Highly efficient dispersive liquid-liquid microextraction assisted by magnetic porous carbon composite-based dispersive micro solid-phase extraction for determination of tramadol and methadone in urine samples by gas chromatography-mass spectrometry.

The recognition of opioids, either as prescription drugs or illicit narcotics, is one of the hot challenges in the analytical field, especially in forensic medicine. Here, a rapid and high efficient air-assisted dispersive liquid-liquid microextraction (DLLME) running after a dispersive magnetic solid-phase extraction (MSPE) is developed for simultaneous extraction and preconcentration of tramadol and methadone in urine samples prior to gas chromatography-mass spectrometry (GC-MS) determination technique. The samples were first mixed with a new magnetic and porous adsorbent, based on a metal-organic framework (MOF) derived NH2-functionalized Fe3O4 nanoparticles-carbon nanocomposite (NH2-Fe3O4@C). Then, the eluent, containing the retrieve analytes, was directly applied as the disperser solvent, along with dichloromethane extracting solvents, to perform DLLME. The combination of MSPE, using the new high surface area sorbent, with a high-performance DLLME resulted in exceptional enrichment factors and extraction recoveries. Under the optimized conditions, linear ranges of 0.1-30 ng mL-1 and 0.1-35 ng mL-1, and detection limits of 73 and 32 pg mL-1, were obtained for tramadol and methadone, respectively. The developed system was utilized for the extraction and preconcentration of tramadol and methadone in some urine samples of suspected drug users, with a reasonable reproducibility (2.4-4.5%). The results were in good agreement with those of the official HPLC/MS-MS technique.

A simple fluorometric method for rapid screening of aflatoxins after their extraction by magnetic MOF-808/graphene oxide composite and their discrimination by HPLC.

Herein, a high-performance screening tool for the selective and sensitive monitoring of aflatoxins is reported based on their great quenching effect on the blue emission of graphene quantum dots (GQDs). To make a specific determination, a pre-extraction method was also developed using a new nano-sorbent based on the surface-imprinted Zr metal-organic framework on the magnetic graphene oxide (MGO/MOF-808@MIP). The adsorbing efficiency of the prepared composite was remarkably higher than the pristine MOF-808 or bare GO. The presence of GO nanosheets, as well as nanoporous MOF-808 provided a high accessible surface area to form the MIP layer. It provided a great number of MIP sites for high efficient and rapid extraction of aflatoxins. The presence of magnetic nanoparticles in the structure of nanocomposite also facilitated the extraction process using a magnetic solid-phase extraction (MSPE) system. The combination of this specific and high-performance extraction with simple fluorometric detection caused a potent screening tool for aflatoxins. The method was able to monitor the total aflatoxins content of food samples with a linear range of 0.05-8 ng mL-1, which was more sensitive than the fluorometric system without extraction (5-500 ng mL-1). More developments were made by the application of a high-performance liquid chromatography (HPLC) method for the discrimination of the extracted aflatoxins. The system showed high sensitivity and selectivity and was able to detect different aflatoxins with an acceptable resolution.

Mesoporous MIP-capped luminescent MOF as specific and sensitive analytical probe: application for chlorpyrifos.

Specific recognition of organophosphate pesticides (OPs) is a significant challenge for analytical researchers. Herein, surface imprinted terbium-based luminescent metal-organic framework (MOF-76) are presented as a highly specific probe for the measurement of chlorpyrifos (CP). A mesoporous molecular imprinted polymer (mMIP) layer was generated on the surface of nano-sized MOF-76 using CP, as template. The resulting mMIP-capped MOF-76 (mMIP@MOF-76) contained specific sites for adsorption of CP molecules, guaranteeing the selectivity of the designed probe. The high porosity of rod-shape MOF-76, as well as the mesoporous structure of the MIP layer improved the diffusion process and caused the high sensitivity of the probe. The detection process is based on the remarkable quenching effect of CP on the fluorescence emission of mMIP@MOF-76. Plotting the CP concentration against the fluorescence intensity (λex = 285 nm and λem = 544 nm) gave a linear curve in the concentration range 10-1000 ng mL-1 CP, with 3.41 ng mL-1 limit of detection. The designed probe was utilized for CP determination in fruit juice and environmental samples. The combination of the stable MOF-based support, as well as its remarkable fluorescence features and specific MIP sites, led to a highly selective and ultrasensitive detection system.Graphical abstract.