Determination of Triazine Herbicides and Metabolites by Solid Phase Extraction with HPLC Analysis

An efficient solid phase extractive preconcentration/separation method was developed for the trace determination of herbicides in aqueous samples using Amberlite XAD-4 resin as the adsorbent. The retained herbicides were eluted with methanol at a flow rate of 1.0 mL min^?1 and determined by HPLC-DAD (wavelength of 220 nm) using water (pH:4.7, phosphoric acid) and methanol (ratio 35:65) as the mobile phase with a flow rate of 1.0 mL min^?1. Quantitative recoveries of simazine, atrazine and its metabolities were achieved at optimized analysis conditions that included 0.75 g of resin; a pH of 3.0; an eluent volume of 3.0 mL; an eluent flow rate of 1.0 mL min^?1; and a sample flow rate of 4.0 mL min^?1. The limits of detection, preconcentration factor, and linear ranges for the herbicides were 0.084–0.121 µgL^?1, 1000, and 0.5–20 mg L^?1, respectively. The performance of the method was evaluated by analysis of spiked water samples. The recoveries of simazine, atrazine and their metabolities were found to be quantitative (99.6–104.8%) with RSDs of 2.2–4.8% and 2.8–4.7% for intra-day and inter-day precision, respectively. The proposed method was successfully applied for trace determination of studied analytes in waste water, apple juice, and red wine samples.     

Use of ionic liquid based chitosan as sorbent for preconcentration of fluoroquinolones in milk,egg, fish,bovine, and chicken meat samples by solid phase extraction prior to HPLC determination

The possibility of using ionic liquid based chitosan sorbent for the separation and preconcentration of fluoroquinolone antibiotics (marbofloxacin, enoxacin, ofloxacin, ciprofloxacin, and enrofloxacin) has been studied. For this reason, different ionic liquids were prepared and coated on the chitosan sorbent. The conditions of the preconcentration of fluoroquinolones on a microcolumn have been optimized and the extraction efficiencies of the prepared sorbents have been compared. The compounds were eluted with 5 mL of 20% NH₃ (v/v, MeOH) solution and determined by HPLC with diode array and fluorescence detector. The limits of detection were found as 4.23 µ g L^?1 for marbofloxacin, and 1.09 µg L^?1 for enoxacin; 3.23 × 10^?3 µg L^?1 for ofloxacin; 8.39 × 10^?3 µg L^?1 for ciprofloxacin; and 19.50 × 10^?3 µg L^?1 for enrofloxacin. The developed method was applied for the analysis of fluoroquinolone in milk, egg, fish, bovine, and chicken samples and the recoveries were obtained in the range 70–100%.     

Solvent extraction of Cu,Mo, V,and U from leach solutions of copper ore and flotation tailings

A micro-cloud point extraction method was discussed for preconcentration and spectrophotometric quantification of U(VI). The method depends on complex formation between U(VI) and 2-(4-sulphophenyloazo)-1,8-dihydroxy-3,6-naphtalenedisulphonic acid (SPADNS) at pH 7.0 and subsequent extraction of the complex in a mixed surfactant medium (cethyltrimethyl ammonium bromide and Triton X-114). The separation was carried out in the presence of 1% Na₂SO₄ at room temperature. The calibration curve was linear up to 3000 µg L^?1. The enrichment factor, detection limit and precision were 16.0, 1.05 µg L^?1, and 2.3%, respectively. The method was employed for the determination of U(VI) in real samples with different matrices.     

Determination of Silver with On-Line Preconcentration Using Dithiozone Chelate and Carbon Nanotubes for Preconcentration with Detection by Flame Atomic Absorption Spectrometry

A novel flow injection system incorporating a micro-column packed with carbon nanotubes (CNTs) as an adsorbent has been applied to the on-line preconcentration of trace silver with detection by flame atomic absorption spectrometry. Silver is first chelated by dithizone (H₂Dz), then retained on the CNTs surface and afterward quantitatively eluted by methanol. Influencing parameters, including the concentration of reaction reagent, enrichment variables, and elution variables were investigated. The adsorption mechanisms of Ag-H₂Dz chelate retained onto the CNTs surface have also been studied. By loading 6.9 mL sample solution, a linear calibration graph is obtained within the range of 3–120 µg L^?1 with R of 0.9996, and a detection limit (3σ) of 0.8 µg L^?1 is achieved, along with a precision of 1.6% R.S.D. at the 30 µg L^?1 level (n = 7). The dynamic sorption capacity of CNTs for silver is 122 mg g^?1. The procedure is demonstrated by measurement of spike recovery in a series of water samples, giving rise to spike recoveries in the range of 96.8–99.7%.     

