A Pretreatment Method for GC–MS Determination of Endocrine Disrupting Chemicals in Mollusk Tissues

Automatic soxhlet extraction followed by silica gel cartridge cleanup process was developed as a pretreatment method for GC–MS determination of seven endocrine disrupting chemicals in mollusk tissues. Operation parameters including extraction time, adsorption flow rate and elution flow rate were optimized as 140 min, 2 mL min^?1 and 2 mL min^?1, respectively. Thirty percent dichloromethane in n-hexane and 70% dichloromethane in n-hexane were used as elution solvents in turn. Recovery rates were 93.7, 91.7, 84.5, 83.3, 88.4, 81.2, and 79.7% for nonylphenols (NPs), bisphenol A (BPA), 17α-ethynylestradiol (EE2), estrone (E1), 17α-estradiol (17α-E2), 17β-estradiol (E2), and estriol (E3), respectively. Acceptable relative standard derivations ranged from 8.5 to 12.1%. Method detection limits ranged from 0.27 to 0.68 ng g^?1 dry weight (dw), and quantitative detection limits ranged from 0.62 to 1.26 ng g^?1 dw. The method was successfully applied to five mollusk species in Dapeng Bay of China to verify its practicability, and NPs, BPA, EE2, E1 and 17α-E2 were detected in the range from 1.6 to 131.5 ng g^?1 dw.     

Determination of Aztreonam by liquid Chromatography with UV and Amperometric Detection

Abstract

A comparative study of UV and amperometric detection of aztreonam after HPLC separation is presented. At pH 2.0 and a detection potential of +1.15 V (vs. Ag/AgCl), the detection limits with amperometric detection are about two times higher (3–5 ng) than those obtained with UV detection (1–3 ng) for aztreonam and its main decomposition products, the E-isomer and open-ring aztreonam. With the advantage of specificity for the aminothiazole group of the aztreonam molecule, amperometry can be used as an alternative or complementary mode to UV detection for the determination of aztreonam in injectable formulations and in human serum.     

Reversed-phase high-performance liquid chromatography fingerprint profiles of thirty-nine mosses with chemometric

Thirty-nine land and aquatic mosses were extracted by double maceration and ultrasonic extraction techniques using the mixture of 80% ethanol and water. Obtained extracts were analyzed using the reversed-phase-high-performance liquid chromatography–diode array detector with the Kinetex C18 chromatographic column and mobile phase consisting of acetonitrile–water–0.1% formic acid mixture (gradient 5–100%, 60 min) with detection wavelength of 280 nm. Next, obtained chromatograms were preliminary processed with the smoothing, noise reduction, background subtraction, and alignment using the SpecAlign program (version 2.4.1). The chemometric analysis was performed to obtain the fingerprint chromatograms of selected mosses. The principal component analysis and the cluster analysis (with paired group algorithm and correlation coefficient—r, as similarity measure) confirm the chemical similarity or differences between studied Bryophyta sp.     

Analysis of Pyrimethanil,Metalaxyl, Dichlofluanid,and Penconazol in Must and Wine from Red Grapes by Solid-Phase Extraction and Gas Chromatography

Abstract

This article describes a method for the simultaneous analysis of four fungicides—pyrimethanil, penconazol, metalaxyl, and dichlofluanid—in must and wine by solid-phase extraction. Two cartridges (octadecylsilane and polystyrene-divinylbenzene) were evaluated with different elution solvents. The most efficient solid phase was octadecylsilane together with ethyl acetate as elution solvent. Determination was performed by gas chromatography with a nitrogen–phosphorus detector, using metribuzin as internal quantification standard. To reduce quantitative errors from matrix effects, matrix-matched calibration was used. The linear regression coefficients were at least 0.9990. The quality parameters of the proposed method presented good recoveries from spiked must and wine, ranging from 92.3 to 105.5%, and good precision, indicated by relative standard deviations (RSDs) of less than 10%. The limits of quantification varied from 0.27 µg L^?1 for penconazol in wine to 9.34 µg L^?1 for metalaxyl in wine. An additional confirmation method, gas chromatography with mass spectrometry detection, was used.     

