Determination and comparison of agarwood from different origins by comprehensive two‐dimensional gas chromatography–quadrupole time‐of‐flight mass spectrometry

Agarwood, a species of resinous heartwood, is a precious medicinal plant and a type of rare natural spice, which is widely used in medicine, cosmetics, religious activities, and other fields. In this study, agarwood samples from eight different regions across four countries were analyzed by comprehensive two‐dimensional gas chromatography?quadrupole time‐of‐flight mass spectrometry. A total of 232 species were identified (the match factors of these compounds were above 750). The main compounds of agarwood are oxygenated sesquiterpenes and chromones. The compositions of India1 and Malaysia2 were significantly different from those of other samples, which might be attributed to the different production processes of agarwood. For further investigation, factor analysis was conducted for six agarwood samples. The results showed that the data classification possessed a regional characteristic; according to the retention time and relative content, characteristic compositions were determined by factor scores. Finally, the differences of characteristic compositions were simply analyzed, and the reasons were speculated.     

Solid‐phase extraction using chloropropyl functionalized sol–gel hybrid sorbent for simultaneous determination of organophosphorus pesticides in selected fruit samples

A new sol–gel hybrid methyltrimethoxysilane‐chloropropyltriethoxysilane was prepared as sorbent for solid‐phase extraction. The extraction efficiency of the prepared sol–gel hybrid methyltrimethoxysilane‐chloropropyltriethoxysilane was assessed by using three selected organophosphorus pesticides, namely, chlorpyrifos, profenofos, and malathion. Gas chromatography–mass spectrometry was used for detection of organophosphorus pesticides. Several vital parameters were optimized to identify the best extraction conditions. Under the optimum extraction conditions, solid‐phase extraction‐methyltrimethoxysilane‐chloropropyltriethoxysilane method showed good linearity range (0.05‐1 μg/mL) with coefficient of determination more than 0.995. The limits of detection obtained were in the range of 0.01–0.07 μg/mL and limits of quantification ranging from 0.03 to 0.21 μg/mL. The limits of detection obtained for the developed method were 2.3–6.5× lower than the limits of detection of commercial octadecyl silica sorbent. Real samples analysis was carried out by applying the developed method on red apple and purple grape samples. The developed method exhibited good recoveries (88.33–120.7%) with low relative standard deviations ranging from 1.6 to 3.3% compared to commercial octadecyl silica sorbent, which showed acceptable recoveries (70.3–100.2%) and relative standard deviations (6.3–8.8%). The solid‐phase extraction‐methyltrimethoxysilane‐chloropropyltriethoxysilane method is presented as an alternative extraction method for determination of organophosphorus pesticides.     

Effervescent tablet‐assisted demulsified dispersive liquid–liquid microextraction based on solidification of floating organic droplet for determination of methadone in water and biological samples prior to GC‐flame ionization and GC‐MS

A novel effervescent tablet‐assisted demulsified dispersive liquid–liquid microextraction based on the solidification of floating organic droplet was developed to determine methadone prior to gas chromatography with flame ionization detection and gas chromatography with mass spectrometry. In this method, a tablet composed of citric acid, sodium carbonate, and 1‐undecanol was utilized. The resulting effervescent tablet generated carbon dioxide in situ to disperse 1‐undecanol in the sample. Thus, the dispersive and extraction processes were performed in one synchronous step. An aliquot of acetonitrile as the demulsifier solvent was used for the separation of two phases instead of centrifugation. Under optimal conditions, the developed method was linear up to 50 000 µg/L with correlation coefficients higher than 0.99. Moreover, limits of detection and limits of the quantification were in the range of 3‐10  and 7‐30 µg/L in water and biological samples, respectively. Intra‐ and interday precisions (n = 6) of the spiked methadone at a concentration level of 50 µg/L were over ranges of 5.1‐6.8% and 5.7‐7.1%, respectively. The preconcentration factors and recovery values were obtained in the range of 140‐145 and 98.1 to 101.6% in real samples, respectively.     

Exploring multiple‐cumulative trapping solid‐phase microextraction for olive oil aroma profiling

Headspace solid‐phase microextraction is a solvent‐free sample preparation technique that is based on the equilibrium among a three‐phase system, i.e., sample‐headspace‐fiber. A compromise between sensitivity and extraction time is usually needed to optimize the sample throughput, especially when a large number of samples are analyzed, as usually the case in cross‐samples studies. This work explores the capability of multiple‐cumulative trapping solid‐phase microextraction on the characterization of the aroma profiling of olive oils, exploiting the automation capability of a novel headspace autosampler. It was shown that multiple‐cumulative solid‐phase microextraction has the potential to improve the overall sensitivity and burst the level of information for cross‐sample studies by using cumulative shorter extraction times.     