Dispersive Liquid–Liquid Microextraction for the Preconcentration of Multiple Classes of Pesticides in Water

A simple, rapid, efficient, and environmentally friendly method was developed for the preconcentration of atrazine, simazine, diuron, bentazone, tebuconazole, and fipronil from water. Dispersive liquid–liquid microextraction was employed with determination by liquid chromatography–tandem mass spectrometry. The volumes of extraction and disperser solvents, the concentration of sodium chloride, and the pH were optimized by response surface methodology. The optimum conditions involved the use of 150 µL of 1:1 (v/v) monochlorobenzene:dichlorobenzene as the extraction solvent, 2 mL acetonitrile as the disperser solvent, and 10 mL of sample at pH 3.0. The accuracy was evaluated in terms of recovery values that were from 54 to 112%. The relative standard deviations ranged from 4 to 27%. The limits of quantification were between 0.005 and 0.05 µg L^?1. The optimized method had low matrix effects for the analytes and the results demonstrated application for the determination of pesticides in water.     

Extraction,preconcentration and spectrophotometric determination of trace levels of thiosulfate in environmental waters

In the existing study, a new vortex-assisted cloud point extraction (VA-CPE) method was developed for determination of low levels of thiosulfate in environmental waters at 632 nm by spectrophotometry. The method is selectively based on charge-transfer-sensitive ion-pair complex formation of Ag(S₂O₃)₂ ^3?, which is produced by the reaction of thiosulfate with excess Ag⁺ ions with toluidine blue (3-amino-7-dimethylamino-2-methylphenazathionium chloride, TB⁺) and then its extraction into micellar phase of polyethylene glycol 4-tert-octylphenyl ether (Triton X-45) in presence of Na₂SO₄ as salting-out agent at pH 7.0. All the factors affecting complex formation and VA-CPE efficiency were optimized in detail. Under the optimized conditions, the linear calibration curves for thiosulfate were in the range of 0.2–120 and 5–180 µg L^?1 with sensitivity improvement of 81-folds and 15-folds, respectively, as a result of efficient mass transfer obtained by CPE with and without vortex, while it changed in the range of 260–3600 µg L^?1 without preconcentration at 642 nm. The limits of detection and quantification of the method for VA-CPE were found to be 0.05 and 0.22 µg L^?1, respectively. The precision (expressed as the percent relative standard deviation) was in range of 2.5–4.8% (5, 10 and 25 µg L^?1, n: 5). The method accuracy was validated by comparing the results to those of an independent 5,5′-dithiobis(2-aminobenzoic acid) (DTNB) method as well as recovery studies from spiked samples. It has been observed that the results are statistically in a good agreement with those obtained by DTNB method. Finally, the method developed was successfully applied to the preconcentration and determination of trace thiosulfate from environmental waters.     

Determination of trace amounts of nystatin in water and vaccine samples using sodium dodecyl sulfate-coated iron oxide magnetic nanoparticles followed by high-performance liquid chromatography–ultraviolet detection

