加热毛细管作为飞行时间质谱仪真空接口的研究

介绍了一种自制的毛细管真空接口,用于连接电喷雾离子源(electrospray ionization,ESI)与自制高分辨率垂直引入式飞行时间质谱仪,初步研究了该接口对仪器灵敏度的影响.结果表明,毛细管接口在有效提高离子传输效率的同时也提高了质谱仪真空系统的性能.加热毛细管的最优加热温度为125 ℃,仪器最低检测灵敏度为1.6 amol.该文还介绍了该接口与自制大气压基体辅助激光解析离子源(atmospheric pressure ma-trix-assisted laseT desorption/ionization,AP-MALD15)联用的实验结果,仪器与该离子源联用的最低检测灵敏度为25 fmol.     

基于毛细管液滴技术的血液乙型肝炎病毒DNA提取

基于毛细管液滴技术,建立了提取血液中乙型肝炎病毒(HBV)DNA的方法.方法的基本原理是向聚四氟乙烯毛细管中连续引人油相和水相溶液时,由于表面张力作用,可以形成稳定的油包水型液滴.依次引人含有不同试样的液滴,在毛细管中完成进样、DNA结合、洗涤以及洗脱等过程.实验表明,采用蛋白酶K裂解和提高洗脱温度有利于提高DNA回收...     

运动场地游离甲苯-2，4二异氰酸酯的直接电喷雾萃取电离质谱分析

采用塑胶等饰材在运动场地广泛应用,但其内含的游离甲苯-2,4二异氰酸酯可能释放出来导致运动场上空气的严重污染.国际卫生组织严格规定异氰酸酯聚合物中游离单体含量必须控制在0.5%以下.本实验用注射器直接抽取待测场地的空气,采用直接进样电喷雾萃取电离源(EESI)串联质谱进行检测.工作条件为:离子源电压3 kV;质谱仪毛细管电压21 V;毛细管温度175 ℃.本方法无需样品前处理,操作简单,1 s内就能完成单个样品的测定,无干扰,检出限低于0.04%(S/N=100,n=5);测量的精密度(RSD)为1.4%(n=8).结合实验结果,讨论了解温度光照,通风条件、垂直高度等环境因素对空气中甲苯-2,4-二异氰酸酯含量的影响.     

电喷雾多级串联质谱法研究碱金属硝酸盐和亚硝酸盐簇合物离子的裂解行为

在正常毛细管温度(200 ℃)下,利用电喷雾质谱(ESI-MS)研究了NaNO3、KNO3、NaNO2和KNO2形成的新型簇合物离子,采用电喷雾多级串联质谱(ESI-MSn)研究了簇合物离子裂解行为.实验结果表明: NaNO3和KNO3溶液产生的簇合物离子及这些离子的裂解方式相似;NaNO2溶液产生的簇合物离子比NaNO3和KNO3溶液产生的复杂;KNO2溶液产生了含有Na+离子的簇合物离子,通过分析KNO2簇合物离子的裂解行为证明了Na+与NO-2的亲合势大于K+.此外,还研究了离子源金属毛细管温度和溶液浓度对簇合物离子形成的影响.     

多喷嘴电喷雾阵列离子源对离子迁移谱性能的影响

采用多喷嘴电喷雾阵列作为离子迁移谱仪(IMS)的离子源以提高大气压下离子迁移谱的分析性能.12喷嘴的电喷雾阵列离子源内径为46μm,采用环形排列以提高喷雾电场的均匀度,喷嘴之间的距离为0.5 cm以克服喷嘴之间的电场屏蔽效应.测定了不同比例的甲醇作为ESI溶剂在2～ 30 μL/min流速及2.5～7 kV的喷雾电压下西地那非和苏丹红Ⅱ号的响应值及相应的信噪比.实验结果表明,在优化的条件下,多喷嘴电喷雾阵列可有效的提高ESI对溶液中水含量的容忍度,降低离子化噪音.与此同时,多喷嘴电喷雾阵列可使用更高的ESI流速.在相同的条件下,12喷嘴的电喷雾阵列离子源可提高离子化效率平均达3.8倍.     

