Cr(III) and Cr(VI) was 0.08 and 0.15 mu g l-1, respectively. The total analysis time was about 9.4 min. The developed method was successfully applied to the speciation of chromium in river, tap water and wastewater samples with satisfied results. </p

A sensitive spectrophotometric method for lead determination by flow injection analysis with on-line preconcentration

A new flow injection (FI) system for the determination of Pb(II) at trace level with a preconcentration step and spectrophotometric detection is proposed. It is based on preconcentration of lead ions on chitosan and dithizone-lead complex formation in aqueous medium (pH 9). The chemicals and FIA variables influencing the performance of the system were optimized and applied to the determination of lead in natural, well, and drinking water samples. It is a simple, highly sensitive, and low cost alternative methodology. The method provided a linear rage between 25 and 250 μg l-1, a detection limit of 5.0 ng ml-1 and a sample throughput of 15 h-1. The obtained results of spiked samples are in good agreement between the proposed method and ICP-AES.Fil: Di Nezio, Maria Susana. Universidad Nacional del Sur. Departamento de Química; ArgentinaFil: Palomeque, Miriam Edid. Universidad Nacional del Sur. Departamento de Química; ArgentinaFil: Fernández Band, Beatriz Susana. Universidad Nacional del Sur. Departamento de Química; Argentin

Direct Injection Liquid Chromatography High-Resolution Mass Spectrometry for Determination of Primary and Secondary Terrestrial and Marine Biomarkers in Ice Cores

Many atmospheric organic compounds are long-lived enough to be transported from their sources to polar regions and high mountain environments where they can be trapped in ice archives. While inorganic components in ice archives have been studied extensively to identify past climate changes, organic compounds have rarely been used to assess paleo-environmental changes, mainly due to the lack of suitable analytical methods. This study presents a new method of direct injection HPLC-MS analysis, without the need of pre-concentrating the melted ice, for the determination of a series of novel biomarkers in ice-core samples indicative of primary and secondary terrestrial and marine organic aerosol sources. Eliminating a preconcentration step reduces contamination potential and decreases the required sample volume thus allowing a higher time resolution in the archives. The method is characterised by limits of detections (LODs) in the range of 0.01-15 ppb, depending on the analyte, and accuracy evaluated through an interlaboratory comparison. We find that many components in secondary organic aerosols (SOA) are clearly detectable at concentrations comparable to those previously observed in replicate preconcentrated ice samples from the Belukha glacier, Russian Altai Mountains. Some compounds with low recoveries in preconcentration steps are now detectable in samples with this new direct injection method significantly increasing the range of environmental processes and sources that become accessible for paleo-climate studies

Complex formation and enantioselectivity studies of triazole fungicide and organophosphorus pesticide enantiomers using capillary electrophoresis

Several cyclodextrin modified-micellar electrokinetic chromatography (CDMEKC) methods were developed for the successful triazole fungicides separation. In the first part, an efficient method was developed for the simultaneous enantioseparation of cyproconazole (4 stereoisomer), bromuconazole (4 stereoisomer) and diniconazole (2 stereisomer) enantiomers using CD-MEKC with a dual mixture of neutral cyclodextrins as chiral selector. The best simultaneous separation of cyproconazole, bromuconazole, and diniconazole enantiomers was achieved with a mixture of 27 mM HP-β-CD and 3 mM HP-γ-CD in 25 mM phosphate buffer (pH 3.0) containing 40 mM sodium dodecyl sulfate (SDS) and 15% iso-propanol as organic modifier. Complete separation of 10 stereoisomer of triazole fungicides were obtained in a single run with good resolution (Rs 1.74“26.31) and high peak efficiency (N > 400 000). In the second part of the study, enantioseparation of hexaconazole, penconazole, myclobutanil, and triadimefon was investigated. Simultaneous enantioseparation of penconazole, myclobutanil, and triadimefon was achieved under acidic condition (pH 3.0) using 25 mM phosphate buffer, 50 mM SDS, and 30 mM HP-γ-CD, with Rs greater than 0.9 whereas, simultaneous enantioseparation of hexaconazole, penconazole, and myclobutanil was successfully achieved under neutral condition (pH 7.0) using 25 mM phosphate buffer, 40 mM SDS, and 40 mM HP-γ-CD, with Rs greater than1.6. In order to improve detection sensitivity, on-line preconcentration technique was investigated. It was found that sweeping technique as an on-line preconcentration technique improved the detection sensitivity of the enantioseparation of cyproconazole, bromuconazole, and diniconazole by 30 to 60-fold, with good repeatabilities in the migration time, peak area and peak height were obtained with RSDs in the range of 0.08“0.32%, 0.03“ 2.44%, and 2.13“8.44% respectively. Furthermore, sweeping technique improved the detection sensitivity of the enantioseparation of hexaconazole, penconazole and myclobutanil by 62- to 67-fold. Good repeatabilities in the migration time, peak area and peak height were obtained with RSDs in the range of 2.39“3.90%, 1.96€“6.15%, and 2.80“6.64% respectively. Finally, the formation constant of diniconazole enantiomers with HP-γ-CD under neutral and acidic condition was investigated using CD-MEKC

Influence of the gold nanoparticles electrodeposition method on Hg(II) trace electrochemical detection

Gold nanoparticles (AuNPs) were deposited on Glassy Carbon (GC) substrate by using three electrochemical techniques: Cyclic Voltammetry (CV), Chronoamperometry (CA) and Potentiostatic Double-Pulse (PDP). For each electrodeposition method, the resulting AuNPs-modified electrodes were characterized by CV in H2SO4 and Field Emission Gun Scanning Electron Microscopy (FEG-SEM). CA was found to be the best electrodeposition mode for controlling the morphology and the density of AuNPs. The modified electrodes were used for low Hg(II) concentration detection using Square Wave Anodic Stripping Voltammetry (SWASV). AuNPs obtained by CA afforded the best amperometric response while involving the lowest amount of charge during the electrodeposition step (QAu(III)). This analytical response is correlated to both the smallest particle size (ca. 17 nm in diameter) and the highest particle density (332 particles μm−2), thus displaying high electrode effective surface area. In these optimal conditions, using a Hg(II) preconcentration time of 300 s, the nanosensor array exhibited a linearity range from 0.80 to 9.9 nM with a sensitivity of 1.16 μA nM−1. A detection limit of 0.40 nM (s/n = 3) was reached