Thiodiethanethiol Modified Silica Coated Magnetic Nanoparticles for Preconcentration and Determination of Ultratrace Amounts of Mercury,Lead, and Cadmium in Environmental and Food Samples

A new magnetic adsorbent, 2,2′-thiodiethanethiol grafted with tetraethyl orthosilicate modified Fe₃O₄ nanoparticles, was developed for the separation and preconcentration of Hg, Pb, and Cd in environmental and food samples. The concentrations of Pb and Cd were determined by inductively coupled plasma–optical emission spectrometry; Hg was determined by cold vapor atomic absorption spectrometry. A comprehensive study on the factors affecting the extraction and desorption efficiencies was performed. Under the optimized conditions, the method was linear in the 0.01–750 ng mL^?1 range (before preconcentration) with detection limits of 4, 8, and 2 ng L^?1 for Hg, Pb, and Cd, respectively. Relative standard deviations of 2.3, 2.9, and 2.4% (concentration 50 ng mL^?1, n = 7) and high preconcentration factors of 291, 285, and 288 were also obtained for Hg, Pb, and Cd. The accuracy of the proposed method was validated by analyzing a water certified reference material with satisfactory recoveries. The method was successfully applied to the determination of the analytes in tap and mineral waters and canned tuna fish samples.     

Polythiophene–Chitosan Magnetic Nanocomposite as a Novel Sorbent for Disperse Magnetic Solid Phase Extraction of Triazine Herbicides in Aquatic Media

In this paper, polythiophene/chitosan magnetic nanocomposite as a novel adsorbent is proposed for the preconcentration of triazines in aqueous samples prior to gas chromatography. The synthesized nanoparticles, magnetic chitosan and polythiophene–chitosan magnetic nanocomposite were characterized by scanning electron microscopy. The magnetic polythiophene–chitosan nanocomposite containing analytes could be removed from the sample solution by applying a permanent magnet. The major factors influencing the extraction efficiency including desorption conditions, nanocomposite components ratio, sorbent amount, extraction time, ionic strength and sample pH were optimized. The developed method proved to be rather convenient and offers sufficient sensitivity and good reproducibility. The limit of detection (S/N = 3) and limit of quantification (S/N = 10) of the method under optimized conditions were 10–30 and 100 ng L⁻¹, respectively. Under the optimum conditions, good linearity was obtained within the range of 100–5000 ng L⁻¹ for all triazines with correlation coefficients >0.9994. The relative standard deviation at a concentration level of 150 ng L⁻¹ was 7–12 %. Furthermore, the method was successfully applied to the determination of triazines in real samples, where relative recovery percentages of 96–102 % were obtained. Compared with other methods, the current method is characterized by easy, fast separation and low detection limits.

     

A highly thermal-resistant electrospun-based polyetherimide nanofibers coating for solid-phase microextraction

A high-temperature-resistant solid-phase microextraction (SPME) fiber was prepared based on polyetherimide (PEI) by the electrospinning method. The PEI polymeric solution was converted to nanofibers using high voltages and directly coated on a stainless steel SPME needle. The scanning electron microscopy images of PEI coating showed fibers with diameter range of 500–650 nm with a homogeneous and smooth surface morphology. The SPME nanofibers coating was optimized for PEI percentage, electrospinning voltage, and time. The extraction efficiency of the coating was investigated for headspace SPME of some environmentally important polycyclic aromatic hydrocarbons from aqueous samples followed by gas chromatography–mass spectrometry measurement. In addition, the important extraction parameters including extraction temperature, extraction time, ionic strength, as well as desorption temperature and time were investigated and optimized. The detection limits of the method under optimized conditions ranged from 1 to 5 ng L^?1 using time-scheduled selected ion monitoring mode. The relative standard deviations of the method were between 1.1 and 7.1 %, at a concentration level of 500 ng L^?1. The calibration curves of polycyclic aromatic hydrocarbons showed linearity in the range of 5–1000 ng L^?1. The developed method was successfully applied to real water samples and the relative recovery percentages obtained from the spiked water samples were from 84 to 98 % for all the selected analytes except for acenaphthene which was from 75 to 106 %.     

