Chromatograms of (a) watermelon sample (local market), (b) watermelon sample soaked with 250 ng mL-1 of each neonicotinoid, and (c) watermelon sample with 500 ng mL-1 of each neonicotinoid. Chromatograms of (a) watermelon sample (super market), (b) watermelon sample soaked with 250 ng mL-1 of each neonicotinoid, and (c) watermelon sample with 500 ng mL-1 of each neonicotinoid. Chromatograms of (a) surface water sample I, (b) surface water sample I spiked with 250 ng mL-1 of each neonicotinoid, and (c) surface water sample I spiked with 500 ng mL-1 of each neonicotinoid .
Chromatograms of (a) surface water sample III, (b) surface water sample III spiked with 250 ng mL-1 of each neonicotinoid, and (c) surface water sample III spiked with 500 ng mL-1 of each neonicotinoid .
- Background and rational
- Purposes of the research
- Scope of research
- Benefit of research
- Definition of terms
This technique is based on SPE methodology, but used a small amount of a solid sorbent (μg or mg range) is dispersed in the sample solution containing target analytes to extract target analytes. In d-μ-SPE, the nature and physicochemical properties of the solid sorbent are very important to achieve an accurate, sensitive and selective determination of target analytes. The aim of this work is to develop a simple d-µ-SPE for the preconcentration of neonicotinoid insecticides in surface water and fruit juice samples combined with HPLC for the determination of target analytes.
The purpose of preconcentration is to increase the concentration of target analytes in a sample solution prior to instrumental analysis or detection.
Neonicotinoid insecticides
D-µ-SPE
2015) [38] reported dynamic microwave-assisted extraction coupled with d-μ-SPE using MIL-101 as sorbent for the determination of triazine and phenylurea herbicides in soybean samples by HPLC-DAD. The supernatant was removed and the residue was eluted by 2 ml of methanol under ultrasonication. After centrifugation, the eluate obtained was dried under a stream of nitrogen and the resulting residue was dissolved in 250 ml of methanol.
Next, the analytes in PCX sorbent were eluted with ammonium hydroxide/acetonitrile v/v) through a simple unit device equipped with 1 mL syringe and 0.22 μm nylon syringe filter.
Sample preparation and chromatographic determination of neonicotinoids
SPE condition was: HLB cartridge (200 mg/6 mL) is preconditioned with 5 mL of methanol-dichloromethane mixture (1:1) followed by 10 mL of deionized water; 250 mL of the water sample, with the pH value adjusted to 6, is applied to the preconditioned HLB cartridge at a flow rate of 1 mL min-1; the cartridge is dried under vacuum for 10 minutes; the cartridge is eluted with 10 ml of methanol-dichloromethane mixture (1:1); extract is evaporated to dryness and reconstituted with 1 mL of methanol; the final extract is filtered through a 0.45µm PVDF filter into the autosampler flask. In activated carbon cartridge, the cartridge was conditioned with 5 ml of acetonitrile, flowed through under the action of gravity, 5 ml of acetonitrile as elution solvent and drying on a water bath at 50 °C under a flow of nitrogen. HLB SPE cartridge, the cartridge is conditioned with 5 mL methanol, 5 mL ultra-pure water and flows through under the action of gravity.
The residue was reconstituted into 2 mL mobile phase and filtered through a 0.22 µm PTFE syringe filter. The QuEChERS method was as follows: 2.5 g of thoroughly homogenized sample was placed in a 50 mL polypropylene centrifuge tube, then 50 μL of TPP solution, 10 mL of deionized water, and 10 mL of acetonitrile were added and the tube was sealed. We then performed the DLLME procedure: transfer 1 mL of the acetonitrile extract to a 4 mL test-tube vial and add 50 μL of isotopically labeled internal standards (ISTD) solution, add 100 μL of carbon tetrachloride, quickly transfer the mixture to a 25 mL screw-cap plastic conical-bottomed tube that contains 4 mL of deionized water, close the tube and shake gently by hand for 30 s. After centrifugation for 1 minute (5000 rpm), transfer 100 μL of the settling volume to a vial and inject 1 μL of the extract into a GC-MS system developed by dispersive solid phase extraction (DSPE) and DLLME for the determination of seven neonicotinoid insecticide residues (nitenpyram, dinotefuran , clothianidin, thiamethoxam, acetamiprid, imidacloprid and thiacloprid) in grains by HPLC.
The DLLME condition was as follows: 0.8 mL acetonitrile (as dispersive solvent) was mixed with 100.0 µL CHCl3 (as extracting solvent), vortexed for 1 min, and centrifuged for 5 min at 3500 rpm. The KUECHERS condition was: 2 g of bee bread were weighed into a 50 mL polypropylene centrifuge tube, 5 mL of pure water, 5 mL of heptane, and 10 mL of acetonitrile with. The mixture was then centrifuged at 5000 g for 2 min, and 8 mL of the supernatant (acetonitrile phase) was transferred to a 15 mL tube and incubated for 15 h at −18 °C.
