Hollow‐fiber liquid‐phase microextraction combined with capillary HPLC for the selective determination of six sulfonylurea herbicides in environmental waters

A three‐phase hollow‐fiber liquid‐phase microextraction combined with a capillary LC method using diode array detection was proposed for the determination of six sulfonylurea herbicides, triasulfuron, metsulfuron‐methyl, chlorsulfuron, flazasulfuron, chlorimuron‐ethyl, and primisulfuron‐methyl, in environmental water samples. Different factors that can affect the extraction process such as extraction solvent, acidity of the donor phase, composition and pH of the acceptor phase, salt addition, stirring speed, and extraction time were optimized. Under the optimum conditions, detection and quantitation limits between 0.1 – 1.7 and 0.3 – 5.7 μg/L, respectively, and enrichment factors ranging from 71 to 548 were obtained. The calibration curves were linear within the range of 0.3 – 40 μg/L. Intra‐ and interday RSDs were <6.3 and 8.4%, respectively. The relative recoveries of the spiked ground and river water samples were in the range of 69.4 – 119.2 and 77.4 – 111.7%, respectively. The results of the study revealed that the developed methodology involves an efficient sample pretreatment allowing the preconcentration of analytes, combined with the use of a miniaturized separation technique, suitable for the accurate determination of sulfonylurea herbicides in water.     

A novel equilibrium extraction technique employing hollow fibre liquid phase microextraction for trace enrichment of freely dissolved organophosphorus pesticides in environmental waters

A new design of equilibrium hollow fibre liquid phase microextraction (HF-LPME) was developed for the determination of three freely dissolved organophosphorus pesticides (OPPs), i.e. diazinon (O,O-diethyl-O-2-isopropyl-4-methyl-6-pyrimidyl thiophosphate), chlorpyrifos (O,O-diethyl-O-[3,5,6-trichloro-2-pyridyl] phosphorothioate), and fenthion (O,O-dimethyl-O-4-methylthio-m-tolyl phosphorothioate) as model compounds. In this new design a 1.2–1.4 cm length of a hollow fibre (HF), inserted to the end of 20 cm copper wire and impregnated with organic solvent, was used to extract the freely dissolved concentration of OPPs in various water samples. The limits of detection (LOD) in reagent water using gas chromatography-mass spectrometry in the selected ion monitoring (SIM) mode was in the range of 15–80 ng L^?1. The relative standard deviations of the analysis (inter- and intra-day) were 8.7–30%. The method was applied to the extraction of spiked lake and ground water samples. The ground water sample was spiked at 0.1 and 0.2 µg L^?1 concentrations of the analytes under study and the average extraction efficiency at the two concentrations was below 1% showing the non-depletive nature of the extraction, meaning that the freely dissolved concentrations are measured as opposed to total concentrations. Good linearity was obtained for all of the analytes in both reagent water and lake water samples with correlation coefficients, R ², ranging from 0.991 to 0.996, in the concentration ranges of 25–400 ng L^?1. The method was found to be very simple and inexpensive, with the possibility of running hundreds of samples in parallel with very minimal expenses for the determination of freely dissolved OPPs.     

Roll‐to‐Roll printed PEDOT/PSS/GO Plastic Film for Electrochemical Determination of Carbofuran

In this work, we developed a roll‐to‐roll printed poly(3,4‐ethylenedioxythiophene)/polystyrene sulphoanate without graphene oxide (GO) (PEDOT/PSS) and with graphene oxide (PEDOT/PSS/GO) plastic films for the electrochemical determination of carbofuran. Both the PEDOT/PSS and PEDOT/PSS/GO plastic films showed electroactivity towards the oxidation of carbofuran. Incorporation of graphene oxide (GO) improves the electrochemical activity of carbofuran and increased its sensitivity. The printed plastic films were characterized by cyclic voltammetry (CV), linear sweep voltammetry (LSV), surface profilometer, four point probe and atomic force microscopy (AFM). The effects of pH, deposition time, deposition potential and film thickness on the oxidation peak current of carbofuran were investigated. Under the optimized conditions, a dynamic linear range of 1 μM–90 μM with a detection limit of 1.0×10^?7 M (S/N=3) were obtained. The printed PEDOT/PSS/GO plastic electrode was applied for the determination of carbofuran in vegetable and fruit samples with recoveries between 94.4 and 101.8 %.     

Optimisation of pressurised liquid extraction for the determination of p,p′-DDT and p,p′-DDE in aged contaminated Ethiopian soils

The effectiveness of extracting p,p′-DDT and p,p′-DDE from aged contaminated soil samples by means of pressurized liquid extraction (PLE) was evaluated. Two soil samples, which were contaminated more than 10 years ago, were used in the investigation. The static extraction time was optimised and then validated against the total sum of target analytes obtained from multiple sequential extractions. The PLE results were also compared with Soxhlet extraction (SOX). PLE for 3×10 min at 100 °C was proven to be more exhaustive than SOX in the determination of p,p′-DDE from both soil samples. In the case of p,p′-DDT, PLE was found to be equally as exhaustive as SOX. Additionally, most of the previous PLE investigations used hazardous organic solvents such as n-hexane, toluene and dichloromethane mixed with acetone, whereas in this investigation the less toxic solvent combination n-heptane/acetone has been employed.     

