基于FAIMS谱图峰位置的离子迁移率非线性函数解析

离子迁移率的非线性函数反映了物质本身的微观碰撞特性,是FAIMS技术实现离子分离检测的基础.现有的离子迁移率非线性函数求解方法多是近似求解,存在较大误差.该工作提出了一种基于半正弦分离电压和FAIMS谱图峰位置下的严格求解方法,推导出严格的二阶、四阶系数求解方程.利用自制的高场不对称波形离子迁移谱仪分别对乙醇、间二甲苯和正丁醇三种典型的醇和苯类物质进行检测,获取了三种物质的FAIMS谱图,通过谱图峰位置获得了不同分离电压值下的补偿电压,利用最小二乘法求出三种离子非线性函数二阶、四阶系数.拟合后的均方误差表明FAIMS非线性函数严格求解的方法,明显优于现有的求解方法.有助于提高FAIMS检测分辨率,进而有助于建立更加准确的FAIMS图谱,实现FAIMS对检测物质的精准识别.     

痕量挥发性有机物的高场不对称波形离子迁移谱研究

高场不对称波形离子迁移谱(high-field asymmetric waveform ion mobility spectrometry,FAIMS)技术是一种快速、高灵敏的痕量物质检测技术.利用自制的高场不对称波形离子迁移谱仪分别对丙酮、苯和甲苯样品进行了检测,结果表明三种挥发性物质在谱图中的分离效果优于传统离子迁...     

混合载气高场不对称波形离子迁移谱中He‐N2 比例对挥发性有机物混叠峰分离的影响研究

载气混合是提高高场不对称波形离子迁移谱（FAIMS）离子分离能力的一个重要方法，在生物大分子质谱研究领域已得到广泛应用，但缺乏在环境小分子领域的研究。选取挥发性有机物（VOCs）中芳香烃、醇、烷烃、酸、酮类中的五种物质（邻二甲苯、异丁醇、正己烷、乙酸、丙酮）为研究对象，研究了混合气体中He-N₂比例对VOCs中单体-二聚体离子混叠峰峰位置、分离度及总离子通过率的影响。实验结果表明，随着FAIMS载气中He比例的增加，5种VOCs中单体及二聚体离子峰峰位置发生偏移，且单体峰与二聚体峰偏移程度不同，单体峰偏移量先增加后减少，而二聚体峰峰位置偏移量逐渐增加；随着FAIMS载气中He比例的增加，五种VOCs离子混叠峰的分离度逐渐增加并趋于饱和，邻二甲苯、异丁醇、正己烷、乙酸、丙酮5种样品的混叠峰分离度达到饱和时对应He比例分别是：20%，30%，10%，40%和20%；随着FAIMS载气中He比例的增加，邻二甲苯、异丁醇、正己烷、丙酮的离子信号强度无明显变化，乙酸的离子信号强度下降明显。该研究为提高FAIMS对环境小分子的分离能力提供了一种可行的方法。同时，也验证了高电场下布朗定律在小分子离子应用上的有效性。     

Separation of Ions from Volatile Organic Compounds Using High-Field Asymmetric Waveform Ion Mobility Spectrometry-Mass Spectrometer

对高场非对称波形离子迁移谱-质谱联用(FAIMS-MS)进行了分析. FAIMS将离子从气态的挥发性有机化合物中分离出来. 采用真空紫外灯离子源在常压下对样品进行电离，紫外灯发射的光子能量为10.6 eV，波长116.5 nm. 迁移区由两块平行的金属平板电极构成，尺寸为10 mm×8 mm ×0.5 mm. 采用频率1 MHz、电压峰值1.36 kV、占空比30%的高场非对称方波电压，对丙酮、丁酮和两者混合物进行FAIMS-MS实验. 质谱结果表明，离子和中性分子之间存在分子离子反应，同时在丙酮和丁酮的混合物中有质子转移. 调节补偿电压从-30～10 V以0.1 V的步长扫描，实现了在质谱仪之前进行离子分离的功能.     

