用大气压离子质谱测定高纯氮中的痕量N_2O和NO

本文介绍了用大气压离子质谱 (API -MS)分析气体中痕量组分的方法 ,并用API-MS测定了高纯氮中的痕量组分N2 O和NO ,不确定度分别为 1 5%和1 7%。探讨了API-MS分析条件和影响因素。     

Air-borne laser induced fluorescence system for measuring OH and other trace gases in the parts-per-quadrillion to parts-per-trillion range

Described in detail is a laser induced fluorescence system which has been successfully interfaced with two aircraft sampling platforms (i.e., Sabreliner jet and an L-188C Electra). This system, which has been under development for four years, presently consists of the following major components: (1) a Nd-Yag laser driven oscillator-amplifier dye laser; (2) a sampling manifold with associated fluorescence detection optics; (3) an OH calibration chamber; (4) a laser beam steering assembly; and (5) sampling electronics and data processing hardware. During the last three years, this system has been flown some 50 000 air miles making tropospheric OH radical measurements over the latitude range of 70 degrees N to 57 degrees S. OH concentrations measured during these flights have ranged from 30 parts-per-quadrillion (3.7x10(5) molecules/cm(3)) at altitudes of 6 km to 0.8 parts-per-trillion (2.0x10(7) molecules/cm(3)) at 0.5 km. Computations have been completed which indicate that the existing aircraft system with modest modifications should also be capable of detecting natural tropospheric levels of NO, SO(2), CH(2)O, NO(2), HNO(2), NO(3), H(2)O(2), and CS(2) by using both conventional laser-induced fluorescence methodology and multiphoton techniques.     

Cavity ring-down spectroscopy with an automated control feedback system for investigating nitrate radical surface chemistry reactions

Nitrate radical (NO(3) (●)) surface chemistry of indoor environments has not been well studied due to the difficulty in generating and maintaining NO(3) (●) at low concentrations for long term exposures. This article presents the Surface Chemistry Reactant Air Delivery and Experiment System (SCRADES), a novel feedback controlled system developed to deliver nitrate radicals at specified concentrations (50-500 ppt, ±30 ppt) and flow rates (500-2000 ml min(-1)) to a variety of indoor surfaces to initiate reaction chemistry for periods of up to 72 h. The system uses a cavity ring-down spectrometer (CRDS), with a detection limit of 1.7 ppt, to measure the concentration of NO(3) (●) supplied to a 24 l experiment chamber. Nitrate radicals are introduced via thermal decomposition of N(2)O(5) and diluted with clean dry air until the desired concentration is achieved. Additionally, this article addresses details concerning NO(3) (●) loss through the system, consistency of the NO(3) (●) concentration delivered, and stability of the CRDS cavity over long exposure durations (72 h).     

NOx分析仪转换效率检查方法研究

为了解决氮氧化物(NOx)分析仪二氧化氮转换器转换效率的检查问题,将气体分割器(GDC)应用到转换效率检查中,GDC-703与NOx分析仪组合成多种工作状态,通过NOx分析仪测量出了不同工作状态下的NO浓度,按照算法公式计算出了NO2转换器的转换效率;介绍了NOx分析仪的化学发光法检测原理和NOx转换效率检查的必要性,提出了利用GDC-703对NOx分析仪进行转换效率检查的方法;通过对转换效率检查过程分解和浓度分析,从理论上证明了该效率检查方法的正确性和优点,推导了转换效率的计算公式,指出在NOx效率检查中,GDC-703的实质作用是提供一个外置的臭氧发生器。研究结果表明,该NOx分析仪转换效率检查方法减小了分析仪固有测量误差对计算结果的影响,使检查结果更加准确可靠。     

Preparation and accurate measurement of pure ozone

Preparation of high purity ozone as well as precise and accurate measurement of its pressure are metrological requirements that are difficult to meet due to ozone decomposition occurring in pressure sensors. The most stable and precise transducer heads are heated and, therefore, prone to accelerated ozone decomposition, limiting measurement accuracy and compromising purity. Here, we describe a vacuum system and a method for ozone production, suitable to accurately determine the pressure of pure ozone by avoiding the problem of decomposition. We use an inert gas in a particularly designed buffer volume and can thus achieve high measurement accuracy and negligible degradation of ozone with purities of 99.8% or better. The high degree of purity is ensured by comprehensive compositional analyses of ozone samples. The method may also be applied to other reactive gases.     

