Determination of Six Organophosphorus Pesticides in Water by Single-Drop Microextraction Coupled with GC-NPD

Chemometric Optimization of SPE for the Determination of Multiclass Pesticides in Portable Water Samples by UHPLC-MS/MS

This study aimed on the development of a SPE-UHPLC-MS/MS method for the simultaneous determination of pesticide residues in drinking water samples. A chemometric approach was applied to optimize the efficiency of the SPE pretreatment procedure. This study involved (i) the application of a Full Factorial Design for the screening of the significant factors, (ii) the application of a Central Composite Design for the determination of the optimal conditions and (iii) the evaluation and validation of the significance of the statistically proposed models. Oasis HLB cartridges were used for the extraction. The optimum sample volume was 300 mL and the elution solvent 3 mL of the mixture of methanol:ethylacetate 70:30 v/v. The method was validated according to the international guidelines. Recoveries were ranged from 63 to 116% and the detection limits were between 0.1 and 1.5 pg mL- 1. The validated method could be used in routine analysis for pesticides screening.

A biobased magnetic dual-dummy-template molecularly imprinted polymer using a deep eutectic solvent as a coporogen for highly selective enrichment of organophosphates

An eco-friendly magnetic dual-dummy-template molecularly imprinted polymer (MDDMIP) was prepared by a "one-pot" green synthesis using mixed-valence iron hydroxide as the magnetic material, a deep eutectic solvent as the coporogen, and caffeic acid and glutamic acid as binary monomers. The adsorption properties toward organophosphorus pesticides (OPPs) were investigated. High adsorption capacities (269.65-304.93 mg g^-1), quick adsorption times (20 s), and high imprinting factors (2.28-3.83) were obtained. The proposed MDDMIP was utilized for magnetic solid phase extraction (MSPE) of OPPs prior to quantification by high performance liquid chromatography (HPLC). The developed method exhibited outstanding linearity (0.05-500 μg L^-1), low detection limits (0.003-0.015 μg L^-1), and excellent enrichment factors (940-1310 folds). The MSPE-HPLC method was successfully applied for the detection of OPPs in vegetable, fruit, and grain samples with acceptable recoveries (80-119%). This method is a good potential method for the analysis of pesticide residues in complex matrices.

Flow Injection Chemiluminescence Determination of Ethion and Computational Investigation of the Adsorption Process on Molecularly Imprinted Polymerized High Internal Phase Emulsion

The lack of sufficient selectivity is the main limitation of chemiluminescence (CL) methods; because the CL reagent is not restricted to a specific analyte. This study investigated the preconcentration and determination of ethion by a flow injection CL (FIA-CL) method using a molecularly imprinted poly high internal phase emulsion (MIP-polyHIPE) adsorbent. Preliminary studies showed that ethion could be determined with high sensitivity in the Ru (bipy)₃ ²⁺ -acidic Ce (IV) CL system. A MIP-polyHIPE adsorbent was synthesized and used for preconcentration to increase the selectivity and sensitivity of the method. The adsorption of ethion on the adsorbent was investigated using density functional theory (DFT) and molecular dynamics (MD), UV-Vis and FTIR spectrophotometry and liquid chromatography-tandem mass spectrometry (LC-MS-MS). Response surface methodology (RSM) and central composite design (CCD) were used to find optimized concentrations of variables. The linear dynamic range (LDR) and limit of detection (LOD) for ethion in the FIA-CL method were calculated 1.0✕10^-9 -2.0✕10^-7 and 6.0✕10^-10 mol L^-1 , respectively. The percentage of relative standard deviation for 5 repetitive measurements of 5.0⨯10^-8 mol L^-1 ethion was 4.2%. The proposed method was successfully used to separate and preconcentrate ethion from drinking and surface water sources.

Facile and highly efficient three-phase single drop microextraction in-line coupled with capillary electrophoresis

A high-performance version of in-line, three-phase direct immersion-single drop microextraction (DI-SDME) coupled with capillary electrophoresis (CE) was demonstrated using a commercial CE instrument, and all the major and minor details were described to provide an easy-to-follow and user-friendly protocol. The excellent sample cleanup and enrichment power of this method was demonstrated with nonsteroidal anti-inflammatory drugs (NSAIDs) in human urine. The only preparation of urine samples was the addition of HCl to acidify the urine sample to pH 2. The acidic NSAIDs in the acidified urine sample were extracted into a basic acceptor drop covered with a thin organic layer attached to the inlet tip of a capillary immersed in the sample. A simple but powerful DI-SDME-CE method could be carried out automatically without any modification of the existing CE instrument. For improved performance, sample agitation and heating were employed by installing a microstirrer and a thermostating jacket in the sample tray. With 10 min of DI-SDME at 35°C with stirring, NSAIDs such as ketoprofen, ibuprofen, and naproxen in urine were enriched 340-970-fold with intraday and interday RSDs of 0.8-2.4% and 1.1-3.6%, respectively. The LODs obtained with in-line coupled CE/UV were 10-50 nM (2-10 µg/L). The performance of DI-SDME-CE/UV was also demonstrated by determining the naproxen level in human urine collected 24 h after taking a single oral dose of the drug. The spike recovery of naproxen from a single-point standard addition to the urine sample was 80%. Our high-performance three-phase DI-SDME-CE method is quite promising for the analysis of ionizable trace analytes in a complex sample matrix.

