实时在线单颗粒气溶胶飞行时间质谱仪的研制

针对大气气溶胶单颗粒粒径及成分同时检测的要求,自行研制了一台实时在线单颗粒气溶胶飞行时间质谱仪,并对仪器各部分的原理和结构进行了描述。用实验室产生的标准气溶胶粒子对仪器进行粒径和质量数校正,同时考察激光能量对邻苯二甲酸二辛脂(DOP)气溶胶颗粒的打击效率及其谱图的影响。室内气溶胶颗粒采样证明了该仪器具有较高的同位素测量精度及质量分辨率。     

高分辨率高灵敏度飞行时间质谱仪

本文讨论了提高飞行时间质谱仪的分辨率和灵敏度的基本问题，给出了仪器的结构设计。实验表明，其分辨率Ｒ＞２５００，灵敏度为３０Ａ／Ｐａ。     

高灵敏VOCs在线真空紫外单光子电离飞行时间质谱仪的研制

研制了一种高灵敏度在线膜进样真空紫外电离源飞行时间质谱仪（MI-SPI-TOF MS）用于检测低浓度挥发性有机物（VOCs）。仪器包括真空系统、膜进样接口、真空紫外单光子电离源、垂直加速反射式飞行时间质量分析器和数据采集系统等。该仪器使用聚二甲基硅氧烷（PDMS）膜作为大气压下直接进样的接口,膜的选择透过性能直接、快速地富集大气中VOCs,可实现快速在线进样检测。真空紫外单光子灯作为电离源,能将电离能低于10.6 eV的VOCs电离,形成分子离子峰。结果表明,该仪器的分辨率优于750 FWHM,对苯、甲苯、二甲苯和氯苯的检测限达10^-12 mol/mol级别,检测速度达秒级,可用于低浓度VOCs的实时在线检测。     

高分辨飞行时间质谱仪的原理及设计

讨论了影响飞行时间质谱仪分辨率的因素,包括基质辅助激光解吸离子化所产生的对分辨率的影响因素。参照近代文献资料,提出了自行设计制造的飞行时间质谱仪的基本设计方案,指出这种仪器在我国的应用前景。     

四极杆/飞行时间质谱/质谱仪

本文介绍了一种新型的四极杆/飞行时间质谱/质谱仪技术及其广泛的应用     

飞行时间质谱仪的故障分析及排除

本文归纳总结了飞行时间质谱仪使用过程中，分子泵停止工作、MCP击穿、信号不稳定等经常产生的故障，并分析了产生故障的因素，提出了排除方法。     

瞬短脉冲辉光放电飞行时间质谱仪

本文介绍了本实验室研制的瞬短脉冲辉光放电飞行时间质谱仪。其中，辉光放电离子源具有离子产额高、工作稳定可靠等特点，可用于对金属（合金）样品的直接分析。该仪器为国内首台自制的常压（低真空）等离子体飞行时间质谱仪，亦为国际上首台瞬短脉冲辉光放电质谱仪，为研究瞬短脉冲辉光放电及其应用这一新兴领域打下了基础，仪器的分辨本领优于５００。     

气溶胶飞行时间质谱仪单颗粒质谱偏移问题及其纠正算法

在单颗粒气溶胶质谱分析中,不同颗粒质谱图之间发生质谱偏移,谱峰质量数难以准确测定的现象已经被多次观察到。这种现象的存在使得应用单一的校准参数校准质谱图时,产生质谱峰辨认的不确定性。不同颗粒质谱图之间最大的偏移取决于电离激光光斑的大小。当校准参数不准确时,某质谱峰偏离正确m/z值的大小与该质谱峰的质量数呈线性相关。从理论上证明了这种偏移产生于颗粒物在激光光斑内电离位置的不同。为解决单一校准参数带来的不可避免的误差,提出了一种可编程的算法来自动找出每个颗粒物质谱的最优校准参数,以实现单颗粒质谱图的准确的质量校准。     

提高直线式飞行时间质谱仪分辨率方法的研究

直线式飞行时间质谱仪的缺点之一是质量分辨率较低,造成这种情况的主要原因是离子的初始空间分散和能量分散,以及电场的不均匀性。本文在自制直线式辉光放电飞行时间质谱仪的基础上,探讨了提高分辨率的方法。     

便携式飞行时间质谱仪在汽车尾气在线检测中的应用

汽车尾气中的挥发性有机物（VOCs）是主要的人为排放污染源之一,排放到大气环境中的VOCs具有很高的反应活性,能够参与臭氧的生成,是形成二次有机气溶胶等污染物的重要前体物质。因此,研制开发适用于现场实时、在线检测VOCs的便携式分析仪器,是现代科学仪器发展的重要方向之一。本工作利用苯系物标准气体对自行研制的便携式膜进样真空紫外灯单光子电离飞行时间质谱仪整机进行性能测试,仪器的质量分辨率优于350,质量精度优于1×10^-4,对苯系物的检测限可达μg/m³级,动态范围优于3个数量级,仪器的总质量小于25 kg。将仪器放置户外对汽车尾气进行现场测试,基于该仪器高时间分辨率的特点,初步研究了汽车尾气排放VOCs的变化趋势与发动机工作状态的相关性。该仪器有望应用于环境应急事故、现场长期监测、化工园区生产工艺过程监控以及无组织排放等领域。     

