Bidirectional ion transfer between quadrupole arrays: MSn ion/ion reaction experiments on a quadrupole/time-of-flight tandem mass spectrometer

Methods for bidirectional ion transmission between distinct quadrupole arrays were developed on a quadrupole/time-of-flight tandem mass spectrometer (QqTOF) containing three quadrupoles (ion guide Q0, mass filter Q1, and collision cell Q2) and a reflectron TOF analyzer, for the purpose of implementing multistage ion/ion reaction experiments. The transfer efficiency, defined as the percentage of ions detected after two transfer steps relative to the initial ion abundance, was found to be about 60% between Q2 and Q0 (with passage through the intermediate array (Q1)) and almost 100% between Q2 and Q1. Efficient ion transfer enabled new means for executing MSn experiments on an instrument of this type by operating Q1 in rf/dc mode for performing multiple steps of precursor/product ion isolation while passing ions through Q1 or trapping ions in Q1. In the latter case, the Q1 functioned as a linear ion trap. Either collision induced dissociation (CID) or ion/ion reactions can be conducted in between each stage of mass analysis. MS3 or MS4 experiments were developed to illustrate the charge increase of peptide ions via two steps of charge inversion ion/ion reactions, CID of electron-transfer dissociation (ETD) products and CID of a metal-peptide complex formed from ion/ion reactions.     

Implementation of ion/ion reactions in a quadrupole/time-of-flight tandem mass spectrometer

A commercial quadrupole/time-of-flight (QqTOF) tandem mass spectrometer has been adapted for ion/ion reaction studies. To enable mutual storage of oppositely charged ions in a linear ion trap, the oscillating quadrupole field of the second quadrupole of the system (Q2) serves to store ions in the radial dimension while auxiliary radio frequency is superposed on the end lenses of Q2 during the reaction period to create barriers in the axial dimension. A pulsed dual electrospray (ESI) source is directly coupled to the instrument interface for the purpose of proton transfer reactions. Singly and doubly charged protein ions as high in mass as 66 kDa are readily formed and observed after proton-transfer reactions. For the modified instrument, the mass resolving power is approximately 8000 for a wide m/z range, and the mass accuracy is approximately 20 ppm for external calibration and approximately 5 ppm for internal calibration after ion/ion reactions. Parallel ion parking is demonstrated with a six-component protein mixture, which shows the potential application of reducing spectral complexity and concentrating certain charge states. The current system has high flexibility with respect to defining MS(n) experiments involving collision-induced dissociation (CID) and ion/ion reactions. Protein precursor and CID product masses can be determined with good accuracy, providing an attractive platform for top-down proteomics. Electron transfer dissociation ion/ion reactions are implemented by using a pulsed nano-ESI/atmospheric pressure chemical ionization dual source for ionization. The reaction between protonated peptide ions and radical anions of 1,3-dinitrobenzene formed exclusively c- and z-type fragment ions.     

Performance characteristics of a new hybrid quadrupole time-of-flight tandem mass spectrometer (TripleTOF 5600)

The TripleTOF 5600 System, a hybrid quadrupole time-of-flight mass spectrometer, was evaluated to explore the key figures of merit in generating peptide and protein identifications that included spectral acquisition rates, data quality, proteome coverage, and biological depth. Employing a Saccharomyces cerevisiae tryptic digest, careful consideration of several performance features demonstrated that the speed of the TripleTOF contributed most to the resultant data. The TripleTOF system was operated with 8, 20, and 50 MS/MS events in an effort to compare with other MS technologies and to demonstrate the abilities of the instrument platform.     

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.     

MALDI analysis of Bacilli in spore mixtures by applying a quadrupole ion trap time-of-flight tandem mass spectrometer

A novel ion trap time-of-flight hybrid mass spectrometer (qIT-TOF MS) has been applied for peptide sequencing in proteolytic digests generated from spore mixtures of Bacilli. The method of on-probe solubilization and in situ proteolytic digestion of small, acid-soluble spore proteins has been recently developed in our laboratory, and microorganism identification in less than 20 min was accomplished. In this study, tryptic peptides were generated in situ from complex spore mixtures of B. subtilis 168, B. globigii, B. thuringiensis subs. Kurstaki, and B. cereus T, respectively. MALDI analysis of bacterial peptides generated was performed with an average mass resolving power of 6200 and a mass accuracy of up to 10 ppm using a trap-TOF tandem configuration. Precursor ions of interest were usually selected and stored in the quadrupole ion trap with their complete isotope distribution by choosing a window of +/- 2 Da. Sequence-specific information on isolated protonated peptides was gained via tandem MS experiments with an average mass resolving power of 4450 for product ion analysis, and protein and bacterial sources were identified by database searching.     

