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Ion Spectra (ion + spectrum)
Kinds of Ion Spectra Selected AbstractsMass defect filter technique and its applications to drug metabolite identification by high-resolution mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 7 2009Haiying Zhang Abstract Identification of drug metabolites by liquid chromatography/mass spectrometry (LC/MS) involves metabolite detection in biological matrixes and structural characterization based on product ion spectra. Traditionally, metabolite detection is accomplished primarily on the basis of predicted molecular masses or fragmentation patterns of metabolites using triple-quadrupole and ion trap mass spectrometers. Recently, a novel mass defect filter (MDF) technique has been developed, which enables high-resolution mass spectrometers to be utilized for detecting both predicted and unexpected drug metabolites based on narrow, well-defined mass defect ranges for these metabolites. This is a new approach that is completely different from, but complementary to, traditional molecular mass- or MS/MS fragmentation-based LC/MS approaches. This article reviews the mass defect patterns of various classes of drug metabolites and the basic principles of the MDF approach. Examples are given on the applications of the MDF technique to the detection of stable and chemically reactive metabolites in vitro and in vivo. Advantages, limitations, and future applications are also discussed on MDF and its combinations with other data mining techniques for the detection and identification of drug metabolites. Copyright © 2009 John Wiley & Sons, Ltd. [source] Do collisions inside the collision cell play a relevant role in CID-LIFT experiments?,JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 1 2007Gloriano Moneti Abstract Collision experiments are a valid approach to characterize the ionic species generated by matrix assisted laser desorption ionization (MALDI). When a time-of-flight analyzer is employed, three different approaches are available for these experiments: the postsource decay (PSD), the LIFT and the MALDI-TOF/TOF. The last two are of particular interest because of the overcoming of the PSD problems related to mass calibration of the product ion spectra. Experiments performed by LIFT on linear or cyclic peptides, in presence or in absence of collision gas in the collision cell, gave evidence of an unexpected behavior: the two spectra were practically superimposable, and in the former case only a few new fragmentation channels were activated with low yield. These results mean that the selected ion exhibits a large amount of internal energy, capable of promoting fragmentation processes in the time window corresponding to the flight time between ion source and the acceleration electrode placed after the collision cell. Experiments performed by varying the plume density show that this internal energy uptake occurs in the expanding plume, through multiple collisions. The LIFT data have been compared with those achieved by collisions of ESI-generated [MH]+ ions of angotensin II performed under ,in-source' conditions and by triple-quadrupole experiments. The obtained results show a strong similarity among the spectra, indicating that the internal energy uptake in a MALDI source is comparable with that of 40-eV ions colliding with Ar in a triple-quadrupole instrument. Copyright © 2006 John Wiley & Sons, Ltd. [source] Identification and fragmentation of hydrolyzed aluminum species by electrospray ionization tandem mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 10 2004Arja Sarpola Abstract Earlier characterization of some hydrolysis products of AlCl3·6H2O was confirmed by electrospray ionization tandem mass spectrometry with increasing collision energy of projectile ions. At lower collision energies, the aqua ligands were stripped off. At higher energies, two hydroxo groups formed a bridging oxo group with loss of one water molecule. Aluminum complexes could also capture aqua ligands in the collision chamber so long as the parent ion did not fragment, and the fragment ion spectra broadened toward higher m/z values. The chloro ligands were eliminated as hydrochloric acid. The aluminum cores remained highly intact. Copyright © 2004 John Wiley & Sons, Ltd. [source] Metabolism of a novel antiangiogenic agent KR-31831 in rats using liquid chromatography-electrospray mass spectrometryJOURNAL OF SEPARATION SCIENCE, JSS, Issue 14 2005Hui-Hyun Kim