Poly(lauryl methacrylate-co-1,6-hexanediol ethoxylate diacrylate) modified silica-based dispersive solid-phase extraction for determination of phenylurea herbicides in environmental water samples

In this study, poly(lauryl methacrylate-co-1,6-hexanediol ethoxylate diacrylate) (LMA-HEDA) was synthesised on silanised silica through free-radical cross-linking polymerisation process. The optimal preparation process was obtained by investigating the effects of polymerisation temperature and reaction time. Characterisation of the LMA-HEDA-modified silica was achieved using diffuse reflectance FT-IR. The resulting LMA-HEDA-modified silica was then utilised as a sorbent for dispersive solid-phase extraction (dSPE) of phenylurea herbicides (PUHs) from various environmental water samples. The optimisation of LMA-HEDA-based dSPE process was achieved by investigating the effect of the following parameters including extraction time, pH of sample solution, composition of elution solvent and addition of salt on the extraction recovery of PUHs from water samples. Gradient elution was performed to analyse the extracted PUHs by high performance liquid chromatography (HPLC) with UV-photodiode array detection. Acceptable matrix effect was observed using the proposed LMA-HEDA-based dSPE-HPLC-UV for determining PUHs in environmental water samples. Relatively low detection limits (0.027–0.053 ng mL^?1) and good linearity (0.1–4.0 ng mL^?1; r² > 0.999) for individual PUHs were obtained using the proposed method. The proposed method offered detection limits lower than the allowed permissible level (0.1 ng mL^?1) set by European Union. The enrichment factors of target PUHs were also estimated at 40.3–47.7. Good extraction recoveries (80.1–97.9%) for PUHs-spiked water samples were obtained with relative standard deviations lower than 8.7%. The intra-day/inter-day precision (0.7–4.6%/0.2–5.9%) and accuracy (96.7–104.2%/95.3–103.6%) of the proposed method were also evaluated in this study. In addition, the applicability of the developed method was demonstrated by the measurement of PUHs in various environmental water samples.     

Simultaneous determination of flavonoids and anthraquinones in chrysanthemum by capillary electrophoresis with amperometry detection

<正>A high-performance capillary electrophoresis with amperometry detection method(CE-AD) has been developed for the analysis of flavonoids and anthraquinones(emodin,kaempferol,apigenin,luteolin and rhein) in chrysanthemum.Under optimum conditions,these five analytes were base-line separated within 17 min using a borate-phosphate running buffer(1.5×10~(-2) mol/L borate-3×10~(-2) mol/L phosphate running buffer,pH 9.0) at a working potential of +0.90 V(vs.SCE) and a separation voltage of 19 kV.The linear relationship between concentration and current response was obtained with detection limits(S/N = 3) ranging from 1.0×10~(-7) to 2.1×10~(-7) g/mL for all analytes.This proposed method was successfully used in the analysis of four kinds of chrysanthemum with relatively simple extraction procedures,the assay results were satisfactory.     

Determination of Amifostine and WR1065 in Rat Plasma by CE with Amperometric Detection

A method based on capillary electrophoresis with amperometric detection (CE–AD) was developed for the determination of amifostine (a cytoprotective agent, WR2721) and 2-(3-aminopropylamino)ethanethiol) (WR1065, the active metabolite of WR2721) in rat plasma. The contents of WR1065 and amifostine were determined by measuring WR1065 in deproteinized rat plasma using CE–AD before and after it was incubated at 37 °C for 4 h in acidic solution, respectively. During the incubation, amifostine was quantitatively converted to WR1065. In addition, cysteine and uric acid in rat plasma were also determined simultaneously. The detection electrode was a 500 μm diameter platinum disc electrode at a detection potential of +1.0 V (vs. saturated calomel electrode). The analytes can be well separated within 9 min in a 50-cm-long fused-silica capillary at a separation voltage of 18 kV in a 100 mM phosphate buffer (pH 7.5). The relation between peak current and analyte concentration was linear over about 3 orders of magnitude with the limits of quantification (S/N = 3) ranging from 0.60 to 1.40 μM. The method has been validated. Satisfactory within-day and between-day precisions were obtained with relative standard deviations of ≤4.9 and ≤5.1 % for WR1065 and ≤5.0 and ≤5.3 % for amifostine, respectively. The within-day and between-day accuracy was in the range of 98.6–102.3 % and 95.7–97.2 % for WR1065 and 97.5–98.6 and 95.3–97.1 % for amifostine, respectively.

