Analysis and residue levels of forchlorfenuron (CPPU) in watermelons

This paper describes the application of liquid chromatography-tandem mass spectrometry (LC/MS-MS) for analysis of residues of forchlorfenuron (CPPU), a new plant growth regulator, in watermelons, after a sample preparation step based on the buffered Quick, Easy, Cheap, Effective, Rugged and Safe extraction method. Analytical determinations were carried out in a triple quadrupole system fitted with an electrospray interphase operating in the positive ionisation mode (ESI+). Three simultaneous MS-MS transitions of the quasi-molecular ion m/z 248 (precursor ion) were monitored for data adquisition (248 > 129, 248 > 155, and 248 > 248), using the transition 248 > 129 for quantitation. Recovery studies on watermelons at levels of 1–200 μ g/kg, performing five replicates at each level and using bracketing single-level calibration with matrix-matched standards for quantitation, gave forchlorfenuron mean recoveries ranging from 82 to 106% with relative standard deviations (RSD) lower than 18%. The limit of determination was established at 1 μ g/kg. The method was applied to evaluate the persistence of forchlorfenuron residues in watermelons grown in plastic greenhouses, after applying an individual spray treatment to the flower ovary at the anthesis stage (45 μ g/flower and 60 μ g/flower for cv “Extazy” and cv “reina de corazones” watermelons, respectively). One month after treatment, 20 “Extazy” watermelon units (1.5–2 kg/unit) and 20 “Reina de corazones” watermelon units (4–5 kg/unit) were collected and analyzed individually. None of the samples contained forchlorfenuron residues higher than 1 μ g/kg.     

Effects of a carbon monoxide-dominant gas mixture on the explosion and flame propagation behaviors of methane in air

This work aimed to experimentally evaluate the effects of a carbon monoxide-dominant gas mixture on the explosion characteristics of methane in air and report the results of an experimental study on explosion pressure measurement in closed vessel deflagration for a carbon monoxide-dominant gas mixture over its entire flammable range. Experiments were performed in a 20-L spherical explosion tank with a quartz glass window 110 mm in diameter using an electric spark (1 J) as the ignition source. All experiments were conducted at room temperature and at ambient pressure, with a relative humidity ranging from 52 to 73%. The peak explosion pressure (P_max), maximum pressure rise rate ((dp/dt)_max), and gas deflagration index (K_G) were observed and analyzed. The flame propagation behavior in the initial stage was recorded using a high-speed camera. The spherical outward flame front was determined on the basis of a canny method, from which the maximum flame propagation speed (S_n) was calculated. The results indicated that the existence of the mixture had a significant effect on the flame propagation of CH₄-air and increased its explosion risk. As the volume fraction of the mixed gas increases, the P_max, (dp/dt)_max, K_G and S_n of the fuel-lean CH₄-air mixture (7% CH₄-air mixture) increase nonlinearly. In contrast, addition of the mixed gas negatively affected the fuel-rich mixture (11% CH₄-air mixture), exhibiting a decreasing trend. Under stoichiometric conditions (9.5% CH₄-air mixture), the mixed gas slightly lowered P_max, (dp/dt)_max, K_G, and S_n. The P_max of CH₄-air mixtures at volume fractions of 7%, 9.5%, and 11% were 5.4, 6.9, and 6.8 bar, respectively. The S_n of CH₄-air mixtures at volume fractions of 7%, 9.5%, and 11% were 1.2 m/s, 2.0 m/s, and 1.8 m/s, respectively. The outcome of the study is comprehensive data that quantify the dependency of explosion severity parameters on the gas concentration. In the storage and transportation of flammable gases, the information is required to quantify the potential severity of an explosion, design vessels able to withstand an explosion and design explosion safety measures for installations handling this gas.     

