High resolution time-of-flight mass analysis of the entire range of intact singly-charged proteins

The proof of principle for high-resolution analysis of intact singly charged proteins of any size is presented. Singly charged protein ions were produced by electrospray ionization followed by surface-induced charge reduction at atmospheric pressure. The inlet and trapping system "stops" the forward momentum of the protein ions over a very broad range to be captured by the digitally produced electric fields of a large radius linear ion trap whereupon they are moved into a smaller radius linear ion trap and collected and concentrated in front of its exit end-cap electrode using digital waveform manipulation. The protein ions are then ejected on demand from the end of the small radius linear quadrupole in a tightly collimated ion beam with an instrumentally defined kinetic energy into the acceleration region of an orthogonal acceleration reflectron time-of-flight mass analyzer where their flight times were measured and detected with a Photonis BiPolar TOF detector. We present results that clearly prove that massive singly charged ions can yield high-resolution mass spectra with very low chemical noise and without loss of sensitivity with increasing mass across the entire spectrum. Analysis of noncovalently bound protein complexes was demonstrated with streptavidin-Cy5 bound with a biotinylated peptide mimic. Our results suggest proteins across the entire range can be directly quantified using our mass analysis technique. We present evidence that solvent molecules noncovalently adduct onto the proteins while yielding consistent flight time distributions. Finally, we provide a look into future that will result from the ability to rapidly measure and quantify protein distributions.     

Postacquisition mass resolution improvement in time-of-flight secondary ion mass spectrometry

Good mass resolution can be difficult to achieve in time-of-flight secondary ion mass spectrometry (TOF-SIMS) when the analysis area is large or when the surface being analyzed is rough. In most cases, a significant improvement in mass resolution can be achieved by postacquisition processing of raw data. Methods are presented in which spectra are extracted from smaller regions within the original analysis area, recalibrated, and selectively summed to produce spectra with higher mass resolution than the original. No hardware modifications or specialized instrument tuning are required. The methods can be extended to convert the original raw file into a new raw file containing high mass resolution data. To our knowledge, this is the first report of conversion of a low mass resolution raw file into a high mass resolution raw file using only the data contained within the low mass resolution raw file. These methods are applicable to any material but are expected to be particularly useful in analysis of difficult samples such as fibers, powders, and freeze-dried biological specimens.     

A small analytical quadrupole mass spectrometer designed for operation in high and ultra high vacuum systems

The characteristics of a small quadrupole mass spectrometer are described in detail. These show that the requirements of an analytical instrument for use in high and ultra high vacuum systems have been met. The performance is adequate for the measurement of partial pressures down to and below 10^?11 torr. This is achieved with constant sensitivity over the range 0–200 amu with a resolution adequate to separate completely individual peaks up to 50 amu. The instrument does not have an electron multiplier. The consequent disadvantages of a relatively slow response and a limitation to the minimum detectable pressure are compensated by a higher stability and a smaller, simpler, and reliable instrument. Observations with a number of units over a period of many months indicate a maximum change in sensitivity of any one and a difference between individual instruments to be of the order of ±20%. This is therefore a gauge head of approximately the same size as a modulated BA gauge with the same sensitivity, stability and baking characteristics.     

基于统计特征的水下目标一维距离像识别方法研究

目标探测与识别是水下预警监视、信息对抗的重要组成部分。针对水下目标一维距离像识别问题,通过提取目标的长度、重心、高阶中心矩等特征,分析了所提取特征的统计分布特性,利用假设检验构建了目标识别特征的统计模型。结合Bayes统计分类器开展了5类水下目标的识别实验,并与基于距离像回波匹配相关的识别方法进行对比分析,对比结果显示所提出的方法在识别率和运算量方面均有明显改善。     

Interpretation of mass spectra from organic compounds in aerosol time-of-flight mass spectrometry

Organic compounds containing a variety of functional groups have been analyzed using aerosol time-of-flight mass spectrometry. Both positive and negative laser desorption/ionization mass spectra have been acquired for compounds of relevance to ambient air particulate matter, including polycyclic aromatic hydrocarbons, heterocyclic analogues, aromatic oxygenated compounds such as phenols and acids, aliphatic dicarboxylic acids, and reduced nitrogen species such as amines. In many cases, positive ion mass spectra are similar to those found in libraries for 70-eV electron impact mass spectrometry. However, formation of even-electron molecular ions due to adduct formation also plays a major role in ion formation. Negative ion mass spectra suggest that organic compounds largely disintegrate into carbon cluster fragments (C(n)- and C(n)H-). However, information about the heteroatoms present in organic molecules, especially nitrogen and oxygen, is carried dominantly by negative ion spectra, emphasizing the importance of simultaneous analysis of positive and negative ions in atmospheric samples.     

