Fourier Transform Ion Cyclotron Resonance Mass Resolution and Dynamic Range Limits Calculated by Computer Modeling of Ion Cloud Motion

Particle-in-Cell (PIC) ion trajectory calculations provide the most realistic simulation of Fourier transform ion cyclotron resonance (FT-ICR) experiments by efficient and accurate calculation of the forces acting on each ion in an ensemble (cloud), including Coulomb interactions (space charge), the electric field of the ICR trap electrodes, image charges on the trap electrodes, the magnetic field, and collisions with neutral gas molecules. It has been shown recently that ion cloud collective behavior is required to generate an FT-ICR signal and that two main phenomena influence mass resolution and dynamic range. The first is formation of an ellipsoidal ion cloud (termed “condensation”) at a critical ion number (density), which facilitates signal generation in an FT-ICR cell of arbitrary geometry because the condensed cloud behaves as a quasi-ion. The second phenomenon is peak coalescence. Ion resonances that are closely spaced in m/z coalesce into one resonance if the ion number (density) exceeds a threshold that depends on magnetic field strength, ion cyclotron radius, ion masses and mass difference, and ion initial spatial distribution. These two phenomena decrease dynamic range by rapid cloud dephasing at small ion density and by cloud coalescence at high ion density. Here, we use PIC simulations to quantitate the dependence of coalescence on each critical parameter. Transitions between independent and coalesced motion were observed in a series of the experiments that systematically varied ion number, magnetic field strength, ion radius, ion m/z, ion m/z difference, and ion initial spatial distribution (the present simulations begin from elliptically-shaped ion clouds with constant ion density distribution). Our simulations show that mass resolution is constant at a given magnetic field strength with increasing ion number until a critical value (N) is reached. N dependence on magnetic field strength, cyclotron radius, ion mass, and difference between ion masses was determined for two ion ensembles of different m/z, equal abundance, and equal cyclotron radius. We find that N and dynamic range depend quadratically on magnetic field strength in the range 1–21 Tesla. Dependences on cyclotron radius and Δm/z are linear. N depends on m/z as (m/z)^–2. Empirical expressions for mass resolution as a function of each of the experimental parameters are presented. Here, we provide the first exposition of the origin and extent of trade-off between FT-ICR MS dynamic range and mass resolution (defined not as line width, but as the separation between the most closely resolved masses).     

傅立叶变换离子回旋共振质谱及其研究进展

本文综述了傅立叶变换离子回旋共振质谱的基本原理及其颇具特色的数据处理方法.以两种典型的离子化方法为代表,介绍了目前主要使用的离子源,并总结了该方法在分析科学,尤其是在大分子分析、气相离子反应动力学研究和复杂体系分析等领域中的广泛应用.     

Charge Reversal Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

We report the first charge reversal experiments performed by tandem-in-time rather than tandem-in-space MS/MS. Precursor odd-electron anions from fullerene C₆₀, and even-electron ions from 2,7-di-tert-butylfluorene-9-carboxylic acid and 3,3′-bicarbazole were converted into positive product ions (^–CR⁺) inside the magnet of a Fourier transform ion cyclotron resonance mass spectrometer. Charge reversal was activated by irradiating precursor ions with high energy electrons or UV photons: the first reported use of those activation methods for charge reversal. We suggest that high energy electrons achieve charge reversal in one step as double electron transfer, whereas UV-activated ^–CR⁺ takes place stepwise through two single electron transfers and formally corresponds to a neutralization-reionization (^–NR⁺) experiment.      

傅里叶变换离子回旋共振质谱仪:过去、现在与未来

对傅里叶变换离子回旋共振高分辨率质谱仪的发展历程、串联质谱解离技术及最新的应用进行了详细描述,并对其发展趋势进行了展望。     

Phase Correction of Fourier Transform Ion Cyclotron Resonance Mass Spectra Using MatLab