A mixture of acetonitrile and ethanol: water (12:88) was used as the extraction solvent and 2 mL of acetonitrile as the dispersing solvent. 5 mL of water, 20 mL of acetonitrile and 3.0 g of sodium chloride were added to the centrifuge tube, and vortex for 3 min and centrifuge for 5 min at 4000 rpm. Sample cleanup was performed with SPE cartridge packed with 20 mg (dry weight) CH3NH-G. Before the sample cleanup procedure, the SPE. cartridge was conditioned with 3 mL methanol, 3 mL acetonitrile, 3 mL acetone, and 9 mL water.
Finally, analytes were eluted using 1 mL of acetonitrile reported for dispersive solid phase extraction (DSPE) using polyaniline-modified NaY zeolite (PANI) as a sorbent for multi-class pesticides in food and environmental samples from HPLC-PDA.
- Reagents and standards
- Instrumentation
- Surface water and fruit juice samples
- Experimental
- Preparation of standard neonicotinoid insecticides
- Linearity, detection limits and repeatability
- Sample preconcentration
- D-µ-SPE procedure
- Preparation of samples
- Analysis of neonicotinoids in natural surface water and fruit juice samples
- Data analysis
The natural surface water samples were taken from several areas near rice fields in Maha Sarakham Province, Northeast Thailand. The standard stock solutions were stored in dark bottles, stored at 4°C, and used for no more than six months. The sensitivity of the method was evaluated by the limit of detection (LOD), using a signal-to-noise ratio (S/N) of 3:1 and the limit of quantitation (LOQ) using a signal-to-noise ratio (S/N) ) of 10. :1.
The effect of sample volume on the extraction of neonicotinoids was studied in the range of 1-15 ml. The salt addition can reduce the solubility of the target analytes and either reduce the solubility of organic solvent in water or enhance the partitioning of the target analytes in organic phase [51]. The vortex was used for agitation during the extraction step to improve the extraction efficiency as it vigorously agitated sample and the sorbent.
Therefore, we studied the effect of centrifugation time in the range of 5-20 min at 3500 revolutions per minute. Three samples of natural surface water were taken from different areas near rice fields in Maha Sarakham Province (Northeastern Thailand) and were filtered through Whatman no. Before analysis, a 30.0 ml aliquot of fruit juice was centrifuged at 3500 rpm for 15 minutes. and was filtered through Whatman no.
Then the solution was filtered through a 0.45 mm nylon membrane filter before extraction by the proposed method. Neonicotinoid in natural surface water and fruit juice samples were analyzed using the optimum conditions.
Determination of neonicotinoid insecticide residues in surface water and fruit
- Optimization of the d-µ-SPE procedure
- Effect of amount of MMT sorbent
- Effect of sample volume
- Salt addition
- Effect of type and volume of the desorption solvent
- Effect of vortex time
- Effect of centrifugation time
- Reusability of adsorbent
- Analytical performance of the developed d-µ-SPE procedure
- Application to real samples
The effect of sample volume on extraction efficiency was studied in the range of 1–15 mL. It can reduce the solubility of the target analytes and either reduce the solubility of the organic solvent in water or enhance the partitioning of the target analytes in the organic phase [51]. A series of experiments were investigated to find out the optimal volume of desorbing solvent such as 70% (v/v) acetonitrile.
As can be seen from Figure 8, the highest extraction efficiency in terms of peak areas of the target analytes was obtained with 150 µL of desorption solvent and remained almost unchanged thereafter. As shown in Figure 9, it was found that a rapid attainment of equilibrium was obtained within 60 s of loading time and 120 s of elution time. Other parameters that can affect the extraction efficiency of the developed method are the centrifugation time, the optimal centrifugation time is still required because the mass transfer process between the two phases in the extraction procedure must be time dependent.
The optimal conditions of d-µ-SPE for the analysis of neonicotinoid insecticides are summarized in Table 6. To study the analytical performance of the proposed method, the analytical parameters included linear ranges, correlation coefficients (R2), precision, limit of detection (LOD), limit of quantification (LOQ ) and enrichment factors (EFs) were examined under the selected condition. To test the reproducibility of the proposed method, precision in terms of intra-day and inter-days was investigated by replicate injection of the standard mixture of 50 ng mL-1 each on one day (n = 3) and several days (n = 3× 3).
Chromatograms of the studied neonicotinoid insecticides obtained from direct HPLC and pre-concentrated by the proposed d--SPE are shown in Figure 11. It was found that no residue of the studied neonicotinoids was observed in the natural surface water and longan samples. To validate the accuracy of the established method, the fruit juice samples were treated with neonicotinoid insecticides at concentration levels of 250 and 500 ng mL-1.
As shown in Table 9, the recoveries of the studied neonicotinoid insecticides in fruit and natural surface water samples were achieved in the range of 12-138% and 62-151%, respectively.
Comparison of the proposed d--SPE method with other sample preparation
Comparison of the proposed d-µ-SPE with other sample preparation methods for the determination of neonicotinoids.
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![Table 1. Properties of the studied neonicotinoid insecticides from other chemical classes [35]](https://thumb-ap.123doks.com/thumbv2/filepdfco/10213957.0/18.892.128.784.215.1040/table-properties-studied-neonicotinoid-insecticides-chemical-classes-35.webp)
