The qualitative and quantitative capability of the ion trap mass analyzer could be greatly affected by the accumulation time. However, the importance of the accumulation time has not so far been thoroughly explored. Here, the influence of ion accumulation time on qualitative and quantitative analysis of complicated components was systematically investigated based on the case study of 40 ophiopogonins in Ophiopogon extract by hybrid ion trap time-of-flight mass spectrometry (LCMS-IT-TOF). In this process, the accumulation time was set at 10, 25, 50, 100, and 200 ms, respectively. The effect of accumulation time on qualitative analysis of ophiopogonins was studied by comparing the total ion current (TIC) of MS1, TIC of MS2, and the number and signal of fragmental ions. The results demonstrated that the signal could be greatly influenced by varying the accumulation time. The number and signal of the fragmental ions were increased significantly with a longer accumulation time in the range of 10–100 ms. Also, the effect of accumulation time on quantitative analysis of ophiopogonins was investigated by comparing the linearity, accuracy, and precision measured on LCMS-IT-TOF. Importantly, quantitative parameters could all be significantly improved by choosing an appropriate accumulation time. 相似文献
The rapid separation of isomeric precursor ions of oligosaccharides prior to their analysis by mass spectrometry to the nth power (MSn) was demonstrated using an ambient pressure ion mobility spectrometer (IMS) interfaced with a quadrupole ion trap. Separations
were not limited to specific types of isomers; representative isomers differing solely in the stereochemistry of sugars, in
their anomeric configurations, and in their overall branching patterns and linkage positions could be resolved in the millisecond
time frame. Physical separation of precursor ions permitted independent mass spectra of individual oligosaccharide isomers
to be acquired to at least MS3, the number of stages of dissociation limited only practically by the abundance of specific product ions. IMS–MSn analysis was particularly valuable in the evaluation of isomeric oligosaccharides that yielded identical sets of product
ions in tandem mass spectrometry experiments, revealing pairs of isomers that would otherwise not be known to be present in
a mixture if evaluated solely by MS dissociation methods alone. A practical example of IMS–MSn analysis of a set of isomers included within a single high-performance liquid chromatography fraction of oligosaccharides
released from bovine submaxillary mucin is described. 相似文献
This article describes a comprehensive characterization of bovine β-lactoglobulin peptides glycated with an aldohexose (galactose) or a ketohexose (tagatose), derived from in vitro gastrointestinal digestion, by liquid chromatography coupled to positive electrospray ion trap tandem mass spectrometry. In addition to the dissociation pathway previously described for aldohexoses-derived Amadori compounds, i.e. formation of the pyrylium ([M+H]+-54) and furylium ions ([M+H]+-84) via the oxonium ion ([M+H]+-18), another and more direct fragmentation route involving the formation of the imminium ion ([M+H]+-150) is also reported following extensive glycation rates of β-lactoglobulin with both carbohydrates. These results indicated that the analysis of digested proteins by LC-ESI-MS2 on a three-dimensional ion trap monitoring neutral losses is an efficient and direct method to identify peptides glycated not only through the Amadori rearrangement but also via the Heyns rearrangement. Nevertheless, as the predominating MS2 fragmentation pattern of the glycated peptides is derived from the sugar moiety, the sequence-informative b- and y-ions resulting from peptide backbone cleavage were undetected. To overcome this drawback, and taking advantage of multi-stage fragmentation capabilities of ion traps, the indicative Amadori and Heyns-derived imminium ions were successfully used in MS3 analyses to identify the peptide backbone, as well as the specific glycation site. In addition, further MS4 analyses were needed to carry out the characterization of doubly glycated peptides. 相似文献
The ability to obtain daughter ion formulas via comparison of MSn spectra of parent ions containing only 12C with those of parent ions with one 13C (from the natural 13C abundance) is shown for cases in which isobaric interferences with the 13C-containing ion preclude the use of the conventional tandem mass spectrometric approach. This method allows the presence of isobaric daughter ions to be ascertained, and unexpected, complex dissociation pathways to be identified. A three-dimensional quadrupole ion trap is used for these experiments. Its high tandem mass spectrometry efficiency makes possible this type of experiment. 相似文献
