Solvent-loaded metal-organic framework of type MIL-101(Cr)-NH2 for the dispersive solid-phase extraction and UHPLC-MS/MS analysis of herbicides from paddy field waters.

A novel solvent-loaded dispersive solid-phase extraction (SL-DSPE) method integrated with liquid-phase microextraction (LPME) has been developed by the direct loading of solvent into the pores of a metal-organic framework (MOF), MIL-101(Cr)-NH2. Despite numerous advantages of MOFs, they are usually highly hydrophobic which limits their dispersibility and therefore effective contact with the analytes in aqueous samples. To overcome this and promote its interactions with polar compounds, MIL-101(Cr) was functionalized with -NH2 and loaded with a comparatively polar organic solvent, dichloromethane. The purpose of dichloromethane was to condition the MIL-101(Cr)-NH2, promote LPME of the analytes and facilitate the re-collection of the materials after the extraction. Five chlorophenoxy acid herbicides, including 2,4-dichlorophenoxyacetic acid, 2,4,5-trichlorophenoxyacetic acid, 4-chlorophenoxyacetic acid, 2-(2,4-dichlorophenoxy)propionic acid, and 2-(2,4,5-trichlorophenoxy)propionic acid, were studied and determined by ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). MIL-101(Cr)-NH2 was characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and surface area measurement. Several extraction parameters were optimized, and under the most favorable conditions, the SL-DSPE-UHPLC-MS/MS method achieved enrichment factors between 25 and 66. Low limits of detection (2.66-19.7 ng·L-1) and wide dynamic working ranges with good linearity (r2 ≥ 0.991) were attained for all analytes. The method was repeatable, with intra- and inter-day relative standard deviations (RSDs) below 4.5 and 7.6%, respectively, for three replicate determinations. The application of SL-DSPE-UHPLC-MS/MS to paddy field waters gave satisfactory relative recoveries ranging between 80.2 and 108%, with RSDs better 8.4%. Several of the CPAs were detected in these samples. Graphical abstract Schematic of the solvent-loaded dispersive solid-phase extraction procedure. By directly loading dichloromethane into the pores of MIL-101(Cr)-NH2, this method improves the extraction capability of the sorbent through the combination of solvent- and sorbent-based microextraction.

Fully automated graphitic carbon nitride-based disposable pipette extraction-gas chromatography-mass spectrometric analysis of six polychlorinated biphenyls in environmental waters.

A fully automated online emulsification-enhanced disposable pipette extraction-gas chromatography-mass spectrometry (EE-DPX-GC-MS) method has been developed for the extraction of six polychlorinated biphenyls (PCBs) from environmental waters. An in-house prepared material, graphitic carbon nitride (g-C3N4), was used as sorbent in a home-packed DPX device. The six PCBs studied include PCB 10, 28, 52, 153, 138 and 180. g-C3N4 was characterized successfully by X-ray diffraction, elemental analysis, scanning electron microscopy, Fourier-transform infrared and Raman spectroscopy. As a C-N analogue of graphite, the two-dimensional structure of g-C3N4 allows rapid analyte adsorption and desorption to take place. With a significant number of nitrogen functionalities in g-C3N4, the material dispersed well in aqueous sample, increasing the active surface area of contact between the sorbent and the sample. When coupled with a pre-emulsification step, PCBs in each portion of sample could be efficiently extracted by g-C3N4 within 20 s of gentle turbulence. Under the most favorable conditions, the automated online EE-DPX-GC-MS method achieved wide dynamic working ranges with good linearity (r2 ≥ 0.998) for all analytes. Limits of detection ranging between 4.35 and 7.82 ng L-1 were attained, with enrichment factors of between 34 and 57 and relative standard deviations (RSDs) for intra- and inter-day precision of ≤ 8.95% and ≤ 12.6%, respectively. Absolute recoveries were between 69.3% and 109%. The fully automated online EE-DPX-GC-MS approach was applied to industrial wastewaters and reservoir waters where good relative recoveries of PCBs of between 89.3% and 105% were obtained, with RSDs ≤ 11.6%.