高场不对称波形离子迁移谱非线性函数系数误差分析

离子迁移率非线性函数系数α2和α4是高场不对称波形离子迁移谱(FAIMS)实现物质识别的基础。现有的α2和α4缺少先验值和误差分析方法,因此有必要建立关于α2和α4求解结果误差的评估标准,进而在此基础上提高α2和α4的求解精度。通过自制FAIMS分别对丙酮、异丙醇和1,2二氯苯三种物质在不同分离电压下的检测实验,获取样本在不同分离电压下的谱图和谱图特征值,运用组合的方法从多组分离电压值和相应补偿电压值的数据中选取指定组数,计算出大量的α2和α4数据。通过对α2和α4的数值分析,探究了α2和α4的分布特点和二者之间的相关性,研究了分离电压取点数量和取点方式对其求解结果误差的影响。在拟合α2和α4数据不同范围的频数后,发现α2和α4符合正态分布,其拟合度均在0.96以上,可以利用α2和α4分布的标准差来评估其求解结果的误差。通过对(α2,α4)散点进行拟合,发现α2和α4之间具有很强的负相关性,三样本的相关度分别为-0.977,-0.968,-0.992。随着分离电压选取点数的增加,其相应的求解结果误差在不断减少。通过不同分离电压取点方式的对比,发现当分离电压取VDmax和0.7 VDmax时求解结果最优。在保证α2和α4求解的准确性的前提下有效降低了检测次数,为FAIMS实现快速现场检测和精确的谱图解析创造了有利的条件。     

基于UV-FAIMS的挥发性氯代苯检测方法

挥发性氯代苯是一类典型的环境有机污染物,离子迁移谱(IMS)是一种大气压下基于离子迁移率的快速现场检测技术。采用自制的真空紫外离子源-高场不对称波形离子迁移谱(UV-FAIMS),对空气中氯苯、对二氯苯、邻二氯苯、间二氯苯进行了检测。获取了不同分离电压条件下的CV-I谱图,并以此得到了四种物质的CV-DV指纹谱图。在指纹谱图支持下,设计了对二氯苯、邻二氯苯、间二氯苯三种同分异构体最优化分离检测参数,结果表明在800和1 000V的分离电压下,通过特征峰的选取,在补偿电压(CV)为20.4V(DV=800V),3.2V(DV=800V)和11.9V(DV=1 000V)处三种物质的混合物可以得到有效的分离识别。研究了流速对谱图峰位置和峰形的影响,得到不同流速下灵敏度和识别精度关系,为优化流量的选取提供了依据。在特征识别前提下考察了DV=450 V条件下,CV=4.3 V的对二氯苯特征峰的UVFAIMS检测限,结果高达0.05mg·m-3。该研究为卤代苯等多同分异构体苯类环境污染物的快速高精度检测提供了一种方法参考。     

Corona Discharge Ion Mobility Spectrometry of Ten Alcohols

利用电晕放电离子源离子迁移谱装置对十种醇类有机物的迁移谱进行了研究. 在质子化的水合氢离子为反应离子和纯净空气为迁移气体的条件下，各种醇类有机物在其离子迁移谱中都获得了不同的产物离子峰. 利用指数稀释法得到各种样品的检测限在几个pmol/L量级. 利用所得到的离子迁移谱，以硬球碰撞为模型，得到了大气压下离子-分子相互作用的多个化学物理参数，包括离子分子碰撞、扩散系数、碰撞速率常数和离子半径.     

一种离子迁移谱谱图重构及特征峰提取算法

离子迁移谱(IMS)是一种常压下快速、高灵敏度的痕量化学物质检测方法,广泛应用于化学战剂、爆炸物和毒品等检测领域。在离子迁移谱定性和定量分析中,采集到的原始谱图除了包含样品自身信息外,还包含了电噪声、背景干扰等噪声,特别是当分析物浓度低时,噪声会严重影响定性和定量分析的准确性。为提高离子迁移谱技术化学物质识别准确率,需要对离子迁移谱谱图信号进行重构。本文提出一种可同时实现离子迁移谱谱图重构和特征峰提取的新方法。通过建立优化目标函数,采用l_1范数作为线性惩罚项,λ为正则化参数用来调节惩罚项在优化过程中的比例。为了求解优化目标函数,首先构造一个由Gaussian分布函数构成的超完备字典来表示离子迁移谱离子特征峰峰形,采用替代函数方法对优化目标函数进行迭代求解,当达到重构谱图与原始谱图均方根误差小于设定的阈值时停止迭代。为了验证提出的方法性能,分别采用仿真数据和甲基磷酸二甲酯(DMMP)样本数据进行验证,其中仿真数据由高斯分布函数字典原子及高斯白噪声组成。与此同时,我们对仿真数据和真实样本数据分别采用小波软阈值、小波硬阈值及S-G平滑滤波算法进行去噪重构。采用均方根误差(RMSE)和信噪比(SNR)作为评价指标,实验结果表明该方法成功实现离子迁移谱谱图重构和特征峰提取,预处理结果比其他三种方法有显著的性能提升,为开展离子迁移谱定性和定量分析研究提供了基础。     

