Evaluation of headspace-gas chromatography/mass spectrometry for the analysis of benzene in vitamin C drinks; pitfalls of headspace in benzene detection

Recently, there have been reports regarding the presence of benzene in vitamin C drinks. This is caused by sodium benzoate and ascorbic acid (vitamin C), which can react together to induce benzene formation. While the headspace gas chromatography method is well known for the detection of benzene, there could be pitfalls in the process of benzene extraction. This study was performed to check if benzene could be generated under high-temperature incubation conditions. As a result, the amount of benzene detected by headspace-gas chromatography/mass spectrometry (HSGC/MS) was affected by temperature changes. As the temperature of the sample vial was increased, newly generated benzene from the headspace also increased, causing false-positive determination of benzene. Although 80 degrees C is generally accepted for the temperature of headspace sample vials, lower temperatures, such as 40 degrees C, minimize the false-positive identification of benzene. Considering that this minimization allows benzene to be quantified at around 5 ppb, this lower temperature should definitely be considered since benzene, which is formed in sodium benzoate, can appear in vitamin C drinks under certain circumstances. The proposed analysis method of benzene in vitamin C drinks by HSGC/MS at 40 degrees C is an accurate and universal method for the monitoring of benzene without false-positive identification.     

Effect of intrinsic properties of metals on the adsorption behavior of molecules: benzene adsorption on Pt group metals

Investigation of benzene adsorption on different metal surfaces closer to a practical system appears to be a very important intermediate stage to utilize the conclusion obtained on single-crystal surfaces. In this paper, we studied the electrochemical adsorption behaviors of benzene on roughened Pt group electrodes using surface enhanced Raman spectroscopy (SERS). The effects of potential, surface roughness, and benzene concentration were investigated. Significant difference in surface Raman spectra of benzene on Ru, Rh, Pd, and Pt surfaces were found. On Pt surfaces, the parallel-chemisorbed benzene, the vertical dissociated chemisorbed benzene, and the physisorbed benzene were observed, evidenced by the ring vibration mode appearing at 872, 1012, and 991 cm(-1), respectively. On Pd, only parallel-chemisorbed benzene and physisorbed benzene were found. On Rh and Ru, the SERS signals were mainly from the parallel-chemisorbed benzene, with an extremely weak signal from the physisorbed benzene. The potential dependent study reveals that the parallel-chemisorbed species interacts strongest with the substrate, while the physisorbed species can be easily removed at positive potentials. The models for the adsorbed benzene were given to account for the different types of benzene on these Pt group metals. The difference in the atomization heat of the four metals was used to interpret the different interaction strength of benzene with Pt group metals.     

苯与丙烯在MCM-22型分子筛内吸附行为的Monte Carlo研究

采用巨正则统计系综Monte Carlo模拟方法研究了不同温度、不同吸附方式下纯硅MCM-22型分子筛ITQ-1上苯与丙烯分子的吸附行为. 分子筛内吸附质粒子云分布模拟结果显示, 苯和丙烯主要吸附在超笼和十元环孔道内, 其中丙烯分子几乎充满了孔道内部大部分区域, 在链接超笼之间的十元环窗口也充满了丙烯分子, 而苯分子在超笼内和十元环孔道内的吸附却较为分散、均匀. 丙烯与分子筛之间相互作用能高于苯与分子筛之间的相互作用能, 使苯分子吸附相对丙烯分子更为稳定. 温度变化对分子筛上丙烯吸附远大于对苯吸附的影响, 100 kPa时温度由298 K升高至443 K导致丙烯分子吸附量迅速减少, 而对苯分子却没有显著的影响. ITQ-1分子筛上存在苯和丙烯分子的竞争吸附, 使两者吸附相互作用能最可几分布朝着折中方向移动. 苯与丙烯在分子筛内吸附等温线的模拟结果表明, 在温度较高、压力较低时, 丙烯的吸附量小于苯的吸附量.     