     

Microwave Assisted Extraction of Polycyclic Aromatic Hydrocarbons and their Determination by Gas Chromatography–Mass Spectrometry: Validation of the Method and Application to Marine Sediments

Microwave-assisted extraction of sixteen polycyclic aromatic hydrocarbons and their gas chromatographic mass spectrometric detection are presented herein. An efficient extraction was achieved in 15 minutes using 10 mL of 1:1 n-hexane-acetone while a clean-up step was developed studying the elution curves on solid phase extraction silica cartridges. The analytical method was optimized and validated using a certified reference marine sediment; satisfactory figures of merit were obtained with limits of detection in the range 0.001–0.004 µg/g, precision within 6%, and good linearity (regression coefficients generally higher than 0.998, in the concentration range 0.010–1.000 µg/mL). The developed method was successfully applied to the determination of polycyclic aromatic hydrocarbons in real marine sediments collected in two coastal areas of Italy exposed to different anthropic impact: three tourist sites of Liguria and the Venetian Lagoon. The total concentration of the analytes in the samples was in the range 1.027–3.827 µg/g and the use of common markers suggested their probable pyrolytic origin.     

Design of a new hypoxanthine biosensor: xanthine oxidase modified carbon film and multi-walled carbon nanotube/carbon film electrodes

A new and simple-to-prepare hypoxanthine biosensor has been developed using xanthine oxidase (XOD) immobilised on carbon electrode surfaces. XOD was immobilised by glutaraldehyde cross-linking on carbon film (CF) electrodes and on carbon nanotube (CNT) modified CF (CNT/CF). A comparison of the performance of the two configurations was carried out by the current response using amperometry at fixed potential; the best characteristics being exhibited by XOD/CNT/CF modified electrodes. The effects of electrolyte pH and applied potential were evaluated, and a proposal is made for the enzyme mechanism of action involving competition between regeneration of flavin adenine dinucleotide and reduction of hydrogen peroxide. Under optimised conditions, the determination of hypoxanthine was carried out at ?0.2 V vs. a saturated calomel electrode (SCE) with a detection limit of 0.75 μM on electrodes with CNT and at ?0.3 V vs. SCE with a detection limit of 0.77 μM on electrodes without CNT. The applicability of the biosensor was verified by performing an interference study, reproducibility and stability were investigated, and hypoxanthine was successfully determined in sardine and shrimp samples.     

Determination of Amifostine and WR1065 in Rat Plasma by CE with Amperometric Detection

A method based on capillary electrophoresis with amperometric detection (CE–AD) was developed for the determination of amifostine (a cytoprotective agent, WR2721) and 2-(3-aminopropylamino)ethanethiol) (WR1065, the active metabolite of WR2721) in rat plasma. The contents of WR1065 and amifostine were determined by measuring WR1065 in deproteinized rat plasma using CE–AD before and after it was incubated at 37 °C for 4 h in acidic solution, respectively. During the incubation, amifostine was quantitatively converted to WR1065. In addition, cysteine and uric acid in rat plasma were also determined simultaneously. The detection electrode was a 500 μm diameter platinum disc electrode at a detection potential of +1.0 V (vs. saturated calomel electrode). The analytes can be well separated within 9 min in a 50-cm-long fused-silica capillary at a separation voltage of 18 kV in a 100 mM phosphate buffer (pH 7.5). The relation between peak current and analyte concentration was linear over about 3 orders of magnitude with the limits of quantification (S/N = 3) ranging from 0.60 to 1.40 μM. The method has been validated. Satisfactory within-day and between-day precisions were obtained with relative standard deviations of ≤4.9 and ≤5.1 % for WR1065 and ≤5.0 and ≤5.3 % for amifostine, respectively. The within-day and between-day accuracy was in the range of 98.6–102.3 % and 95.7–97.2 % for WR1065 and 97.5–98.6 and 95.3–97.1 % for amifostine, respectively.     