甲基异戊酮的离子迁移谱

在自行研制的离子迁移谱仪器上,制备了反应离子质子化水团蔟离子[H＋（H2O）n],并研究了甲基异戊酮的迁移谱。甲基异戊酮的产物离子峰的个数由浓度决定,当浓度在0.004μg/L时出现一个产物离子峰,当浓度达到0.1μg/L时出现两个产物离子峰,当浓度达到1μg/L时出现一个产物离子峰。甲基异戊酮与反应离子发生反应,生成单体团簇离子和二聚体团簇离子。实验测量了各种离子的约化迁移率。     

非对称离子门控制方法和对离子迁移谱分辨率的改善

为了改进离子门的驱动方式,简化离子门驱动电源设计和提高离子迁移谱分辨率,通过增加一组电阻实现离子门两端的不对称供电,再对低电压端的电压进行控制实现离子门功能。分析了该方式下的两种情况对迁移管内的电场、离子迁移谱的分辨率和信噪比的影响。借助SIMION7.0对离子门两边的电场分布进行了模拟和比较,并应用数值化拉普拉斯方程的方法计算了迁移管轴线的电场数据。实验证明：相比常规迁移谱的离子门浮地驱动电源,这种驱动方法成本低,离子门电源的设计简单,能够明显提高离子迁移谱的分辨率。该方法能够应用于离子迁移谱的测量仪器或实验设备。     

Influence of radial electric field on trajectories of plug potential bounce ion in the tandem mirror

Bouncing ions between the plug potentials play an important role in improvement of the axial confinement in the tandem mirror. We examined the influence of the radial electric field on the trajectories of the ions passed through the anchor cell with nonaxisymmetric magnetic configuration on the assumption that the shape of the magnetic flux tube was shifted from the shape of the equipotential surface of the plasma at the mirror throats of the anchor cells. The discrepancy between the shapes enhanced the radial drift of the bounce ion. Radial potential profile of the core plasma was controlled by adjustment of the radially separated endplate potentials, and it was found that the flattened radial potential profile was effective for the decrease of the radial drift. Presented at 5th Workshop “Role of Electric Fields in Plasma Confinement and Exhaust”, Montreux, Switzerland, June 23–24, 2002.     

A study of time-of-flight spectra of excited krypton molecular ions in an electron gun

Investigation of time-of-flight spectra of excited krypton molecular ions observed under electron-beam bombardment of excitation tube electrodes is continued. Particular attention is focused on a study of the profile of the light signal produced in the dissociation of the molecular ions. An analysis of the light signal profile provides information on the processes involved in the formation and destruction of molecular ions. A model developed for these processes permitted calculation of the light signal profile. A comparison is made with experimental data on the spectral lines of krypton atoms and ions, whose excitation is caused by the destruction of the molecular ions.     

Formation of CO2 gas and OH groups in CR-39 plastics due to gamma-ray and ions irradiation

FT-IR spectral studies have been made for CR-39 detectors irradiated by gamma-rays, protons and carbon ions. An absorption peak for CO₂ appeared and grew with the fluence. The peak height was found to decrease gradually by storing in air. Absorbance of the OH group produced by ion bombardment was observed separately from that of adsorbed water using an FT-IR system on the beam line. The concentration of OH group would govern the rate of penetration of chemical agents along the track.     