水中9种微囊藻毒素的质谱分析

通过对离子源、毛细管电压等质谱条件的研究,建立了高效液相色谱-串联质谱分析水中9中微囊藻毒素的方法,并对特征母离子及子离子进行了解析。水样经过过滤,以高效液相色谱-电喷雾离子源正离子多反应模式进行检测。在0~50μg/L范围内9种微囊藻毒素具有良好的线性关系和回收率,相对标准偏差小于10%。方法的检出限(以3倍信噪比计)能够满足WHO及我国地表水体中关于微囊藻毒素控制标准的要求。     

基于纳升电喷雾-便携式离子阱质谱的苯扎氯铵快检方法

采用纳升电喷雾源(Nano-ESI)-便携式离子阱质谱(Portable Ion Trap MS)建立了滴眼液杀菌成分苯扎氯铵(BAC)的快速检测方法。在正离子模式下,将滴眼液样品稀释后注入纳升电喷雾源的毛细管,毛细管出口与离子阱质谱进样口距离为10 mm、喷雾电压为2000 V;毛细管电压,毛细管温度和离子漏斗电压分别设为5 V,30℃和40 V。用3种苯扎氯铵的[M-Cl]+峰作为定性判据;用纯物质配制溶液制作定量分析校准曲线。3种苯扎氯铵校准曲线的线性范围1～500 mg/L,相关性系数(R2 0.99);用11次空白样品测试结果评估方法检出限和定量限为0.1,0.33 mg/L,满足限量判定要求。4种实际样品中3类BAC的定量测定结果同高效液相色谱-质谱法无显著性差异。该方法无需联用色谱,分析时间仅为2 min,可应用于滴眼液等保健品中添加剂苯扎氯铵的快速筛查。     

电喷雾离子源原理与研究进展

电喷雾离子源(ESI)是蛋白质组学研究采用的LC-MS/MS中最常用的接口之一,其作为一种软电离技术,具有可直接测定热不稳定化合物、形成多电荷离子等特征,在蛋白质组学研究中具有独特优势.本文介绍了电喷雾离子源(ESI)的工作原理与研究进展,并对各种新型离子化方法与应用进行了系统评述.     

同轴式电化学电喷雾质谱离子源研究蒽电化学衍生十二胺

提出一种同轴式电化学电喷雾质谱离子源, 用于电化学与质谱分析在线联用. 离子源结构简单, 造价低廉, 容易制作. 离子源内的电化学反应器工作在两电极模式, 利用自制的悬浮在电喷雾高压上的无线电化学工作站控制. 使用二苯基蒽或三乙胺的乙腈溶液作为分析物, 全面测试了离子源的性能, 包括电势控制精度、电化学转化率、响应时间和抗污能力等. 测试溶液添加浓度约10 mmol·L^-1的银盐作为电解质和去极剂, 将溶液电阻降至250 Ω, 提高了在线联用的电势控制精度. 所测二苯基蒽溶液流动时的伏安曲线与常规三电极体系的循环伏安曲线基本一致. 在3.6 μL·min^-1的流速下, 离子源的响应时间不超过5 s, 三乙胺的电化学转化率高达77%. 利用此离子源, 研究了蒽的电化学衍生反应, 衍生试剂为十二胺. 蒽作为一种非极性物质, 不能为常规电喷雾质谱检测. 而利用电化学电喷雾质谱离子源, 蒽首先发生电化学氧化反应, 进而与衍生试剂作用生成各种极性物质, 被电喷雾质谱检测. 依据质谱检测到的主要反应产物的相对分子质量与结构提出了衍生反应的机理, 有助于理解蒽的复杂电化学行为.     