Liquid Chromatographic Determination of Glyoxal and Methylglyoxal from Serum of Diabetic Patients using Meso‐Stilbenediamine as Derivatizing Reagent

Abstract

Meso‐stilbenediamine has been used as derivatizing reagent for liquid chromatographic (LC) determination of glyoxal (Go), methylglyoxal (MGo), and dimethylglyoxal (DMGo) at pH 3. Liquid chromatographic elution and separation was carried out from the column Kromasil 100 C‐18, 5 µm (15×0.46 mm i.d.) with methanol: water:acetonitrile (59:40:1, v/v/v) with a flow rate of 1 mL/min and ultraviolet detection at 254 nm. The linear calibration curves were obtained for Go, MGo, and DMGo within 0.97–4.86 µg/mL, 1.52–7.6 µg/mL, and 1.41–7.08 µg/mL with detection limits of 48 ng/mL, 76 ng/mL, and 70.8 ng/mL, respectively. The method was applied for the determination of Go and MGo from serum of patients suffering from diabetes and ketosis. The amounts of Go and MGo found were 0.150–0.260 µg/mL and 0.160–0.270 µg/mL with coefficient of variation (C.V.) 2.6–4.7% and 2.5–4.6%, respectively. The results obtained were compared with normal subjects with Go and MGo contents of 0.025–0.065 µg/mL and 0.030–0.070 µg/mL with C.V 1.5–4.9% and 1.6–4.8% in the serum.     

Thionine-functionalized graphene oxide,new electrocatalyst for determination of nitrite

In this work, thionine (Th) was assembled on the surface of graphene oxide as an electron transfer mediator using diazonium reaction (Th–GO). Then, Th–GO was characterized by different methods such as scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy. Afterward, Th–GO was used for the modification of carbon paste electrode. Several electrochemical methods including cyclic voltammetry, differential pulse voltammetry, and hydrodynamic amperometry were used to investigate the behavior of the modified electrode. Then, the role of the modified electrode for oxidation of nitrite has been studied. For this purpose, the effect of critical experimental parameters including step potential and pulse amplitude (in differential pulse voltammetry technique), applied potential, the rotating speed of the disk (in amperometry technique), and the solution pH was investigated. Under the optimized conditions, the currents were found to be linear with the nitrite concentration in the range 0.05–33.0 and 0.5–800 µmol L^?1 with detection limits of 0.02 and 0.2 µmol L^?1 using differential pulse voltammetry and hydrodynamic amperometry, respectively. The introduced modified electrode showed good repeatability (RSD% = 3.2) and reproducibility (RSD% = 4.7). This electrochemical sensor was exerted successfully for the determination of nitrite and nitrate in real samples including water and wastewater samples.     

Simple strategy for the optimization of solid-phase extraction procedures through the use of solid-liquid distribution coefficients application to the determination of aliphatic lactones in wine

A practical strategy for the optimization of solid-phase extraction (SPE) systems is presented. Critical SPE volumes (sample loaded, rinsing and elution solvent) are calculated from solid–liquid extraction coefficients and from basic bed parameters determined in simple experiments, using the Lövkist Jonsson model and other expressions derived from the general theory of chromatography. The agreement between calculated and measured volumes is satisfactory, which makes it possible to consider different sorbents and rinsing and elution solvents in the SPE optimization with a relatively low experimental effort. The strategy has been successfully applied to the optimization of a SPE method directed to the selective extraction of aliphatic lactones from wine. Six different reversed-phase sorbents were studied and the one showing maximum extraction selectivity was selected. Wine (50 ml) is extracted in a 200 mg cartridge filled with Bond Elut-ENV resins. Interferences are removed with 20 ml of methanol–water (40:60) with 1% NaHCO₃. Elution is carried out with 1.8 ml of dichloromethane. The extract is concentrated to 0.15 ml and analyzed by GC–ion trap MS. Eight odor-active aliphatic γ and δ lactones (with 8–12 C atoms) from wine are recovered (R>75%) in an extract free from wine major volatiles. Detection limits are in the 40–300 ng/l range, well below the odor detection threshold of these compounds. Linearity (r²>0.996) and precision (average R.S.D. 3.5%) are satisfactory in all cases. The levels in wine of some of these lactones (γ-octa, undeca and dodecalactones) are reported by first time and results demonstrate that can be present at concentrations above or close to their corresponding odor thresholds.     

