Alternative solvent‐based methyl benzoate vortex‐assisted dispersive liquid–liquid microextraction for the high‐performance liquid chromatographic determination of benzimidazole fungicides in environmental water samples

Vortex‐assisted dispersive liquid–liquid microextraction using methyl benzoate as an alternative extraction solvent for extracting and preconcentrating three benzimidazole fungicides (i.e., carbendazim, thiabendazole, and fluberidazole) in environmental water samples before high‐performance liquid chromatographic analysis has been developed. The selected microextraction conditions were 250 μL of methyl benzoate containing 300 μL of ethanol, 1.0% w/v sodium acetate, and vortex agitation speed of 2100 rpm for 30 s. Under optimum conditions, preconcentration factors were 14.5–39.0 for the target fungicides. Limits of detection were obtained in the range of 0.01–0.05 μg/L. The proposed method was then applied to surface water samples and the recovery evaluations at three spiked concentration levels of 5, 30, and 50 μg/L were obtained in the range of 77.4–110.9% with the relative standard deviation <7.4%. The present method was simple, rapid, low cost, sensitive, environmentally friendly, and suitable for the trace analysis of the studied fungicides in environmental water samples.     

In-Situ Formation of Modified Nickel–Zinc-Layered Double Hydroxide Followed by HPLC Determination of Neonicotinoid Insecticide Residues

A single-step preconcentration procedure using the in-situ formation of modified nickel–zinc-layered double hydroxides (LDHs) prior to high-performance liquid chromatography (HPLC) is investigated for the determination of neonicotinoid insecticide residues in honey samples. The LDHs could be prepared by the sequential addition of sodium hydroxide, sodium dodecyl sulfate, nickel nitrate 6-hydrate and zinc nitrate 6-hydrate, which were added to the sample solution. The co-precipitate phase and phase separation were obtained by centrifugation, and then the precipitate phase was dissolved in formic acid (concentrate) prior to HPLC analysis. Various analytical parameters affecting extraction efficiency were studied, and the characterization of the LDHs phase was performed using Fourier-transformed infrared spectroscopy and scanning electron microscopy. Under optimum conditions, the limit of detection of the studied neonicotinoids, in real samples, were 30 μg L⁻¹, for all analytes, lower than the maximum residue limits established by the European Union (EU). The developed method provided high enrichment, by a factor of 35. The proposed method was utilized to determine the target insecticides in honey samples, and acceptable recoveries were obtained.     

Catanionic surfactant ambient cloud point extraction and high-performance liquid chromatography for simultaneous analysis of organophosphorus pesticide residues in water and fruit juice samples

A mixed anionic–cationic surfactant cloud point extraction (CPE) has been developed using sodium dodecyl sulfate (SDS) and tetrabutylammonium bromide (TBABr) for the extraction and preconcentration of organophosphorus pesticides (OPPs) at ambient temperature before analysis by high-performance liquid chromatography. The studied OPPs were azinphos-methyl, parathion-methyl, fenitrothion, diazinon, chlorpyrifos, and prothiophos. The optimum conditions of the mixed anionic–cationic CPE were 50 mmol L⁻¹ SDS, 100 mmol L⁻¹ TBABr, and 10% (w/v) NaCl. The extracted OPPs were successfully separated within 11 min using the conditions of a Waters Symmetry C8 column, a flow rate of 0.8 mL min⁻¹, a gradient elution of methanol and water, and detection at 210 nm. Linearity was found over the range 0.05–5 μg mL⁻¹, with the correlation coefficients higher than 0.996. The enrichment factor of the target analytes was in the range 6–11, which corresponds to their limits of detection from 1 to 30 ng mL⁻¹. High precisions (intra-day and inter-day) were obtained with relative standard deviation <1.5% (t _R) and 10% (peak area). Accuracies (% recovery) of the different spiked OPP concentrations were 82.7–109.1% (water samples) and 80.3–113.3% (fruit juice samples). No contamination by the OPPs was observed in any studied samples.     

Alternative Green Preconcentration Approach Based on Ultrasound-Assisted Surfactant-Enhanced Emulsification Microextraction and HPLC for Determination of Benzimidazole Anthelmintics in Milk Formulae

An alternative green microextraction method based on ultrasound-assisted surfactant-enhanced emulsification microextraction (UASEME) using a low-density extraction solvent coupled with HPLC has been developed for preconcentration and determination of six benzimidazole anthelmintics, namely, oxfendazole, albendazole, mebendazole, flubendazole, fenbendazole, and niclosamide. The separation was achieved within 12 min, using an Inertsil^® C18 column (4.6 × 150 mm, 5.0 µm), with a gradient mobile phase of acetonitrile and 0.1 % (v/v) formic acid. Under the optimum UASEME conditions using Tergitol^® TMN-6 and 1-octanol as emulsifier and extraction solvent, respectively, linearity was in the range of 0.5–5,000 μg L⁻¹ with the coefficients of determination (R ²) ranging from 0.9959 to 0.9999. Enrichment factors were obtained up to 89, corresponding to limits of detection ranging from 0.50 to 6.00 µg L⁻¹. Intra-day (n = 8) and inter-day (n = 3 × 3) precisions were obtained with relative standard deviations for retention time and peak area of lower than 2 and 15 %, respectively. The proposed method was successfully applied to determine the target benzimidazoles in milk formulae.

