Home About us Contact
|
Home About us Contact | ||
|
|
||
Characteristic Fragment Ions (characteristic + fragment_ion)
Selected AbstractsOptimization of the ESI and APCI experimental variables for the LC/MS determination of s-triazines, methylcarbamates, organophosphorous, benzimidazoles, carboxamide and phenylurea compounds in orange samplesJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 10 2007Guilherme M. Titato Abstract In this work, ten selected pesticides of different chemical groups, indicated to orange culture, were extracted and determined by liquid chromatography,mass spectrometry using both electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) operating in the positive ion detection mode. Applying a variables selection technique verified that cone voltage, source temperature and drying-gas flow-rate are the critical variables when the ESI was used, while cone voltage was found to be the only critical variable for the MS system, operating with the APCI ionization mode. After optimization of the most important parameters through the variables selection technique, the selected ion-recording (SIR) mode, monitoring the [M + H]+ species for all the compounds, was applied for the method validation of the pesticides, in both ionization modes. In orange samples, matrix effects did not interfere with the determination of the pesticides. Pesticides quantification limits ranged from 10 to 50 µg kg,1 for ESI and from 8.2 to 45 µg kg,1 for APCI. Linearity was studied from LOQ upto 200 times LOQ values (r > 0.98). Recoveries obtained were in the range of 70.2,100.5% (RSDs less than 10%). In order to guarantee that the identification and confirmation of the studied pesticides in real samples were unequivocal, characteristic fragment ions of the pesticides were obtained by varying the cone voltage (in-source CID). Copyright © 2007 John Wiley & Sons, Ltd. [source] Tuning compounds for electrospray ionization/in-source collision-induced dissociation and mass spectra library searchingJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 9 2001Wolfgang Weinmann Abstract Tuning compounds for positive and negative electrospray ionization (ESI) were tested for the tuning of in-source collision-induced dissociation (ESI/CID) with three types of SCIEX API instruments (API 365, 2000 and 3000) in the single-quadrupole mode. The vacuum interfaces of these instruments differ slightly in geometry, but the principles of ionization and solvent evaporation by nebulizer and curtain gases, orifice and skimmer are identical. For comparison of in-source CID, breakdown curves of haloperidol, paracetamol, metronidazole and metamizole were acquired by increasing the orifice voltages. The API 2000 and 3000 required higher orifice voltages than did the API 365 to induce a similar degree of fragmentation of the protonated or deprotonated molecules to characteristic fragment ions. This increase of orifice voltage could be demonstrated with each of the four compounds tested by a shift of the maxima of the breakdown curves to higher orifice voltages. A procedure with three collision energy (CE) levels for drug identification with a mass spectra library set up with an API 365 therefore required an adjustment of the orifice voltages to higher values when being transferred to an API 2000 or API 3000. The corresponding orifice voltages for the three instruments were 20/50/80 V (API 365), 30/90/130 V (API 2000) and 40/80/120 V (API 3000). However, a change in orifice voltage of ±10 V (with the API 2000 and 3000) hardly influenced the fit values of a library search for each single CE level. For adjusting orifice voltages with different instruments, a tuning procedure with haloperidol and paracetamol is presented. With this tuning procedure an ESI/CID mass spectra library set up for API 365 and API 150 could also be used for drug identification with an API 2000 and an API 3000 with good library search results. Copyright © 2001 John Wiley & Sons, Ltd. [source] Simultaneous determination of 103 pesticide residues in tea samples by LC-MS/MSJOURNAL OF SEPARATION SCIENCE, JSS, Issue 9 2009Zhiqiang Huang Abstract A simple and sensitive method was developed and validated for the simultaneous determination of 103 pesticide residues in tea by LC-MS/MS. For the analysis of the pesticide with polarity, thermal lability or low volatility, this LC-MS/MS method has an advantage over GC. In this work, residual pesticides were extracted from the tea sample with ACN and then purified using Carb-NH2 SPE cartridges. Using the multiple reaction monitoring mode, the pesticides were quantified and identified by the most abundant and characteristic fragment ions. The recoveries obtained for each pesticide ranged between 65 and 114% at three spiked concentration levels. The intra-day precisions were lower than 19.6%. Good linear relationships were observed with the correlation coefficients r2 >0.996 for all analytes. The established method was successfully applied to the determination of pesticide residues in real tea samples. [source] High-speed separation and characterization of major constituents in Radix Paeoniae Rubra by fast high-performance liquid chromatography coupled with diode-array detection and time-of-flight mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 1 2009E-Hu Liu A fast high-performance liquid chromatography (HPLC) method coupled with diode-array detection (DAD) and electrospray ionization time-of-flight mass spectrometry (ESI-TOFMS) has been developed for rapid separation and sensitive identification of major constituents in Radix Paeoniae Rubra (RPR). The total analysis time on a short column packed with 1.8-µm porous particles was about 20,min without a loss in resolution, six times faster than the performance of a conventional column analysis (115,min). The