FT-ICR mass spectrometry has been limited to magnitude mode for almost 40 years due to the data processing methods used. However, it is well known that phase correction of the data can theoretically produce an absorption-mode spectrum with a mass-resolving power that is as much as twice as high as conventional magnitude mode, and that it also improves the quality of the peak shape. Temporally dispersed frequency sweep excitation followed by a time delay before detection results in a steep quadratic variation in the signal phase with frequency. Viewing this, it is possible to find the correct phase function by performing a quadratic least squares fit, modified by iterating through phase cycles until the correct quadratic function is found. Here, we present a robust manual method to rotate these signals mathematically and generate a “phased” absorption-mode spectrum. The method can, in principle, be automated. Baseline correction is also included to eliminate the accompanying baseline drift. The resulting experimental FT-ICR absorption-mode spectra exhibit a resolving power that is at least 50% higher than that of the magnitude mode.     

傅立叶变换离子回旋共振质谱法分析铝材封闭剂中的成分

该文采用傅立叶变换离子回旋共振质谱(FT-ICR-MS)技术,对一种铝材封闭剂(表面处理剂)中的未知成分进行了分析,发现了萘磺酸钠、醋酸镍、苯甲酸钠等成分。根据FT-ICR-MS测定得到的精确分子离子数据,以及同位素精细结构,推测出未知物离子分子式,再结合电感藕合等离子体质谱(ICP-MS)和气相色谱-质谱(GC-MS)分析,推断出未知成分的结构,确认其为萘磺酸钠等成分。文中还发现质谱图中有2组质量数相差62的簇离子:234.8、296.8、358.9和410.7、472.7、534.7,结合二级质谱分析,推断出这两组离子为醋酸镍与醋酸、苯甲酸加合产生的准分子离子,同时还产生二聚体、三聚体离子,合理地解析了质谱图中所出现的未知离子的归属。该研究对化工产品中未知物剖析及产品创新提供了一种新的思路和方法,并发现了镍金属离子与有机酸结合后在质谱中的离子化规律。     

环糊精对托品烷手性识别的电喷雾傅立叶变换离子回旋共振质谱研究

用电喷雾傅立叶变换离子回旋共振质谱仪分别研究了以α-环糊精、β-环糊精和γ-环糊精作为手性拆分剂对手性托品烷的手性区分效应,实验结果表明β-环糊精具备较α-环糊精和γ-环糊精更强的手性区分能力,β-环糊精和托品烷的二聚体复合物离子的强度随激发能量的变化和托品烷对映体含量值呈现出一定的线性关系.     

21 Tesla Fourier Transform Ion Cyclotron Resonance Mass Spectrometer Greatly Expands Mass Spectrometry Toolbox

We provide the initial performance evaluation of a 21 Tesla Fourier transform ion cyclotron resonance mass spectrometer operating at the Environmental Molecular Sciences Laboratory at the Pacific Northwest National Laboratory. The spectrometer constructed for the 21T system employs a commercial dual linear ion trap mass spectrometer coupled to a FTICR spectrometer designed and built in-house. Performance gains from moving to higher magnetic field strength are exemplified by the measurement of peptide isotopic fine structure, complex natural organic matter mixtures, and large proteins. Accurate determination of isotopic fine structure was demonstrated for doubly charged Substance P with minimal spectral averaging, and 8158 molecular formulas assigned to Suwannee River Fulvic Acid standard with root-mean-square (RMS) error of 10 ppb. We also demonstrated superior performance for intact proteins; namely, broadband isotopic resolution of the entire charge state distribution of apo-transferrin (78 kDa) and facile isotopic resolution of monoclonal antibody under a variety of acquisition parameters (e.g., 6 s time-domains with absorption mode processing yielded resolution of approximately 1 M at m/z?=?2700).