Surface modification using a commercial triple quadrupole mass spectrometer

We report instrumental modifications to a commercial mass spectrometer that allow surface modification experiments to be performed using low-energy (electronvolt range) mass-selected ion beams. The design of the detector housing allows placement of the surface on the ion optical axis and some distance beyond the off-axis detector. Manipulation of the potentials applied to the final lens, detector housing, conversion dynode, and electron multiplier allow the ions to pass through the detector housing and impinge upon the surface without loss of the normal mode of detector operation. Ex situ analysis of the modified surface is performed using a home-built multisector mass spectrometer. The ability to modify organic thin films is demonstrated by a number of soft landing and surface modification experiments including (i) soft landing of (CH3)2SiNCS+ ions formed from trimethylsilyl isothiocyanate upon a fluorinated self-assembled monolayer (F-SAM) surface, (ii) soft landing and dissociative soft landing of the pseudomolecular cation of triphenylpyrylium tetrafluoroborate, viz. the triphenylpyrylium cation, upon an F-SAM surface, (iii) dissociative soft landing of 35ClCH2(CH3)2SiOSi(CH3)2+ formed from 1,3-bis(chloromethyl)disiloxane upon an F-SAM surface, (iv) surface passivation by reaction of the trimethylsilyl cation, Si(CH3)3+, with a hydroxyl-terminated self-assembled monolayer (OH-SAM), and (v) transhalogenation by reaction of CCl3+ (m/z 119) with an F-SAM surface.     

A variable frequency supply for a quadrupole mass spectrometer

A circuit is described which generates potentials of the form ±(U+ Vcosωt) suitable for operating a quadrupole mass spectrometer in the frequency scanning mode.     

Quantitative profiling of phospholipids by multiple precursor ion scanning on a hybrid quadrupole time-of-flight mass spectrometer

A hybrid quadrupole time-of-flight mass spectrometer featured with ion trapping capabilities was employed for quantitative profiling of total extracts of endogenous phospholipids. Simultaneous acquisition of precursor ion spectra of multiple fragment ions allowed detection of major classes of phospholipids in a single experiment. Relative changes in their concentration were monitored using a mixture of isotopically labeled endogenous lipids as a comprehensive internal standard. Precursor ion scanning spectra were acquired simultaneously for acyl anions of major fatty acids in negative ion mode and identified the fatty acid moieties and their relative position at the glycerol backbone in individual lipid species. Taken together, a combination of multiple precursor ion scans allowed quantitative monitoring of major perturbation in phospholipid composition and elucidating of molecular heterogeneity of individual lipid species.     

Enrichment of rare gas isotopes using a quadrupole mass spectrometer

A small quadrupole mass spectrometer was operated in the static mode to enrich selected rare gas isotopes. Memory effects in the apparatus were observed and attributed to the re-emission of atoms implanted by the electron-impact ion source. Studies of the pumping mechanism led us to a practical means for reducing the rate of noble gas pumping     

四极质谱计在一些外星球大气成份分析中的应用

四极质谱计多次搭载在探测器上对金星、土星、木星、土卫六等外星球表面大气成份进行了分析,获得了一些有价值的信息.本文分析了四极质谱计在空间应用时面临的问题;以具体的空间探测任务为例.探讨了质谱计设计的成功和不足之处,以及未来空间探测任务对四极质谱计提出的新要求.     

Quantitative proteomic analysis using a MALDI quadrupole time-of-flight mass spectrometer

We describe an approach to the quantitative analysis of complex protein mixtures using a MALDI quadrupole time-of-flight (MALDI QqTOF) mass spectrometer and isotope coded affinity tag reagents (Gygi, S. P.; et al. Nat. Biotechnol. 1999, 17, 994-9.). Proteins in mixtures are first labeled on cysteinyl residues using an isotope coded affinity tag reagent, the proteins are enzymatically digested, and the labeled peptides are purified using a multidimensional separation procedure, with the last step being the elution of the labeled peptides from a microcapillary reversed-phase liquid chromatography column directly onto a MALDI sample target. After addition of matrix, the sample spots are analyzed using a MALDI QqTOF mass spectrometer, by first obtaining a mass spectrum of the peptides in each sample spot in order to quantify the ratio of abundance of pairs of isotopically tagged peptides, followed by tandem mass spectrometric analysis to ascertain the sequence of selected peptides for protein identification. The effectiveness of this approach is demonstrated in the quantification and identification of peptides from a control mixture of proteins of known relative concentrations and also in the comparative analysis of protein expression in Saccharomyces cerevisiae grown on two different carbon sources.     