Abstract KR-31831 ((2S,3R,4S)-4-(((1H-imidazol-2-yl)methyl)(4-chlorophenyl)amino)-6-amino-2-(dimethoxymethyl)-2-methyl-3,4-dihydro-2H-chromen-3-ol) is a novel antiangiogenic agent. In vitro and in vivo metabolism of KR-31831 in rats has been investigated using LC-MS and LC-MS/MS analysis. Incubation of rat liver microsomes and hepatocytes with KR-31831 produced three metabolites (M1,M3). M1, M2, and M3 were identified as N -((1H-imidazol-2-yl)methyl)-4-chlorobenzenamine, (2R,3R,4S)-4-(((1H-imidazol-2-yl)methyl)(4-chlorophenyl) amino)-6-amino-2-(hydroxymethyl)-2-methyl-3,4-dihydro-2H-chromen-3-ol, and N -((2S,3R,4S)-4-(((1H-imidazol-2-yl)methyl)(4-chlorophenyl)amino)-2-(dimethoxymethyl)-3-hydroxy-2-methyl-3,4-dihydro-2H-chromen-6-yl)acetamide, respectively, by co-chromatography with the authentic standards and by comparison with product ion spectra of the authentic standards. Those in vitro metabolites were also detected in bile, plasma, or urine samples after an intravenous administration of KR-31831 to rats. The metabolic routes for KR-31381 included the metabolism of acetal group to hydroxymethyl group (M2), N -dealkylation to M1, and N -acetylation at the 6-amino group (M3). [source] The detection, correlation, and comparison of peptide precursor and product ions from data independent LC-MS with data dependant LC-MS/MSPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 6 2009Scott J. Geromanos Abstract The detection, correlation, and comparison of peptide and product ions from a data independent LC-MS acquisition strategy with data dependent LC-MS/MS is described. The data independent mode of acquisition differs from an LC-MS/MS data acquisition since no ion transmission window is applied with the first mass analyzer prior to collision induced disassociation. Alternating the energy applied to the collision cell, between low and elevated energy, on a scan-to-scan basis, provides accurate mass precursor and associated product ion spectra from every ion above the LOD of the mass spectrometer. The method therefore provides a near 100% duty cycle, with an inherent increase in signal intensity due to the fact that both precursor and product ion data are collected on all isotopes of every charge-state across the entire chromatographic peak width. The correlation of product to precursor ions, after deconvolution, is achieved by using reconstructed retention time apices and chromatographic peak shapes. Presented are the results from the comparison of a simple four protein mixture, in the presence and absence of an enzymatically digested protein extract from Escherichia coli. The samples were run in triplicate by both data dependant analysis (DDA) LC-MS/MS and data-independent, alternate scanning LC-MS. The detection and identification of precursor and product ions from the combined DDA search results of the four protein mixture were used for comparison to all other data. Each individual set of data-independent LC-MS data provides a more comprehensive set of detected ions than the combined peptide identifications from the DDA LC-MS/MS experiments. In the presence of the complex E. coli background, over 90% of the monoisotopic masses from the combined LC-MS/MS identifications were detected at the appropriate retention time. Moreover, the fragmentation pattern and number of associated elevated energy product ions in each replicate experiment was found to be very similar to the DDA identifications. In the case of the corresponding individual DDA LC-MS/MS experiment, 43% of the possible detectable peptides of interest were identified. The presented data illustrates that the time-aligned data from data-independent alternate scanning LC-MS experiments is highly comparable to the data obtained via DDA. The obtained information can therefore be effectively and correctly deconvolved to correlate product ions with parent precursor ions. The ability to generate precursor-product ion tables from this information and subsequently identify the correct parent precursor peptide will be illustrated in a companion manuscript. [source] Increasing high-throughput Discovery bioanalysis using automated selected reaction monitoring compound optimization, ultra-high-pressure liquid chromatography, and single-step sample preparation workflowsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 21 2009James Smalley QuickQuan is an integrated software package for Thermo Scientific triple quadrupole mass spectrometers that allows users to automate