A method of gas chromatography-mass spectrometry (GC-MS) was established to determine the migration of dibutyl sebacate, dioctyl sebacate, diisooctyl sebacate, decanedioic acid bis(2,2,6,6-tetramethyl-4-piperidinyl)ester in water-based, acidic and alcoholic food simulants, and olive oil and chemical alternative solvents. The 95% ethanol and isooctane chemical substitution solutions were directly analyzed by GC-MS. The olive oil samples were extracted with acetonitrile followed by QuEChERS purification, and then analyzed by GC-MS. Other simulants (water, 4% acetic acid, 10% ethanol, 20% ethanol, and 50% ethanol) were extracted with n-hexane and then determined by GC-MS. The results showed that the method is well performed under optimized conditions, with the correlation coefficient (r2) greater than 0.995. The limits of detection and the limits of quantitation of the four sebacic acid ester compounds in water, 4% acetic acid, 10% ethanol, 20% ethanol, 50% ethanol, 95% ethanol, isooctane, and olive oil simulants are 0.1-0.2 mg/kg, 0.3-0.5 mg/kg, respectively. Migration experiments on plastic samples were conducted, and spiking experiments at three concentration levels of 0.30, 2.0, 4.0 mg/kg in water, 4% acetic acid, 10% ethanol, 20% ethanol, 50% ethanol, 95% ethanol, and isooctane food simulants, and three concentration levels of 0.50, 2.0, 4.0 mg/kg in olive oil food simulants were carried out. The spiking recoveries range from 92.5% to 108%, and the relative standard deviations (RSDs) are 2.4%-8.8%. The method solves the problem that decanedioic acid bis(2,2,6,6-tetramethyl-4-piperidinyl)ester cannot be extracted into n-hexane in 4% acetic acid by adjusting pH value using ammonium hydroxide, the optimal pH range was determined by comparing the responses of four targets at different pH values. QuEChERS was firstly used for migration experiments of sebacic acid esters in food contact materials to solve the turbidity and partial oil precipitation of olive oil simulants in the concentration process after extraction. By optimizing the QuEChERS filling material, the interference of organic acids, fatty acids, sugar and other impurities on the targets were reduced, producing greater separation effect of the targets. The separation efficiency of four chromatographic columns with different polarity was compared, and the DB-17HT column was selected to detect the four sebacic acid esters simultaneously. Plastics such as polypropylene, polyethylene terephthalic acid terephthalate, polyvinyl chloride, composite membranes, paper cups, recycled PET and recycled PVC were collected and migration experiments were carried out, the migration of sebacic acid esters in these plastics materials was investigated. This method is highly sensitive, precise, and accurate, fully meeting the requirement for determining the migration of the sebacic acid esters in food contact materials and their products.
The SWSRA-DS combined algorithm is proposed with the goal of sharing the near infrared analysis model of the holocellulose content of pulpwood on three different types of spectroscopic instruments. That is, the screening wavelengths based on spectrum ratio analysis (SWSRA) algorithm is used to select the wavelengths with good stability and consistency. These important wavelength variables, which are insensitive to the measured sample parameters, can reduce the differences in sample information response by different instruments or measurement conditions. Then the systematic errors that still existed after the SWSRA method calibration are further calibrated using the Direct Standardization (DS) method on the basis of these wavelengths. This combined algorithm can improve the generalizability of the master model, reduce the spectrum matrix dimension, and make the model transfer more stabilized and simple. The results show that the SWSRA-DS combined algorithm is able to reduce the RMSEP of the master model to predict the holocellulose content of samples measured on the target 1 and target 2 instruments from 2.01% and 9.45% to 0.96% and 1.08%, respectively. The SWSRA-DS algorithm result is compared with the calibration results of SWSRA and DS alone and the commonly used PDS and S/B model transfer algorithms to transfer performance is significantly improved, which provides a new idea for the sharing of NIR analysis models among different types of spectroscopic instruments.
The magnetic solid phase extraction material (MnFe 2 O 4 @TiO 2 ) was prepared by coating TiO 2 on MnFe 2 O 4 through an in-situ formation method. The structure and properties of MnFe 2 O 4 @TiO 2 were characterized by Xray diffractometer (XRD), scanning electron microscope (SEM), nitrogen adsorption -desorption experiment, and vibrating sample magnetometer (VSM). The conditions for magnetic solid phase extraction (MSPE) of quinolone antibiotics were optimized, and an MSPE-HPLC method was established to determine quinolone antibiotics in water samples. The optimal conditions for MSPE are MnFe 2 O 4 @TiO 2 amount of 15 mg, extraction time of 15 min, 5 mL of methanol solution with 20 % ammonia as eluent, and elution time of 1 min. Under the optimal conditions, 50 mL 0.1 mg/L mixed standard solutions of fleroxacin, ofloxacin, norfloxacin, ciprofloxacin, and enrofloxacin have achieved enrichment multiples of 67.8, 72.1, 59.6, 55.8, and 60.7, respectively. The linear range of five antibiotics determined by MSPE-HPLC is 0.004 -1 mg/L with the relative standard deviations (RSDs) of 2.1 % -4.9 % and the limits of detection (LODs) of 0.0006 -0.0020 mg/L. The method is applied to the determination of the five antibiotics in rice paddy water and fish pond water; the recoveries range from 78.9 to 105.8 %, and the RSDs (n = 5) are 3.6 % -8.7 %.
A new compound, 5-methyl-2-phenyl-1,2,3-triazole-5-hydrazid (PT) was designed and synthesized based on "click chemistry". The fluorescence probe 5-methyl-2-phenyl-1,2,3-triazole-5-hydrazid Schiff base (PTSB) was further constructed by a chemical reaction between PT and 4-(diethylamino) salicylaldehyde. PTSB could be used to determine Al3+ in EtOH with high sensitivity and strong anti-interference performance by fluorescence and UV-vis spectroscopic methods. The limit of detection to Al3+ is 5.84 nM and it showed an obvious sol-vatochromic effect under ultraviolet light. Furthermore, the sensing mechanism of PTSB detecting Al3+ was confirmed in the form of planar structure and 1:1 complexation ratio based on MS, Job's plot, 1H NMR titration, DFT calculation, and the single-crystal structure of PTSB, respectively. PTSB showed less low cytotoxicity to HeLa cells and was successfully used for chromatic bioimaging Al3+ in HeLa cells. It is expected to be developed and utilized as a fluorescence probe for detecting Al3+ in vivo.
A novel fluorescent molecule TPE-SA with aggregation-induced emission(AIE)properties was designed and synthesized based on the structure of tetraphenyl ethylene(TPE).The fluorescent molecule had favorable optical performance,a large Stokes shift and high fluorescent efficiency,and is capable of being employed as a fluorescent probe for the selective detection of Cu2+ based on the phenomena that its fluorescence intensity in the solution(VDMSO:VH2O=5:95)decreased after addition of Cu2+.The detection range was 0.05-8 μmol/L,and the limit of detection was 25 nmol/L.The probe can be applied for measuring Cu2+ in lake samples.
