Analysis of nisin A,nisin Z and their degradation products by LCMS/MS

The peptides nisin A and nisin Z belong to type-A lantibiotics applied as preservatives in cheese production. The present study optimised and validated a liquid chromatography–tandem mass spectrometry (LCMS/MS) method for the analysis of nisin A in cheese. Since nisin A was not detectable in nisin-containing commercial cheese samples, an additional LCMS/MS method for the quantification of nisin Z was developed and validated. Quantification was performed by external calibration and standard addition. The latter method provided a non-significantly higher recovery rate for the tested cheese matrix. During the production of processed cheese, nisin A and nisin Z undergo significant degradation. Six degradation products of nisin A or nisin Z, respectively, were detected and assigned to nisin A/Z + H₂O, nisin A/Z^1–32, and nisin A/Z^1–32 + H₂O. In two out of eight commercial processed cheese samples, 1.6, resp. 1.7 mg nisin Z/kg cheese was measured, whereas nisin A was not detectable in any of the samples.     

离子交换树脂在污酸净化中的应用

以烟气制酸排放污酸为研究对象,使用离子交换树脂脱出污酸中重金属。通过试验得出：该材料对重金属的脱出效率达到99.82%。当材料吸附饱和之后进行反冲洗脱附,脱附之后材料再次恢复吸附重金属之功能,从而开辟了一条污酸净化的技术途径。     

Au dissolution during the anodic response of short-chain alkylthiols with polycrystalline Au electrodes

The electrochemical characteristics of polycrystalline Au in LiClO₄ electrolyte solutions containing 3-mercaptopropionic acid (MPA) or meso-2,3-dimercaptosuccinic acid (DMSA) were studied with linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) over a wide range of positive potentials vs. Ag/AgCl. The EIS data exhibited linear capacitive behaviour at 0.0 V with either MPA or DMSA added directly to the electrolyte suggesting the formation of an adsorbed layer of the alkylthiol on the electrode surface. Above this potential, a single well-defined impedance loop appeared for electrolyte solutions containing DMSA or MPA, an observation indicative of a charge transfer reaction that could be related to several processes including oxidative desorption, oxidation of the alkylthiol, or Au oxidation/dissolution. To test for Au dissolution, the electrode was held at 0.8 V vs. Ag/AgCl for 12 h in electrolytes containing MPA or DMSA followed by surface analysis with Atomic Force Microscopy and solution analysis with Atomic Absorption Spectroscopy. When the electrolyte contained MPA, the extended potential holding procedure resulted in significant roughening of the electrode with no detectable quantities of Au in the electrolyte. X-ray photoelectron spectroscopy (XPS) analysis of the Au surface revealed an additional species in the Au 4f_7/2 spectrum indicating the presence of an insoluble electrochemically generated Au(I)–MPA species. When the electrolyte contained DMSA, the Au electrode appeared smoother, 56.6 ± 9.6 ppb of Au was detected in the electrolyte and the XPS analysis displayed a single species in the Au 4f_7/2 spectrum indicative of metallic Au after the potential holding procedure. Both observations with MPA and DMSA support the charge transfer resistance to be at least partially related to the corrosion of Au, but also suggest that an electrochemically generated Au–DMSA species is soluble and of potential industrial relevance.     

Parallel FTIR-ATR and gravimetrical in-situ measurements on sodium alanate powder samples during hydrogen desorption

An experimental set-up has been developed to carry out in-situ measurements on hydrogen storage materials. It has been used to perform FTIR–ATR measurements on sodium alanate samples during hydrogen desorption and, in parallel, to perform gravimetrical measurements on the same sample. The ATR spectra showed the typical broad Al–H vibrational features, changing according to the phase change the material undergoes during the load cycle. It is shown that the absorbance of the material at these bands and the hydrogen content correspond to each other in a reproducible way. This behavior may be used to measure the hydrogen mass released by an alanate hydrogen reservoir by measuring the optical absorbance at defined wavelengths. In this paper the results of these experiments that may give rise to the realization of a level sensor in future hydrogen storage applications are presented.     