routine operations ranging from method development to data processing. QuickQuan automated optimization of compound-selected reaction monitoring (SRM) transitions by evaluating both positive and negative polarities during an infusion. Whichever mode produces the most intense Q1 scan is then carried to product ion spectra. QuickQuan then writes these SRM methods to a shared network database. The total volume of compound needed is 100,µL infused over approximately 1.6,min. The auto-optimization is carried out in 96-well plates and does not require an operator present. The SRM database was shared between two identical TSQ Quantum mass spectrometers. For data acquisition, QuickQuan automatically created a sequence file complete with a data processing method pre-populated with compound IDs and corresponding SRM transitions. To increase throughput we coupled each Finnigan Quantum with ultra-high-pressure liquid chromatography (uHPLC) accomplished using 4× Ultra Flux quaternary pumps that were designed to handle pressures up to 15 000,psi. The total run time for all analyses was 1.2,min using BEH 1.7,µm particle C18 columns. Further time reductions were realized with sample preparation accomplished using Strata Impact protein precipitation plates which provided an in-well protein crash and 0.20 micron filtering in a one-step process. Pharmacokinetic data turnaround time was significantly improved by combining these three techniques of automated method development with the speed efficiency of uHPLC and a single step in well sample preparation. Copyright © 2009 John Wiley & Sons, Ltd. [source] Assigning glucose or galactose as the primary glycosidic sugar in 3- O -mono-, di- and triglycosides of kaempferol using negative ion electrospray and serial mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 19 2009Geoffrey C. Kite Kaempferol 3- O - , -glucopyranoside, kaempferol 3- O - , -galactopyranoside and higher glycosides of these two flavonoids with , -rhamnose at C-2 and/or C-6 of the primary sugar were studied by negative ion electrospray ionisation and serial mass spectrometry in a three-dimensional (3D) ion trap mass spectrometer. Kaempferol 3- O - , -glucopyranoside and kaempferol 3- O - , -rhamnopyranosyl(1,6)- , -glucopyranoside could be distinguished from their respective galactose analogues by differences in the ratio of the radical aglycone ion [Y0 , H],, to the rearrangement aglycone ion Y following MS/MS of the deprotonated molecules. Kaempferol 3- O -rhamnopyranosyl(1,2)- , -glucopyranoside and kaempferol 3- O - , -rhamnopyranosyl(1,2)[, -rhamnopyranosyl(1,6)]- , -glucopyranoside could be distinguished from their respective galactose analogues by differences in the product ion spectra of the [(M , H) , rhamnose], ion following serial mass spectrometry. In the triglycoside, it was deduced that this ion resulted from the loss of the rhamnose substituted at 2-OH of the primary sugar by observing that MS/MS of deprotonated kaempferol 3- O - , -glucopyranosyl(1,2)[, -rhamnopyranosyl(1,6)]- , -glucopyranoside showed the loss of glucose and not rhamnose. Thus the class of sugar (hexose, deoxyhexose, pentose) at C-2 and C-6 of the primary sugar can be determined. These observations aid the assignment of kaempferol 3- O -glycosides, having glucose or galactose as the primary glycosidic sugar, in LC/MS analyses of plant extracts, and this can be done with reference to only a few standards. Copyright © 2009 John Wiley & Sons, Ltd. [source] Observations on the detection of b- and y-type ions in the collisionally activated decomposition spectra of protonated peptidesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 10 2009King Wai Lau Tandem mass spectrometric data from peptides are routinely used in an unsupervised manner to infer product ion sequence and hence the identity of their parent protein. However, significant variability in relative signal intensity of product ions within peptide tandem mass spectra is commonly observed. Furthermore, instrument-specific patterns of fragmentation are observed, even where a common mechanism of ion heating is responsible for generation of the product ions. This information is currently not fully exploited within database searching strategies; this motivated the present study to examine a large dataset of tandem mass spectra derived from multiple instrumental platforms. Here, we report marked global differences in the product ion spectra of protonated tryptic peptides generated