Removal, preconcentration and spectrophotometric determination of U(VI) from water samples using modified maghemite nanoparticles

Arsenazo III modified maghemite nanoparticles (A-MMNPs) was used for removing and preconcentration of U(VI) from aqueous samples. The effects of contact time, amount of adsorbent, pH and competitive ions was investigated. The experimental results were fitted to the Langmuir adsorption model in the studied concentration range of uranium (1.0 × 10^?4–1.0 × 10^?2 mol L^?1). According to the results obtained by Langmuir equation, the maximum adsorption capacity for the adsorption of U(VI) on A-MMNPs was 285 mg g^?1 at pH 7. The adsorbed uranium on the A-MMNPs was then desorbed by 0.5 mol L^?1 NaOH solution and determined spectrophotometrically. A preconcentration factor of 400 was achieved in this method. The calibration graph was linear in the range 0.04–2.4 ng mL^?1 (1.0 × 10^?10–1.0 × 10^?8 mol L^?1) of U(VI) with a correlation coefficient of 0.997. The detection limit of the method for determination of U(VI) was 0.01 ng mL^?1 and the relative standard deviation (R.S.D.) for the determination of 1.43 and 2.38 ng mL^?1 of U(VI) was 3.62% and 1.17% (n = 5), respectively. The method was applied to the determination of U(VI) in water samples.     

Trace analysis of benzophenone-derived compounds in surface waters and sediments using solid-phase extraction and microwave-assisted extraction followed by gas chromatography–mass spectrometry

This study describes a procedure for determining eight benzophenone-derived compounds in surface waters and sediments. These include the pharmaceutical ketoprofen, its phototransformation products 3-ethylbenzophenone and 3-acetylbenzophenone, and five benzophenone-type ultraviolet (UV) filters. The proposed analytical method involves the pre-concentration of water samples by solid-phase extraction (SPE) and microwave-assisted extraction (MAE) of sediment samples followed by derivatization and analysis by gas chromatography–mass spectrometry. Different parameters were investigated to achieve optimal method performance. Recoveries of 91 to 96 % from water samples were obtained using HLB Oasis SPE cartridges, whereas MAE of sediments (30 min at 150 °C) gave recoveries of 80 to 99 %. Limits of detection were between 0.1 and 1.9 ng L^?1 for water samples and from 0.1 to 1.4 ng g^?1 for sediment samples. The developed method was applied to environmental samples and revealed the presence of UV filters in the majority of the surface waters with up to 690 ng L^?1 of 2-hydroxy-4-methoxybenzophenone. By contrast, ketoprofen (≤2,900 ng L^?1) and its degradation products (≤320 ng L^?1) were found in only two rivers, both receiving wastewater treatment plant effluents. Sediment analysis revealed benzophenone to be present in concentrations up to 650 ng g^?1, whereas concentrations of other compounds were considerably lower (≤32 ng L^?1). For the first time, quantifiable amounts of two ketoprofen transformation products in the aqueous environment are reported.     

Dispersive liquid–liquid microextraction combined with flow injection inductively coupled plasma mass spectrometry for simultaneous determination of cadmium, lead and bismuth in water samples

Dispersive liquid–liquid microextraction (DLLME) was combined with flow injection inductively coupled plasma mass spectrometry for simultaneous determination of cadmium, lead and bismuth in water samples. The metal elements were complexed with sodium diethyldithiocarbamate, and then the complexes were extracted into carbon tetrachloride by using DLLME. Under the optimized conditions, the enrichment factors for Cd, Pb and Bi are 460, 900 and 645 in 5 mL of a spiked water sample, respectively. The calibration graphs for the three metals are linear in the range of concentrations from <10 ng L^?1 to 1,000 ng L^?1. The detection limits are 0.5 ng L^?1, 1.6 ng L^?1 and 4.7 ng L^?1, respectively. The relative standard deviations for ten replicate measurements of 50 ng L^?1 cadmium, lead and bismuth are 2.6%, 6.7%, and 4.9%, respectively, and the relative recoveries in various water samples at a spiking level of 50 ng L^?1 range from 83.6% to 107.0%.     

