Solid-phase purification and extraction for the determination of trace neonicotinoid pesticides in tea infusion.

An analytical protocol that includes solid-phase purification and extraction is successfully developed for the determination of trace neonicotinoid pesticides in tea infusion. The method consists of a purification on amino-functionalized mesoporous silica SBA-15 followed by a solid-phase extraction based on graphene oxide before ultra high performance liquid chromatography with tandem mass spectrometry analysis. Parameters that significantly affected the extraction of the neonicotinoids onto graphene oxide, such as the amount of adsorbent, extraction time, pH, elution solvent, etc. were optimized. The amino-functionalized mesoporous silica SBA-15 has been proved to be an efficient adsorbent for removal of polyphenols especially catechins from tea infusion. Graphene oxide exhibits a very rapid adsorption rate (within 10 min) and high adsorption capacities for neonicotinoids at low initial concentration (0.01-0.5 mg/L). The analysis method gave a good determination coefficient (r(2) > 0.99) for each pesticide and high recoveries in the range of 72.2-95.0%. Powder X-ray diffraction, Raman spectroscopy, transmission electron microscopy, and UV-vis spectroscopy were utilized to identify the structure and morphology of graphene oxide. The adsorption driving force of neonicotinoids on graphene oxide mainly depends on π-π electron donor-acceptor interaction and electrostatic interaction.

Bimetal heterointerfaces towards enhanced electro-activation of O2 under room condition.

Efficient catalysts for oxygen (O2) activation under room condition are required for effective wet air oxidation (WAO) technology. Here, we report a novel manganese-cobalt-based composite (MnO-CoO@Co) fabricated on a graphite felt (GF) support for catalyzing the electro-activation of O2 under room condition. Abundant Co-MnO and CoO-MnO heterointerfaces are formed in the composite. In comparison to the single-metal counterparts, i.e. CoO@Co/GF (16.99 wt% Co) and MnO/GF (26.83 wt% Mn), the bimetal MnO-CoO@Co/GF (5.29 wt% Co and 8.79 wt% Mn) displays an improved oxygen storage capacity and provides more active sites to accommodate surface adsorbed oxygen species. Notably, the strong synergy derived from bimetal heterointerfaces enhances the electron transfer and oxygen mobilization during the electro-activation of O2, thereby significantly reducing the reaction barrier. MnO-CoO@Co/GF exhibits excellent efficiency and stability in electrocatalytic WAO (ECWAO) towards the removal of pharmaceuticals and personal care products (PPCPs) over a wide pH range from 4.0 to 10.0. A model pollutant sulfamethoxazole (SMX) acquires mineralization efficiency of 78.4 ± 2.1% and mineralization current efficiency of 157.89% at +1.0 V of electrode potential. The toxicity of PPCPs can be totally eliminated after the ECWAO treatment. This work highlights the synergy derived from bimetal heterointerfaces in O2 electrocatalysis, and provides a promising approach for advanced WAO catalysts in PPCPs pollution control.

Impact of Various Microbial-Fermented Methods on the Chemical Profile of Dark Tea Using a Single Raw Tea Material.

In the present study, we produced Pu-erh, Liubao, Qingzhuan, and Fuzhuan teas using a single raw tea material and applied widely targeted metabolomics to study the impact of various microbial-fermented methods on the chemical profile of dark tea. The contents of catechins and free amino acids decreased drastically, whereas the contents of gallic acid and theabrownins increased significantly during microbial fermentation. Pu-erh tea had the highest content of theabrownins (11.82 ± 0.49%). Moreover, MS-based metabolomics analysis revealed that the different types of dark teas were significantly different from their raw material. A total of 85 differential metabolites were screened among 569 metabolites identified referring to self-compiled database. Glycosylated, hydroxylated, methylated, and condensed and oxidated products originating from microbial bioconversion of their corresponding primitive forms were significantly increased in dark teas. These results suggest that various microbial-fermented methods greatly affect the metabolic profile of dark tea, which can provide useful information for dark tea biochemistry research.

[Studies on ANN models of determination of tea polyphenol and amylose in tea by near-infrared spectroscopy].

The objectives of the present paper were to build the models for the determination of tea polyphenol (TP) and tea amylose (TA) in tea by near-infrared spectroscopy (NIR). According to the range of 7432.3-6155.7 cm(-1) and 5484.6-4192.5 cm(-1) of NIR spectra, the models are built for determining the contents of TP and TA in tea with the input layer, hidden layer and node ((8, 4, 1) and (7, 5, 1) respectively) in network structure by the artificial neural network. The correlation coefficient (r), the root mean square error of cross validation (RMSECV) and the root mean square error of prediction (RMSEP) were selected as the indexes for evaluating the performance of calibration models. The results show that r, RMSECV and RSECV by the model samples for TP and TA are 0.9847, 0.460 and 0.123, and 0.9470, 0.136 and 0.224 respectively, and r, RMSEP and RSEP by the prediction samples for TP and TA are 0.9804, 0.529 and 0.017, and 0.9682, 0.111 and 0.0298 respectively. These indicated that the NIRANN models can be used to determine the contents of TP and TA in tea.

Monitoring and risk assessment of 74 pesticide residues in Pu-erh tea produced in Yunnan, China.

A number of 100 Pu-erh tea samples from the 2013 harvest in Yunnan Province (China) were analysed for 74 pesticides. A total of 11 pesticides were detected. At least one pesticide was detected in 56% of the samples. None of these samples contained the 74 monitored pesticides at concentrations above the Chinese maximum residual levels. Imidacloprid, bifenthrin and acetamiprid were most frequently found, with percentages of 53%, 46% and 31%, respectively. These were also the top three pesticides with maximum concentrations of 140, 246 and 672 µg kg⁻¹, respectively. Residual levels of the monitored pesticides showed no significant correlation with the production time or area of Pu-erh tea. Whereas a high incidence of pesticide residues was detected in Pu-erh tea, the contamination levels observed do not pose any serious health risks.

Simultaneous determination of thiophanate-methyl and its metabolite carbendazim in tea using isotope dilution ultra performance liquid chromatography-tandem mass spectrometry.

A rapid method has been developed for the determination of thiophanate methyl and its metabolite carbendazim in tea samples using ultra-high-performance liquid chromatography tandem mass. Dispersive solid-phase extraction was optimized and employed as a sample preparation technique without concentration and solvent exchange. Degradation of thiophanate methyl and its isotope were observed and they declined at the similar rate during sample preparation. The results showed that calibration by isotope internal standards was reliable to correct the degradation. With the extraction solvent at pH range of 2.3-10.3, difference for thiophanate methyl degradation was not much significant due to the buffer action of tea matrix solution. Matrix effects were dependent on the nature of the analytes and tea categories, but calibrated effectively by isotope internal standards. Recoveries ranged 97.2-110.6%, and relative standard deviations were <25.0%. The limit of quantification was both 0.010 mg kg(-1) for thiophanate methyl and carbendazim. The developed method was utilized to measure concentrations of thiophanate methyl and carbendazim in tea samples from seven provinces of China, as well as to investigate the degradation of thiophanate methyl in tea crop.