Concurrent sensing of benzene and oxygen by a crystalline salt of tris(5,6-dimethyl-1,10-phenanthroline)ruthenium(II)

The complex [Ru(5,6-Me2Phen)3]tfpb2 has been examined as a solid-state benzene and oxygen sensor. The crystalline solid undergoes a reversible vapochromic shift of the emission lambda max to higher energy in the presence of benzene. Additionally, in the presence of oxygen the solid exhibits linear Stern-Volmer quenching behavior. When simultaneously exposed to benzene vapor and oxygen the crystals uptake benzene which inhibits the diffusion of oxygen in the lattice; very little quenching is observed. However, when benzene is removed from the carrier gas, partial loss of benzene occurs and oxygen diffusion is restored resulting in quenching of the emission. The practicality of this crystalline solid as a benzene sensor was investigated by examination of a lower concentration of benzene vapor (0.76%).     

Polymerization of ionized acetylene clusters into covalent bonded ions: evidence for the formation of benzene radical cation

Since the discovery of acetylene and benzene in protoplanetary nebulae under powerful ultraviolet ionizing radiation, efforts have been made to investigate the polymerization of ionized acetylene. Here we report the efficient formation of benzene ions within gas-phase ionized acetylene clusters (C2H2)n+ with n = 3-60. The results from experiments, which use mass-selected ion mobility techniques, indicate that the (C2H2)3+ ion has unusual stability similar to that of the benzene cation; its primary fragment ions are similar to those reported from the benzene cation, and it has a collision cross section of 47.4 A2 in helium at 300 K, similar to the value of 47.9 A2 reported for the benzene cation. In other words, (C2H2)3+ structurally looks like benzene, it has stability similar to that of benzene, it fragments such as benzene, therefore, it must be benzene!     

Simple evaluation of the adsorption states of benzene molecule on the hydroxyl,H+ and Na+ sites of Y-zeolite surfaces by using UV absorption spectroscopy

Chemical properties of benzene molecules adsorbed on the hydroxyl, H⁺ and Na⁺ sites of Y-zeolite surfaces were investigated by using UV absorption and FT-IR spectroscopies. The analyses on the IR peaks assigned to a C–H out-of-plane vibration mode revealed two different adsorption states of benzene: (1) a benzene molecule located a little distance from the hydroxyl groups of zeolite inner walls, and (2) a benzene molecule positioned a short distance from the H⁺ or Na⁺ sites of zeolite walls. Furthermore, the electronic properties of benzene molecules adsorbed on these Y-zeolites were investigated by UV absorption measurements. The vibrational splitting in UV absorption spectra of benzene provided the information about IR-inactive skeletal vibrations of the benzene ring, such as C–C–C in-plane bending and breathing modes. The benzene molecules strongly interacting with H⁺ or Na⁺ sites of Y-zeolites showed smaller breathing vibration energy as compared to benzene in gas or liquid phases, clearly indicating the stabilization of the benzene ring. In contrast, the benzene molecules weakly interacting with hydroxyl groups of siliceous USY zeolite were barely stabilized.     

Hydrogen-bonding-driven self-assembly nonporous adaptive crystals for the separation of benzene from BTX and cyclohexane

Benzene is a volatile organic compound that can seriously harm human health, while it can serve as a precursor to produce chemicals of more complex structures in chemical industry. Capturing benzene using adsorbents is of great importance for human health, when the separation of hydrocarbons including benzene from crude oil was referred to as one of the “seven chemical separations to change the world”. In this work, we reported the efficient and selective separation of benzene from BTX and cyclohexane by hydrogen bonding self-assembly nonporous adaptive crystals AdaOH for the first time under mild and user-friendly conditions. Separation of benzene and cyclohexane (v/v = 1:1) can be achieved by AdaOH with a purity of benzene up to 96.8%. Separation of BTX (v/v; benzene:toluene:o-xylene:m-xylene:p-xylene= 1:1:1:1:1) can be achieved by AdaOH with a purity of benzene increased from 20% to 82.9%. Our results suggest that separation of benzene using the activated AdaOH as a non-porous adaptive crystal for selectively and efficiently capturing benzene can solve the challenge in separation of benzene from other chemicals such as cyclohexane in chemical industry, and can be helpful for removal of benzene that is released from the vehicles to air. The advantages of commercially availability, easy preparation, high separation efficiency and selectivity for benzene might endow this material with enormous potential for practical uses in areas like petrochemical industry.     