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傅里叶变换离子回旋共振质谱测定复杂表面活性剂组分

利用傅里叶变换离子回旋共振质谱(FT-ICR-MS)，分析了两类复杂的离子型表面活性剂样品。实验结果表明：高分辨FT-ICR-MS，可以简单、快速、准确地获得两类化合物的结构信息，利用其高准确度的质量测定数据，计算出复杂样品中各组分的元素组成，鉴定出具体化合物，显示了FT-ICR-MS在分子结构分析和未知物鉴定中的强大能力。     

傅立叶变换离子回旋共振质谱用于金属加工助剂中的成分分析

金属加工助剂是金属加工生产过程中必不可少的化工产品,其组成复杂,易形成螯合物干扰成分分析。该文利用傅立叶变换离子回旋共振质谱(Fourier transform ion cyclotron resonance mass spectrometry,FT-ICR MS)技术的高分辨性能,结合电感耦合等离子体质谱(ICP-MS)、红外光谱(IR)和核磁共振谱(NMR)对一种含未知成分的金属加工助剂进行成分分析。结果表明,该金属加工助剂中含有柠檬酸钠、乙二胺四乙酸(EDTA)与金属铋螯合物。该方法简便、准确,适用于含有金属螯合物的金属加工助剂成分的快速鉴定。     

傅立叶变换离子回旋共振质谱法测定生物样品中的溶血磷脂酰胆碱

建立了一种快速、同时测定复杂生物样品中4种溶血磷脂酰胆碱(LPCs)的傅立叶变换离子回旋共振质谱(FTICR-MS)分析方法。生物样品以甲醇-氯仿(9∶1,体积比)超声萃取30 min,离心后取上清液过0.22μm滤膜,进行FTICR-MS分析。质谱分析采用250μL微量进样器直接进样,进样流速为120μL/h;电喷雾(ESI)正离子模式检测,扫描质荷比范围为m/z 50～1 000,采用外标法进行定量分析。结果表明,4种LPCs在0.5～100μg/L质量浓度范围内呈良好的线性关系,相关系数(r~2)均不小于0.993 0。4种LPCs的检出限为0.02～0.03μg/L,定量下限为0.07～0.1μg/L。在血液和大鼠肝脏样本中,3个加标水平下4种LPCs的平均回收率为70.8%～95.0%,相对标准偏差(RSD)为1.2%～9.8%。该方法简单快速,灵敏度高,准确性和重复性好,适用于复杂生物样品中LPCs的快速测定。     

Application of Optimal Control Theory to Fourier Transform Ion Cyclotron Resonance

We study the application of Optimal Control Theory to Ion Cyclotron Resonance. We test the validity and the efficiency of this approach for the robust excitation of an ensemble of ions with a wide range of cyclotron frequencies. Optimal analytical solutions are derived in the case without any pulse constraint. A gradient-based numerical optimization algorithm is proposed to take into account limitation in the control intensity. The efficiency of optimal pulses is investigated as a function of control time, maximum amplitude and range of excited frequencies. A comparison with adiabatic and SWIFT pulses is done. On the basis of recent results in Nuclear Magnetic Resonance, this study highlights the potential usefulness of optimal control in Ion Cyclotron Resonance.     

激光解吸电离傅立叶变换离子回旋共振质谱用于食用油的快速分析

利用激光解吸电离傅立叶变换离子回旋共振质谱(Laser desorption ionization,LDI-FTICR-MS)建立了一种快速分析食用油中甘油三酯(TAG)的方法。在激光能量为45%,激光频率100 Hz和辐照次数100shots的条件下,可以获得稳定重复的信号(RSD10%)。通过TAG的一级质谱图和二级碎片信息可以初步区别不同类型的食用油。在置信度为95%条件下,利用主成分分析法和聚类分析法可以有效地将34种食用油归类。此外,利用该方法可直接识别橄榄油中掺杂5%的菜籽油且根据线性公式可初步预测橄榄油中掺杂油品的种类。分析数据表明,LDI-FTICR-MS技术具有快速筛查和识别食用油的潜力。     

类肝素化合物的傅立叶变换离子回旋共振-电喷雾质谱研究

采用负离子模式的电喷雾傅立叶变换离子回旋共振质谱(ESI-FTICR-MS)对3个合成的肝素类化合物DHα、THα和THβ进行了全扫描一级谱和持续非共振辐照碰撞诱导解离(SORI-CID)串联质谱分析。样品浓度10μmol/L,流动泵注射直接进样。化合物中的磺酸胺和磺酸酯结构容易在一般电喷雾条件下发生分解,失去一个或者多个SO3,一级全扫描谱图中得到的谱峰均是带有单电荷或者双电荷的准分子离子峰。在串联质谱中,部分双电荷离子发生解离时,其二级谱图中子离子由单电荷子离子和双电荷子离子共同组成。通过对谱峰的局部放大,利用同位素峰的峰间距,能直接给出子离子的带电荷情况。同时,结合FTICRMS提供的高质量精度质谱数据,能够对所选取母离子的碎裂途径进行确认。离子质荷比测量的平均误差小于3.0×10-6。为结构复杂的类肝素化合物的质谱分析提供了借鉴。     