用于蛋白质分析的毛细管等电聚焦-电喷雾质谱接口的改进

蛋白质组学对其分析技术提出了大规模、高通量的要求 [1] .传统的等电聚焦 ( p I) -分子量 ( MW)双向电泳技术 ( 2 D- Gel)尽管在蛋白质组学研究中占有重要地位 ,但其操作繁杂、工作周期长 .Pandey等[1] 将毛细管等电聚焦 ( CIEF)与电喷雾质谱 ( ESIMS)联用 ,使得 p I和 MW两维分离鉴定技术变得简单迅速 .但 CIEF- MS的接口操作需中断高压和将毛细管阴极端插入电喷雾管 ,故引起分析蛋白质的散焦和不重现 .本工作改进了 CIEF- MS接口 ,采用毛细管阴极端和电喷雾针一体化的电喷雾接口 ,无需中断高压 ,实现了 CIEF- MS的在线联…     

A cylindrical capacitor ionization source: droplet generation and controlled charge reduction for mass spectrometry

A cylindrical capacitor ionization source was used in conjunction with corona discharge charge reduction for generation of singly charged ions for mass spectrometric analysis. The source consists of a fused-silica capillary threaded with a platinum wire and placed inside a stainless steel tube. Application of an electric potential to the wire results in the production of a linear stream of charged droplets when an aqueous solution is pumped through the capillary. Subsequent solvent evaporation yields ions, providing a continuous ion source for mass spectrometry. Passage of the ions through a corona discharge charge reduction chamber permits reduction of the charge state to predominantly singly charged species, facilitating analysis of DNA and protein mixtures. The change from production of multiply charged ions to production of singly charged ions is extremely simple, requiring only modulation of the voltage applied to the corona discharge electrode. A simple technique for construction of the ionization source is reported.     

Electrospray mass spectrometry of methanol and water solutions suppression of electric discharge with SF6 gas

An equation by D. P. H. Smith predicts the capillary voltage required for the onset of electrospray (ES). For different solvents the voltage increases with the square root of the surface tension. Water requires a potential that is 1.8 times higher than that for methanol. This is verified experimentally. The higher potential required for water leads to ES in the presence of corona electric discharge. For low total ES plus corona currents, the electrosprayed analyte ion intensity is not adversely affected by the presence of discharge. At high total currents, there is a large decrease of analyte sensitivity. The sensitivity decrease is probably due to adverse space charge effect at high currents. The discharge can be suppressed by adding sulfur hexafluoride to the ambient gas. Both sensitivity and signal stability are improved. However, the sensitivity still remains lower by a factor of ≈ 4 relative to that observed with methanol. This is attributed to lower efficiency of gas-phase ion formation from charged water, relative to methanol, droplets.     

Super-Atmospheric Pressure Electrospray Ion Source: Applied to Aqueous Solution

This is a follow-up paper of our previous report on an ion source, which was operated at an operating pressure higher than the atmospheric pressure. Besides having more working gas for desolvation, the reduction of mean free path of electrons in a higher pressure environment increases the threshold voltage for gaseous breakdown, thus enabling a stable electrospray for the sample solution with high surface tension without the occurrence of electric discharge. In our previous work, the ion source was not coupled directly to the mass spectrometer and significant amount of ions were lost before entering the vacuum of the mass spectrometer. In this paper, we report the new design of our second prototype in which, by using a modified ion transport capillary, the pressurized ESI ion source was coupled directly to the first pumping stage of the mass spectrometer without additional modification on the vacuum pumping system. Demonstrations of the new ion source on the sensitive detection of native proteins from aqueous solution in both positive and negative ion modes are presented.     

