In this study, Mn-substituted siderites with different substitution amounts were prepared and characterized by using XRD (X-ray diffraction), TEM (transmission electron microscope), TG and DTG (thermogravimetry and derivative thermogravimetry) and Raman spectroscopy. The effect of Mn substitution on the crystal structure of siderite and thermal decomposition processes of synthetic siderite was investigated. The substitution of Mn for Fe in the crystal structure of siderite resulted in an increase in a and c dimensions from 4.702 and 15.374 to 4.718 and 15.43 Å as the substitution amount increased from 0 to 7.4%, respectively. The substitution of Mn also decreased the crystallinity of siderite. The thermal decomposition of synthetic siderite took place at approximately 350 °C. However, the substitution of Mn for Fe increased the decomposition temperature and improved the activation energy (Ed) values from 126.3, 155.7, 156.8 to 164.5, 167.6, 170.3 kJ mol−1 when Mn substitution increased from 0 to 7.4 mol%.
A method was developed for the determination of nine volatile N‐nitrosamines in tobacco and smokeless tobacco products. The targets are N‐nitrosodimethylamine, N‐nitrosopyrrolidine, N‐nitrosopiperidine, N‐nitrosomorpholine, N‐nitrosoethylmethylamine, N‐nitrosodiethylamine, N‐nitrosodipropylamine, N‐nitrosobuylmethylmine, and N‐nitrosodibutylamine. The samples were treated by dispersive solid‐phase extraction using 1 g of primary secondary amine and 0.5 g of carbon and then analyzed by gas chromatography with tandem mass spectrometry with an electron impact ion source. The recoveries for the targets ranged from 84 to 118%, with <16% relative standard deviations at three spiking levels of 0.5, 1.25, and 2.5 ng/g. The limits of detection ranged from 0.03 to 0.15 ng/g. With the use of the proposed method, we detected the presence of six nitrosamines in the range of 0.4–30.7 ng/g. The study demonstrated that the method could be used as a rapid, convenient, and high‐throughput method for N‐nitrosamines analysis in tobacco matrix. 相似文献
A rapid and accurate method for the quantification of cis-abienol in oriental tobacco leaves by normal phase liquid chromatography was developed. Freeze-dried tobacco samples were
sonicated in methylene chloride for 10 min. The supernatant was purified using a silica gel solid phase extraction cartridge.
Ten milliliter of the resulting methylene chloride eluate was collected, then separated on a 250 × 4.6 mm, 5 μm particle-size
CN column with n-hexane: ethyl acetate, 100:2 (v/v) at a flow rate of 1 mL min−1. cis-Abienol was detected by UV absorption at 254 nm. The linear range was from 2.14 × 10−4 to 4.28 × 10−2 mg mL−1 and the correlation coefficient was 1.000. The average recovery was 98.7, 105.2 and 103.1% in five replicated sets of tobacco
samples spiked with 0.2856, 0.7140 and 1.904 mg cis-abienol. The relative standard deviations (RSDs) were 1.04, 0.63 and 1.25%, respectively (n = 5). Limit of detection (S/N = 3) was 21.84 μg g−1 and limit of quantification (S/N = 10) was 72.80 μg g−1. The method was found to be suitable for determination of cis-abienol in oriental tobacco leaves. Furthermore, pure cis-abienol used for method validation was obtained by preparative reversed phase high-performance liquid chromatography. Identification
was performed by UV detection, nuclear magnetic resonance and mass spectrometry. 相似文献
Following an initial clean-up step on the AB-8 resin (polystyrene resin, 0.3-1.25 mm: NanKai Chemical Factory, Tianjin, China), high-speed counter-current chromatography (HSCCC) was used to purify an arctiin from an extract of the fruits of the Arctium lappa L. Arctiin is a major lignan compound in the traditional Chinese medicinal herb A. lappa L. The two-phase solvent system used was composed of ethyl acetate-n-butanol-ethanol-water at an optimized volume ratio of 5:0.5:1:5 (v/v/v/v). The upper phase was used as the mobile phase in the head to tail elution mode. A total amount of 159 mg of arctiin at 98% purity was obtained from 350 mg of the crude extract (containing 49% arctiin) with 91% recovery. The preparative isolation and purification of arctiin by HSCCC was completed in 5 h in a separation. Identification of the target compound was performed by LC-electrospray ionization MS and 13C-NMR. The structure of the product was further confirmed by comparison with authentic sample (National Institute of the Control of Pharmaceutical and Biological Products, Beijing, China). 相似文献
The synthesis, characterization and reactivity studies of the NHC-stabilized complex IDipp ⋅ GeH2BH2OTf ( 1 ) (IDipp=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) are reported. Nucleophilic substitution of the triflate (OTf) group in 1 by phosphine or arsine donors provides access to the cationic group 13/14/15 chains [IDipp ⋅ GeH2BH2ERR1R2]+ ( 2 E=P; R, R1=H; R2=tBu; 3 E=P; R=H; R1, R2=Ph; 4 a E=P; R, R1, R2=Ph; 4 b E=As; R, R1, R2=Ph). These novel cationic chains were characterized by X-ray crystallography, NMR spectroscopy and mass spectrometry. Moreover, the formation of the parent complexes [IDipp ⋅ GeH2BH2PH3][OTf] ( 5 ) and [IDipp ⋅ GeH3][OTf] ( 6 ) were achieved by reaction of 1 with PH3. Accompanying DFT computations give insight into the stability of the formed chains with respect to their decomposition. 相似文献