Emulsification-assisted micro-solid-phase extraction using a metal-organic framework as sorbent for the liquid chromatography-tandem mass spectrometric analysis of polar herbicides from aqueous samples.

Two miniaturized sample preparation techniques, ultrasound-assisted emulsification microextraction (USAEME) and micro-solid-phase extraction (µ-SPE) have been integrated for the pre-concentration of four polar chlorophenoxy acid (CPA) herbicides from environmental aqueous samples. An metal-organic framework, MIL-101(Cr), characterized by its high porosity and large surface area, was explored as a sorbent. Despite the simplicity and convenience of µ-SPE, its use can potentially be limited by a long equilibration time, especially when applied to polar analytes. However, as demonstrated in this work, this drawback can be overcome by employing 1-octanol as a medium during the USAEME step to concentrate, and transport the polar herbicides through the polypropylene membrane of the µ-SPE device, onto the MIL-101(Cr). After µ-SPE, the herbicides were desorbed using 125 µL of organic solvent, and analyzed by ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). Under the most favorable conditions, wide calibration ranges with good linearity (r2 ≥ 0.995) are attained for all the herbicides. The limits of detection of the method range between 7.20 and 58.1 ng L-1 while the limits of quantification (LOQs) range between 24.0 and 194 ng L-1. The LOQs determined are lower than the guidelines set by the World Health Organization for the respective herbicides. USAEME-µ-SPE-UHPLC-MS/MS also shows good repeatability, with relative standard deviations ≤ 15.2%. Enrichment factors are between 21 and 70. The method was applied to the analysis of tap and reservoir waters, in which satisfactory relative recoveries ranging between 64.4% and 106% were obtained. The MIL-101(Cr) exhibited superior extraction capability in comparison to activated carbon and multi-walled carbon nanotubes.

Graphitic carbon nitride as sorbent for the emulsification-enhanced disposable pipette extraction of eight organochlorine pesticides prior to GC-MS analysis.

Graphitic carbon nitride (g-C3N4) was explored as a sorbent for the emulsification-enhanced (EE) disposable pipette extraction (DPX) of eight organochlorine pesticides (OCPs) from environmental waters. The OCPs, including α-hexachlorocyclohexane, Aldrin, α-Chlordane, Dieldrin, 4,4'-dichlorodiphenyldichloroethylene, 4,4'-dichlorodiphenyldichloroethane, Heptachlor and Heptachlor epoxide (Isomer A), were analyzed by gas chromatography-mass spectrometry. The sorbent g-C3N4 was characterized by elemental analysis, X-ray diffraction, scanning electron microscopy, Fourier-transform infrared and Raman spectroscopy. As a C-N analogue of graphite, g-C3N4 exhibits good water dispersibility and allows easy analyte recovery - a characteristic not commonly observed in carbon-based materials. When applied to DPX, g-C3N4 rapidly establishes strong interactions with the OCPs. Consequently, g-C3N4 displays superior extraction capability in comparison to six other commercial sorbents. An emulsification step prior to DPX was found to enhance the overall extraction efficiency by pre-concentrating the OCPs into the microdroplets of an organic solvent. The microdroplets were then adsorbed onto g-C3N4. Under the most favorable conditions, wide linear responses spanning over two to four orders of magnitudes are established. The limits of detection range between 2.4 ng·L-1 and 46.2 ng·L-1. The method is reproducible (relative standard deviations ≤ 7.4%) and enrichment factors are between 42 and 57. When applied to the analysis of lake and river water samples, EE-DPX-gas chromatography-mass spectrometry exhibits good resilience against matrix interferences. The relative recoveries range between 77.7% and 106.3%. In comparison to other sorbent-based extraction techniques reported for the analysis of OCPs in aqueous samples, EE-DPX utilizes the minimal amount of sample and solvent, and requires the shortest sample preparation time. Graphical abstractSchematic representation of the emulsification-enhanced disposable pipette extraction (DPX) of organochlorine pesticides (OCPs) using graphitic carbon nitride (g-C3N4) as sorbent. Emulsification and DPX work synergistically, thus allowing rapid dissolution of analytes into microdroplets of organic solvent, before being extracted by g-C3N4.