from two of the most common proteomic platforms, namely tandem quadrupole-time-of-flight and quadrupole ion trap instruments. Specifically, quadrupole-time-of-flight tandem mass spectra show a significant under-representation of N-terminal b-type fragments in comparison to quadrupole ion trap product ion spectra. Energy-resolved mass spectrometry experiments conducted upon test tryptic peptides clarify this disparity; b-type ions are significantly less stable than their y-type N-terminal counterparts, which contain strongly basic residues. Secondary fragmentation processes which occur within the tandem quadrupole-time-of-flight device account for the observed differences, whereas this secondary product ion generation does not occur to a significant extent from resonant excitation performed within the quadrupole ion trap. We suggest that incorporation of this stability information in database searching strategies has the potential to significantly improve the veracity of peptide ion identifications as made by conventional database searching strategies. Copyright © 2009 John Wiley & Sons, Ltd. [source] Precursor ion scan profiles of acylcarnitines by atmospheric pressure thermal desorption chemical ionization tandem mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 23 2008Giuseppe Paglia The fatty acyl esters of L-carnitine (acylcarnitines) are useful biomarkers for the diagnosis of some inborn errors of metabolism analyzed by liquid chromatography/tandem mass spectrometry. In this study the acylcarnitines were analyzed by atmospheric pressure thermal desorption chemical ionization using a commercial tandem mass spectrometer (APTDCI-MS/MS). The method is based on the precursor ion scan mode determination of underivatized acylcarnitines desorbed from samples by a hot desolvation gas flow and ionized by a corona pin discharge. During desorption/ionization step the temperature induces the degradation of acylcarnitines; nevertheless, the common fragment to all acylcarnitines [MH,59]+ is useful for analyzing their profile. APTDCI parameters, including angle of collection and incidence, gas flows and temperatures, were optimized for acylcarnitines. The experiments were performed drying 2,µL of an equimolar mixture of acylcarnitine standards on a glass slide. The specificity was evaluated by comparing product ion spectra and the precursor ion spectra of 85 m/z of acylcarnitines obtained by the APTDCI method and by electrospray ionization flow injection analysis (ESI-FIA). The method was also employed to analyze acylcarnitines extracted from a pathological dried blood spot and a control. The method enables analysis of biological samples and recognition of some acylcarnitines that are diagnostic markers of inherited metabolic diseases. The intrinsic high-throughput analysis of the ambient desorption ionization methods offers a new opportunity either for its potential application in clinical chemistry and for the expanded screening of some inborn errors of metabolism. Copyright © 2008 John Wiley & Sons, Ltd. [source] Towards a universal product ion mass spectral library , reproducibility of product ion spectra across eleven different mass spectrometersRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 12 2008Chris Hopley Product ion spectra produced by collision-induced dissociation (CID) in tandem mass spectrometry experiments can differ markedly between instruments. There have been a number of attempts to standardise the production of product ion spectra; however, a consensus on the most appropriate approach to the reproducible production of spectra has yet to be reached. We have previously reported the comparison of product ion spectra on a number of different types of instruments , a triple quadrupole, two ion traps and a Fourier transform ion cyclotron resonance mass spectrometer (Bristow AWT, Webb KS, Lubben AT, Halket JM. Rapid Commun. Mass Spectrom. 