Top-down analyses of protonated insulin cations of charge states of 4+, 5+, or 6+ were performed by exposing the isolated precursor ions to a beam of helium cations with kinetic energy of more than 6 keV, in a technique termed charge transfer dissociation (CTD). The ~100 ms charge transfer reaction resulted in approximately 20% conversion efficiency to other intact charge exchange products (CTnoD), and a range of low abundance fragment ions. To increase backbone and sulfide cleavages, and to provide better structural information than straightforward MS2 CTD, the CTnoD oxidized products were isolated and subjected to collisional activation at the MS3 level. The MS3 CTD/CID reaction effectively broke the disulfide linkages, separated the two chains, and yielded more structurally informative fragment ions within the inter-chain cyclic region. CTD also provided doubly oxidized intact product ions at the MS2 level, and resonance ejection of the singly oxidized product ion revealed that the doubly oxidized product originates directly from the isolated precursor ion and not from consecutive CTD reactions of a singly oxidized intermediate. MS4 experiments were employed to help identify potential radical cations and diradical cations, but the results were negative or inconclusive. Nonetheless, the two-electron oxidation process is a demonstration of the very large potential energy (>20 eV) available through CTD, and is a notable capability for a 3D ion trap platform.
An ultra‐high‐pressure liquid chromatography/MS3 (UPLC‐MS3) method has been developed and validated for the quantitative determination of four major TSNAs in mainstream cigarette smoke using MS3 scan mode on a hybrid triple quadrupole‐linear ion trap mass spectrometer. The new method combining the UPLC with MS3 scan mode offers decreased sample analysis time and good selectivity. After mainstream cigarette smoke was collected on a Cambridge filter pad, the particulate matter was extracted with ammonium acetate solution and analyzed by UPLC‐MS3 using isotopically labeled analogues as internal standards. Four TSNAs were completely separated on an Agilent XDB‐C18 UPLC column using isocratic elution during a 6 min LC run time. Excellent linearity was obtained over the concentration range of 1.0‐150.0 ng/mL for all TSNAs with values for correlation coefficient (r) between 0.9985‐0.9994. Limits of detection (LOD) of each TSNA varied from 0.023 to 0.067 ng/mL, and lower limits of quantification (LLOQ) varied from 0.077 to 0.223 ng/mL, respctively. The recovery of each TSNA was from 89.2 to 106.8%. The method achieved excellent reproducibility with RSD 2.1‐6.8% for intra‐assay and 3.4‐9.1% for inter‐assay. This method can be used as an effective approach to significantly improve the detection capability for TSNAs in complex matrices. 相似文献
Obtaining unambiguous linkage information between sugars in oligosaccharides is an important step in their detailed structural analysis. An approach is described that provides greater confidence in linkage determination for linear oligosaccharides based on multiple-stage tandem mass spectrometry (MSn, n >2) and collision-induced dissociation (CID) of Z1 ions in the negative ion mode. Under low energy CID conditions, disaccharides 18O-labeled on the reducing carbonyl group gave rise to Z1 product ions (m/z 163) derived from the reducing sugar, which could be mass-discriminated from other possible structural isomers having m/z 161. MS3 CID of these m/z 163 ions showed distinct fragmentation fingerprints corresponding to the linkage types and largely unaffected by sugar unit identities or their anomeric configurations. This unique property allowed standard CID spectra of Z1 ions to be generated from a small set of disaccharide samples that were representative of many other possible isomeric structures. With the use of MSn CID (n = 3 – 5), model linear oligosaccharides were dissociated into overlapping disaccharide structures, which were subsequently fragmented to form their corresponding Z1 ions. CID data of these Z1 ions were collected and compared with the standard database of Z1 ion CID using spectra similarity scores for linkage determination. As the proof-of-principle tests demonstrated, we achieved correct determination of individual linkage types along with their locations within two trisaccharides and a pentasaccharide.