Electrode‐assisted desorption electrospray ionization mass spectrometry

A new ion source has been developed for rapid, noncontact analysis of materials at ambient conditions. The method provides desorption of analytes under ambient conditions directly from different surfaces with little or no sample preparation. The new method, termed electrode‐assisted desorption electrospray ionization (EADESI), is on the basis of the ionization of molecules on different surfaces by highly charged droplets produced on a sharp‐edged high voltage tip, and ions produced are introduced into the mass spectrometer through a capillary. The EADESI technique can be applied to various samples including amino acids, peptides, proteins, drugs and human fluids such as urine and blood. EADESI is promising for routine analyses in different fields such as forensic, environmental and material sciences. EADESI interface can be fit to a conventional ion‐trap mass spectrometer. It can be used for various types of samples with a broad mass range. EADESI can also provide real‐time analysis which is very valuable for biomedical applications. Copyright © 2010 John Wiley & Sons, Ltd.     

Solid‐to‐Liquid Charge Transfer for Generating Droplets with Tunable Charge

Charged liquid droplets are typically generated by a high‐voltage power supply. Herein, a previously unreported method is used for charging liquid droplets: by transferring charge from an insulating solid surface charged by contact electrification to the droplets. Charging the solid surface by contact electrification involves bringing it into contact with another solid surface for generating static charge. Subsequently, water droplets that flow across the surface are found to be charged—thus, the charge is readily transferred from solid to liquid. The charge of the droplets can be tuned continuously from positive to negative by varying the way the solid surface is charged. The amount of charge generated is sufficient for manipulating, coalescing, and sorting the water droplets by solid surfaces charged by contact electrification. This method of generating charged droplets is general, simple, inexpensive, and does not need any additional equipment or power supply.     

Investigation on the role of pneumatic aspects in electrospray, desorption electrospray surface ionization and surface activated chemical ionization

This review reports the results of some studies carried out by us on the role of pneumatic aspects in electrospray and desorption electrospray surface ionization, with the aim to propose some relevant aspects of the mechanisms involved in these ionization methods. Electrospray ion sources, with the exception of the nano- electrospray source, operate with the concurrent action of a strong electrical field and a supplementary coaxial gas flow. The electrical field is responsible for electrospraying of the analyte solution but the use of a coaxial gas flow leads to a significant increase of the analyte signal and allows the use of higher solution flows. However, by employing capillary voltages much lower than those necessary to activate the electrospray phenomenon, analyte ions are still observed and this indicates that different mechanisms must be operative for ion production. Under these conditions, ion generation could take place from the neutral pneumatically sprayed droplet by field-induced droplet ionization. Also in the case of desorption electrospray ionization (DESI), and without any voltage on the spraying capillary as well as on the surface of interest, ions of analytes present on the surface become detectable and this shows that desorption/ionization of analytes occurs by neutral droplets impinging the surface. Consequently, the pneumatic effect of the impinging droplets plays a relevant role, and for these reasons the method has been called pneumatic assisted desorption (PAD). Some analogies existing between PAD and surface activated chemical ionization (SACI), based on the insertion of a metallic surface inside an atmospheric pressure chemical ionization source operating without corona discharge, are discussed.     

Delayed coalescence behavior of droplets with completely miscible liquids

Because of capillary forces, sessile droplets usually fuse instantaneously after contact. We find however a delay of the droplet fusion by many seconds if the droplets consist of different but completely miscible liquids. After the initial contact, the main bodies of the droplets remain separated, connected only through a shallow conduit with a flow from the low to the high surface tension liquid. Sporadically, this connecting film can thicken with turbulent or pulsating flows. The droplets will finally fuse when the flow has sufficiently reduced the difference in composition and surface tension. We present calculations which explain this delayed droplet fusion with the compensation of the fusion-promoting capillary pressure by a droplet-separating dynamic pressure caused by the flow between the droplets. Droplets with high contact angles fuse instantaneously. In this case, no separation-stabilizing dynamic pressure can build up because the interdroplet flow becomes turbulent.     