Aerosol laser time-of-flight mass spectrometer for the on-line measurement of secondary organic aerosol in smog chamber

An aerosol laser time of flight mass spectrometer (ALTOFMS) that can be used for real-time measurement of the size and composition of individual aerosol particles has been designed and utilized to provide on-line measurement of secondary organic aerosol (SOA) particles resulted from Cl-initiated oxidation of toluene in smog chamber. Both the size and chemical compositions of individual aerosol particles were obtained in real-time. According to a large number of single aerosol diameters and mass spectra, the size distribution and chemical composition of aerosol were determined statistically. Experimental results indicate that aerosol particles produced from Cl-initiated oxidation of toluene were predominantly in the form of PM 2.5 particles, and nine positive laser desorption/ionization mass spectra peaks: m/z 18, 29, 30, 44, 46, 52, 65, 77, and 94 may come from the fragment ions of the products of the SOA: aromatic aldehydes, aromatic acids, phenolic compounds, and nitrogenated organic compounds. These results were in good agreement with those ones from previous Cl-initiated oxidation of toluene. These were demonstrated that ALTOFMS is a useful tool to reveal the formation and transformation processes of SOA particles in smog chamber.     

The design of single particle laser mass spectrometers

This review explores some of the design choices made with single particle mass spectrometers. Different instruments have used various configurations of inlets, particle sizing techniques, ionization lasers, mass spectrometers, and other components. Systematic bias against non-spherical particles probably exceeds a factor of 2 for all instruments. An ionization laser tradeoff is the relatively poor beam quality and reliability of an excimer laser versus the longer wavelengths and slower response time of an Nd-YAG laser. Single particle instruments can make special demands on the speed and dynamic range of the mass spectrometers. This review explains some of the choices made for instruments that were developed for different types of measurements in the atmosphere. Some practical design notes are also given from the author's experience with each section of the instrument.     

国产过程质谱仪在环氧乙烷/乙二醇催化剂活化及驯化过程中的应用

环氧乙烷/乙二醇工艺通常在银催化剂作用下,乙烯和氧气反应生成环氧乙烷,环氧乙烷水解生成乙二醇。在反应过程中,需要监测反应器中气体组分的浓度,通过调节气体组成浓度比例,使催化剂充分激活。在线质谱仪具有实时在线测量组分多、灵敏度高、稳定性好、动态范围宽等优点。所以质谱仪可以应用在EO/EG催化剂活化过程中,快速分析气体浓度及对反应过程进行闭环控制,确保反应安全和高效。     

Using ultrasonic pulse-echo B-scan signals for estimation of time of flight

Time of flight based methods are extensively used for detecting, locating and sizing faults in ultrasonic non-destructive testing and evaluation. In this paper, we investigate model-based estimation of the ultrasonic time of flight using B-scan signals. The Cramer–Rao bounds on the time of flight estimator for B-scan signals are derived and then compared to the Cramer–Rao bounds on the time of flight estimator for A-scan signals. Through this theoretical analysis, we show that the estimation based on B-scan signals significantly reduces the Cramer–Rao bound on the time of flight estimator. In addition, the resulting theoretical equation allows evaluating the improvement in the accuracy of estimating the time of flight. The theoretical lower bound is then compared to the variance of a maximum likelihood estimator which is obtained using a Monte Carlo simulation. The results show that the maximum likelihood estimator can achieve the lower bound on the variance of the time of flight estimator and hence it is an efficient estimator. This numerical result will complement the theoretical analysis by showing that the Cramer–Rao bound can be reached if a proper estimator is selected.     

Subsample interpolation bias error in time of flight estimation by direct correlation in digital domain

This work presents an investigation of the bias error introduced in time of flight estimation realized by subsample interpolation in digital domain. The time of flight estimation is accomplished based on the evaluation of the peak position of the cross correlation function. In order to cope with the discrete nature of the cross-correlation function, subsample estimation exploits three time domain interpolation techniques: parabolic, cosine, Gaussian and frequency domain interpolation using phase angle. An empirical equation relating the maximum value of the bias error to sampling frequency and signal parameters (center frequency and envelope bandwidth) has been derived. It is found that the maximum value of the bias error is in inverse cubic relation to sampling frequency and in quadratic relation envelope bandwidth for cosine interpolation. The maximum value of the bias error is in inverse cubic relation to sampling frequency and in quadratic relation to center frequency and envelope bandwidth for parabolic interpolation. The coefficients related to the approximation technique are given. Results can be applied for bias errors estimation or correction when fast subsample interpolation is used and application of phase domain interpolation is unacceptable due to processing speed limitations. The equations for minimum required sampling frequency are derived by balancing the interpolation error against Cramer–Rao lower bound.     