Determination of polychlorinated dibenzo-p-dioxins,dibenzofurans, and biphenyls by gas chromatography/mass spectrometry in the negative chemical ionization mode with different reagent gases

Reagent gases that are used in mass spectrometry in the NCI mode for the determination of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs) are discussed. Ion-molecule reactions and respective characteristic ions that form while using reagent gases (CH(4), O(2), i-C(4)H(10), NH(3), H(2), He, Ar, Xe, SF(6)) or gas mixtures (CH(4)/O(2), Ar/CH(4), CH(4)/H(2)O, Ar/O(2), i-C(4)H(10)/CH(2)Cl(2)/O(2)) are reviewed. It is shown that only CH(4), O(2), CH(4)/O(2), and CH(4)/N(2)O are widely used and well studied, even though-in the case of these reagent gases-there are contradictions between the publications of various authors. Such reagent gases as NH(3) and He are not well studied, but further investigations of their use for the determination of organochlorine pollutants could be of interest. The possibilities of more sensitive and selective determination of PCDDs, PCDFs, and PCBs are discussed.     

化学发光法检测1O-12(体积比)臭氧

利用O3与NO的化学发光反应检测气相中O3,积分时间为120秒时,检测分辨率达到2.5×10-12(体积比).采用标准臭氧发生器标定的结果显示,在0～50×10.(体积比)的浓度范围内,化学发光的光子计数值与臭氧浓度之间的线性关系很好.还讨论了低浓度检测过程中臭氧耗损问题.     

Real-time method for NO(2) flow measurements

Measurements of NO(2) flows are made without requiring prior experimental calibration of the flow meter. A tapered, variable area flow meter with a diameter ratio scale is used to make the real-time NO(2) flow measurements. The necessary parameters and calculations used to determine the viscosity and density of the flowing N(2)O(4)2NO(2) gas are presented. The limits of error associated with these parameters and errors associated with controlled flow measurement conditions are considered. Disregarding the scale reading error, which depends on the flow meter utilized, the limits of error are found to yield a measurement error less than 7%.     

NO2和O3氧化柴油机微粒的对比试验研究

柴油机微粒物质（PM）后处理最有效的措施是微粒捕集器（DPF）技术,而DPF技术的关键点在于其再生。为了降低DPF的再生温度,首先采用玻璃纤维无胶滤筒捕集PM,然后在管式反应器内加入氧化性气体氧化PM,并通过试验对比研究了NO2和O3对PM的氧化效果。研究结果表明,NO,氧化PM的起燃温度为250℃,而O3在155cc时开始明显氧化PM,适宜温度为200℃～240oC;提高了臭氧或NO2气体浓度,明显加快了氧化速度;O3可以在低温下快速氧化PM,且不需任何催化剂。     

The differential reactivity of octahydridosilsesquioxane on Si(100)-2x1 and Si(111)-7x7: a comparative experimental study

Scanning tunneling microscopy (STM), in conjunction with X-ray photoemission (XPS) and reflection-absorption infrared (RAIRS) spectroscopy, has been used to investigate the reaction of octahydridosilsesquioxane clusters (H(8)Si(8)O(12)) on the Si(100)-2x1 and Si(111)-7x7 surfaces. The clusters exhibit a markedly different reactivity upon exposure to the two clean silicon surfaces. STM data is presented that, in conjunction with XPS and RAIRS data, provides numerous constraints upon possible geometries for the chemisorbed clusters. The sum of the data is consistent with a dissociative reaction mechanism on Si(100)-2x1, resulting in cluster attachment to the surface via a single vertex. Conversely, data of Si(111)-7x7 subject to a saturation exposure of H(8)Si(8)O(12) is presented that is highly suggestive of cluster decomposition on the surface.     