Estimating the precision of exact mass measurements on an orthogonal time-of-flight mass spectrometer

The combination of orthogonal TOF/ESI MS exact mass measurement and on-line chromatography represents a powerful analytical tool for identifying unknown components in complex mixtures and is being widely utilized. The precision of these mass data is often incorrectly estimated as the precision or mean deviation obtained for reference standards under standard conditions. But, the precision of a mass measurement is dependent on the number of ions sampled in the measurement and, thus, is likely to be different for every measurement. A simple procedure for correctly estimating the precision of a specific mass measurement is presented, the limits of the procedure are investigated, and the utility and validity of the procedure are demonstrated.     

Method of calculating the image resolution of a near-infrared time-of-flight tissue-imaging system

A new method for calculating the image resolution for a near-infrared time-of-flight tissue-imaging system is presented. The image resolution is calculated from the full width at half-maximum of the photon-path function along the midplane of the medium, integrated over all times of flight, and weighted by the time-resolved detector response. Detailed treatment of the optical gating mechanism shows that for some types of gating mechanism, there exists an optimal gating time beyond which the image resolution is not improved by arbitrarily decreasing the gating time. This theory predicts a limiting image resolution of~20% of the medium thickness, which is consistent with the research of others.     

Extending the laserspray ionization concept to produce highly charged ions at high vacuum on a time-of-flight mass analyzer

A new matrix compound, 2-nitrophloroglucinol, is reported which not only produces highly charged ions similar to electrospray ionization (ESI) under atmospheric pressure (AP) and intermediate pressure (IP) laserspray ionization (LSI) conditions but also the most highly charged ions so far observed for small proteins in mass spectrometry (MS) under high vacuum (HV) conditions. This new matrix extends the compounds that can successfully be employed as matrixes with LSI, as demonstrated on an LTQ Velos (Thermo) at AP, a matrix-assisted laser desorption/ionization (MALDI)-ion mobility spectrometry (IMS) time-of-flight (TOF) SYNAPT G2 (Waters) at IP, and MALDI-TOF Ultraflex, UltrafleXtreme, and Autoflex Speed (Bruker) mass spectrometers at HV. Measurements show that stable multiple charged molecular ions of proteins are formed under all pressure conditions indicating softer ionization than MALDI, which suffers a high degree of metastable fragmentation when multiply charged ions are produced. An important analytical advantage of this new LSI matrix are the potential for high sensitivity equivalent or better than AP-LSI and vacuum MALDI and the potential for enhanced mass selected fragmentation of the abundant highly charged protein ions. A second new LSI matrix, 4,6-dinitropyrogallol, produces abundant multiply charged ions at AP but not under HV conditions. The differences in these similar compounds ability to produce multiply charged ions under HV conditions is believed to be related to their relative ability to evaporate from charged matrix/analyte clusters.     

飞行时间质谱——光离子成像技术的设计

简述了飞行时问质谱——光离子成像技术的原理和设计。详细介绍了国内相关设备的技术特点和系统结构。     

Fe isotope variations in natural materials measured using high mass resolution multiple collector ICPMS