In this work, magnetic solid-phase extraction based on sodium dodecyl sulfate-coated Fe₃O₄ nanoparticles has been successfully applied for extraction and preconcentration of trace amounts of nystatin from water and vaccine samples prior to high-performance liquid chromatography–ultraviolet detection. Various experimental parameters affecting extraction and recovery of the analyte, such as the amount of sodium dodecyl sulfate, pH of the sample solution, salt concentration, extraction time, sample volume and desorption conditions, were systematically studied and optimized. Under optimized conditions, nystatin was quantitatively extracted. Proper linear range with good coefficient of determination, (R ² > 0.99) and limit of detection and quantification (based on signal-to-noise ratios of 3 and 10) of 2.0 and 5.0 µg L^?1, over the investigated concentration range (5–700 µg L^?1), were obtained, respectively. The intra-day and inter-day relative standard deviations at 50 µg L^?1 level of NYS were 1.4 and 4.5% based on six replicate determinations. The accuracy of the method was evaluated by recovery measurements on spiked samples. Suitable recoveries of 96–102 and 26–44% were achieved (at spiked levels of 50, 300 and 500 µg L^?1) for water and vaccine samples, respectively.     

Preparation of a Robust and Sensitive Gold-Coated Fiber for Solid-Phase Microextraction of Polycyclic Aromatic Hydrocarbons in Environmental Waters

A robust gold-coated solid-phase microextraction fiber was rapidly prepared on an etched stainless-steel wire based on chemical deposition. Gold(III) was reduced to produce a mechanically robust fiber with a stable coating. Subsequently, it was applied for solid-phase microextraction of five polycyclic aromatic hydrocarbons in water samples coupled to high performance liquid chromatography with an ultraviolet-visible detector. The preconcentration conditions were optimized, including extraction and desorption time, temperature, stirring rate, and ionic strength. Under the optimized conditions, the calibration graphs were linear in the range from 1 to 500 µg · L^?1 for naphthalene and 0.20–500 µg · L^?1 for phenanthrene, anthracene, fluoranthene, and pyrene. Limits of detection were between 0.016 and 0.22 µg · L^?1 (signal-to-noise ratio = 3). The analysis of water samples showed that the recoveries ranged from 86.0% to 112.9% with relative standard deviations between 2.03% and 11.7%. The fiber coating was sensitive and suitable for the preconcentration and determination of polycyclic aromatic hydrocarbons in environmental waters. Compared with previously reported solid-phase microextraction methods, this device offered easy preparation, low cost, resistance to organic solvents, good stability, and high durability.     

Improving the Detectability of Sequential Injection Chromatography (SIC): Determination of Triazines by Exploiting Liquid Core Waveguide (LCW) Detection

Coupling a liquid core waveguide cell to a sequential injection chromatograph improved the detection limits for determination of triazine herbicides without compromising peak resolution. Separation of simazine, atrazine, and propazine was achieved in water samples by a 25 mm long C₁₈ monolithic column. Detection was made at 238 nm using a type II LCW (silica capillary coated with Teflon® AF2400) cell with 100 cm of optical path length. Detection limits for simazine, atrazine, and propazine were 2.3, 1.9, and 4.5 µg L^?1, respectively. Reduced analysis time and low solvent consumption are other remarkable features of the proposed method.     

Selective Determination of Copper in Water Samples by Atomic Absorption Spectrometry after Cloud Point Extraction

A preconcentration methodology utilizing the cloud point phenomenon is described for the determination of copper by flame atomic absorption spectrometry. The reagent Sulfathiazolylazo resorsin was used as a complexing agent. The preconcentration factor of 25-fold was obtained. The calibration curve is linear in the range of 4–400 µ g L^?1 with a limit of detection of 0.64 µ g L^?1. The relative standard deviation (n = 5, 12 µ g L^?1) was 3.5%. The cloud point is formed in the presence of phenol at room temperature. The method was successfully applied to the determination of copper in water samples and a standard reference material.     

Voltammetric Determination of Rosiglitazone in Pharmaceutical Preparations and Human Plasma

Abstract

The voltammetric behavior of rosiglitazone was studied using direct current (DC_t), differential pulse (DPP), and alternating current (AC_t) polarography. The drug manifests cathodic waves over a pH range of 2–11.2. In Britton‐Robinson buffer (BRb; pH 4), the diffusion current–concentration relationship was found to be rectilinear over a range of 4–24 µg · mL^?1 and 0.1–16 µg · mL^?1 using DC_t and DPP modes, respectively, with minimum limits of detection (LOD) of 0.15 µg · mL^?1 and 0.07 µg · mL^?1 using the DC_t and DDP modes, respectively. The diffusion‐current constant (I _d) was 6.63±0.03 (n=5). The proposed method was successfully applied to the determination of the studied compound both in pure form and in formulations. The mean percentage recoveries in tablets were 100.09±1.18 and 100.85±0.88 (n=5) using DC_t and DPP modes, respectively. Furthermore, the proposed method, adopting the DPP mode, was applied to the determination of rosiglitazone in spiked human plasma and the obtained mean percentage recoveries were 99.14±3.29 (n=4).     