Desorption ionization by charge exchange (DICE) for sample analysis under ambient conditions by mass spectrometry

An ambient pressure ionization technique for mass spectrometric analysis of substances present on solid surfaces was developed. A nebulized spray containing molecular ions of a solvent such as toluene can be generated by passing the solvent through a stainless steel capillary held at a high voltage. When the stream of charged droplets produced in this way is directed onto a solid surface, the analytes present on the surface are desorbed and ionized by a charge exchange process. This technique was shown to desorb and generate positively charged molecular ions from compounds that are not readily ionized by some other ambient methods, under positive-ion generation mode. For example, intense signals representing radical cations of 1,4-hydroquinone, limonene, thymol, and several other compounds were observed when the analytes were deposited on a metal surface and exposed to a toluene spray nebulized from the metal capillary maintained at a potential of about +5 kV. In contrast, when the same samples were exposed to a spray of water/methanol/formic acid under customary DESI-like (positive-ion mode) conditions, no peaks representing the analytes were observed.     

Quasi-continuous infrared matrix-assisted laser desorption electrospray ionization source coupled to a quadrupole time-of-flight mass spectrometer for direct analysis from well plates

High-throughput screening (HTS) is a technique mostly used by pharmaceutical companies to rapidly screen multiple libraries of compounds to find drug hits with biological or pharmaceutical activity. Mass spectrometry (MS) has become a popular option for HTS given that it can simultaneously resolve hundreds to thousands of compounds without additional chemical derivatization. For this application, it is convenient to do direct analysis from well plates. Herein, we present the development of an infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) source coupled directly to an Agilent 6545 for direct analysis from well plates. The source is coupled to a quadrupole time-of-flight (Q-TOF) mass spectrometer to take advantage of the high acquisition rates without sacrificing resolving power as required with Orbitrap or Fourier-transform ion cyclotron resonance (FTICR) instruments. The laser used for this source operates at 100 Hz, firing 1 pulse-per-burst, and delivers around 0.7 mJ per pulse. Continuously firing this laser for an extended duration makes it a quasi-continuous ionization source. Additionally, a metal capillary was constructed to extend the inlet of the mass spectrometer, increase desolvation of electrospray charged droplets, improve ion transmission, and increase sensitivity. Its efficiency was compared with the conventional dielectric glass capillary by measured signal and demonstrated that the metal capillary increased ionization efficiency due to its more uniformly distributed temperature gradient. Finally, we present the functionality of the source by analyzing tune mix directly from well plates. This source is a proof of concept for HTS applications using IR-MALDESI coupled to a different MS platform.     

Relating chromatographic retention and electrophoretic mobility to the ion distribution within electrosprayed droplets

Ions that are observed in a mass spectrum obtained with electrospray mass spectrometry can be assumed to originate preferentially from ions that have a high distribution to the surface of the charged droplets. In this study, a relation between chromatographic retention and electrophoretic mobility to the ion distribution (derived from measured signal intensities in mass spectra and electrospray current) within electrosprayed droplets for a series of tetraalkylammonium ions, ranging from tetramethyl to tetrapentyl, is presented. Chromatographic retention in a reversed-phase system was taken as a measure of the analyte’s surface activity, which was found to have a large influence on the ion distribution within electrosprayed droplets. In addition, different transport mechanisms such as electrophoretic migration and diffusion can influence the surface partitioning coefficient. The viscosity of the solvent system is affected by the methanol content and will influence both diffusion and ion mobility. However, as diffusion and ion mobility are proportional to each other, we have, in this study, chosen to focus on the ion mobility parameter. It was found that the influence of ion mobility relative to surface activity on the droplet surface partitioning of analyte ions decreases with increasing methanol content. This effect is most probably coupled to the decrease in droplet size caused by the decreased surface tension at increasing methanol content. The same observation was made upon increasing the ionic strength of the solvent system, which is also known to give rise to a decreased initial droplet size. The observed effect of ionic strength on the droplet surface partitioning of analyte ions could also be explained by the fact that at higher ionic strength, a larger number of ions are initially closer to the droplet surface and, thus, the contribution of ionic transport from the bulk liquid to the liquid/air surface interface (jet and droplet surface), attributable to migration or diffusion will decrease.