Streamlined Water-Leaching Preconcentration Method As a Novel Analytical Approach and Its Coupling to Dispersive Micro-Solid-Phase Extraction Based on Synthetically Modified (Fe/Co) Bimetallic MOFs

Abstract

The streamlined water-leaching preconcentration method is introduced as a novel preconcentration method in this study. The approach has many benefits including low consumption of organic solvent and deionized water and operation time, energy-saving, no need for dispersion or evaporation, and implementation of more efficient preconcentration. Also, a methodological study was done on the synthesis of (Fe/Co) bimetallic-organic framework that eased the synthesis procedure, decreased its time, and enhanced its analytical performance by increasing its surface area, total pore volume, and average pore diameter parameters. To perform the extraction, bi-MOF particles were added into the solution of interest enriched with sodium sulfate. After vortexing to adsorb the analytes, centrifugation isolated the sorbent particles. A microliter-volume of acetonitrile and 1,2-dibromoethane mixture was used for desorption aim via vortexing. After the separation of the organic phase and transferring it into a conical bottom glass test tube, a milliliter volume of sodium chloride solution was applied to leach the organic phase. A gas chromatograph equipped with a flame ionization detector was applied for the injection of the extracted phase. The method was applied for the extraction and preconcentration of some pesticides from juice samples. Wide linear ranges (5.44-1600 μg L^-1), low relative standard deviations (3.1-4.5% for intra- (n = 6) and 3.5-5.2% for interday (n = 4) precisions), high extraction recoveries (61-95%), enrichment factors (305-475), and low limits of detection (0.67-1.65 μg L^-1) and quantification (2.21-5.44 μg L^-1) were obtained for the developed method.

Figure 1

XRD pattern (a), FTIR spectrum (b), SEM images of (Fe/Co) Bi-MOF* (c and d), SEM images of (Fe/Co) Bi-MOF (e and f), EDX spectrum of (Fe/Co) Bi-MOF* (g), EDX spectrum of (Fe/Co) Bi-MOF (h), BET plot of (Fe/Co) Bi-MOF* (i), BET plot of (Fe/Co) Bi-MOF (j), image of (Fe/Co) Bi-MOF* (k), image of (Fe/Co) Bi-MOF (l), and the volume comparison of 100 mg of (Fe/Co) Bi-MOF* and (Fe/Co) Bi-MOF (m).

Figure 2

Optimization of the weight of (Fe/Co) Bi-MOF. Extraction conditions: DμSPE procedure: aqueous solution, 5 mL of deionized water spiked with 500 μg L^–1 of each analyte having 1.0 mol L^–1 dissolved Na₂SO₄; vortexing time in adsorption step, 5 min; desorption solvent (volume), ACN (200 μL); vortexing time in desorption step, 5 min; and centrifugation speed and time, 7000 rpm and 5 min, respectively. SWLP procedure: preconcentration solvent (volume), 1,2-DBE (13 μL); leaching solution (volume), deionized water (2 mL); MOF synthesis process, (Fe/Co) Bi-MOF. The error bars show the minimum and maximum of three repeated determinations.

Figure 3

Influence of ionic strength on ERs of the analytes. Extraction conditions: the same as those used in Figure 2, except 20 mg of (Fe/Co) Bi-MOF was applied.

Figure 4

Influence of Na₂SO₄ concentration on ERs of the analytes. Extraction conditions: the same as those used in Figure 3, except Na₂SO₄ was selected as the salting-out agent.

Figure 5

Influence of solution pH on ERs of the analytes. Extraction conditions are the same as those used in Figure 4, except 1 mol L^–1 concentration of Na₂SO₄ was selected.

Figure 6

Selection of desorption solvent type. Extraction conditions are the same as those used in Figure 5, except no pH variation was done.

Figure 7

Optimization of ACN volume. Extraction conditions are the same as those used in Figure 6, except ACN was selected as the desorption solvent.

Figure 8

Selection of preconcentration solvent. Extraction conditions are the same as those used in Figure 7, except 400 μL of ACN was chosen as the desorption solvent volume.

Figure 9

Selection of leaching solution. Extraction conditions are the same as those used in Figure 8, except 1,2-DBE was used as the preconcentration solvent.

Figure 10

Optimization of NaCl concentration in the leaching solution. Extraction conditions are the same as those used in Figure 9, except NaCl was used as the antiback-extraction agent in the SWLP step.

Figure 11

Optimization of leaching solution volume. Extraction conditions are the same as those used in Figure 10 except, 10%, w/w of NaCl solution was used in the SWLP step.

Figure 12

Comparison of the extraction efficiency between the synthesized Bi-MOFs. Extraction conditions are the same as those used in Figure 11, except 2 mL of 10%, w/v NaCl solution was used in the SWLP step.

Figure 13

Choosing the desorption solvent composition. Extraction conditions are the same as those used in Figure 12, except (Fe/Co) Bi-MOF* was chosen as the adsorbent.

Figure 14

GC-FID chromatograms of: (A) standard solution (500 mg L^–1 of each pesticide in methanol), (B) deionized water spiked with 500 μg L^–1 of each pesticide, and (C) orange juice. Except chromatogram A in which direct injection without preconcentration was done, in the other chromatograms, the final extracted phase was injected into the separation system. Peaks identification: (1) acetochlor, (2) fenitrothion, (3) malathion, (4) haloxyfop-R-methyl, (5) hexaconazole, (6) oxadiazon, and (7) diniconazole.