Electrochemical Behavior of Hydroquinone at Poly (Acridine Orange)–Modified Electrode and Its Separate Detection in the Presence of o‐Hydroquinone and m‐Hydroquinone

Abstract

Poly (acridine orange) (PAO) film–modified electrode was prepared by the electrooxidation of Acridine orange on a glassy carbon electrode (GCE) for the detection of hydroquinone in the presence of o‐hydroquinone and m‐hydroquinone. The electrochemical behavior of hydroquinone on the modified electrode was investigated with respect to different solution acidity, scan rate, and accumulation time. A pair of sharp and well‐defined peaks was obtained at 0.45 and 0.42 V [vs. a saturated calomel electrode (SCE)] at the PAO film–modified electrode. The potential difference between this pair of cathodic and anodic peaks was decreased to only 30 mV as compared to the 241 mV that was obtained on the bare glassy carbon electrode (GCE). As to o‐hydroquinone and m‐hydroquinone, their corresponding oxidation peaks appeared at 0.55 V and 0.89 V (vs. SCE), respectively. The oxidation potential differences between these three isomers enabled the separate detection of hydroquinone. Under the optimum experimental situation, the oxidation peak current of hydroquinone was proportional to the concentration at the range of 6.8×10^?7–9.6×10^?5 M. The detection limit was been estimated as 3×10^?7 M with 130 s accumulation. This method was applied to the hydroquinone detection in tap water samples.     

Glassy carbon electrode modified with a film of poly(Toluidine Blue O) and carbon nanotubes for nitrite detection

This work describes the modification of a glassy carbon electrode with poly(Toluidine Blue O) (GC/poly-TBO) and single-walled carbon nanotubes (SWCNT) for the electrocatalytic oxidation of nitrite. GC/poly-TBO was prepared by electropolymerization and used as such or after immobilizing SWCNT on the polymeric film to give a composite GC/poly-TBO-SWCNT electrode. The electrochemical and catalytic behavior of both electrodes was studied comparatively. It was observed that the presence of SWCNT contributed to enhance the electrocatalytic response for nitrite oxidation, as measured by amperometry at +0.92 V vs. Ag/AgCl/KCl_sat and pH 7. The response was linear with respect to the nitrite concentration in the 0.001–4 mM range, with a detection limit of 0.37 μM (based on signal to noise ratio of 3) for GC/poly-TBO-SWCNT. The proposed method was also applied to the determination of nitrite in a wastewater sample and compared to the spectrophotometric method.     

The Development and Validation of a Liquid Chromatography–Tandem Mass Spectrometry Procedure for the Determination of Dioctyldiethylenetriamine Acetate Residues in Soil,Green and Cured Tobacco Leaves Using a Modified QuEChERS Approach

A liquid chromatography with electrospray ionization tandem mass spectrometry method was developed and validated for the determination of dioctyldiethylenetriamine acetate in soil and tobacco. The separation was performed on a Restek Ultra AQ C₁₈ column (2.1?×?100 mm i.d., particle size 3 µm) at 40 °C with a gradient elution. Methanol and trifluoroacetic acid (0.1%) were used as mobile phase, and the flow rate was set at 0.3 mL min^?1. A modified quick, easy, cheap, effective, rugged, and safe (QuEChERS) method was used for sample extraction and cleanup pretreatment. The recovery was tested in the real samples and calculated to be 86.3–97.4%, the relative standard deviations were 1.1–11.9%. The limits of detection and quantitation were 3.3–16.7 and 10–50 µg kg^?1, respectively. The method was demonstrated to be reliable for the routine monitoring of dioctyldiethylenetriamine acetate in tobacco samples.     