Determination of Low-Molecular-Mass Aldehydes in Water Samples by Liquid Chromatography and Chemiluminescence Detection Using Continuous in situ Derivatization/Preconcentration with Dansylhydrazine

Abstract

A simple, expeditious, and sensitive method has been developed for the determination of low-molecular-mass aldehydes in water samples by liquid chromatography and peroxyoxalate–chemiluminescence detection. The method is based on continuous solid-phase extraction with in situ derivatization/preconcentration of the aldehydes using dansylhydrazine, which was first adsorbed on an RP–C₁₈ mini-column. For 10 mL of aqueous sample, the limits of detection (LOD) for C₁ to C₄ aldehydes were 20–30 ng L^?1, except for formaldehyde, which had an LOD of 400 ng L^?1. Application was illustrated by the determination of these aldehydes in water samples; the interday precision was always less than ca. 7%, and relative recoveries were more than 96%.     

Simultaneous Determination of Gallium(III) and Indium(III) in Urine and Water Samples with Cloud Point Extraction and by Inductively Coupled Plasma Optical Emission Spectrometry

A simple, sensitive, and selective method for the determination of gallium and indium in different samples at trace levels is presented. This method was based on complexation of analyzes with 2-(5-bromo-2- pyridylazo)-5-diethylaminophenol (5-Br-PADAP) in the presence of t-octylphenoxy-polyethoxyethanol (Triton X-100). After phase separation, the analyzed concentrations were determined by inductively coupled plasma optical emission spectrometry. Quantitative extraction of gallium and indium was performed at pH 7.0, 1.7 mmol L^?1, 5-Br-PADAP, 1.3% (w/v) Triton X-100 and at 75°C. The relative standard deviations (RSD) of this method were between 0.3% and 1.6% (C = 20 ng mL^?1, n = 9). The calibration curve is linear over the concentration range 6–200 ng mL^?1 for gallium and 2–200 ng mL^?1 for indium, respectively. The limits of detection (LOD) for gallium and indium were 0.72 and 0.28 ng mL^?1, respectively. The results showed the developed method was not susceptible to matrix effects, providing recoveries between 98% and 102%. The accuracy of the developed method was evaluated by the analysis of spiked certified reference materials. The developed method was successfully applied to gallium and indium determination in urine and lake water with satisfactory results.     

Determination of methyl mercury in water samples with electromagnetic induction thermal desorption/pyrolysis coupled to atomic fluorescence spectrometry

A novel non-chromatographic method for the pre-concentration and determination of trace methyl mercury in water samples has been proposed. This method included two main steps: (1) The methyl mercury in sample solution was adsorbed on PDMS of the Fe/SiO₂/PDMS bed enrichment column; (2) the analyte was thermally desorbed from the enrichment column and pyrolysed to Hg⁰ in an iron particle bed pyrolysis column by using electromagnetic induction heating technique, and then detected by an on-line coupled atomic fluorescence detector. Several factors affecting the enrichment column preparation and concentration procedure have been investigated and optimised. Under optimal condition, the detection limit (3σ) was 0.2 ng L^–1, along with relative standard deviations of 2.4% (10 ng L^–1, N = 11) for the repeatability study. The enrichment factor obtained was 108. The two standard reference materials (GBW08675, GBW10029) were analysed to validate the present method. This method was successfully applied to the determination of ng L^–1 methyl mercury in water samples.     

Custom-Made C18 Column for Simultaneous Determination of Endocrine Disrupting Substances in Water by Diode-Array and Fluorescence Detectors

A C₁₈ stationary phase was synthesized for a custom-made HPLC column. When compared to a commercial C₁₈ column, better chromatographic performances were obtained. This column was successfully applied for simultaneous determination of p,p′-DDT, o,p′-DDT, benzo(a)anthracene, benzo(b)fluoranthene, and benzo(a)pyrene in waters by high performance liquid chromatography coupled with dual detectors (diode array and fluorescence detectors) combined with solid phase extraction. Low method detection limits were obtained, i.e., p,p′-DDT: 0.5 µg L^?1, o,p′-DDT: 1 µg L^?1, benzo(a)anthracene: 2.5 ng L^?1, benzo(b)fluoranthene: 5 ng L^?1, and benzo(a)pyrene: 2.5 ng L^?1. High recoveries that ranged from 82 to 94% were obtained for all compounds.     