A hydrogel composite prepared from alginate, an amino-functionalized metal-organic framework of type MIL-101(Cr), and magnetite nanoparticles for magnetic solid-phase extraction and UHPLC-MS/MS analysis of polar chlorophenoxy acid herbicides.

A regenerable hydrogel composite is described that is comprised of alginate, amino-functionalized metal-organic framework (MIL-101(Cr)-NH2) and magnetite nanoparticles. The composite was characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy, vibrating-sample magnetometry and Brunauer-Emmett-Teller measurement. The material was applied to the magnetic solid-phase extraction of six polar chlorophenoxy acid (CPA) herbicides. Specifically, the herbicides clofibric acid, 4-chlorophenoxyacetic acid, 2,4-dichlorophenoxyacetic acid, 2-(2,4-dichlorophenoxy)propionic acid, 2,4,5-trichlorophenoxyacetic acid and 2-(2,4,5-trichlorophenoxy)propionic acid were extracted from environmental aqueous samples and analyzed by ultra-HPLC-tandem mass spectrometry. The abundance of hydroxyl and carboxyl groups on the natural polymer renders alginate a superior hydrophilic coating. It brings the polar acidic herbicides into closer proximity to the porous metal-organic framework. When integrated with MIL-101(Cr)-NH2, the composite material combines the favorable attributes of high hydrophilicity and large adsorption capacity. An orthogonal array design matrix was employed for the optimization of the extraction parameters. Under the most favorable conditions, the method displays a wide linear response and low limits of detection (0.43-16 ng⋅L-1). Precision and reproducibility (with relative standard deviations of ≤13%) are satisfactory. Enrichment factors range between 27 and 107. The composite was applied to the extraction of CPA herbicides from lake and pond water samples. A markedly improved sorbent-based extraction procedure and performance (compared to previous methods) is found. Graphical abstract Schematic of the magnetic solid-phase extraction of polar herbicides using a hydrogel composite as sorbent. The amino-functionalized MIL-101(Cr) and hydrophilic alginate work in synergy resulting in a material which possess favorable attributes of both components that are beneficial for extraction.

A metal-organic framework of type MIL-101(Cr) for emulsification-assisted micro-solid-phase extraction prior to UHPLC-MS/MS analysis of polar estrogens.

A seamless two-step extraction procedure integrating ultrasound-assisted emulsification microextraction (USAEME) and vortex-assisted micro-solid-phase extraction (µ-SPE) was developed. A highly porous metal-organic framework of type MIL-101(Cr) is used as the sorbent, and ultra-high-performance liquid chromatography in combination with tandem mass spectrometry is used for detection. The steroid hormones estrone 17ß-estradiol, estriol, and 17α-ethynylestradiol were extracted from water samples by using this method. These steroids are polar and do not pass through the polypropylene membrane that is conventionally used in µ-SPE. In the method presented here, 1-octanol is used in USAEME to extract and pre-concentrate the steroids. This facilitates the transfer to the MIL-101(Cr) phase retained by the membrane in the subsequent µ-SPE step. MIL-101(Cr) was characterized by various methods, and the parameters affecting the overall extraction efficiency were optimized. Under the most favorable conditions, the limits of detection are between 0.95 and 23 ng L-1. Good intra-day and inter-day precisions were obtained, with relative standard deviations of ≤ 9.9%. Enrichment factors are between 34 and 52. The method was applied to genuine environmental water samples in which estrone was detected. Relative recoveries ranged between 85.4% and 120.8%. Graphical abstract Schematic of the emulsification-assisted micro-solid-phase extraction (µ-SPE). By emulsifying 1-octanol in the water sample, polar estrogens dissolved in the solvent can easily pass the hydrophobic polypropylene membrane and then are adsorbed onto the unmodified MIL-101(Cr) held within the µ-SPE device.