Home About us Contact
|
Home About us Contact | ||
|
|
||
Ionization Conditions (ionization + condition)
Kinds of Ionization Conditions Selected AbstractsIntermolecular Phenolic Hydroxy Methylation Occurring between Chiral N,N, -Bis(2-hydroxyphenyl)-2,2-dimethyl-1,3-dioxolane-4,5-dicarbamide and Co-crystallized Methanol under Electron Impact Ionization ConditionsCHINESE JOURNAL OF CHEMISTRY, Issue 5 2004Jia-Xi Xu Abstract An intermolecular phenolic hydroxy methylation occurring between chiral N,N, -bis(2-hydroxyphenyl)-2,2-dimethyl-1,3-dioxolane-4,5dicarbamide and co-crystallized methanol under electron impact ionization conditions was observed. The result was confirmed by X-ray diffraction structural analysis of a co-crystalline of (R,R)-enantiomer and methanol. [source] Identification of diphenhydramine metabolites in human urine by capillary electrophoresis-ion trap-mass spectrometryELECTROPHORESIS, Issue 10-11 2004Andrea Baldacci Abstract The identification of diphenhydramine (DH) metabolites that are frequently observed in the capillary zone electrophoresis (CZE) and micellar electrokinetic capillary chromatography (MEKC) analyses of alkaline liquid/liquid and solid-phase extracts of patient urines is demonstrated. Having standards for DH and diphenhydramine- N -oxide (DHNO), the presence of these two compounds could be confirmed in urines that were collected overnight after administration of 25 mg DH chloride. Using CZE coupled to ion-trap mass spectrometry (CE-MSn) with positive electrospray ionization and an acetate buffer at pH 5.6, the [M+H]+ ions of DH (m/z = 256), DHNO (m/z = 272), and nordiphenhydramine (NDH, m/z = 242) and their fragmentation to a common m/z 167 product ion (diphenylcarbinol moiety) was monitored. The data indicate that all three compounds are cations in an acidic environment, the migration order being NDH, DH, and DHNO. Data obtained under negative electrospray ionization conditions suggest the presence of diphenylmethoxyacetic acid-glycine amide ([M-H], ion of m/z 298 and fragmentation to m/z 254, loss of CO2), a metabolite that could tentatively be assigned to a characteristic peak observed in the MEKC electropherogram at alkaline pH. The data presented in this paper illustrate the value of using CE-MSn for identification of urinary drug metabolites for which no standards are available. [source] Formation and reactions of cluster ions from aromatic carboxylic acids together with amino acidsISRAEL JOURNAL OF CHEMISTRY, Issue 2 2001Anja Meffert The cluster formation of several aromatic carboxylic acids, ferulic acid, vanillic acid, sinapinic acid, and 3,4-dihydroxybenzoic acid was investigated by means of laser desorption into a supersonic beam followed by multiphoton ionization-time-of-flight mass spectrometry. The formation of not only homogeneous clusters, but also of heterogeneous clusters with some small amino acids was studied. The different neutral clusters formed in the supersonic expansion were ionized by a multiphoton process employing either nano- or femtosecond laser pulses. Strong differences in the detection of cluster ions due to the laser pulse length employed for multiphoton ionization were observed. Only femtosecond activation led to mass spectra with intense signals of the cluster ions. In addition, in the case of femtosecond ionization, protonated amino acids were detected in the mass spectra. As direct ionization of the free amino acids is not possible under the chosen ionization conditions because they lack an adequate chromophore, these protonated amino acids are assumed to be formed via an intracluster proton transfer in the heterogeneous dimer and subsequent decay of the ionized cluster (dissociative proton transfer). Such well-known processes for heterogeneous clusters consisting of a substituted aromatic molecule and small polar solvent molecules may be involved in the matrixassisted laser desorption ionization (MALDI) process. [source] Distinguishing N -oxide and hydroxyl compounds: impact of heated capillary/heated ion transfer tube in inducing atmospheric pressure ionization source decompositionsJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 6 2004Dilrukshi M. Peiris Abstract In the pharmaceutical industry, a higher attrition rate during the drug discovery process means a lower drug failure rate in the later stages. This translates into shorter drug development time and reduced cost for bringing a drug to market. Over the past few years, analytical strategies based on liquid chromatography/mass spectrometry (LC/MS) have gone through revolutionary changes and presently accommodate most of the needs of the pharmaceutical industry. Among these LC/MS techniques, collision induced dissociation (CID) or tandem mass spectrometry (MS/MS and MSn) techniques have been widely used to identify unknown compounds and characterize metabolites. MS/MS methods are generally ineffective for distinguishing isomeric compounds such as metabolites involving oxygenation of carbon or nitrogen atoms. Most recently, atmospheric pressure ionization (API) source decomposition methods have been shown to aid in the mass spectral distinction of isomeric oxygenated (N -oxide vs hydroxyl) products/metabolites. In previous studies, experiments were conducted using mass spectrometers equipped with a heated capillary interface between the mass analyzer and the ionization source. In the present study, we investigated the impact of the length of a heated capillary or heated ion transfer tube (a newer version of the heated capillary designed for accommodating orthogonal API source design) in inducing for-API source deoxygenation that allows the distinction of N -oxide from hydroxyl compounds. 