Pulverized Banana Peel as an Economical Sorbent for the Preconcentration of Metals

A procedure for the determination of trace levels of Cd, Co, Cr, Fe, Mn, Ni, and Pb by flame atomic absorption spectrometry using a column preconcentration system is described in which the metals were adsorbed on pulverized banana peel, an economically and environmentally acceptable sorbent. In the optimization procedure, five variables (sample pH, mass of biosorbent, type of eluent, sample flow rate, and volume) were optimized and the capacity of the biosorbent was established. Under the optimized conditions, the detection limits of the method were 2.4, 27.0, 49.4, 31.1, 6.7, 29.6, and 46.2 µg L^?1 for Cd, Co, Cr, Fe, Mn, Ni, and Pb, respectively. The precision, expressed as relative standard deviation, was less than 4% based on twelve measurements. The recoveries were 81.1% (Cd), 91.4% (Co), 87.2% (Cr), 90.1% (Fe), 88.0% (Mn), 94.1% (Ni), and 93.2% (Pb) under the optimum conditions (pH; 9, sample flow rate; 3 mL min^?1, mass of biosorbent; 200 mg; eluent; 1 mol L^?1 nitric acid, preconcentration factor; 10). The sorption capacity of pulverized banana peel was 15.12, 28.85, 32.70, 30.44, 30.94, 28.97, and 8.21 µmol per gram of adsorbent for Cd, Co, Cr, Fe, Mn, Ni, and Pb, respectively.     

Stripping voltammetric determination of mercury(II) and lead(II) using screen-printed electrodes modified with gold films, and metal ion preconcentration with thiol-modified magnetic particles

A novel approach to the electrochemical determination of heavy metals in tap water using anodic stripping voltammetry was developed using screen-printed electrodes modified with gold films. After optimisation of the experimental conditions, the screen-printed electrodes modified with gold films displayed excellent linear behaviour in the examined concentration range from 2 to 16 µg L^-1 mercury and lead in 50 mM HCl with a detection limit of 1.5 µg L^-1 and 0.5 µg L^-1 for mercury and lead, respectively. In order to decrease the working range down to less than 1 µg L^-1, a preconcentration step based on the use of magnetic particles modified with thiols was introduced into the protocol. Applying optimum binding conditions, the assay using screen-printed electrodes modified with gold films displayed excellent linear behaviour in the concentration range 0.1 to 0.8 µg L^-1 in 50 mM HCl. The detection limit after a 120 s deposition time for mercury and lead were 0.08 µg L^-1 and 0.02 µg L^-1, respectively. The method has been applied to the determination of mercury and lead traces in tap water     

Application of Ni(II)-imprinted cross-linked poly(methacrylic acid) synthesised through double-imprinting method for the on-line preconcentration of Ni(II) ions in aqueous media

The present paper describes the feasibility of on-line preconcentration of nickel ions from aqueous medium on Ni(II)-imprinted cross-linked poly(methacrylic acid) (IIP) synthesised through a double-imprinting method and their subsequent determination by FAAS. The proposed method consisted in loading the sample (20.0 mL, pH 7.25) through a mini-column packed with 50 mg of the IIP for 2 min. The elution step was performed with 1.0 mol L^?1 HNO₃ at a flow rate of 7.0 mL min^?1. The following parameters were obtained: quantification limit (QL) – 3.74 µg L^?1, preconcentration factor (PF) – 36, consumption index (CI) – 0.55 mL, concentration efficiency (CE) – 18 min^?1, and sample throughput – 25 h^?1. The precision of the procedure assessed in terms of repeatability for ten determinations was 5.6% and 2.5% for respective concentrations of 5.0 and 110.0 µg L^?1. Moreover, the analytical curve was obtained in the range of 5.0–180.0 µg L^?1 (r = 0.9973), and a 1.64-fold increase in the method sensitivity was observed when compared with the analytical curve constructed for the NIP (non-imprinted polymer), thus suggesting a synergistic effect of the Ni(II) ions and CTAB on the adsorption properties of the IIP. The practical application of the adsorbent was evaluated from an analysis of tap, mineral, lake and river water. Considering the results of addition and recovery experiments (90.2–100 %), the efficiency of this adsorbent can be ensured for the interference-free preconcentration of the Ni(II) ions.     