Spectroscopic study of mutual solubilities of water and benzene at high temperatures and pressures

Near-infrared and ultraviolet absorption of water-benzene mixtures has been measured at temperatures and pressures in the ranges of 323-673 K and 50-400 bar, respectively. Concentrations of water and benzene in both the water-rich phase and the benzene-rich phase of the mixtures were obtained from absorption intensities of near-infrared bands of water and benzene and ultraviolet bands of benzene. Mutual solubilities in molar fractions increase remarkably with increasing temperature at pressures in the two-liquid-phase coexistence region, and are consistent with previously reported values. It proves that the solubility of benzene in water is an order of magnitude smaller than that of water in benzene throughout the two-phase region. In addition, it is found that effect of pressure on the solubilities is opposite between water in benzene and benzene in water. These solubility properties are discussed on the basis of a cavity-based solvation model. It is suggested that the asymmetry in the mutual solubility and the opposite direction of the pressure effect are caused by difference in molecular size and difference in thermal compressibility, respectively, between water and benzene.     

CO2气氛苯尖端放电等离子体转化试验研究

本文研究了CO2为气化介质时,等离子体辅助煤气化过程中焦油组分苯发生的非热转化特性,建立了焦油组分苯、CO2单电极尖端放电非平衡态等离子体反应体系。通过煤气分析仪对转化反应的产物进行分析,并采用可见发射光谱技术对等离子体进行诊断。结果表明,在该反应体系中,苯转化生成的气态产物是CO与CO2的混合气,而H元素直接被氧化生成H20。能量密度对于苯转化反应起主导作用。在相同能量密度条件下,降低苯浓度也能够提高苯的转化率,但改变气速增加反应时间并不能提高苯的转化率。此外,通过光谱分析可得苯的非热转化可由CO2直接解离产生的O自由基触发。     

苯与丙烯在β分子筛上吸附行为的蒙特卡罗研究

采用巨正则统计系综蒙特卡罗模拟方法研究了β分子筛上苯与丙烯分子的吸附行为. 由分子筛内吸附质粒子云分布可知, 在100 kPa时, 丙烯在分子筛上的吸附量要远远大于苯的吸附量. 由吸附相互作用能分布来看, 苯与分子筛之间相互作用能比丙烯与分子筛之间的相互作用能更负, 这就使苯分子的吸附相对于丙烯分子稳定. 相对而言, 温度变化对丙烯吸附影响远大于对苯吸附的影响, 如100 kPa时, 温度由298 K升高至443 K导致丙烯分子吸附量明显减少, 由每8个晶胞吸附98个丙烯分子减少到80个; 而对苯分子吸附却没有显著的影响. β分子筛上存在着苯和丙烯的竞争吸附, 并且吸附分子之间存在相互作用使两者与分子筛之间的相互作用能分布改变. 在压力范围1×10－3～5.0 kPa, 不同温度下苯与丙烯在分子筛内吸附等温线的模拟结果表明, 在较高温度、较低压力下丙烯的吸附量要小于苯的吸附量.     