Simulation of plasma flow in toroidal solenoid filters

An improved drift approximation model with an added radial electrostatic field has been successfully developed. Our model provides a computationally efficient way of quantitatively describing the plasma motion and predicting the plasma behavior in the toroidal solenoid in a filtered cathodic vacuum arc (FCVA) system. Storer's (1989) experimental results have been successfully simulated by this model. A good quantitative fit is obtained for our simulation results to the measured ion currents versus distance along the torus for various B field strengths, the attenuation length, and the wall current. The model describes the change of plasma density along the torus and provides the value of the electron-ion collision frequency at various conditions. The effect of the magnetic field and radial electric field on the plasma transportation can be assessed by the simulation and various plasma parameters can be determined. It is found that the radial electric field confines the 3-directional drift of the ions and is one of the most important parameters in determining the ion throughput. For any given B field strength and plasma parameters, there is a peak ion output corresponding to an optimal potential difference which can be obtained by the simulation. Over three times more ion output can be achieved when the torus wall is appropriately biased     

DPF中子峰下波形测量数据计算中长电缆滤波影响的研究

建立了一套门控闪烁测量系统（门控ST-PMT系统）, 测量了稠密等离子体聚焦（DPF）波形后沿中子峰下3～4个量级的物理图像, 分别讨论了长电缆对 DPF D-D, D-T中子峰下3～4个量级波形测量的影响, 采用数学方法分析了长电缆作为频率滤波函数在解逆卷积函数中的应用, 解析了电缆带宽对测量结果的影响。The influence of the Fourier Transform on long cable in the measurement of fall time of DPF neutron profile is discussed by mathematical methods. The application of anti convolution function with the Fourier Transform on long cable is analysed. The time interval between the peak time and the time that the height falls 3 orders of magnitude after peak is measured with gated detector array system which consists of PMT(photomultiplier tube) and organic scintillation crystal.     

用同电离态离子的光谱线对测量等离子体离子温度

 利用压电晶体驱动Fabry-perot干涉仪并选择合适的板距,通过测量托卡马克等离子体同电离态杂质离子光谱线对的叠加轮廓分布,给出对应的离子温度。该方法的优点是光谱分辨率高,待测谱线有更广泛的选择范围。     

New figuring model based on surface slope profile for grazing‐incidence reflective optics

Surface slope profile is widely used in the metrology of grazing‐incidence reflective optics instead of surface height profile. Nevertheless, the theoretical and experimental model currently used in deterministic optical figuring processes is based on surface height, not on surface slope. This means that the raw slope profile data from metrology need to be converted to height profile to perform the current height‐based figuring processes. The inevitable measurement noise in the raw slope data will introduce significant cumulative error in the resultant height profiles. As a consequence, this conversion will degrade the determinism of the figuring processes, and will have an impact on the ultimate surface figuring results. To overcome this problem, an innovative figuring model is proposed, which directly uses the raw slope profile data instead of the usual height data as input for the deterministic process. In this paper, first the influence of the measurement noise on the resultant height profile is analyzed, and then a new model is presented; finally a demonstration experiment is carried out using a one‐dimensional ion beam figuring process to demonstrate the validity of our approach.     

Radial Distributions of Dusty Plasma Parameters in a DC Glow Discharge

A non‐stationary non‐local kinetic model for radial distributions of dusty plasma parameters based on the solution of Boltzmann equation for electron energy distribution function is presented. Electrons and ions production in ionizing collisions and their recombination on dust particle surface were taken into account. The drift‐diffusion approximation for ions was used. To obtain the self‐consistent radial distribution of electric potential the Poisson equation was used. It is shown that at high dust particle density the recombination of electrons and ions can exceed their production in ionization collisions in the region of dusty cloud. In this case the non‐monotonous radial distribution of the electric field is formed, the radial electric field becomes reversed and the radial electron and ion fluxes change their direction toward the center of the tube (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Calculations of the Concentrations,of the Radial Distributions,and of the Radial Particle Currents of Excited and of Doubly Charged Ions in Low Pressure Discharges

A system of differential equations describing the radial profiles of the number densities and of the radial drift velocities of the ions and of the electrons in positive columns at low pressure containing several species of ions is derived. Excited ions and doubly charged ions, generated in two-step processes by electron impacts, the inertia of the ions and space charge effects are taken into account. For the excited ions de-excitation processes by electron collisions and by spontaneous emission are regarded. A set of nonlinear equations to determine the population densities and the initial values of the differential equations and corresponding boundary conditions are put up. Numerical solutions are given for discharges in argon under free-fall conditions similiar to argon ion lasers. One notices that without stepwise processes via excited ion levels the concentration of double charged ions remains small. In some cases the radial drift of the ions considerably reduces the population of the metastable ion levels. The radial density profiles of the double charged ions and of long-living excited ions considerably deviate from the squared radial profile of the electron density. In addition, for low degrees of ionization the theory of the free-fall column given by Tonks and Langmuir is extended to plasmas containing two species of ions.