An efficient and fast microwave-assisted extraction method developed for the simultaneous determination of 18 organochlorine pesticides in sediment

An efficient and fast microwave-assisted extraction (MAE) method followed by gas chromatographic separation with mass spectrometric detection (GC–MS) was developed for the extraction of 18 organochlorine pesticides (OCPs) from sediment. Parameters affecting the MAE procedure such as the type and volume of the extraction solvent, irradiation power, temperature and irradiation time were successfully optimised. Under the optimal conditions, extraction efficiencies in the range of 73.4–119% were obtained with THF–HEX (9:1, v/v) for all OCPs studied. The method was linear over the range of 2.9–5000 ng g^?1 with determination coefficients (r²) higher than 0.992 for all analytes. The limits of detection, LODs (S/N = 3), obtained varied from 1.0 to 2.2 ng g^?1 and limits of quantification, LOQs (S/N = 10) were between 2.9 and 6.8 ng g^?1. The proposed method was successfully applied to the analysis of real sediment samples and acceptable recoveries from 70.1 to 124% with RSDs ≤14.8% were obtained. 10 OCPs were determined below their LOQ and 8 OCPs in the range of 124–2830 ng g^?1. The MAE method was compared with Soxhlet, shake flask and ultrasonic solvent extraction techniques. Thus, the MAE–GC–MS method could efficiently be used for selective extraction and quantification of the target analytes from the complex sediment matrices.     

Square Wave Anodic Stripping Voltammetric Determination of Hg(II) with N1-Hydroxy-N1,N2-diphenylbenzamidine Modified Carbon Paste Electrode

Mercury is a highly toxic metal, of which even small doses (<200 ng mL⁻¹) can cause serious problems for humans, plants, animals and microorganisms, including marine species and freshwater organisms. Hence, a simple, fast, highly selective and sensitive and accurate method for the detection of mercury in the environmental, clinical or biological samples is necessary. A new, sensitive and selective method for the determination of Hg(II) with 5 % N¹-hydroxy-N¹,N²-diphenylbenzamidine modified carbon paste electrode has been developed. Hg(II) was accumulated for 210 s on the surface of the modified electrode using 0.1 M CH₃COONa of pH 7 at −0.8 V vs Ag/AgCl, followed by electrochemical stripping with SWASV in 0.1 M NH₄Cl at pH 4. The linear range is 0.02–10 μM Hg(II) with limit of detection of 1.28 nM. The method has RSDs of 3.7 %. The method was applied for the determination Hg(II) in five types of water samples. The recoveries were in the range 97.8–103 %. The proposed method was found to be highly selective and sensitive and has many attractive features compared to previous reports such as low cost, simplicity of electrode preparation, long term stability, fast response, easy renewable ability, and reasonable short accumulation time.     

Development of a pressurized liquid extraction and clean-up procedure for the determination of alpha-endosulfan, beta-endosulfan and endosulfan sulfate in aged contaminated Ethiopian soils

Pressurized liquid extraction (PLE) was investigated for the extraction of two endosulfan isomers and their metabolite from two real contaminated soil samples. PLE for 3x10min at 100 degrees C was proven to be more exhaustive than Soxhlet extraction (SOX) in one soil sample. On the other soil sample investigated the method was found to be equally exhaustive as SOX. The use of hazardous organic solvents such as n-hexane, toluene, and diethyl ether has been avoided in PLE and clean-up. Instead less toxic solvents have been used both at the extraction step (acetone/n-heptane) and clean-up step (ethyl acetate/n-heptane). A column Florisil clean-up procedure that consumes relatively low solvent volumes has been optimized and applied to purify soil extracts. The developed analytical procedure was validated by applying it to a certified reference soil material (CRM811-050). A recovery of 103% total endosulfan residue was obtained versus certified values.     

Di[tris(trimethysilyl)methyl]-zinc and -cadmium

Tris(trimethylsilyl)methyllithium reacts with the anhydrous halides MC1₂ (M = Zn or Cd) to give the compounds [(Me₃Si)₃C]₂M, which show high thermal and chemical stability. They decompose only above 300°C, with formation of (Me₃Si)₃CH, and are not attacked by water in refluxing THF. The zinc compound can be steam-distilled without decomposition, and does not react with boiling concentrated hydrochloric acid or with bromine in carbon tetrachloride.     

Synthesis and Characterization of 2,4,6-tris(hydrazino)-s-triazine and its Metal Complexes

A new multidentate ligand related to s-triazine herbicides 2,4,6-tris(hydrazino)-s-triazine (THSTZ) and its metal complexes was synthesized. The complexes were investigated by m.s., n.m.r., i.r., u.v.–vis and AA spectroscopic techniques. Furthermore, carbon, nitrogen, hydrogen, chloride, and metal analyses, conductivity, magnetic susceptibility measurements, and thermal analyses were carried out. The Co(II), Ni(II), Cu(I), and Zn(II) metal complexes were synthesized in methanolic media. Metal-to-ligand ratios were found to be 1:1 for Co(II) and Zn(II), 2:1 for Cu(I) and 3:2 for Ni(II) complexes. N.m.r. spectral and thermal analyses showed the presence of MeOH in all of the complexes. Conductivity measurements suggested that the complexes were 1:2 electrolytes. Ring nitrogens as well as the terminal nitrogens of hydrazine side chains in THSTZ were proposed as metal binding centres. Magnetic moments of Ni(II) (4.12μ_B) and Co(II) (4.2μ_B) indicate tetrahedral and octahedral geometry, respectively. Tetrahedral geometry for Cu(I) and Zn(II) complexes was suggested. V. J. T. Raju - Previously working as Professor of Chemistry, Osmania University, Hyderbad, India     

(Bio)sensors based on manganese dioxide-modified carbon substrates: retrospections, further improvements and applications

An overview is presented which summarizes our accomplishment in the development of sensors and biosensors based on heterogenous carbon electrodes modified with manganese dioxide. Brief account of each sensor and biosensor has been given and example of real sample applications provided where appropriate.