Quantitative analysis of transient surface reactions on planar catalyst with time-resolved time-of-flight mass spectrometry

A procedure for the quantitative analysis of transient surface catalytic reactions in millisecond time resolution has been studied constructing a specially designed apparatus employing (1) pulsed-gas valves for the injection of reactant molecules onto catalysts and (2) a time-of-flight mass spectrometer (TOF-MS) to detect every reaction product simultaneously. For a better understanding of the catalytic activity and selectivity for products quantitatively, a procedure for measuring an amount of reactant molecules injected onto catalyst surface and calibrating the intensity of mass signal were proposed and implemented. We tested the applicability of this procedure for the quantitative analysis of products of NO+H(2) reaction on Pt-Al(2)O(3) catalysts (a planar catalyst: Pt-Al(2)O(3)Si substrates inserted into a micro-tube-reactor with SiC balls). Although the surface area of the planar catalyst was very small, the mass signal intensities of the reaction products were found to be sufficient for the above procedure. We measured the fragmentation patterns and the inherent sensitivity factors in the TOF-MS using the mixture of the internal standard gas Ar and the N-containing gases. The relative sensitivity factors for NH(3), N(2), NO, and N(2)O and the relative intensities of fragment peaks to the molecular ion peak of H(2)O and N(2)O were estimated. The procedure constructed here has enabled us to analyze the transient consecutive secondary catalytic reactions as well as primary reactions based on the formation rate of product molecules per millisecond instead of the mass signal intensities of the reaction products.     

多参数动态气体校准仪的设计与实现

为产生ppb～ppm级微量浓度的高精准校准气体,设计了MFC-2000多参数动态气体校准仪,采用了具有强大功能模块的嵌入式微处理器MC9S12XDT512,完成了气体校准仪的结构及软硬件设计,提出了将臭氧发生器及光度计嵌入在仪器内部,实现了高精度的各种浓度校准气体的产生。试验结果表明,该仪器运行稳定,可靠性好,可以产生100 ppb～6 ppm级的臭氧、二氧化硫等标准气体,并可将产生的臭氧标气直接与NO零气反应产生特定浓度的NO2标气,为监测仪器的校准提供了更为简便的手段。     

PreCon-IRMS测定土壤游离氨基酸态氮稳定同位素丰度

土壤氮大部分为有机氮,大分子类有机氮-蛋白质转化成可溶性氨基酸态氮是土壤氮循环的关键过程和土壤氮素有效性的主要限制因子,其中氨基酸态氮消耗速率在研究土壤肥力、生物机制等方面有着重要的指示作用.本研究建立了一种蒸馏结合化学转化N2 O产生法的氨基酸态氮稳定同位素丰度测定前处理方法,并结合气体预浓缩装置与稳定同位素质谱仪(...     

稀土强韧化陶瓷刀具材料的研制

研制出一种稀土钇强韧化Al2O3/Ti(C,N)新型陶瓷刀具材料,并对其力学性能和切削性能作了研究,表明稀土钇的适量添加能有效改善Al2O3/Ti(C,N)陶瓷刀具材料的力学性能,其抗变强度和断裂专访性分别达到1010MPa和6.1MPam^1/2。大量的切削实验表明,在切削淬硬45钢时,该刀具材料不仅具有良好的耐磨性能。而且具有较好的抗破损性能,其抗破损性能比相应不含稀土钇的Al2O3/Ti(C,N)陶瓷刀具材料高约20%。     

发射药老化样品中氧化亚氮气相色谱测定方法

研究了用气相色谱电子捕获检测器（GC-ECD）和气相色谱热导池检测器（GC-TCD）测定发射药老化后N2O含量的方法。考察了电子捕获检测器和热导池检测器对N2O含量的不同测量范围和不同固定相以及不同色谱条件对测定的影响。采用GDX-104为固定相的色谱柱和热导池检测器,对不同批次发射药老化后样品中的N2O含量进行了测定。结果表明,N2O的色谱保留时间在1.6min左右,4批老化后发射药样品中的N2O含量分别为376.8、264.7、1036和1812μL/L,RSD分别为4.11%、2.64%、3.87%和0.78%。     

Absolute calibration of 14N(d, α) and 14N(d,p) reactions for surface adsorption studies

The (d, α) and (d, p) reactions on ¹⁴N have been calibrated relative to the ¹⁶O(d, p₁)¹⁷O reaction at deuteron energies of 972 and 1200 keV, using high purity NO and N₂O condensed on a thick Au or Pt substrate at 20 K. Six clearly resolvable nitrogen groups have been calibrated with an overall accuracy of ±3%. With the aid of two primary standards (Ta₂O₅ and Bi-implanted Si), all relative cross-sections have been converted into absolute values. Excellent agreement with earlier measurements of the ¹⁶O(d, p₁) cross-section is obtained; the nitrogen groups, however, all exhibit markedly smaller cross-sections than previously reported.One very weak ¹⁴N group fell under the p₁ peak of the ¹⁶O reactions; hence, the spectrum from a frozen NH₃ target was used to evaluate the necessary background correction to the observed ¹⁶O p₁ yields.     