2004; 18: 1). The study showed that a high degree of reproducibility was achievable. The goal of this study was to improve the comparability and reproducibility of CID product ion mass spectra produced in different laboratories and using different instruments. This was carried out experimentally by defining a spectral calibration point on each mass spectrometer for product ion formation. The long-term goal is the development of a universal (instrument independent) product ion mass spectral library for the identification of unknowns. The spectra of 48 compounds have been recorded on eleven mass spectrometers: six ion traps, two triple quadrupoles, a hybrid triple quadrupole, and two quadrupole time-of-flight instruments. Initially, 4371 spectral comparisons were carried out using the data from eleven instruments and the degree of reproducibility was evaluated. A blind trial has also been carried out to assess the reproducibility of spectra obtained during LC/MS/MS. The results suggest a degree of reproducibility across all instrument types using the tuning point technique. The reproducibility of the product ion spectra is increased when comparing the tandem in time type instruments and the tandem in space instruments as two separate groups. This may allow the production of a more limited, yet useful, screening library for LC/MS/MS identification using instruments of the same type from different manufacturers. Copyright © 2008 John Wiley & Sons, Ltd. [source] Product ion mass spectra of amphetamine-type substances, designer analogues, and ketamine using ultra-performance liquid chromatography/tandem mass spectrometry,RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 15 2006Luigino G. Apollonio This paper describes the application of ultra-performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) technology to separate and identify amphetamine-type substances (amphetamine, methamphetamine), common and novel designer analogues (MDA, MDMA, PMA, 4-MTA, MBDB), and ketamine using Acquity UPLC/Micromass Quattro Micro API mass spectrometer instrumentation (Waters Corporation, USA). From injection of drug reference standards, it was demonstrated that these compounds can be identified by product ion mass spectra in less than 4,min total analysis time, indicating that the technological advancements associated with UPLC/MS/MS allow it to serve as a powerful analytical tool for high-throughput testing. In addition to demonstrating the separation and response of these drug compounds under the stated UPLC/MS/MS conditions, we believe the acquired product ion spectra will be a beneficial reference to laboratories interested in incorporating the use of this technology in the routine analysis of drugs of abuse. Copyright © 2006 John Wiley & Sons, Ltd. [source] Characterisation of sulphoxides by atmospheric pressure ionisation mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2005Patricia Wright An observation that a series of proprietary compounds containing a methyl thiophenyl group all underwent metabolic S-oxidation, and that the product ion spectra of the resulting S-oxides showed methyl radical loss under low-energy atmospheric pressure ionisation tandem mass spectrometry (API-MS/MS) conditions, has led to an investigation of the fragmentation of commercially available sulphoxides. The phenyl methyl sulphoxides studied do lose methyl radicals under MS/MS conditions on triple quadrupole mass spectrometers. In addition, the phenyl sulphoxides, with simple substituents other than a methyl group, also showed a tendency to lose the substituent as a radical. It was concluded that radical loss from these simple sulphoxides was characteristic of S-oxidation of these molecules. Radical losses, such as those reported here, are used in-house to distinguish S-oxidation from N- and C-oxidation in metabolism studies. Copyright © 2005 John Wiley & Sons, Ltd. [source] Ion trap mass spectrometry in the structural analysis of haemoglobin peptides modified by epichlorohydrin and diepoxybutaneRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 9 2002Nadia Miraglia Ion trap mass spectrometry has been shown to be particularly suitable for the structural analysis of high molecular weight peptides directly fragmented in the mass analyser without needing further sub-digestion reactions. Here we report the advantages of using multi-stage ion trap mass spectrometry in the structural characterisation of haemoglobin alkylated with epichlorohydrin and diepoxybutane. Alkylated globins were digested with trypsin and the peptide mixtures were analysed by MS3. This technique allows the sequential fragmentation of peptides under analysis, giving rise to MS3 product ion spectra with additional information with respect to MS2 mass spectra. The results obtained complete the previously reported structural characterisation of alkylated haemoglobin, demonstrating the potential of ion trap mass spectrometry. Copyright © 2002 John Wiley & Sons, Ltd. [source] Determination of phenolic compounds in rose hip (Rosa canina) using