Magnetic Solid Phase Extraction Based on Modified Magnetite Nanoparticles Coupled with Dispersive Liquid–Liquid Microextraction as an Efficient Method for Simultaneous Extraction of Hydrophobic and Hydrophilic Drugs

In this work, surfactant-coated Fe₃O₄@decanoic acid nanoparticles was synthesized as a viable nanosorbent for coextraction of drugs with different polarities (hydrophobic, hydrophilic). To reach desirable enrichment factors, efficient clean-up and low limits of detection (LODs), the method was combined with dispersive liquid–liquid microextraction (DLLME). The coupling of these extraction methods with GC-FID detection was applied to simultaneous extraction and quantification of venlafaxine (VLF) as a hydrophilic model drug and desipramine (DESI) and clomipramine (CLO) as hydrophobic model drugs in urine samples. The effect of sample pH, nanosorbent amount, sorption time, surfactant concentration, eluent type, eluent volume, salt content, elution time in magnetic solid phase extraction step and extraction solvent and its volume along with sample pH in DLLME step were optimized. Under the selected conditions, linearity was achieved within the range of 5–5000 µg L^?1. The LOD values were obtained in the range of 1.5–3.0 µg L^?1 for DESI, 1.2–2.5 µg L^?1 for VLF and 2.0–4.0 µg L^?1 for CLO, respectively. The percent of extraction recoveries and relative standard deviations (n?=?5) were in the range of 82.4–95.9 and 6.1 for DESI, 60.5–92.8 and 6.9 for VLF and 57.2–58.0 and 5.5 for CLO, respectively. Ultimately, the applicability of the new method was successfully confirmed by the extraction and quantification of DESI, VLF and CLO from human urine samples.     

Complexation of herbicide bentazon with native and modified β-cyclodextrin

For first time the complexation of bentazon (Btz) with native β-cyclodextrin (β-CD) and modified sulfobutylether-β-CD (SBE-CD) was studied by differential pulse voltammetry. In addition, a spectrophotometry UV–Visible study was carried out. In presence of CDs there is a decrease of the anodic peak current with the increase of the amount of CD. This decrease is due to the lower diffusion coefficient of Btz/CD complex compared with the free guest. Using the variation in current, association constants of 118 ± 20 and 317 ± 25 M^?1 for β-CD and SBE-CD were determined. The solubility of bentazon was 8 fold higher with SBE-CD as compared with bentazon-free. Phase solubility diagrams performed using UV–Vis experiments permit to obtain the same association constants which were compared with the values obtained by electrochemical techniques.     

Dispersive Solid Phase Extraction with an Ionic Liquid Modified Polymer for Determination of Cyanazine and Atrazine in Tomatoes

A novel ionic liquid modified polymer was employed as an adsorbent for dispersive solid phase extraction for the determination of cyanazine and atrazine in tomatoes. This polymer was advantageous over conventional solid phase extraction in terms of the operational simplicity, speed, handling of large sample volumes, and recovery. Extraction parameters, such as the adsorbent amount, adsorbent time, elution solvent, elution time, and pH of aqueous samples were optimized. The optimized extraction conditions included 50 mg of 1-ethyl-3-methylimidazolium bromide modified polymer as the adsorbent, dichloromethane as the eluent, and 6 min as the adsorption time. Under the optimized conditions, the recovery from tomato samples ranged from 72.0 to 95.1%, which was comparable to tomato juice. The limits of detection for cyanazine and triazine were 0.51 ng/mL and 0.35 ng/mL, respectively.     

Simultaneous Analysis of Seven Bioactive Compounds in Sambucus Chinensis Lindl by HPLC

Following optimization of extraction, separation, and analytical conditions, a simple, rapid, and sensitive HPLC-UV method was developed for the simultaneous determination of seven major bioactive components in Sambucus chinensis Lindl, including chlorogenic acid, caffeic acid, p-coumaric acid, ferulic acid, kaempferol-3-O-β-D-galactopyranoside, kaempferol-3-O-β-D-glucopyran-oside, and kaempferol-3-O-(6-actyl)-β-D-galacto-pyranoside. The good chromatographic separation was performed on a Gemini C₁₈ reversed-phase analytical column (250 mm × 4.6 mm, 5 μm) by gradient elution with acetonitrile and formate aqueous buffer (containing 0.8% formic acid, V/V) at a flow rate of 1.0 mL/min. The detection wavelength was set at 326 nm. The intra-day and inter-day precisions were evaluated with the R.S.D. values less than 4.0%. The mean recoveries of the seven compounds were in the range of 92.4%–104.8%. The method was successfully applied to determine the seven bioactive compounds in six different origins of Sambucus chinensis Lindl samples, and there was a significant variation in the contents of the seven compounds among the six samples. Therefore, this method provided a new basis of overall assessment for routine use in the quality control of Sambucus chinensis Lindl.