Exact mass measurements on-line with high-performance liquid chromatography on a quadrupole mass spectrometer

Exact mass measurements were performed on-line with high-performance liquid chromatography on a quadrupole mass spectrometer. Compounds with molecular weights from 98 to 797, mainly aromatic sulfonates and sulfonamides, were analyzed with electrospray ionization in positive or negative mode. Internal mass calibration compounds were continuously added after separation. A Gaussian fit of the mass errors of 808 individual measurements (concentrations of 1-10 mg/L, 20-200 ng absolute on column) resulted in a mean error of 0.1 mmu (0.45 ppm) and a standard deviation sigma of 1.5 mmu (5.4 ppm). The 99.7% confidence intervals (3sigma) were +/-4.5 mmu (+/-16.2 ppm) for single mass measurements. Averaging 10 measurements further reduced the errors to less than +/-1.5 mmu (+/-5 ppm). Isobaric interferences with ions resulting from the mass calibrants were avoided by the use of complementary mass calibrants. The results were verified (differences below +/-4.5 mmu) with a LC/ oa-TOFMS. Limited mass range chromatograms were used to enhance selectivity in the analysis of mixtures. The method was applied to determine the elemental composition of a potential dye metabolite detected in anaerobically treated textile wastewater.     

Effects of fragile ions on mass resolution and on isolation for tandem mass spectrometry in the quadrupole ion trap mass spectrometer.

In the quadrupole ion trap, it has been noted that factors other than an ion's mass and charge may affect its measured m/z, resulting in compound-dependent, or "chemical", mass shifts. We propose that ions can exhibit a chemical mass shift because they are "fragile" and may fragment during the application of resonance ejection during mass analysis; these effects were studied using ions that include protonated, deprotonated, and adduct ions of explosives, acylcarnitines, and macrolide antibiotics. Fragile ions affect mass resolution by causing broader peaks than nonfragile ions, especially at slower scan speeds, as the result of the application of resonance ejection. Fragile ions may also be fragmented by the application of the isolation waveform during selection of the parent ion for tandem mass spectrometry experiments, making it impossible to achieve unit isolation of a fragile ion. To obtain adequate isolation intensity, the isolation waveform notch width must be increased and the time period of isolation must be decreased. Fragile ions also require lower optimum collision energy to achieve efficient collision-induced dissociation. We have developed criteria for the determination of the degree of ion fragility based upon experimental results.     

High-throughput mass-directed parallel purification incorporating a multiplexed single quadrupole mass spectrometer

We report on the development of a parallel HPLC/MS purification system incorporating an indexed (i.e., multiplexed) ion source. In the method described, each of the flow streams from a parallel array of HPLC columns is directed toward the multiplexed (MUX) ion source and sampled in a time-dependent, parallel manner. A visual basic application has been developed and monitors in real-time the extracted ion current from each sprayer channel. Mass-directed fraction collection is initiated into a parallel array of fraction collectors specific for each of the spray channels. In the first embodiment of this technique, we report on a four-column semipreparative parallel LC/MS system incorporating MUX detection. In this parallel LC/MS application (in which sample loads between 1 and 10 mg on-column are typically made), no cross talk was observed. Ion signals from each of the channels were found reproducible over 192 injections, with interchannel signal variations between 11 and 17%. The visual basic fraction collection application permits preset individual start collection and end collection thresholds for each channel, thereby compensating for the slight variation in signal between sprayers. By incorporating postfraction collector UV detection, we have been able to optimize the valve-triggering delay time with precut transfer tubing between the mass spectrometer and fraction collectors and achieve recoveries greater than 80%. Examples of the MUX-guided, mass-directed fraction purification of both standards and real library reaction mixtures are presented within.     