Dynamic failure probability analysis of urban gas pipeline network

The gas pipeline network is an essential infrastructure for a smart city. It provides a much-needed energy source; however, it poses a significant risk to the community. Effective risk management assists in maintaining the operational safety of the network. The risk management of the network requires reliable dynamic failure probability analysis. This paper proposes a methodology of condition monitoring and dynamic failure probability analysis of urban gas pipeline network. The methodology begins with identifying key design and operational factors responsible for pipeline failure. Subsequently, a causation-based failure model is developed as the Bowtie model. The Bowtie model is transformed into a Bayesian network, which is analyzed using operational data. The key contributory factors of accident causation are monitored. The monitored data is used to analyze the updated failure probability of the network. The gas pipeline network's dynamic failure probability is combined with the potential consequences to assess the risk. The application of the approach is demonstrated in a section of the urban gas pipeline.     

Prediction of distance to maximum intensity of turbulence generated by grid plate obstacles in explosion-induced flows

The interaction of unburnt gas flow induced in an explosion with an obstacle results in the production of turbulence downstream of the obstacle and the acceleration of the flame when it reaches this turbulence. Currently, there are inadequate experimental measurements of these turbulent flows in gas explosions due to transient nature of explosion flows and the connected harsh conditions. Hence, majority of measurements of turbulent properties downstream of obstacles are done using steady-state flows rather than transient flows. Consequently, an empirical based correlation to predict distance to maximum intensity of turbulence downstream of an obstacle in an explosion-induced flow using the available steady state experiments was developed in this study. The correlation would serve as a prerequisite for determining an optimum spacing between obstacles thereby determining worst case gas explosions overpressure and flame speeds. Using a limited experimental work on systematic study of obstacle spacing, the correlation was validated against 13 different test conditions. A ratio of the optimum spacing from the experiment, x_exp to the predicted optimum spacing, x_pred for all the tests was between 2-4. This shows that a factor of three higher than the x_pred would be required to produce optimum obstacle spacing that will lead to maximum explosion severity. In planning the layout of new installations, it is appropriate to identify the relevant worst case obstacle separation in order to avoid it. In assessing the risk to existing installations and taking appropriate mitigation measures it is important to evaluate such risk on the basis of a clear understanding of the effects of separation distance and congestion. It is therefore suggested that the various new correlations obtained from this work be subjected to further rigorous validation from relevant experimental data prior to been applied as design tools.     

受限空间中CO与水蒸汽阻尼瓦斯爆炸的反应动力学模拟研究

为了探求一氧化碳与水蒸汽参与瓦斯爆炸的化学反应动力学过程的阻尼效应,建立了受限空间中瓦斯爆炸反应的数学模型。数值计算结果表明,结果表明在瓦斯爆炸过程中,瓦斯-空气混合气体含有10%的一氧化碳,虽然会延迟瓦斯爆炸时间,抑制瓦斯爆炸,但是H、O自由基浓度、瓦斯爆炸温度和压力比不加入一氧化碳时升高,同时对CO2、NO的生成起促进作用;当混合气体中含有10%的水蒸汽时,H、O自由基浓度降低,瓦斯爆炸温度和压力也随之降低,致灾性气体CO2、NO的生成得到抑制。虽然一氧化碳对瓦斯爆炸有一定的阻尼效应,但是由于一氧化碳对部分致灾性气体的生成有促进作用,因此,在阻尼瓦斯爆炸方面,水蒸汽的效果要好于一氧化碳。     

机场周边大气中非甲烷总烃时空分布特征

为了研究机场周边大气中非甲烷烃的污染情况,于2011年4月21日起连续5天对某机场起降点附近2个采样点以及对照点农田区的大气中NMHCs进行测定.结果表明,NMHCs的含量为飞机开始滑行点（3.22mg/m3）＞降落点（2.92mg/m3）＞农田区（2.91 mg/m3）,均超出以色列的标准（2.0mg/m3）.非甲烷总烃在一天中下午16点达到最小值.飞机的起降对周边大气NMHCs排放有一定的影响.而对照点农田排放可能是当地NMHCs排放的重要来源. 3个采样点中,排放的碳氢化合物以非甲烷烃为主,占总烃的63.4％.NMHCs和总烃的线性关系良好,用统计回归的方法得到了研究区总烃和非甲烷烃的换算公式.     