Fluorescence assay for three organophosphorus pesticides in agricultural products based on Magnetic-Assisted fluorescence labeling aptamer probe

There has been increasing recent concern about the agricultural use of organophosphorus pesticides. A rapid and sensitive fluorescence assay for the detection of three organophosphorus pesticides has therefore been developed using 6-carboxy-fluorescein labeling aptamer as the probe and functionalized magnetic nanoparticles as the separation carrier. The aptamer hybridized with complementary DNA conjugated on the surface of the magnetic nanoparticles to form a magnetic aptamer-complementary DNA complex. Upon introducing the target organophosphorus pesticide, the aptamer departed from the complementary DNA, resulting in the fluorescence signal. Under optimized conditions, the limits of detection (LODs, S/N = 3) for trichlorfon, glyphosate, and malathion were 72.20 ng L-1, 88.80 ng L-1, and 195.37 ng L-1, respectively. The method was applied for the detection of trichlorfon, glyphosate, and malathion in spiked lettuce and carrot samples. The recoveries were in the range of 79.4%-118.7%, which were in good agreement with those obtained by gas chromatography, and the relative standard deviations were also acceptable. The method therefore has high sensitivity, so provides a means for the detection of multiple organophosphorus pesticides.

A simple spectroscopic method to determine dimethoate in water samples by complex formation

A simple and rapid method for the determination of dimethoate in water was developed based on the monitoring of the complex formation between bis 5-phenyldipyrrinate of nickel (II) and the herbicide dimethoate. The method showed a short response time (10 s), high selectivity (very low interference from other sulfate and salts), high sensitivity (limit of detection (LOD) 0.45 µM, limit of quantitation (LOQ) of 1.39 µM), and a K_d of 2.4 µM. Stoichiometry experiments showed that complex formation occurred with a 1:1 relation. The method was applied to different environmental water samples such as lagoon, stream, urban, and groundwater samples. The results indicated that independently from the water source, the method exhibited high precision (0.25-2.47% variation coefficient) and accuracy (84.42-115.68% recovery). In addition, the method was also tested using an effluent from a wastewater treatment plant from Mexico; however, the results indicated that the presence of organic matter had a pronounced effect on the detection.

Preparation and application of chlorpyrifos molecularly imprinted solid-phase microextraction probes for the residual determination of organophosphorous pesticides in fresh and dry foods

A solid-phase microextraction probe was prepared on the surface of a stainless-steel wire through molecular sol-gel imprinting technology using chlorpyrifos as a template molecule, tetraethoxysilane as a sol-gel precursor, and acrylamide and β-cyclodextrin as functional monomers. The polymer was characterized by infrared spectrometry and scanning electron microscopy. Moreover, the selectivity and the parameters including the type and volume of the extraction solvents, ionic strength, pH, temperature, extraction time, stirring speed, and desorption time affecting extraction performance were evaluated. Under the optimum solid-phase microextraction and gas chromatography conditions, the linear ranges were 0.25-25.0 μg/L for chlorpyrifos, quinalphos, triazophos, pirimiphos-methyl, and chlorpyrifos-methyl with the correlation coefficient above 0.99. The detection limits (S/N = 3) were in the range of 0.02-0.07 μg/L and the RSDs were <7.3%. The developed method was successfully used to determine the multi-residues of chlorpyrifos, quinalphos, triazophos, pirimiphos-methyl, and chlorpyrifos-methyl in green peppers and cinnamon with satisfactory recoveries.

Development of a Single-Drop Microextraction with Derivatization Procedure for Analysis of Volatile Fatty Acids in Water Samples

A single-drop microextraction (SDME) was developed for the analysis of volatile fatty acids (VFAs) (C₂–C₇) in water by gas chromatography (GC) with flame ionization detection. The significant parameters affecting the SDME performance such as selection of microextraction solvent, extraction time, stirring rate, sample pH and temperature, and ionic strength were studied and optimized. To lower limits of detection, derivatization of VFAs by N-methyl-N-(tert-butyldimethylsilyl)trifluoroacetamide (MTBSTFA) was performed. The method developed requires very short time of extraction and derivatization (13 min) and it is characterized by a good precision (max RSD = 11.4%), linearity and relatively low limits of detection (from 8.3 mg L⁻¹ for acetic acid to 0.008 mg L⁻¹ for heptanoic acid). The results of the SDME in combination with GC show promising potential for the analysis of VFAs in water samples.