Collision-activated infrared multiphoton dissociation in a quadrupole ion trap mass spectrometer

We propose and demonstrate a new method for multiple-stage mass spectrometry (MSn), collision-activated infrared multiphoton dissociation (CA-IRMPD), which is very effective for the quadrupole ion trap mass spectrometer (QITMS). CA-IRMPD uses a combination of focused laser irradiation (beam radius, approximately 0.4 mm) and collisional activation by a supplemental AC voltage between endcap electrodes. This combination enables IRMPD, which has conventionaLly been ineffective above 10(-4) Torr, to be used under a standard bath gas pressure of 2-8 mTorr. CA-IRMPD can produce richer spectra of product ions than CID or IRMPD while maintaining high sensitivity and mass resolution; thus, it will contribute to an accurate determination of peptide sequences.     

Design and characterization of a multisource hand-held tandem mass spectrometer

A wireless-controlled miniature rectilinear ion trap mass spectrometer system, total weight with batteries 5.0 kg, consuming less than 35 W of power, and having dimensions of 22 cm in length by 12 cm in width by 18 cm in height, is characterized. The design and construction of the mass spectrometer including mass analyzer, vacuum system, electronics system, and data acquisition and processing systems, is detailed. The mass spectrometer is compatible with various types of ionization sources including a glow discharge electron impact ionization source used in the internal ionization mode, and various atmospheric pressure ionization sources, including electrospray ionization, atmospheric pressure chemical ionization, and desorption electrospray ionization, which are employed for external, atmospheric pressure ionization. These external sources are coupled to the miniature mass spectrometer via a capillary interface that is operated in a discontinuous fashion (discontinuous atmospheric pressure interface) to maximize ion transport. The performance of the mass spectrometer for large and small molecules is characterized. Limits of detection in the parts-per-billion range were obtained for selected compounds examined using both the internal ionization and external ionization modes. Tandem mass spectrometry and fast in situ analysis capabilities are also demonstrated using a variety of compounds and ionization sources. Protein molecules are analyzed as the multiply protonated molecules with mass/charge ratios up to 1500 Da/charge.     

Multiplexed MS/MS in a quadrupole ion trap mass spectrometer

A multiplexing method for performing MS/MS on multiple peptide ions simultaneously in a quadrupole ion trap mass spectrometer (QITMS) has been developed. This method takes advantage of the inherent mass bias associated with ion accumulation in the QITMS to encode the intensity of precursor ions in a way that allows the corresponding product ions to be identified. The intensity encoding scheme utilizes the Gaussian distributions that characterize the relationship between ion intensities and rf trapping voltages during ion accumulation. This straightforward approach uses only two arbitrary waveforms, one for isolation and one for dissociation, to gather product ion spectra from N precursor ions in as little as two product ion spectra. In the example used to illustrate this method, 66% of the product ions from five different precursor peptide ions were correctly correlated using the multiplexing approach. Of the remaining 34% of the product ions, only 6% were misidentified, while 28% of the product ions failed to be identified because either they had too low intensity or they had the same m/z ratio as one of the precursor ions or the same m/z ratio as a product ion from a different precursor ion. This method has the potential to increase sample throughput, reduce total analysis times, and increase signal-to-noise ratios as compared to conventional MS/MS methods.     

High-resolution mass spectrometry with a multiple pass quadrupole mass analyzer

The peak shape narrows and the resolution improves if the ions are simply reflected back and forth through a conventional quadrupole mass analyzer. CO(+) and N(2)(+) at m/z = 28 are separated to 50% valley with half of the original signal remaining. These two ions can be resolved to baseline (m/Δm) = 5000 with 1% of the original signal remaining.     

四极质谱计在真空检漏中的应用

介绍了使用四极质谱计进行真空检漏的原理和方法,分别对超高和极高真空系统做了检漏实验研究，并取到了满意的结果。四极质谱计检漏有检漏仪检漏无法比拟的优点，适合在真空工程中推广应用。     

四极质谱计用作等离子体诊断时的几个问题

四极质谱计用于等离子体诊断时常常面临质谱计工作上限问题和四极质谱计离子源所产生的本底组分分压强导致测量结果有较大误差的问题，为使四极质谱分析能作为等离子体诊断的常规手段，必须拓展四极质谱计量量上限和分析离子源产生的附加本底的特点并加以扣除，确保作为等离子诊断时的测量精度。