liquid chromatography coupled to electrospray ionisation tandem mass spectrometry and diode-array detectionRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 7 2002Erlend Hvattum Liquid chromatography coupled with negative and positive electrospray ionisation (ESI) tandem mass spectrometry (MS/MS) and diode-array detection (DAD) was used for determination of phenols in rose hip (Rosa canina) extract. ESI mass spectra of the chromatographically separated phenols gave the molecular weight of the compounds through prominent [M,,,H], ions for most of the compounds and M+ ions for the anthocyanins. Collision induced dissociation (CID) of the [M,,,H], (or M+) precursor ions yielded product ions which determined the molecular weight of the aglycones. In-source fragmentation followed by CID of the resulting deprotonated aglycone ([A,,,H],) provided product ions for the identification of the unconjugated phenols. The identification was based on comparison with product ion spectra of commercial standards. UV-diode-array spectra were used for identity confirmation. This combined approach allowed the identification in rose hip extract of an anthocyanin, i.e. cyanidin-3- O -glucoside, several glycosides of quercetin and glycosides of taxifolin and eriodictyol. Phloridzin was identified, and several conjugates of methyl gallate were also found, one of which was tentatively identified as methyl gallate-rutinoside. Catechin and quercetin were found as the aglycones in the extract. Copyright © 2002 John Wiley & Sons, Ltd. [source] Ion chemistry of chloroethanes in air at atmospheric pressureRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 20 2001Anna Nicoletti Ion chemistry at atmospheric pressure is of major relevance to novel methods for the abatement of volatile organic compounds (VOCs) that employ non-thermal plasmas. For this reason, positive and negative APCI (atmospheric pressure chemical ionization) mass spectra of all six di-, tri- and tetrachloroethanes diluted in air (500,1500,ppm) at atmospheric pressure were investigated at 30,°C and at 300,°C. Spectral changes due to collisional activation of the ions achieved by increasing ,V, the potential difference between sampling and skimmer cones, are informative of structures and ion-molecule reactions. Positive ion chemistry of the chloroethanes (M) can, in general, be ascribed to C-C and C-Cl cleavages of the molecular ion, M+·, never detected but likely formed via exothermic charge exchange from primary ions of the APCI plasma. Exceptions to this characteristic pattern were observed for 1,1-dichloroethane and 1,1,2,2-tetrachloroethane, which give [M,,,H]+ and [M,,,HCl]+· species, respectively. It is suggested that both such species are due to ionization via hydride transfer. Upon increasing ,V, the [M,,,HCl]+· ion formed from 1,1,2,2-tetrachloroethane undergoes the same fragmentation and ion-molecule reactions previously reported for trichloroethene. A nucleophilic reaction of water within the [C2H4Cl+](H2O)n ionic complexes to displace HCl is postulated to account for the [C2H5O+](H2O)m species observed in the positive APCI spectra of the dichloroethanes. Negative ion spectra are, for all investigated chloroethanes, dominated by Cl, and its ion-neutral complexes with one, two and, in some cases, three molecules of the neutral precursor and/or water. Another common feature is the formation of species (X,)(M)n where X, is a background ion of the APCI plasma, namely O2,,O3, and, in some cases, (NO)2,. Peculiar to 1,1,1-trichloroethane are species attributed to Cl, complexes with phosgene, (Cl,)(Cl2C=O)n(n,=,1,2). Such complexes, which were not observed for either the isomeric 1,1,2-trichloroethane or for the tetrachloroethanes, are of interest as oxidation intermediates in the corona-induced decomposition process. No conclusions can be drawn in the case of the dichloroethanes, since, for these compounds, the ions (Cl,)(Cl2C=O)n and (Cl,)(M)n happen to be isobaric. Copyright © 2001 John Wiley & Sons, Ltd. [source] Automatic function switching and its usefulness in peptide and protein analysis using direct infusion microspray quadrupole time-of-flight mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 19 2001Emmy Hoyes Automatic function switching has been investigated for high-throughput protein identification and sequencing of peptides using direct infusion of tryptic digests on a quadrupole time-of-flight instrument. The increase in speed and the high quality