We present the first measurements of Fe isotope variations in chemically purified natural samples using high mass resolution multiple-collector inductively coupled plasma source mass spectrometry (MC-ICPMS). High mass resolution allows polyatomic interferences at Fe masses to be resolved (especially, (40)Ar(14)N(+), (40)Ar(16)O(+), and (40)Ar(16)OH(+)). Simultaneous detection of Fe isotope ion beams using multiple Faraday collectors facilitates high-precision isotope ratio measurements. Fe in basalt and paleosol samples was extracted and purified using a simple, single-stage anion chemistry procedure. A Cu "element spike" was used as an internal standard to correct for variations in mass bias. Using this procedure, we obtained data with an external precision of 0.03-0.11 per thousand and 0.04-0.15 per thousand for delta(56/54)Fe and delta(57/54)Fe, respectively (2sigma). Use of Cu was necessary for such reproducibility, presumably because of subtle effects of residual sample matrix on mass bias. These findings demonstrate the utility of high-resolution MC-ICPMS for high-precision Fe isotope analysis in geologic and other natural materials. They also highlight the importance of internal monitoring of mass bias, particularly when using routine methods for Fe extraction and purification.     

Pulsed oscillating mass spectrometer: a miniaturized type of time-of-flight mass spectrometer

We report the development, characterization, and performance of a new type of time-of-flight mass analyzer that employs an oscillatory ion flight path and uses secondary electrons to record the mass spectrum. The analyzer is simple in concept and design and inexpensive to build and has been made as small as 6-cm total length. The oscillating ions produce a periodic secondary electron signal whose frequency is mass dependent in mathematically the same way as a conventional time-of-flight analyzer. Because of the oscillating nature of the ions, we have called the analyzer the pulsed oscillating mass spectrometer.     

Baseline mass resolution of peptide isobars: a record for molecular mass resolution

Baseline resolution of two peptides, RVMRGMR and RSHRGHR, of neutral monoisotopic mass, approximately 904 Da, has been achieved by microelectrospray ionization Fourier transform ion cyclotron resonance mass spectrometry at a mass resolving power of approximately 3 300 000. The elemental compositions of these molecules differ by N40 vs. S2H8 (0.000 45 Da), which is less than one electron's mass (0.000 55 Da)! This result establishes a new record for the smallest resolved mass difference between any two molecules. This achievement is made possible by a combination of high magnetic field (9.4 T), large-diameter (4-in.) Penning trap, and low ion density. The implications for proteomics based on accurate mass measurements are discussed briefly.     

Matrix with high salt tolerance for the analysis of peptide and protein samples by desorption/ionization time-of-flight mass spectrometry

High concentrations of urea and guanidine hydrochloride are commonly used for the denaturation of protein, which was digested by enzymatic proteolysis for the identification by MS analysis. The presence of these contaminants seriously suppresses the ion signal of analytes in MALDI-TOF MS analysis. Herein, a novel MALDI matrix, 3, 4-diaminobenzophenone (DABP), has been found with high tolerance for these contaminants in MALDI MS analysis. The ion signal of analyte insulin can be detected in the presence of 2 M guanidine hydrochloride and 1.5 M urea using DABP as matrix. The tryptic digest of BSA (400 fmol) in 1 M guanidine hydrochloride or 1 M urea was successfully analyzed without any pretreatment prior to MS analysis. Furthermore, it has been found that this matrix can also effectively suppress the cation ion adduction of the peptides in the presence of high concentrations of metal ions in sample solution.     

Miniaturized ultra high field asymmetric waveform ion mobility spectrometry combined with mass spectrometry for peptide analysis

Miniaturized ultra high field asymmetric waveform ion mobility spectrometry (ultra-FAIMS) combined with mass spectrometry (MS) has been applied to the analysis of standard and tryptic peptides, derived from α-1-acid glycoprotein, using electrospray and nanoelectrospray ion sources. Singly and multiply charged peptide ions were separated in the gas phase using ultra-FAIMS and detected by ion trap and time-of-flight MS. The small compensation voltage (CV) window for the transmission of singly charged ions demonstrates the ability of ultra-FAIMS-MS to generate pseudo-peptide mass fingerprints that may be used to simplify spectra and identify proteins by database searching. Multiply charged ions required a higher CV for transmission, and ions with different amino acid sequences may be separated on the basis of their differential ion mobility. A partial separation of conformers was also observed for the doubly charged ion of bradykinin. Selection on the basis of charge state and differential mobility prior to tandem mass spectrometry facilitates peptide and protein identification by allowing precursor ions to be identified with greater selectivity, thus reducing spectral complexity and enhancing MS detection.