薄膜基荧光传感检测的研究进展

薄膜基荧光传感器是继离子迁移谱之后,业界公认的一种最具发展潜力的微痕量物质探测技术.由于其具有灵敏性、便携性、实时检测、响应速度快、易于制造、不污染待测体系等优点,在食品检测、环境监测、质量控制和生物医学分析等领域引起了广泛的关注和研究.本文主要综述了近年来薄膜基荧光传感在挥发性气体检测、有毒化学品检测、爆炸物检测、溶液相离子检测以及生物监测等领域的研究进展,并提出了薄膜基荧光传感所面临的挑战与未来的发展方向.     

基于光滑粒子流体动力学的滑油泵数值仿真

基于光滑粒子流体动力学方法,构建齿轮泵壳体及内部流体的粒子模型,对内啮合齿轮泵在不同工况下的流量特性进行数值模拟。首先设置了均匀分布的油泵出入口压强,计算得到的流量结果与试验结果吻合,且在中低转速下流量与转速呈线性关系;针对高转速下油泵流量降低的问题,通过适当减小周期模型内部的流体粒子数反映流量降低,获得了与试验值相吻合的连续转速流量的模拟结果;针对影响齿轮泵性能的间隙和空化现象,结合模型特点给出了相应的近似处理方法。通过以上研究,将SPH方法成功地应用于滑油泵问题的分析计算。     

Vacuum-assisted headspace solid phase microextraction: Improved extraction of semivolatiles by non-equilibrium headspace sampling under reduced pressure conditions

A new headspace solid-phase microextraction (HSSPME) procedure carried out under vacuum conditions is proposed here where sample volumes commonly used in HSSPME (9 mL) were introduced into pre-evacuated commercially available large sampling chambers (1000 mL) prior to HSSPME sampling. The proposed procedure ensured reproducible conditions for HSSPME and excluded the possibility of analyte losses. A theoretical model was formulated demonstrating for the first time the pressure dependence of HSSPME sampling procedure under non equilibrium conditions. Although reduced pressure conditions during HSSPME sampling are not expected to increase the amount of analytes extracted at equilibrium, they greatly increase extraction rates compared to HSSPME under atmospheric pressure due to the enhancement of evaporation rates in the presence of an air-evacuated headspace. The effect is larger for semivolatiles whose evaporation rates are controlled by mass transfer resistance in the thin gas film adjacent to the sample/headspace interface. Parameters that affect HSSPME extraction were investigated under both vacuum and atmospheric conditions and the experimental data obtained were used to discuss and verify the theory. The use of an excessively large headspace volume was also considered. The applicability of Vac-HSSPME was assessed using chlorophenols as model compounds yielding linearities better than 0.9915 and detection limits in the low-ppt level. The repeatability was found to vary from 3.1 to 8.6%.     

Synthesis,structure and magnetic properties of ultra-high purity CrO2 prepared under high O2-gas pressure

Ultra-high purity CrO₂ was prepared by decomposing CrO₃ in O₂ with gas pressures up to 40 MPa, which were maintained throughout the decomposition process of CrO₃ to prevent the formation of any other phases of chromium oxides. Our method is different from the traditional methods that start from or under ambient pressures. The high oxygen pressure makes the meta-stable CrO₂ stable from the initial stage of preparation. As a result, the purity of the as-prepared CrO₂ is improved, and this has been further proved by the highest magnetization of the samples. The as-prepared CrO₂ particles show very large grains with flat surfaces, octagonal cross-section, and straight edges, owing to the high mobility of Cr ions in CrO₂ at temperatures above its melting point. The lattice parameters of CrO₂ are a = 4.4176 Å and c = 2.9144 Å. The maximum value of the magnetic entropy change of the high purity CrO₂ particles is ∼2.83 J/kg·K for an applied field of 1.5 T. The preparation of pure CrO₂ is important for studying its intrinsic properties and for applications in spintronic devices.     

Pt coated Cr2O3 thin films for resistive gas sensors

The resistive response of atomic layer deposited thin epitaxial α-Cr₂O₃(0 0 1) films, to H₂ and CO in air, was studied. The films were covered with Pt nanoislands formed by electron-beam evaporation of a sub-monolayer amount of the material. The gas measurements were performed at 250°C and 450°C. These temperatures led to different proportion of chemical states, Pt²⁺ and Pt⁴⁺, to which the Pt oxidized. The modification was ascertained by the X-ray photoelectron spectroscopy method. As a result of the modification, the response was fast at 250°C, but slowed at 450°C. A disadvantageous abundance of Pt⁴⁺ arising at 450°C in air could be diminished by high-vacuum annealing thus restoring the response properties of the system at 250°C.