of data make it a favourable technique for tandem mass spectrometry when compared to manual selection of each precursor ion; these advantages are not restricted to combined LC/MS/MS analyses for which the automatic function-switching mode was originally developed. This mode was compared to analyses performed using a slow scan of the quadrupole analyzer with repeated recording of product ion spectra. For the specific purpose of generating product ion data for sequence determination (as opposed to surveying all precursors of a selected product ion), the automatic function-switching mode was, as expected, markedly superior with respect to speed of analysis and quality of data. Furthermore, the automatic function-switching mode provides greater versatility with respect to selection of optimal collision energies. Copyright © 2001 John Wiley & Sons, Ltd. [source] Phosphopeptide analysis by positive and negative ion matrix-assisted laser desorption/ionization mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 17 2001Katharina Janek This article describes a simple procedure for the detection of phosphorylated peptides by comparable positive and negative ion mode matrix-assisted laser desorption/ionization mass spectrometry measurements. Based on studies with phosphorylated peptides (EAIXAAPFAK, X,=,pS, pT, pY) and their corresponding non-phosphorylated analogs, it was found that phosphopeptides, which are characterized by a low ionization efficiency in the positive ion mode, exhibit drastically increased signal intensities in the negative ion mode compared to their non-phosphorylated analogs. The effect was successfully used to identify phosphorylated sequences of the commonly used phosphoprotein standards, protein kinase A and ,-casein, by peptide mass fingerprint analyses of the corresponding Lys C and trypsin digests using both (positive and negative) ion modes. The comparison of positive and negative ion spectra of a given protein digest (relative intensity[M,,,H],/relative intensity[M,+,H]+) can be used to identify any phosphopeptides present which may then be separated and analyzed further. Copyright © 2001 John Wiley & Sons, Ltd. [source] High-performance liquid chromatography/electrospray ionization tandem mass spectrometry of hydroxylated uroporphyrin and urochlorin derivatives formed by photochemical oxidation of uroporphyrinogen IBIOMEDICAL CHROMATOGRAPHY, Issue 5 2007Malcolm Danton Abstract Hydroxylated uroporphyrin I and urochlorin I derivatives formed by photochemical oxidation of uroporphyrinogen I were separated by high-performance liquid chromatography and fully characterized by electrospray ionization tandem mass spectrometry. The porphyrins and chlorins were identified by analysis of their product ion spectra with each hydroxylated derivative giving a characteristic collision-induced dissociation fragmentation pattern. The porphyrins and chlorins characterized were meso -hydroxyuroporphyrin I, , -hydroxypropionic acid uroporphyrin I, , -hydroxypropionic acid uroporphyrin I, hydroxyacetic acid uroporphyrin I, trans- 7-hydroxy-8-spirolactoneurochlorin I, cis- 7-hydroxy-8-spirolactoneurochlorin I and trans- and cis- 7,8-dihydroxyurochlorins I. Copyright © 2007 John Wiley & Sons, Ltd. [source] Static SIMS studies of the oxides and hydroxides of aluminiumJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 1 2007S. Verdier Abstract The degree of hydroxylation or hydration of aluminium surfaces has been examined by static secondary ion mass spectroscopy (SSIMS). The SSIMS spectra of a series of aluminium oxide, oxyhydroxide and hydroxide surfaces have been obtained using instruments in three configurations. Similarities were observed in both negative and positive secondary ions spectra. Even though a direct comparison of the relative intensities cannot be made from one instrument to the other, a similar ranking of the various aluminium hydroxylation states was observed. Several ranking methods are discussed, as well as the similarities and differences observed while using the three instruments. Similar secondary ions were detected whatever the degree of hydroxylation of the aluminium oxide. This argues in favour of the formation of fragments by the combination of individually sputtered atoms or clusters to form the more stable secondaries, rather than the kick-off of ,structure-related' clusters originating directly from the upper surface layer. Copyright © 2006 John Wiley & Sons, Ltd. [source] | ||||||||||