Determination of Veterinary Pharmaceuticals in Production Wastewater by HPTLC-Videodensitometry

An SPE-HPTLC method for simultaneous identification and quantification of seven pharmaceuticals in production wastewater was optimized and validated. The studied compounds were enrofloxacine, oxytetracycline, trimethoprim, sulfamethazine, sulfadiazine, sulfaguanidine and penicillin G/procaine. The method involves solid-phase extraction on hydrophilic-lipophilic balance cartridges with methanol and HPTLC analysis of extracts on CN modified chromatographic plates followed by videodensitometry at 254 and 366 nm. Optimization of chromatographic separation was performed by systematic variation of the mobile phase composition using genetic algorithm approach and the optimum mobile phase composition for TLC separation was 0.05 M H₂C₂O₄:methanol = 0.81:0.19 (v/v). Linearity of the method was demonstrated in the ranges from 1.5 to 15.0 μg L⁻¹ for enrofloxacine, 100–500 μg L⁻¹ for oxytetracycline, 150–600 μg L⁻¹ for trimethoprim, 300–1100 μg L⁻¹ for sulfaguanidine and 100–400 μg L⁻¹ for sulfamethazine, sulfadiazine and penicillin G/procaine with coefficients of determination higher than 0.991. Mean recoveries ranged from 74.6 to 117.1% and 55.1 to 108.0% for wellspring water and production wastewater, respectively. Only sulfaguanidine showed lower results. The described method has been applied to the determination of pharmaceuticals in wastewater samples from pharmaceutical industry.     

Determination of Phenolic Acids in Root Exudates of Allelopathic Rice by Solid Phase Extraction-Ion Chromatography with Conductivity Detection

A simple, effective, and green ion chromatography method with conductivity detection was developed for the determination of benzoic acid, cinnamic acid, syringic acid, and p-hydroxybenzoic acid in the root exudates of allelopathic rice. The analytes were well separated within 25 min in an anion exchange column (150 mm × 4.0 mm i.d., 5 µm particle size) with mixtures of 6.4 m mol L^?1 Na₂CO₃ and 2.0 m mol L^?1 NaHCO₃ as the mobile phase at a flow-rate of 0.7 mL min^?1. Detection limits of benzoic acid, cinnamic acid, syringic acid, and p-hydroxybenzoic acid were 0.05, 0.20, 0.50, and 0.05 µg mL^?1, respectively. Intra- and inter-day precision was ≤4.0% and 3.2%, respectively, and the intra- and inter-day accuracy, indicated by relative error, ranged from ?8.0% to 9.0%. The developed method was successfully used to determine phenolic acids in the root exudates of allelopathic rice. The average recoveries of the analytes were between 90.7% and 103.0%.     

Simultaneous Measurement of Cyclosporine A,Everolimus, Sirolimus and Tacrolimus Concentrations in Human Blood by UPLC–MS/MS

