A headspace sorptive extraction method with magnetic mesoporous titanium dioxide@covalent organic frameworks composite coating for selective determination of trace polychlorinated biphenyls in soils.

It's crucial to develop some simple, selective and rapid extraction pretreatments for detection of trace polychlorinated biphenyls (PCBs) residues in soils. Herein, a new magnetic mesoporous titanium dioxide@covalent organic frameworks (Fe3O4@mTiO2@COFs) composite coating was fabricated and adsorbed onto a Nd-Fe-B magnet for headspace sorptive extraction (HSSE) of seven indicative PCBs (PCB28, PCB52, PCB101, PCB118, PCB138, PCB153 and PCB180) in soils. The coating was assembled layer by layer using hydrothermal method. After being extracted by the magnetic stir bar, the adsorbed PCBs can be desorbed in thermal desorption unit (TDU) and measured by gas chromatography-mass spectrometry (GCMS). Under the optimal conditions, the limit of detection (S/N = 3) was measured less than 0.06 ng/g and the linear range was from 0.01 to 100 ng/g. The new coating exhibited good extraction capacity (its saturated adsorption amount was found to be 35 mg/g), selectivity and can be reused for at least 80 times with a recovery above 90%. The HSSE assay showed the following distinctive advantages: Firstly, the outer COFs coating has a uniform size of cavities (about 3.9 nm), thus PCBs (less than 2 nm) can freely pass through them, while the larger macromolecules can be effectively excluded. Secondly, the inner flower-like mTiO2 coating has good affinity towards chlorine-containing organic compounds, which further improves the selectivity for PCBs. Thirdly, both mTiO2 and COFs have large specific surface area. The synergistic effects of the composite coating make the HSSE assay exhibit high capacity, selectivity and prominent sensitivity towards PCBs detection coupling with TDGCMS. Finally, it is an environmentally friendly pretreatment method that does not require any organic solvents.

A molybdenum disulfide/reduced graphene oxide fiber coating coupled with gas chromatography-mass spectrometry for the saponification-headspace solid-phase microextraction of polychlorinated biphenyls in food.

In this work, the molybdenum disulfide/reduced graphene oxide (MoS2/RGO) composite material was synthesized as a fiber coating to extract seven indicator polychlorinated biphenyls (PCBs; PCB28, PCB52, PCB101, PCB118, PCB138, PCB153, and PCB180) present in food via a saponification-headspace solid-phase microextraction assay (saponification-HS-SPME). The MoS2/RGO coating was prepared and deposited on a stainless steel wire with the help of a silicone sealant and used as an SPME fiber. The alkali solution dissolved the fat and helped in releasing the PCBs present in milk to the headspace for extraction under 100°C. Following desorption in the inlet, the targets were quantified by gas chromatography-mass spectrometry. The effects of sorbent dosage, extraction time, added salts, and stirring rate on the extraction efficiency were investigated. The new coating was able to adsorb a higher amount of analytes, which was about 1.1-2.9 times in comparison with the commercially available SPME fiber (coated with divinylbenzene/carboxen/polydimethylsiloxane). It also showed the highest adsorption capability toward PCBs, which was 1.5-2.7 times that of the prepared RGO modified fiber. Moreover, MoS2 also showed a strong affinity toward PCBs in a manner similar to its affinity for graphene. The developed method is simple and environmentally friendly as it does not require any organic solvents. Furthermore, it exhibits good sensitivity with detection limits less than 0.1ngmL-1, linearity (0.25-100ngmL-1), and reproducibility (relative standard deviation below 10% for n=3). The novel SPME fibers are inexpensive, reusable, and can be easily prepared and manipulated. In addition, the saponification-HS-SPME assay was also found to be suitable for screening persistent organic pollutants in dairy products.

Determination of aliphatic amines in food by on-fiber derivatization solid-phase microextraction with a novel zeolitic imidazolate framework 8-coated stainless steel fiber.

Some harmful aliphatic diamines, e.g., putrescine (Put) and cadaverine (Cad), play important roles in food safety evaluation. In this study, we proposed on-fiber derivatization solid-phase microextraction analysis of non-volatile aliphatic diamines in fish using zeolitic imidazolate framework 8 (ZIF-8) as a solid-phase microextraction (SPME) coating. It was employed to encapsulate isobutyl chloroformate (IBCF, 40°C, 15min) for aqueous extraction of Put and Cad. After that, the derivatized aliphatic amines were thermally desorbed in the GC injection port and analyzed by GC-MS. The porous and hydrophobic ZIF-8 with high surface area can increase the IBCF loading amount and prevent it from decomposing, thus increasing the amine extraction effectiveness and sensitivity. In SIM mode and using the molecular ion for quantification, the limits of detection for Put and Cad were 27.1 and 33.2µgL-1, respectively under the optimal conditions. The fiber-to-fiber reproducibility values (RSDs) for three ZIF-8 coated fibers were less than 11.4% for both Put and Cad. The extraction with the new fiber was reproducible for at least 30 cycles without a noticeable decrease of performance (RSD<10%). The new fiber was successfully applied to the detection of putrescine and cadaverine in several fish samples and showed good recoveries (78.6-104%).

Environmentally friendly solid-phase microextraction coupled with gas chromatography and mass spectrometry for the determination of biogenic amines in fish samples.

In this work, a facile and environmentally friendly solid-phase microextraction assay based on on-fiber derivatization coupled with gas chromatography and mass spectrometry was developed for determining four nonvolatile index biogenic amines (putrescine, cadaverine, histamine, and tyramine) in fish samples. In the assay, the fiber was firstly dipped into a solution with isobutyl chloroformate as derivatization reagent and isooctane as extraction solvent. Thus, a thin organic liquid membrane coating was developed. Then the modified fiber was immersed into sample solution to extract four important bioamines. Afterwards, the fiber was directly inserted into gas chromatography injection port for thermal desorption. 1,7-Diaminoheptane was employed as internal standard reagent for quantification of the targets. The limits of detection of the method were 2.98-45.3 µg/kg. The proposed method was successfully applied to the detection of bioamines in several fish samples with recoveries ranging 78.9-110%. The organic reagent used for extraction was as few as microliter that can greatly reduce the harm to manipulator and environment. Moreover, the extraction procedures were very simple without concentration and elution procedures, which can greatly simplify the pretreatment process. The assay can be extended to the in situ screening of other pollutant in food safety by changing the derivatization reagent.