Edge-on bonding of benzene molecules in the second adsorbed layer on Cu(110)

The bilayer of benzene on Cu(110) was studied with temperature-programmed desorption (TPD), time-of-flight electron stimulated desorption ion angular distribution (TOF-ESDIAD), and scanning tunneling microscopy (STM). TPD spectra show that three well-defined adsorption states exist. The alpha layer corresponds to the first layer containing flat-lying benzene molecules. As coverage increases, the beta layer forms on top of the alpha layer, and eventually, a multilayer, gamma, forms. TPD measurements show that the number of benzene molecules in the beta layer is equal to the number of benzene molecules in the alpha layer. ESDIAD measurements establish that the orientation of the benzene molecules in the beta layer is edge-on, with two C-H bonds directed toward the surface. STM images of the beta layer reveal closely spaced edge-on benzene molecules arranged in repeating hexagons, as well as loosely spaced benzene molecules with greater apparent height, which are also edge-on species. Correlation between the different measurements suggests a structural model for the benzene bilayer.     

Computational Study of the Interactions between Benzene and Crystalline Ice Ih: Ground and Excited States

Ground‐state geometries of benzene on crystalline ice cluster model surfaces (I_h) are investigated. It is found that the binding energies of benzene‐bound ice complexes are sensitive to the dangling features of the binding sites. We used time‐dependent DFT to study the UV spectroscopy of benzene, ice clusters, and benzene–ice complexes, by employing the M06‐2X functional. It is observed that the size of the ice cluster and the dangling features have minor effects on the UV spectral characteristics. Benzene‐mediated electronic excitations of water towards longer wavelengths (above 170 nm) are noted in benzene‐bound ice clusters, where the cross‐section of photon absorption by water is negligible, in good agreement with recent experimental results (Thrower et al., J. Vac. Sci. Technol. A, 2008, 26 , 919–924). The intensities of peaks associated with water excitations in benzene–ice complexes are found to be higher than in isolated ice clusters. The π→π* electronic transition of benzene in benzene–ice complexes undergoes a small redshift compared with the isolated benzene molecule, and this holds for all benzene‐bound ice complexes.     

Adsorption of Benzene and Propylene in Zeolite ZSM-5： Grand Canonical Monte Carlo Simulations

The adsorption behavior of benzene and propylene in zeolite ZSM-5 was studied by Grand Canonical Monte Carlo(GCMC) simulations. It could be found that benzene and propylene molecules showed different adsorption behavior in the zeolite cavities. The loadings of propylene were significantly larger than those of benzene at 100 kPa. From the figures of potential energy distribution,the potential energy of benzene/zeolite was more negative than that of propylene/zeolite,so benzene could be adsorbed more stably t...     

Unexpected Si:Al effect on the binary mixtures liquid phase adsorption selectivities in faujasite zeolites

A batch technique was applied to determine the equilibrium adsorption of benzene from its benzene/octane and benzene/octene mixture on NaX (Si:Al 1.20) and NaY (Si:Al 2.79) in liquid phase. Benzene was preferentially adsorbed from both mixtures on NaX and NaY. Regardless whether octane or octene was present in the binary mixture, benzene was adsorbed more selectively on the high-silica NaY compared to NaX, which contained more cations. The presence of cations on the SIII/SIII' site inside the supercages of NaX causes a more difficult hosting of benzene inside the supercages of NaX and especially on the 12-membered ring site. However, at sufficiently high external benzene concentration (>10 mol %), the 12-membered ring site of NaX will be occupied by benzene, leading to a maximum adsorption capacity of five benzenes per supercage on both NaX and NaY. The double bond present inside octene allows the molecules to compete for the adsorption sites with benzene. The competitive effect of octene prevents the fifth benzene molecule to adsorb in the NaX supercage within the investigated concentration range.     

Determination of Aromatics in Mixed Benzene by Capillary Gas Chromatography

A method for determining content of aromatics in mixed benzene by capillary gas chromatography has been developed. The method, using FFAP capillary column with program temperature and split injection mode, has separated at least 130 contents from mixed benzene. 29 kinds of aromatics and some non-aromatics such as paraffin, double-ring dienes are identified by MS. The results show that alkyl benzene, olefinic benzene, indene, naphthalene and its derivatives are the main aromatic content in mixed benzene.     

