GNP/Al-MOF nanocomposite as an efficient fiber coating of headspace solid-phase micro-extraction for the determination of organophosphorus pesticides in food samples.

The synthesis and utilization of a high porous nanocomposite comprising MIL-53(Al) metal-organic framework (Al-MOF) and graphene nanopowder (GNP) is reported as a fiber coating for headspace solid-phase micro-extraction (HS-SPME) of selected organophosphorus pesticides (OPPs) from apple, potato, grape juice, tomato, and river water. The adsorbed OPPs on the coated fiber were subsequently determined using GC-MS. Several parameters affecting the efficiency of extraction including time and temperature of extraction, desorption condition of extracted analytes, pH and agitation of sample solution, and salt concentration were investigated. The optimum extraction condition was achieved at 70 °C with an extraction time of 40 min, pH = 4-8, and NaCl concentration of 6.0% (w/v). The best condition of desorption were observed at 280 °C for 2.0 min under a flow of helium gas in the GC inlet. Under optimal conditions, the detection limits ranged from 0.2 to 1.5 ng g-1 and the linear ranges between 0.8 and 600 ng g-1. The proposed method showed very good repeatability with RSD values ranging from 4.5 to 7.3% (n = 5). The relative recoveries were between 88% and 109% at the spiked level of 25.0 ng g-1 for the tomato sample. The fabricated fiber exhibited good enrichment factor (62-195) at optimum condition of HS-SPME. The applied HS-SPME technique is facile, fast, and inexpensive. The thermally stable GNP/Al-MOF exhibited a high sensitivity toward OPPs. So, this nanocomposite can be considered as a sorbent for the micro-extraction of other pesticides in food.

Development of a SPE/GC-MS method for the determination of organophosphorus pesticides in food samples using syringe filters packed by GNP/MIL-101(Cr) nanocomposite.

In this study, we report the synthesis and application of a nanocomposite comprising metal-organic framework MIL-101(Cr) and graphene nanopowder (GNP) as a promising sorbent for the extraction of organophosphorus pesticides (OPPs) in juices, water, vegetables and honey samples. A syringe filter, for the first time, was used to host the synthesized nanocomposite and extract the OPPs followed by GC-MS analysis. Different characterization methods including XRD, FTIR, TGA, BET and SEM were employed to confirm the formation of studied nanocomposite. The results indicated that the GNP/MIL-101(Cr) could provide higher capacity for adsorption of OPPs and lower detection limit compared to pristine MIL-101(Cr). The detection limits were 0.005 to 15.0 µg/Kg and the linear range found between 0.05 and 400 µg/Kg. The proposed method showed very good repeatability with the RSD values ranging from 2.9% to 7.1%. The recoveries were between 84% -110% with the spiked levels of 2.0-100.0 µg/Kg.

MIL-53(Al)/Fe2O3 nanocomposite for solid-phase microextraction of organophosphorus pesticides followed by GC-MS analysis.

A novel aluminum terephthalate/Fe2O3 nanocomposite was synthesized by the addition of Fe2O3 nanoparticles into a reaction solution containing aluminum terephthalate MOF. The synthesized nanocomposite was successfully used as a fiber coating material for solid-phase microextraction (SPME) of six organophosphorus compounds (OPPs) from river water, grape juice, and tea samples. The effect of different parameters on the efficiency of SPME including desorption temperature and time, extraction temperature and time, salt concentration, pH, and agitation were thoroughly studied. The OPPs were detected and determined using GC-MS. According to the findings, a wide linear range (0.15-800 µg kg-1), low limit of detection (0.04-10 µg kg-1), and high recoveries from spiked samples (87.5-112%) were achieved with low inter-day relative standard deviation (3.2-6.7%, n = 5). The MIL-53(Al)/Fe2O3 nanocomposite showed  a high extraction ability towards OPPs, and hence, it can be considered a promising adsorbent for the extraction of various pesticides in complex matrices like tea and juice.Graphical abstract.

Continuous sample drop flow-based microextraction method as a microextraction technique for determination of organic compounds in water sample.

Continuous sample drop flow-based microextraction (CSDF-ME) is an improved version of continuous-flow microextraction (CFME) and a novel technique developed for extraction and preconcentration of benzene, toluene, ethyl benzene, m-xylene and o-xylene (BTEXs) from aqueous samples prior to gas chromatography-flame ionization detection (GC-FID). In this technique, a small amount (a few microliters) of organic solvent is transferred to the bottom of a conical bottom test tube and a few mL of aqueous solution is moved through the organic solvent at relatively slow flow rate. The aqueous solution transforms into fine droplets while passing through the organic solvent. After extraction, the enriched analyte in the extraction solvent is determined by GC-FID. The type of extraction solvent, its volume, needle diameter, and aqueous sample flow rate were investigated. The enrichment factor was 221-269 under optimum conditions and the recovery was 89-102%. The linear ranges and limits of detection for BTEXs were 2-500 and 1.4-3.1 µg L(-1), respectively. The relative standard deviations for 10 µg L(-1) of BTEXs in water were 1.8-6.2% (n=5). The advantages of CSDF-ME are its low cost, relatively short sample preparation time, low solvent consumption, high recovery, and high enrichment factor.

Development of dispersive liquid-liquid microextraction method for the analysis of organophosphorus pesticides in tea.

In this article, a new method for the determination of organophosphorus pesticides (OPPs) in tea was developed by using dispersive liquid-liquid microextraction (DLLME) and gas chromatography-flame photometric detection (GC-FPD). A mixture of acetonitrile and n-hexane was used as an extraction solvent for the extraction of OPPs from tea samples. When the extraction process was finished, the mixture of solvents was rapidly dispersed in water; target analyte was extracted to a small volume of n-hexane, using DLLME. Recovery tests were performed for concentration 5.0 microg/kg. The recovery for each target analyte was in the range between 83.3 and 117.4%. The repeatability of the proposed method, expressed as relative standard deviation, varied between 3 and 7.8% (n=3). The detection limit of the method for tea was found ranging from 0.030 to 1 microg/kg for all the target pesticides. Compared with the conventional sample preparation method, the proposed method has the advantage of being quick and easy to operate, and has high-enrichment factors and low consumption of organic solvent.