8-Hydroxyquinoline (HO-Q), quinoline- N -oxide (Q-NO) and 8-hydroxyquinoline- N -oxide (HO-Q-NO) were used as model compounds on three different mass spectrometers (LCQ Deca, LCQ Advantage and TSQ Quantum). Irrespective of heated capillary or ion transfer tube length, N -oxides from this class of compounds underwent predominantly deoxygenation decomposition under atmospheric pressure chemical ionization conditions and the abundance of the diagnostic [M + H , O]+ ions increased with increasing vaporizer temperature. Furthermore, the results suggest that in API source decompostion methods described in this paper can be conducted using mass spectrometers with non-heated capillary or ion transfer tube API interfaces. Because N-oxides can undergo in-source decomposition and interfere with quantitation experiments, particular attention should be paid when developing API based bioanalytical methods. Copyright © 2004 John Wiley & Sons, Ltd. [source] Unusual atmospheric pressure chemical ionization conditions for detection of organic peroxidesJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 9 2003David Rondeau Abstract Organic peroxides such as the cumene hydroperoxide I (Mr = 152 u), the di- tert -butyl peroxide II (Mr = 146 u) and the tert -butyl peroxybenzoate III (Mr = 194 u) were analyzed by atmospheric pressure chemical ionization mass spectrometry using a water,methanol mixture as solvent with a low flow-rate of mobile phase and unusual conditions of the source temperature (,50 °C) and probe temperature (70,200 °C). The mass spectra of these compounds show the formation of (i) an [M + H]+ ion (m/z 153) for the hydroperoxide I, (ii) a stable adduct [M + CH3OH2]+ ion (m/z 179) for the dialkyl peroxide II and (iii) several protonated adduct species such as protonated molecules (m/z 195) and different protonated adduct ions (m/z 227, 389 and 421) for the peroxyester III. Tandem mass spectrometric experiments, exact mass measurements and theoretical calculations were performed for characterize these gas-phase ionic species. Using the double-well energy potential model illustrating a gas-phase bimolecular reaction, three important factors are taken into account to propose a qualitative interpretation of peroxide behavior toward the CH3OH2+, i.e. thermochemical parameters () and two kinetic factors such as the capture constant of the initial stable ion,dipole and the magnitude of the rate constant of proton transfer reaction into the loose proton bond cluster. Copyright © 2003 John Wiley & Sons, Ltd. [source] Attachment of neutrals during tandem mass spectrometry of sulfonic acid dyes andintermediates in an ion trapJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 10 2002Adrian Weisz Abstract Several positional isomers of 2-(2-quinolinyl)-1H -indene-1,3(2H)-dione mono- and disulfonic acids prepared as reference materials for development of analytical methods involved in FDA certification of D&C Yellow No. 10 (Quinoline Yellow) were found consistently to show [MH + 14]+ ions when their electrospray- or atmospheric pressure chemical ionization-prepared MH+ ions were subjected to collisional activation. The source of these ions was found to be the methanol used as solvent in these procedures which combined with their [MH , H2O]+ ions under chemical ionization conditions. The reaction was found to be sensitive to their isomeric and chemical structures and other examples of this process are reviewed. Copyright © 2002 John Wiley & Sons, Ltd. [source] Substituent effect and multisite protonation in the fragmentation of alkyl benzoatesJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 3 2002Chagit Denekamp Abstract The dissociation of protonated alkyl benzoates (para H, CN, OMe and NO2) into protonated benzoic acids and alkyl cations was studied in the gas phase. It was found that the product ratio depends on the substituent at the para position of the phenyl ring. The substituent effect is probably the result of the formation of an ion,neutral complex intermediate that decomposes to an ion and a neutral, according to the relative proton affinities of the two moieties. The experimental results and theoretical calculations indicate that the favored protonation site in these compounds is the ester's carbonyl and that proton transfer from the phenyl ring to the ester group is very likely to occur under chemical ionization conditions. It is most probable that the carbonyl protonated form is a common intermediate in the fragmentation process, regardless of the protonation site. Copyright © 2002 John Wiley & Sons, Ltd. [source] Effect of eluent on the ionization efficiency of flavonoids by ion spray, atmospheric pressure chemical ionization, and atmospheric pressure photoionization mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 12 2001Jussi-Pekka Rauha Abstract The effect of nine different eluent compositions on the ionization efficiency of five flavonoids was studied using ion spray (IS), atmospheric pressure chemical ionization (APCI), and the novel atmospheric pressure photoionization (APPI), in positive and negative ion modes. The eluent composition had a great effect on the ionization efficiency, and the optimal ionization conditions were achieved in positive ion IS and APCI using 0.4% formic acid (pH 2.3) as a buffer, and in negative ion IS and APCI using ammonium acetate buffer adjusted to pH 4.0. For