Estimating ultrasonic time of flight using envelope and quasi maximum likelihood method for damage detection and assessment

Time of flight (TOF) is widely used to locate and size faults in ultrasonic non-destructive evaluation (NDE). In this paper, we propose a novel model-based method for ultrasonic echo parameter estimation. The ultrasonic signal is assumed to be composed of an unknown number of Gaussian echoes corrupted by white Gaussian noise. Firstly, the Hilbert transform is used to extract the envelope of the signal. It is shown that the parameter estimation of the signal is improved by using the envelope. To estimate the parameters of the envelope of the signal, quasi maximum likelihood method is used. The number of echoes is estimated using consistent Akaike information criterion. Two measures are used to evaluate the performance of the proposed method: (a) probability of detection of backscattered echoes and (b) the error of estimated time of flights. The proposed method is then compared to the cross-correlation method and the maximum likelihood method which uses the original signal. Simulated and experimental signals are used to evaluate the performance of each method. Both experimental and simulated results show that the proposed method can improve the parameter estimation which ultimately enhances the damage detection and assessment.     

Time of flight mass spectrometry applied to the liquid chromatographic analysis of pesticides in water and food

Liquid chromatography coupled to mass spectrometry (LC-MS) is an excellent technique to determine trace levels of polar and thermolabile pesticides and their degradation products in complex matrices. LC-MS can be equipped with several mass analyzers, each of which provides unique features capable to identify, quantify, and resolve ambiguities by selecting appropriate ionization and acquisition parameters. We discuss in this review the use of LC coupled to (quadrupole) time-of-flight mass spectrometry (LC-(Q)ToF-MS) to determine the presence of target and non-target pesticides in water and food. This technique is characterized by operating at a resolving power of 10,000 or more. Therefore, it gives accurate masses for both parent and fragment ions and enables the measurement of the elemental formula of a compound achieving compound identification. In addition, the combination of quadrupole-ToF permits tandem mass spectrometry, provides more structural information, and enhances selectivity. The purpose of this article is to provide an overview on the state of art and applicability of liquid chromatography time-of-flight mass spectrometry (LC-ToF-MS), and liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QToF-MS) for the analysis of pesticides in environmental matrices and food. The performance of such techniques is depicted in terms of accurate mass measurement, fragmentation, and selectivity. The final section is devoted to describing the applicability of LC-(Q)ToF-MS to routine analysis of pesticides in food matrices, indicating those operational conditions and criteria used to screen, quantify, and identify target and "suspected" pesticides and their degradation products in water, fruits, and vegetables. The potential and future trends as well as limitations of LC-(Q)ToF-MS for pesticide monitoring are highlighted.     

高分辨电喷雾离子源三级四极杆-飞行时间质谱仪的研制

报道了实验室研制的电喷雾离子源 ,具有射频四极杆接口的高分辨飞行时间质谱 (ESI- QQQ- TOFMS)仪器。该仪器具有以下特点 :在离子调制区使用三组四极杆 ,有效地减少离子束的空间分散和能量分散 ;采用正负双脉冲推斥和离子垂直引入方式 ;经过优化设计的二级有网反射器 ;新颖的 MCP安装方法。经初步调试 ,该仪器的分辨本领已优于 1 0 ,0 0 0 ,质量测定精度优于 1 0× 1 0 - 6 。该仪器于 2 0 0 2年 6月通过了国家教育部科技成果鉴定 [鉴字 [教 2 0 0 2 ]第 0 0 8号 ],其主要性能指标已经达到了国际先进水平     

飞行时间技术和高清重建对PET/CT图像质量和定量分析的影响

飞行时间(TOF)采集和高清(HD)重建是提高正电子发射断层显像(PET)性能的最新技术。本研究通过阳性球状灶NEMA体型试验研究和临床病例分析,比较TOF+HD、HD、TOF+迭代重建和迭代重建4种方法对PET定量分析和图像质量的影响,以明确这些技术的实际应用价值,指导临床更好地选用相关技术和相应设备。     

基于LabVIEW的三重四极杆质谱仪开发平台的设计与应用

相对于单四极杆,三重四极杆质谱仪具有多种工作模式和更复杂的工作时序。为了适应研发需要,本设计采用虚拟仪器技术,开发了一套用于三重四极杆质谱仪的测控平台。平台硬件由工控机、PXIe板卡和辅助电路组成,软件基于LabVIEW开发环境,以状态机为基本架构。该平台能够对仪器各执行单元进行控制和监测;对离子光学系统、高压及四极杆电源的时间响应特性进行测量,获取建立时间等关键参数;测试各工作模式下不同条件的时序特征,从而对抗串扰等仪器性能进行评价。该平台具有界面友好、易维护、功能可扩展等优点,可以作为三重四极杆质谱仪研制过程中一种有效、方便的工具。