Selective preconcentration of Lanthanum(III) by Coriolus versicolor immobilised on Amberlite XAD-4 and its determination by ICP-OES

Coriolus versicolor, a wood fungus, was immobilised on Amberlite XAD-4 and used as solid-phase biosorbent for preconcentrations of rare earth elements. La(III), Th(IV), U(IV) and Ce(III) were subjected to solid-phase extraction procedure. We observed that La(III) was selectively preconcentrated, while other ions remained in solution at pH 6.0. 5.0 mL of 1.0 mol L^?1 HCl was used to elaute La(III) from column. 250 mg of C. versicolor loaded on 1000 mg of XAD-4 was optimised as solid-phase matrix. Concentrations of ions in solutions were determined by inductively coupled plasma– optical emission spectrometry (ICP-OES). The calibration plot after preconcentration was linear in the range from 1.0 to 50.0 ng mL^?1 for La(III). Limit of detection was found as 0.27 ng mL^?1 for La(III) by SPE method. Relative standard deviation was found lower than 6.7% for 1.0 ng mL^?1 of La(III) solution (n = 10). The sensitivity of ICP-OES was improved by a factor of 46.8. The applicability of the method was validated through the analysis of certified reference samples of tea (NCS ZC-73014) and spinach (NCS ZC-73013).     

Determination of ultra traces of lead in water samples after combined solid-phase extraction–dispersive liquid–liquid microextraction by graphite furnace atomic absorption spectrometry

A solid-phase extraction coupled with dispersive liquid–liquid microextraction (DLLME) method followed by graphite furnace atomic absorption spectrometry (GFAAS) was developed for the extraction, preconcentration, and determination of ultra trace amounts of lead in water samples. Variables affecting the performance of both steps were thoroughly investigated. Under optimized conditions, 100 mL of lead solution were first concentrated using a solid phase sorbent. The extracts were collected in 1.50 mL of THF and 18 μL of carbon tetrachloride was dissolved in the collecting solvent. Then 5.0 mL pure water was injected rapidly into the mixture of THF and carbon tetrachloride for DLLME, followed by GFAAS determination of lead. The analytical figures of merit of method developed were determined. With an enrichment factor of 1,800, a linear calibration of 3–60 ng L^?1 and a limit of detection of 1.0 ng L^?1 were obtained. The relative standard deviation for seven replicate measurements of 30 ng L^?1 of lead was 5.2 %. The relative recoveries of lead in mineral, tap, well, and river water samples at spiking level of 10 and 20 ng L^?1 are in the range 94–106 %.     

HPLC for Separation and Quantification of Deoxyribonucleic Acid Fragments and Measurement of Deoxyribonucleic Acid Degradation

DNA quantification has made its mark in pharmaceutical analysis and the life sciences. In particular, in the quality control of nucleic acid drugs and the detection and quantification of genetically modified organisms, evaluation of the DNA degradation rate has become imperative. In this study, by using high-performance liquid chromatography with an anion-exchange column, we established a method for the separation and quantification of DNA fragments in mixed DNA samples. By using a NaCl concentration gradient, DNA fragments in mixed DNA sample were separated well. A calibration curve from 0.05 to 12.4 ng μL^?1 was obtained with high linearity and the correlation coefficient was 0.9999. The limit of detection was 0.02 ng μL^?1 and the limit of quantification was 0.06 ng μL^?1 for S/N = 3 or S/N = 10, respectively. The relative standard deviation was less than 2 % in the measurement of peak area repeatability. The recovery of approximately 1 ng μL^?1 of a specific DNA spiked in a mixed DNA sample was 99.9 ± 3.6 %. The method was able to measure the degradation rate of 600 bp DNA with a variation of approximately 1 %.     

Extraction and preconcentration of ultra trace amounts of beryllium from aqueous samples by nanometer mesoporous silica functionalized by 2,4-dihydroxybenzaldehyde prior to ICP OES determination