MS fragmentation behavior and structural characterization of major compounds in RPR were investigated here for the first time. The targets were rapidly screened from RPR matrix using a narrow mass window of 0.01,Da to restructure extracted ion chromatograms. Accurate mass measurements (less than 5,ppm error) for both the deprotonated molecule and characteristic fragment ions represent reliable identification criteria for these compounds in complex matrices with similar if not even better performance compared with tandem mass spectrometry. A total of 26 components were screened and identified in RPR including 11 monoterpene glycosides, 11 galloyl glucoses and 4 other phenolic compounds. From the point of time savings, resolving power, accurate mass measurement capability and full spectral sensitivity, the established fast HPLC/DAD/TOFMS method turns out to be a highly useful technique to identify constituents in complex herbal medicines. Copyright © 2008 John Wiley & Sons, Ltd. [source] Electron ionization mass spectra of phosphorus-containing heterocycles.RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2006The electron ionization mass spectra of cis - and trans -fused 1,2,3,4,4a,5,6,7,8,8a-decahydro-1,3,2-benzodiazaphosphinine 2-oxides (1,17) were recorded, and the fragmentation pathways were established and compared with those of 1,4,4a,5,6,7,8,8a-octahydro-2H -3,1,2-benzoxazaphosphinine 2-oxides. In general, the mass spectral behaviors of the isomeric compounds were very similar and it was mostly impossible to differentiate them from each other on the basis of the relative abundances of their characteristic fragment ions. The compounds in which R2,=,Ph or OPh exhibited a series of common fragments, e.g. [R2H]+, R2PONHR1(3)+, [M,C3H7]+ and [M,C4H9]+, the latter two ions being present in the spectra of only two of the derivatives with an N(CH2CH2Cl)2 substituent on the P atom. When R2,=,Ph, numerous other alkyl radicals, alkenes and a cycloalkane were also ejected and these compounds also lost NH2, NH3, CH3N, CH4N or CH3NH2. The compounds with an N(CH2CH2Cl)2 substituent on the P atom most closely resembled their 3,1,2-O,N,P analogs in respect of the dominant role of this substituent. Copyright © 2006 John Wiley & Sons, Ltd. [source] Metabolite profiling in rat urine by liquid chromatography/electrospray ion trap mass spectrometry.RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 22 2003Application to the study of heavy metal toxicity This work reports the use of reverse-phase liquid chromatography coupled to electrospray ion trap (QIT) mass spectrometry for the analysis of the metabolome in rat urine. An injection of 20,,L of urine into the chromatographic system is followed by a slow gradient elution and mass spectrometric detection in the scanning mode from m/z 100,1000 in both positive and negative modes. Over a time scale of 90,min, 30 and 20 resolved peaks were observed in the positive and the negative modes, respectively, corresponding to the presence of a few hundred m/z ratios. By using a QIT analyzer, data-dependent tandem mass spectrometry of selected m/z ratios identified several compounds in rat urine and characterized various chemical families, including carboxylic acids, amines, sulfated compounds, glucuronides and glycosides, by the observation of characteristic fragment ions or neutral losses. The method has been applied to the investigation of the chronic toxicity of heavy metals in rat urine. A few tens of m/z ratios, differing in intensity more than threefold from control values, were observed in both positive and negative modes. The time variations for some selected ions suggest that LC/ESI-MS could allow selective characterization of biomarkers in response to specific toxic compounds. Copyright © 2003 John Wiley & Sons, Ltd. [source] Electrospray ionization mass spectrometry of AZT H -phosphonates conjugated with steroidsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 13 2003Qiang Xiao AZT H -phosphonates conjugated with steroids were synthesized and determined by positive and negative ion electrospray ionization mass spectrometry (ESI-MS) in conjunction with tandem mass spectrometry (MS/MS). The fragmentation pathways were investigated in detail. There are very different characteristic fragment ions in the positive and negative ion MS/MS spectra. The azide group of compounds 6a and 6b underwent either elimination of HN3 or rearrangement to an amine in both positive and negative ion mass spectrometry. Copyright © 2003 John Wiley & Sons, Ltd. [source] Simultaneous clinical monitoring of lactic acid, pyruvic acid and ketone bodies in plasma as methoxime/tert-butyldimethylsilyl derivatives by gas chromatography,mass spectrometry in selected ion monitoring modeBIOMEDICAL CHROMATOGRAPHY, Issue 5 2008Man-Jeong Paik Abstract Simultaneous determination of lactic acid, pyruvic acid, 3-hydroxybutyric acid and acetoacetic acid for clinical monitoring of lactic acidosis and ketone body formation in human plasma (20 µL) was performed by gas chromatography,mass spectrometry in selected ion monitoring (SIM) mode after generating methoxime/tert-butyldimethylsilyl derivatives. All of the targeted carboxylic acids were detected by characteristic fragment ions, which permitted sensitive and selective identification in the presence of co-extracted free fatty acids and other acidic metabolites at much higher levels. The method was linear (r , 0.9991), reproducible (% relative standard deviation = 1.2,5.8), and accurate (% relative error = ,7.2,7.6), with detection limits of 0.05,1.7 ng/mL. This rapid, accurate and selective method using minimal plasma samples (20 µL) is useful in the clinical monitoring of lactic acidosis and ketone body formation in plasma. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||