APPI work, the eluent of choice appeared to be a mixture of organic solvent and 5 mM aqueous ammonium acetate. The limits of detection (LODs) were determined in scan mode for the analytes by liquid chromatography/mass spectrometry using IS, APCI and APPI interfaces. The results show that negative ion IS with an eluent system consisting of acidic ammonium acetate buffer provides the best conditions for detection of flavonoids in mass spectrometry mode, their LODs being between 0.8 and 13 µM for an injection volume of 20 µl. Copyright © 2001 John Wiley & Sons, Ltd. [source] Chiral discrimination of , -amino acids by DNA tetranucleotides under electrospray ionization conditionsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 2 2008T. Sivaleela A set of DNA tetranucleotides, which are 3,- or 5,-end extended versions of GCA, was used as chiral selectors for the discrimination of enantiomers of , -amino acids. The [X+Y,2H]2, ions of the 1:1 complexes were generated by electrospraying a mixture of tetranucleotide (X) and amino acid (Y) solution. Chiral discrimination was achieved by studying the collision-induced dissociation spectra of the [X+Y,2H]2, ion and the ratio of relative abundance of precursor ion to that of the product ion was used to measure the extent of discrimination. Among the tetranucleotides used, GCAA and GGCA exhibited better discrimination, in which GCAA showed D-selectivity and GGCA showed L-selectivity for the studied amino acids. In addition, binding constants were measured for the 1:1 complexes of phenylalanine enantiomers with GCAA and GGCA. Copyright © 2007 John Wiley & Sons, Ltd. [source] Method for the elucidation of the elemental composition of low molecular mass chemicals using exact masses of product ions and neutral losses: application to environmental chemicals measured by liquid chromatography with hybrid quadrupole/time-of-flight mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 23 2005Shigeru Suzuki A method for elucidating the elemental compositions of low molecular weight chemicals, based primarily on mass measurements made using liquid chromatography (LC) with time-of-flight mass spectrometry (TOFMS) and quadrupole/time-of-flight mass spectrometry (LC/QTOFMS), was developed and tested for 113 chemicals of environmental interest with molecular masses up to ,400,Da. As the algorithm incorporating the method is not affected by differences in the instrument used, or by the ionization method and other ionization conditions, the method is useful not only for LC/TOFMS, but also for all kinds of mass spectra measured with higher accuracy and precision (uncertainties of a few mDa) employing all ionization methods and on-line separation techniques. The method involves calculating candidate compositions for intact ionized molecules (ionized forms of the sample molecule that have lost or gained no more than a proton, i.e., [M+H]+ or [M,H],) as well as for fragment ions and corresponding neutral losses, and eliminating those atomic compositions for the molecules that are inconsistent with the corresponding candidate compositions of fragment ions and neutral losses. Candidate compositions were calculated for the measured masses of the intact ionized molecules and of the fragment ions and corresponding neutral losses, using mass uncertainties of 2 and 5,mDa, respectively. Compositions proposed for the ionized molecule that did not correspond to the sum of the compositions of a candidate fragment ion and its corresponding neutral loss were discarded. One, 2,5, 6,10, 11,20, and >20 candidate compositions were found for 65%, 39%, 1%, 1%, and 0%, respectively, for the 124 ionized molecules formed from the 113 chemicals tested (both positive and negative ions were obtained from 11 of the chemicals). However, no candidate composition was found for 2% of the test cases (i.e., 3 chemicals), for each of which the measured mass of one of the product ions was in error by 5,6.7,mDa. Copyright © 2005 John Wiley & Sons, Ltd. [source] Analysis of protein ions in the range 3000,12000,Th under partial (no discharge) atmospheric pressure chemical ionization conditions using ion trap mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 12 2002Simone Cristoni A new approach, based on the use of atmospheric pressure chemical ionization ion trap mass spectrometry (APCI-ITMS), but without a corona discharge, was investigated for application to creating and monitoring protein ions. It must be emphasized that APCI is not usually used in protein analysis. In order to verify the applicability of the proposed method to the analysis of proteins, two standard proteins (horse cytochrome c and horse myoglobin) were analyzed. A mixture of the two proteins was also analyzed showing that this novel approach, based on the use of APCI, can be used in the analysis of protein mixtures. Copyright © 2002 John Wiley & Sons, Ltd. [source] Intermolecular Phenolic Hydroxy Methylation Occurring between Chiral N,N, -Bis(2-hydroxyphenyl)-2,2-dimethyl-1,3-dioxolane-4,5-dicarbamide and Co-crystallized Methanol under Electron Impact Ionization ConditionsCHINESE JOURNAL OF CHEMISTRY, Issue 5 2004Jia-Xi Xu Abstract An intermolecular phenolic hydroxy methylation occurring between chiral N,N, -bis(2-hydroxyphenyl)-2,2-dimethyl-1,3-dioxolane-4,5dicarbamide and co-crystallized methanol under electron impact ionization conditions was observed. The result was confirmed by X-ray diffraction structural analysis of a co-crystalline of (R,R)-enantiomer and methanol. [source] | ||||||||||||||||||||||