分光光度法（硫脲还原法）测定矿石及冶金渣中钼含量

M o5＋与硫氰化物作用,生成红色的络合物,颜色深浅与M o5＋含量呈线性正相关,借此进行钼的比色测定。Cu2＋和Fe3＋同时存在,对钼的硫氰化物生成有催化作用。此时,Cu2＋与硫脲生成无色络合物,Fe3＋在Cu2＋的催化下,被硫脲还原为Fe2＋,Fe3＋和Cu2＋对钼的红色络合物无干扰。方法用于矿石和冶金废渣样品分析,测定值的相对标准偏差（n＝6）在0.19％～8.6％之间,回收率在95％～105％之间。实验结果表明该方法具有灵敏度高、定性和定量准确等特点,解决了 Fe3＋和 Cu2＋在分析比色时干扰问题。此方法的原理为2M oO42－＋2CS （NH2）2＋10CNS－＋10H＋＝2[MoO（CNS）5]2 －＋2CS（N2 H3）＋6H2 O     

P1,P4-diadenosine 5'-tetraphosphate induced DNA synthesis in mechanically injured cultured endothelial cells

Rapid re-endothelialization following balloon angioplasty can reduce restenosis by inhibiting smooth muscle cell migration and proliferation. However, formation of a neointima layer following angioplasty can be inhibited due to endothelial cell dysfunction and denudation. In a companion paper, it has been illustrated that mechanical loading causes a decrease in DNA synthesis in bovine aortic endothelial cells (BAECs) thus rendering them dysfunctional. The purpose of this study was to overcome BAEC dysfunction by incubation with pharmacological agents to increase DNA synthesis. Previous studies demonstrated that the adenosine dinucleotides Ap4A and Ap2A induced nitric oxide (NO) production from BAEC while Ap3A, Ap5A and Ap6A did not. This paper demonstrates that Ap4A and Ap2A induce a 1.46- and 1.16-fold increase in DNA synthesis in mechanically stressed BAECs respectively, while Ap3A, Ap5A and Ap6A do not. Additionally, NOC-18, a slow NO release NO donor, significantly increases DNA synthesis in mechanically stressed BAECs without affecting unloaded cells. These results are consistent with NO inducing DNA synthesis in mechanically stressed BAECs.     

TRIPLE Q: a three channel quantum cascade laser absorption spectrometer for fast multiple species concentration measurements

A compact and transportable three channel quantum cascade laser system (TRIPLE Q) based on mid-infrared absorption spectroscopy has been developed for time-resolved plasma diagnostics. The TRIPLE Q spectrometer encompasses three independently controlled quantum cascade lasers (QCLs), which can be used for chemical sensing, particularly for gas phase analysis of plasmas. All three QCLs are operated in the intra-pulse mode with typical pulse lengths of the order of 150 ns. Using a multiplexed detection, a time resolution shorter than 1 μs can be achieved. Hence, the spectrometer is well suited to study kinetic processes of multiple infrared active compounds in reactive plasmas. A special data processing and analysis technique has been established to account for time jitter effects of the infrared emission of the QCLs. The performance of the TRIPLE Q system has been validated in pulsed direct current plasmas containing N(2)O/air and NO(2)/air.     

Qualitative and quantitative flow visualization technique using ozone

We have developed a new flow-visualization technique based on the absorption of ultraviolet light by ozone. Ozone is an excellent tracer, because as a gas it has the same effective physical properties as air. Ozone strongly absorbs the principal line (253.7 nm) of a mercury lamp, varepsilon=310 (atm cm)(-1), where I/Io=exp(-varepsiloncl) such that when an ozone-traced flow passes between a mercury lamp and a fluorescent screen, a sharp, shadow-like image of the ozone tracer is cast on the screen. Quantitative photometry can be carried out by replacing the screen with ultraviolet detectors that yield the path-integrated column density of ozone in the flow. High-speed quantitative point monitoring (10 Hz at 10 ppb O3) is possible with capillary probes and chemiluminescent analysis.