     

An In Situ Formation of Ionic Liquid for Enrichment of Triazole Fungicides in Food Applications Followed by HPLC Determination

An in situ formation of ionic liquid was used for preconcentration of four triazole fungicides in food samples. The microextraction method was used for the first time in the literature for preconcentration of triazole fungicides. In the developed method, tributylhexadecylphosphonium bromide ([P₄₄₄₁₂]Br) and potassium hexafluorophosphate (KPF₆) were used for the formation of hydrophobic ionic liquid. After centrifugation, the fine microdroplets were produced in one step, providing the extraction step in a quick and environmentally friendly manner. The functional group of the hydrophobic ionic liquid was investigated using FT-IR. Various extraction parameters were studied and optimized. In the extraction method, 0.01 g of [P₄₄₄₁₂]Br and 0.01 g of KPF₆, centrifugation at 4500 rpm for 10 min were used. The optimized technique provided a good linear range (90–1000 μg L⁻¹) and high extraction recovery, with a low limit of detection (30–50 μg L⁻¹). Methods for the proposed in situ formation of ionic liquid were successfully applied to honey, fruit juice, and egg matrices. The recoveries were obtained in a satisfactory range of 62–112%. The results confirmed the suitability of the proposed microextraction method for selective extraction and quantification of triazole fungicides.     

Study on the effect of chain-length compatibility of mixed anionic–cationic surfactants on the cloud-point extraction of selected organophosphorus pesticides

The chain-length compatibility of mixed anionic-cationic surfactants was investigated for the extraction of organophosphorus pesticides (OPPs). Cationic surfactants with different chain lengths (n = 12 and 16) were mixed with sodium dodecyl sulfate (SDS; n = 12) for the mixed anionic-cationic surfactants-based extraction. Six OPPs were studied including azinphos-methyl, parathion-methyl, fenitrothion, diazinon, chlorpyrifos, and prothiophos. Reversed-phase high-performance liquid chromatography was used for the determination of the studied OPPs. The extraction was performed using mixtures of SDS and cationic surfactants including dodecyltrimethyl ammonium bromide or dodecyltrimethylammonium bromide (DTAB; n = 12) and cetyltrimethyl ammonium bromide or cetyltrimethyl ammonium bromide (CTAB; n = 16). The parameters affecting the extraction efficiencies of two extraction systems were studied and discussed. The optimum condition for SDS-DTAB was 15 mmol L(-1) SDS and 1 mmol L(-1) DTAB in the presence of 15% (w/v) sodium chloride (NaCl). Meanwhile, the condition for SDS-CTAB was 10 mmol L(-1) SDS and 1.0 mmol L(-1) CTAB with 10% (w/v) NaCl. Under the optimum conditions, the extraction efficiency of SDS-DTAB (66-85%) was slightly higher than that of SDS-CTAB (61-82%). In addition, the SDS-DTAB system also gave greater enrichment factor than SDS-CTAB for all the studied OPPs. This result may be due to the compatibility of chain length between SDS and DTAB. The extraction using SDS-DTAB was successfully applied to determine OPPs in fruit samples (i.e., pomelo, apple, and pineapple). No contamination by the studied OPPs in samples was observed. Good accuracy with recoveries ranging from 77 to 105% was obtained. Low limits of detection were in the range of 0.003-0.01 mg kg(-1) which are below the MRLs established by EU-MRLs for the OPPs residues in fruit samples.     

Alternative Green Preconcentration Approach Based on Ultrasound-Assisted Surfactant-Enhanced Emulsification Microextraction and HPLC for Determination of Benzimidazole Anthelmintics in Milk Formulae

An alternative green microextraction method based on ultrasound-assisted surfactant-enhanced emulsification microextraction (UASEME) using a low-density extraction solvent coupled with HPLC has been developed for preconcentration and determination of six benzimidazole anthelmintics, namely, oxfendazole, albendazole, mebendazole, flubendazole, fenbendazole, and niclosamide. The separation was achieved within 12 min, using an Inertsil^® C18 column (4.6 × 150 mm, 5.0 µm), with a gradient mobile phase of acetonitrile and 0.1 % (v/v) formic acid. Under the optimum UASEME conditions using Tergitol^® TMN-6 and 1-octanol as emulsifier and extraction solvent, respectively, linearity was in the range of 0.5–5,000 μg L^?1 with the coefficients of determination (R ²) ranging from 0.9959 to 0.9999. Enrichment factors were obtained up to 89, corresponding to limits of detection ranging from 0.50 to 6.00 µg L^?1. Intra-day (n = 8) and inter-day (n = 3 × 3) precisions were obtained with relative standard deviations for retention time and peak area of lower than 2 and 15 %, respectively. The proposed method was successfully applied to determine the target benzimidazoles in milk formulae.