A new functionalized nanometer mesoporous silica (MCM-41) using 2,4-dihydroxybenzaldehyde (4-OHsal) was applied as an effective sorbent for solid phase extraction (SPE) of beryllium ions from aqueous solution followed by inductively coupled plasma optical emission spectrometric detection (ICP OES). The influences of some analytical parameters on the quantitative recoveries of the analyte ion were investigated in batch method. In order to perform the batch mode of SPE, known amount of sorbent was added to a test tube containing sample solution buffered at pH 7.2. After manual shaking and centrifugation the aqueous phase was decanted and beryllium was desorbed by adding 1.0 mL of 1.0 mol L^?1 HNO₃ to the sedimented sorbent. The sorbent was separated by centrifugation and the concentration of beryllium in the supernatant was determined by ICP OES. The maximum sorption capacity of the modified MCM-41 was found to be 34 mg g^?1. The sorbent exhibited good stability, reusability and fast rate of equilibrium for sorption/desorption of beryllium ions. The present method was used for preconcentration and determination of beryllium for water samples. Under optimal conditions, the limit of detection (LOD) obtained was 0.3 ng L^?1. The accuracy of the procedure was evaluated by analysis of the certified reference material (NIST 1640).     

Optimization of Sample Preparation of Carrot-Fruit Juice for Determination of Antimony,Arsenic, and Selenium by Hydride Generation-Inductively Coupled Plasma Optical Emission Spectrometry

Sample preparation procedures for the determination of As, Sb, and Se in carrot-fruit juice by hydride generation inductively coupled plasma optical emission spectrometry (HG-ICP OES) were examined. The applicability of a partial decomposition using aqua regia and simple dilution with a 2% (v/v) HNO₃ solution were tested and compared to a traditional treatment based on the wet digestion with a HNO₃/H₂O₂ mixture. The pre-reduction and hydride generation reaction conditions were evaluated. Under the optimal conditions, the hydrides were produced in the reaction of an acidified sample with NaBH₄ after pre-reduction with ascorbic acid [0.5% (m/v)] and KI [0.5% (m/v)] in 3 mol L^?1 HCl for total As and Sb, and boiling with HCl (6 mol L^?1) for total Se. The best results were obtained for the aqua regia procedure, resulting in limits of detection (LODs) between 1.2–2.4 ng g^?1 in the samples and recoveries from 90.9% to 109.1%. The method was successfully applied (without matrix effects) for the determination of As in dense mousse and pulp juice samples and for Sb in pulp juices. Standard solutions, processed in the same way as samples, were used for the calibration. Undecomposed matrix constituents strongly influenced Se; hence this element was determined using the method of standard addition. Concentrations of studied elements in analyzed products were at the trace level, that is, 6–32 ng g^?1, 4–10 ng g^?1, and 4–13 ng g^?1 for Se, As, and Sb, respectively.     

Simultaneous preconcentration and determination of malachite green and fuchsine dyes in seafood and environmental water samples using nano-alumina-based molecular imprinted polymer solid-phase extraction

Molecular imprinted polymer for determination of malachite green (MG) and fuchsine basic (FU) dyes by spectrophotometry has been used, to develop a novel simultaneous extraction and preconcentration method. Molecularly imprinted layer-coated nano-alumina (MIP@Nano-Al₂O₃) as adsorbent was prepared by surface molecular imprinting technique, and characterised by FTIR spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis (EDAX) and thermogravimetric analysis (TGA). The method is based on simultaneous extraction of MG and FU dyes from aqueous solution by using molecularly imprinted polymer and measuring the absorbance at 617 and 546 nm for MG and FU, respectively. Parameters which affect the extraction efficiency such as pH, volume of eluent and amount of adsorbent were investigated and optimised. Linear calibration curves were obtained in the range of 2–750 ng mL^?1 for MG and 1–240 ng mL^?1 for FU under optimum conditions. Detection limit based on three times the standard deviation of the blank (3S_b) was 0.655 and 0.245 ng mL^?1 (n = 10) for MG and FU, respectively. The relative standard deviation (RSD) for 100 ng mL^?1 of MG and FU was 2.35 and 3.06% (n = 7), respectively. The method was applied to the simultaneous determination of the dyes in different seafood and environmental water samples.     

Ultrasensitive electrochemical biosensor for uranium using deoxyribozymes with amplification by gold nanoparticles

A novel highly sensitive and specific electrochemical biosensor for detecting uranium based on specific Deoxyribozymes and gold nanoparticles (AuNPs) is reported. In this work, AuNPs provide excellent electrochemical signal transduction and a large surface area for immobilising numerous Deoxyribozymes, so a low detection limit of 3.24 ng L^?1 uranium and a good linear relationship over the range 5.94–35.1 ng L^?1 (r = 0.994) were obtained. The proposed biosensor presents high specificity and selectivity for uranium and is not affected by other metal ions. Thus, the biosensor protocol offers good selectivity, rapid speed and operational convenience for detection uranium in liquid waste.     