Liquid chromatography coupled with tandem mass spectrometry for therapeutic drug monitoring of immunosuppressants has been widely adopted in clinical chemistry laboratories. However, UPLC is replacing classical LC techniques, providing higher resolution and speed. We developed and validated an UPLC–MS/MS method for the simultaneous measurement of cyclosporine A, everolimus, sirolimus and tacrolimus concentrations in human blood. Following extraction with a zinc sulfate solution and acetonitrile, the chromatographic separation was achieved using an Acquity^® UPLC^® BEH™ (2.1 × 30 mm id, 1.7 µm) reverse-phase C₁₈ column, with a water/methanol linear gradient containing 2 mM ammonium acetate with 0.1 % formic acid at a 0.5 mL min⁻¹ flow rate. All immunosuppressants were detected by ESI mass spectrometry in positive ion multiple reaction monitoring mode using mass-to-charge transitions of 1219.8 → 1202.6/1184.4, 975.5 → 908.3/891.6, 931.5 → 864.3/883.3, 821.4 → 768.2/719.9 for cyclosporine A, everolimus, sirolimus and tacrolimus, respectively. Coefficients of variation and relative bias were less than 5.8 and 9.7 % for cyclosporine A, 8.7 and 6.4 % for everolimus, 8.5 and 7.2 % for sirolimus and 6.7 and 4.7 % for tacrolimus. Limits of quantification were 15.4 µg L⁻¹ for cyclosporine A, 1.42 µg L⁻¹ for everolimus, 1.58 µg L⁻¹ for sirolimus and 0.65 µg L⁻¹ for tacrolimus. Mean recoveries were greater than 77.6 % for all immunosuppressants. Evaluation of the matrix effect showed ion suppression for all the immunosuppressants, except for cyclosporine A, which suffered ion enhancement. No carry-over was observed. The validated method appears to be well adapted for therapeutic drug monitoring of multiple immunosuppressants in daily clinical practice.

     

Selective extraction and preconcentration of ultra-trace amounts of arsenic(V) ions using carbon nanotubes as a novel sorbent

In the present study, multiwalled carbon nanotubes (MWCNTs) as solid phase extraction sorbent were developed for preconcentration of arsenic(V) species prior to graphite furnace atomic absorption spectrometry (GFAAS) determination. Arsenic(V) was selectively sorbed on the packed column with MWCNTs within a pH 9.5 in the presence of 2-(5-bromo-2-pyridylazo)-5-diethyl amino phenol (5-Br-PADAP). The adsorbed species was then desorbed with 1 mL of 2.0 M HNO₃. Experimental parameters including pH, sample volume and flow rate, type, volume and concentration of eluent that influence the recovery of the arsenic(V) species were optimised. Under the optimised conditions, the calibration curve was linear in the range of 0.2–10.0 µg L^?1 with detection limit of 0.016 µg L^?1. The relative standard deviations (RSD) for seven replicate determinations at 1.0 µg L^?1 level of arsenic was 6.69%. The proposed method was successfully applied to the determination of arsenic in water samples and certified reference material (NIST RSM 1643e).     

Dispersive Liquid–Liquid Microextraction of Silver Prior to Determination by Microsample Introduction-Flame Atomic Absorption Spectrometry

Abstract

A new simple and sensitive method has been proposed for rapid determination of trace levels of silver in environmental water samples, using dispersive liquid–liquid microextraction (DLLME) prior to its microsample introduction-flame atomic absorption spectrometry. Under the optimum conditions, the linear range was 0.1–7 µg L^?1 and limit of detection was 0.018 µg L^?1. The relative standard deviation for 0.50 and 5.00 µg L^?1 of silver in water sample was 4.0 and 1.7%, respectively. The relative recoveries of silver from tap, well, river, and seawater samples at spiking levels of 1.00 and 5.00 µg L^?1 were in the range of 86.4–98.6%.     

Study of scandium and thorium sorption from uranium leach liquors

Scandium and thorium sorption from simulated uranium leach liquors by phosphorous containing ion exchange resins was studied. Increase of thorium concentration resulted in a decrease of scandium sorption by 26–65%. Tulsion CH 93 resin was chosen for Sc separation from uranium leach liquors. It was shown that 180 g L^?1 Na₂CO₃ allowed for elution 94.1% of Sc and 98.9% of Th in dynamic conditions. Using (NH₄)₂SO₄ (50 g L^?1) + ACBM (180 g L^?1) mixture for primary Sc/Th separation at the resin/eluent ratio of 1:5 resulted in thorium desorption degree as high as 66–69%, whereas scandium loss did not exceed 10%.