气相动态顶空法分析水源水中61种挥发性有机物

建立了用于饮用水源水中61种挥发性有机物（VOCs）同时进行分析的气相-动态顶空进样-气相色谱-质谱法（D-HS-GC-MS）,VOCs包括集中式生活饮用水地表水源地特定项目中的31种VOCs。用D-HS-GC-MS法对水样中VOCs进行分析,获得良好的标准曲线线性关系（均大于0.995,溴二氯甲烷除外）,除乙醛、丙烯醛、丙烯腈和环氧氯丙烷的方法检出限分别为15 g/L、13 g/L、11 g/L和11 g/L外,其余VOCs的方法检出限均介于0.10～0.58 g/L,饮用水源水实际样品加标回收率和RSD分别为75.8%～116%和1.16%～21.6%（n=3）。气相-动态顶空进样法相对于常见的吹脱捕集法具有不直接接触样品的优势,避免了仪器被样品污染,用于饮用水源水中几十种VOCs的同时分析,在常规监测中可节省大量的人力物力投入。     

上海城区PM2.5中有机组分及硝基芳香化合物分布特征

硝基芳香化合物（NACs）是细颗粒物中含氮化合物的重要组成部分,研究其在大气中的污染特征和季节变化,有助于表征大气细颗粒物中含氮有机化合物特性,并为城市氮氧化物削减提供科学支撑.采集并分析了上海城区2018年3月～2019年2月大气PM_2.5样品,采用超高效液相色谱-轨道阱质谱（UPLC-Orbitrap MS）在PM_2.5样品中定性检测到了2 439～3 695个有机物,内标法定量了9种NACs,春季ρ（NACs）范围为3.12～16.8 ng·m^-3,平均值为9.31 ng·m^-3;夏季ρ（NACs）范围为1.05～9.70 ng·m^-3,平均值4.16 ng·m^-3;秋季ρ（NACs）范围为2.87～36.27 ng·m^-3,平均值9.84 ng·m^-3,冬季ρ（NACs）范围为4.83～56.23 ng·m^-3,平均值为22.37 ng·m^-3. 9种硝基芳香化...     

火焰原子吸收法测定总铜不确定度的评定

依据线性最小二乘法的数学特性,提出采用火焰原子吸收法测定地表水中总铜的不确定度的简化评定方法,通过识别和分析不确定度源,对不确定度进行量化,计算合成标准不确定度。此方法适用于地下水、地表水和废水中的总铜含量直接法测定中不确定度的快速评定。     

蜂蜜中氯霉素残留的检测及净化方法研究

建立了反相高效液相色谱-离子阱质谱法检测蜂蜜中氯霉素残留的方法.前处理采用改良的QuEChERS方法进行快速提取和净化.采用初级次级胺进行固相分散净化,可有效吸附蜂蜜中的糖类及有机色素等杂质.提取物在流动相甲醇:水(0.2%乙酸胺)=45:55(体积比)中,用整体色谱柱进行快速分离和质谱检测.并对MS检测中2种离子化方式(电喷雾ESI及大气压化学APCI)、各种离子化方式下正负离子模式及离子检测方法(总离子检测TIC和选择性离子监测MRM)进行了综合比较,最终确定采用电喷雾电离法(ESI)负离子模式、多反应离子监测(MRM)对氯霉素进行定性定量分析.在0.2～200μg/kgg添加浓度下,添加回收率水平在78%～93%间,变异系数在3.9%以下.该方法的检出限为0.1μg/kg,在0.1～100 μg/L浓度范围内,线性方程为y=58.753x 34867,相关系数R2=0.999 5.