软电离质谱法与聚合物分析

本文简要叙述了软电离质谱法在聚合物分析中的应用实例。     

Theoretical analysis of absorption of chlorine in aqueous slurries of calcium hydroxide: Desorption of hypochlorous acid gas

A theory has been developed for the absorption of chlorine in aqueous slurries of calcium hydroxide accompanied by a two-step instantaneous reaction and desorption and simulation is carried out to study the effects of various parameters. The rates of absorption of chlorine and desorption of HOC1 from the aqueous slurry are enhanced when fine particles are present in two diffusion film regions on the liquid side. It is concluded that intensification in the rates of absorption of chlorine and rates of desorption can be realized by using high loading of smaller particle size. An optimum k_L must be used to enhance rates of Cl₂ absorption and HOG desorption in order to permit the formation of two reaction planes in the diffusion film. Rates can be intensified by an order of magnitude by the proper selection of operating conditions.     

Conversion of N2O to N2 on TiO2(1 1 0)

In this study, we examine the interaction of N₂O with TiO₂(1 1 0) in an effort to better understand the conversion of NO_x species to N₂ over TiO₂-based catalysts. The TiO₂(1 1 0) surface was chosen as a model system because this material is commonly used as a support and because oxygen vacancies on this surface are perhaps the best available models for the role of electronic defects in catalysis. Annealing TiO₂(1 1 0) in vacuum at high temperature (above about 800 K) generates oxygen vacancy sites that are associated with reduced surface cations (Ti³⁺ sites) and that are easily quantified using temperature programmed desorption (TPD) of water. Using TPD, X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS), we found that the majority of N₂O molecules adsorbed at 90 K on TiO₂(1 1 0) are weakly held and desorb from the surface at 130 K. However, a small fraction of the N₂O molecules exposed to TiO₂(1 1 0) at 90 K decompose to N₂ via one of two channels, both of which are vacancy-mediated. One channel occurs at 90 K, and results in N₂ ejection from the surface and vacancy oxidation. We propose that this channel involves N₂O molecules bound at vacancies with the O-end of the molecule in the vacancy. The second channel results from an adsorbed state of N₂O that decomposes at 170 K to liberate N₂ in the gas phase and deposit oxygen adatoms at non-defect Ti⁴⁺ sites. The presence of these O adatoms is clearly evident in subsequent water TPD measurements. We propose that this channel involves N₂O molecules that are bound at vacancies with the N-end of the molecule in the vacancy, which permits the O-end of the molecule to interact with an adjacent Ti⁴⁺ site. The partitioning between these two channels is roughly 1:1 for adsorption at 90 K, but neither is observed to occur for moderate N₂O exposures at temperatures above 200 K. EELS data indicate that vacancies readily transfer charge to N₂O at 90 K, and this charge transfer facilitates N₂O decomposition. Based on these results, it appears that the decomposition of N₂O to N₂ requires trapping of the molecule at vacancies and that the lifetime of the N₂O–vacancy interaction may be key to the conversion of N₂O to N₂.     

大气气溶胶质谱研究进展

文中较为详细地介绍了大气气溶胶粒子质谱研究的发展概况，从离线的质谱测量技术到实时在线的测量技术，特别是目前应用较为广泛的激光电离气溶胶飞行时间质谱技术——一种可以同时测量气溶胶粒子的大小和化学成分的方法的原理和应用。     

吸收稳定系统能量分析及优化

通过对吸收稳定系统工艺模拟计算和过程研究分析,指出冷进料流程无论是在总能量消耗方面,还是扩能增效方面均优于2/3热进料的双股进料流程.说明冷进料是较合理的工艺流程.     

Thermal desorption of gases and solvents from graphite and carbon nanotube surfaces

The interaction of 23 gases and solvents with the basal plane of highly oriented pyrolytic graphite (HOPG) and with single-wall carbon nanotube (SWCNT) samples is studied using thermal desorption spectroscopy. Pre-exponential frequency factors used for analysis of desorption traces are obtained from vapor pressure data. Activation energies for desorption at monolayer coverage are determined using the Redhead peak-maximum method. Binding energies of non-polar adsorbates to the HOPG surface are found to scale with the adsorbate polarizability providing clear evidence for the van der Waals character of the interaction. Low coverage desorption temperatures on SWCNT samples are found to be 50-100% higher than on HOPG. Such increase has previously been attributed to physisorption in higher coordinated sites such as grooves on the external SWCNT rope surfaces. Polar adsorbates on the other hand typically desorb at much higher temperatures from SWCNT samples which is here tentatively attributed to stronger interaction with defect sites.