Determination of benzene in soft drinks and other beverages by isotope dilution headspace gas chromatography/mass spectrometry

An automated, simple, and reproducible method was developed for the determination of benzene in soft drinks, based on isotope dilution headspace gas chromatography/mass spectrometry in the selected-ion monitoring mode. The method was used to assess benzene levels in samples of 124 soft drinks and beverages. Benzene was not detected in 60% of the 124 products. The average benzene levels in 6 products exceeded the Canadian maximum acceptable concentration of 5 microg/L for benzene in drinking water, and 2 of the 6 products had benzene levels above the World Health Organization guideline of 10 microg/L. The highest level of benzene, 23 microg/L, was found in a soft drink product specifically marketed to children.     

The Grand Canonical Monte Carlo Simulations of Benzene and Propylene in ITQ-1 Zeolite

Thealkylationofbenzenewithpropylenetoproducecumene,astartingmaterialfortheproductionofacetoneandphenol,isveryimportantinhydrocarbonprocess.ComparedwithsomemineralacidsincludingAlCl,andothers,zeolitesseemtobemorecleancatalysts,moreoveF,theycaneffectivelyreducetheamountoflessdesiredproductssuchasdiisopropylbenzenes.SeveralzeoIitesincludingH-ZSM-5,USYflandMCM-22havebeentestedforthereactionoftheaIkylationofbenzenewithpropylene,andithasbeenfoundthatP,USYandMCM-22areveryreactiveI.ZeoIiteMC…     

Infrared spectrum of benzene in bromine and carbon tetrachloride solutions

The benzene—bromine complex at room temperature has been re-studied by infrared with bromine in excess of benzene. Solutions of 0.225 M benzene in bromine—carbon tetrachloride mixtures were studied. Under this condition, the spectral changes of measurable benzene absorption bands were observed more clearly than previously. The out-of-plane vibrations of benzene were observed to shift to higher frequencies. The equilibrium constant was found to be 0.11 ? mole^?1. The accord with the equilibrium constant derived from benzene rich systems supports the concept of a specific interaction. A C_6V symmetry is favoured for the geometry of the complex.     

苯对Pt/Ga2O3/WO3/ZrO2 和Pd/Al2O3/ WO3/ZrO2催化剂上正己烷异构化反应的影响

研究了苯对Pt/Ga2O3/WO3/ZrO2 (PtGWZ)和Pd/Al2O3/ WO3/ZrO2(PdAWZ)催化剂上正己烷异构化反应的影响。结果表明,苯可影响PtGWZ和PdAWZ上正己烷异构化反应性能,苯含量越高影响越显著。与PdAWZ相比较,苯对PtGWZ上正己烷异构化反应的影响相对较小;苯对PtGWZ上正己烷异构化反应活性的影响是可逆的,撤除苯后PtGWZ对正己烷异构化的催化性能可完全恢复;苯对PtGWZ上正己烷异构化反应的稳定性没有影响。苯对PdAWZ上正己烷异构化反应活性的影响是不可逆的,PdAWZ用于含苯正己烷异构化反应催化剂会逐渐失活。热失重法积炭分析结果表明,相同条件下,含苯正己烷异构化反应后,PtGWZ上的积炭量较PdAWZ上的积炭量少。分析讨论了苯对PtGWZ和PdAWZ上正己烷异构化反应影响差异性的原因。     

2-叠氮基-1,1-二硝基乙基取代苯衍生物的合成

详细研究了2-叠氮基-1,1-二硝基乙基取代苯衍生物的合成方法。由苯基二硝基甲烷钾盐经羟甲基化，磺酰酯化和叠氮化得到目标化合物：3-硝基-(2-叠氮基-1,1-二硝基乙基)苯(4b)，4-硝基-(2-叠氮基-1,1-二硝基乙基)苯(4c)，m-二(2-叠氮基-1,1-二硝基乙基)苯(10)和p-二(2-叠氮基-1,1-二硝基乙基)苯(15)。