Determination of DNA Methylation and Hydroxymethylation Levels in Biological Samples by Field-Amplified Sample Injection-Capillary Zone Electrophoresis with UV Detection

In this study, a method of field-amplified sample injection coupled with capillary zone electrophoresis with ultraviolet detection was established for evaluation of DNA methylation and hydroxymethylation levels in biological materials. By modifying an existing method, the separation of cytosine (C), 5-methylcytosine (5-mC) and 5-hydroxymethylcytosine (5-hmC) was performed on an uncoated capillary column (40 cm × 75 μm I.D.) using 300 mmol L⁻¹ tris solution (pH 2.90) as running buffer and detected at 280 nm. The detection limits (S/N = 3) of the method were 0.004 ng mL⁻¹ for cytosine (C), 0.01 ng mL⁻¹ for 5-methylcytosine (5-mC), and 0.02 ng mL⁻¹ for 5-hydroxymethylcytosine (5-hmC). The proposed method has been successfully applied to the evaluation of DNA methylation and hydroxymethylation levels of blood samples from 15 hepatocellular carcinoma patients and 5 liver cirrhosis patients and liver tissues from 50 pairs of tumor and matched tumor-adjacent samples.

     

Naked magnetite nanoparticles for both clean-up and solid-phase extraction-trace determination of mercury

A new solid-phase extraction method was developed for trace determination of Hg(II) by using a small amount of naked magnetite nanoparticles as an adsorbent. The magnetite nanoparticles were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The adsorbed Hg(II)-dithizone complex was eluted with 1.0 mL aliquot of an acidic 1-propanol solution prior to electrothermal atomic absorption spectrometry. A huge positive effect was found on the mercury adsorption by ionic strength. Under optimized condition, a linear calibration curve was obtained for mercury in the range of 0.2–50 ng mL^?1 with relative standard deviation in the range of 0.5–2.0%. The limit of detection and enrichment factor were 0.01 ng mL^?1 and 98.3, respectively. The effects of coexisting ions were studied extensively, and a new clean-up procedure was used to remove the matrix effects by using a simple sample pretreatment step using a little amount of magnetite nanoparticles. The method was successfully applied to the determination of Hg(II) in different water and human urine samples and a commercial sodium nitrate.     

Development and Validation of an HPLC–UV–Vis Method for the Determination of Proparacaine in Human Aqueous Humour

A sensitive high performance liquid chromatographic method has been developed and validated for the determination of proparacaine in human aqueous humour. The procedure involved extraction of proparacaine from aqueous humour with cyclohexane. The separation was achieved using a Bondesil C₈ (250 × 4.6 mm i.d., particle size 5 μm) analytical column with a mobile phase consisted of acetonitrile and sodium dihydrogen phosphate (pH 3.0, 20 mM) (30:70, v/v). Proparacaine and lidocaine (internal standard, IS) detection was performed by UV–Vis detector at 220 nm. The retention times for proparacaine and IS were 12.01 and 5.58 min, respectively. HPLC–UV–Vis method was linear in the range of 75–4,000 ng mL⁻¹. The limit of detection (LOD) was 25 ng mL⁻¹ and the limit of quantification (LOQ) of proparacaine was found to be 75 ng mL⁻¹ (RSD ≤ 15%, n = 6). In intra- and inter-day precision and accuracy analysis, the relative standard deviation was found to be in the range of 0.96 and 7.98%, the bias values were 0.64 and 3.33%. Recovery of proparacaine from human aqueous humour was 99.98% at 500 ng mL⁻¹. Proparacaine solutions were stable at least 6 months at +4 and −20 °C. Proparacaine levels of aqueous humour in fifteen volunteers’ were in the range of 80.21 and 459.00 ng mL⁻¹. According to system suitability tests and Shewhart’s quality control charts the proparacaine responses were in the acceptance ranges. Developed method was providing a sufficient quality at least over 3 months for determination of proparacaine in human aqueous humour.