Studies on Fragmentation of Peptide by Nano-electrospray Ionization Fourier Transform Ion Cyclotron Resonance Multi-stage Tandem Mass Spectrometry

The sequence analysis of peptides was performed by nano-electrospray ionization Fourier transform ion cyclotron resonance tandem mass spectrometry(Nano-ESI-FT-ICR-MSn) and several peptides were chosen as examples. With the aid of the collision induced dissociation(CID), FT-ICR provides not only precise mass/charge ratio, but also structure information of the selected peptides. The fragment ions were identified according to the observed molecular weights and peptide sequence was determined successfully. So Nano-ESI-FT-ICR-MSn is a useful tool for identification of the amino acid sequence of peptides with high confidence. Besides, a pathway for the dehydration of y ions without amino acids containing carboxylic acid under sustained off-resonance irradiation collision-induced dissociation(SORI-CID) condition was proposed.     

Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometric Study on Sodium Azide Cluster Ions

Introduction Mass spectrometry (MS) has been an important technique for studying size-dependent cluster properties with unparalleled sensitivity, specificity, and versatil-ity.1,2 Especially Fourier transform ion cyclotron reso-nance (FT-ICR) MS offers the benefits of ultra-high mass resolving power, superior mass accuracy, and the ability of affording useful structure information with tandem MS. The introduction of electrospray ionization (ESI) as a gentle mode of ion generation for MS…     

Study of Cluster Anions Generated by Laser Ablation of Titanium Oxides: A High Resolution Approach Based on Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Laser ablation of titanium oxides at 355 nm and ion–molecule reactions between [(TiO₂)_x]^–• cluster anions and H₂O or O₂ were investigated by Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) with an external ion source. The detected anions correspond to [(TiO₂)_x(H₂O)_yOH]^– and [(TiO₂)_x(H₂O)_yO₂]^–• oxy-hydroxide species with x = 1 to 25 and y = 1, 2, or 3 and were formed by a two step process: (1) laser ablation, which leads to the formation of [(TiO₂)_x]^–• cluster anions as was previously reported, and (2) ion–molecule reactions during ion storage. Reactions of some [(TiO₂)_x]^–• cluster anions with water and dioxygen conducted in the FTICR cell confirm this assessment. Tandem mass spectrometry experiments were also performed in sustained off-resonance irradiation collision-induced dissociation (SORI-CID) mode. Three fragmentation pathways were observed: (1) elimination of water molecules, (2) O₂ loss for radical anions, and (3) fission of the cluster. Density functional theory (DFT) calculations were performed to explain the experimental data.     

傅立叶变换离子回旋共振质谱法对赤灵芝的化学成分鉴定和指纹图谱研究

建立了基于傅立叶变换离子回旋共振超高分辨质谱(FTICR-MS)的赤灵芝化学成分鉴定和指纹图谱分析方法,并应用于不同产地赤灵芝样品的来源区分。样品采用50%甲醇进行回流提取后,以流动注射的进样方式进行直接质谱分析。以ESI离子源在负离子模式下进行检测,质荷比扫描范围为100～1 000 Da。采用精确分子量测定和碰撞诱导解离实验进行化学成分鉴定,通过与文献进行比对,共鉴定出63种化学成分(1种萜烯醛、3种糖、4种三萜醇、6种有机酸和49种三萜酸类成分)。采用聚类分析和主成分分析(PCA)对所获得的质谱指纹图谱进行统计学分析,在95%的置信区间下,多个批次不同产地的赤灵芝样品得到了较好的来源区分。研究结果表明该方法可实现赤灵芝的直接、快速、高效分析和指纹图谱研究,在中药分析领域有着广阔的应用前景。