In clinical or forensic toxicology, general unknown screening procedures are used to identify as many xenobiotics as possible,
belonging to numerous chemical classes. We present here a general unknown screening procedure based on liquid chromatography
coupled with use of a single linear ion trap mass spectrometer, and focus on the identification of pesticides and/or metabolites
in whole blood. After solid-phase extraction (SPE), the compounds of interest were separated using a reversed-phase column
and identified by the mass spectrometer operated first in the full-scan mass spectrometry (MS) mode, in the positive and negative
polarities, followed by MS2 and MS3 scanning of ions selected in data-dependent acquisition. The total scan time was 2.45 s. Two mass spectral libraries (MS2 and MS3), each of 450 spectra, were created for the 320 pesticides and metabolites detected after injection of pure solutions. Robustness
of the spectra and matrix effects were studied and were satisfactory for the present application. Detection limits for the
320 compounds were studied by extracting 1 mL spiked blood at concentrations between 10 μg/L and 10 mg/L. If necessary, it
was possible to decrease the detection limits of some compounds by 10–100-fold by scanning MS2 in only one polarity, owing to a shorter total scan time. However, at the same time, the detection specificity decreased
as no confirmation could be recorded in the following MS3 scan and no information could be registered in the other polarity. So, in these rare cases, confirmation by another method
was required. 相似文献
The application of electrospray ionization (ESI) ion trap mass spectrometry in the characterization of O-glucuronide conjugates of some drugs in urine is described. The conjugated metabolites formed in rabbit and human were separated
by reversed-phase high-performance liquid chromatography (HPLC) and characterized by multi-stage mass spectrometry (MSn) experiments in negative ion mode. The ESI mass spectra showed a deprotonated molecule [M–H]–, which was chosen as precursor ion. Collision-induced dissociation (CID) of [M–H]– in MSn experiments resulted in the appearance of glucuronate ‘fingerprint’ ions at m/z 175 and 113 as well as prominent aglycone
ions which were the same as those produced from authentic specimens. This information can be used to identify this type of
compound directly without the need for derivatization or hydrolysis of enzymes, providing a rapid and specific method for
guiding the isolation and characterization of similar compounds in complex matrices with LC/MS.
Received: 25 January 1999 / Revised: 19 April 1999 / Accepted: 13 May 1999 相似文献
The MSn spectra of three bimetallic oxovanadium complexes were obtained using an ion trap. The fragmentation pathways were elucidated.
Common features and major differences between ESI–QTOF–MS/MS and ESI–IT–MSn spectra were compared. Electron affinities of several radical molecular anions were calculated by DFT and these could be
used as an indicator of the ions’ stability. 相似文献
Two native ganglioside mixtures from normal human fetal cerebellum in the 15th (Cc15) and 40th (Cc40) gestational week were subjected to NanoMate high capacity ion trap (HCT) mass spectrometric (MS) and collision induced dissociation (CID) tandem MS (MS2) analysis under thoroughly optimized experimental conditionns. An total of 56 different species were identified in Cc15 and 54 in Cc40. By employing CID MS2 molecular ions, related GD1 (d18:1/20:0) and GM2 (d18:1/19:0) species were structurally characterized in a high throughput mode. The method provided elevated ionization efficiency, high speed of analysis, almost 100% reproducibility at sample consumption per experiment situated in the femtomole range. 相似文献
Three methods of operating an ion trap mass spectrometer (ITMS) were investigated for the determination of quantitative information by combined capillary GC/MS and GC/MS/MS. Separate regression Lines for a hexynone drug were examined by using bath unlabeled and stable-isotope-labeled internal standards. The ITMS modes of operation examined were (1) the full-scan, rf-voltage-only mode, useful on ion trap detectors as well as on the ITMS, (2) a scan using combined rf and dc voltages (rf/dc) for mass-selective storage analyses, and (3) rf/dc followed by collision-induced dissociation, Results of over 200 analyses in the 0.1–10 ng on-column range, with 5 ng of internal standard, showed that the unlabeled internal standard, separated by retention time on the capillary GC column, gave the best relative standard deviatiod (less than 5% over the range) and linear correlations (r2 typically > 0.9992). 相似文献
In the traditional research of volatile compounds, some trace-level compounds could not be identified by gas chromatography-mass spectrometry. Target and post-targeted methods were applied in the investigation of trace-level volatile compounds in fresh turf crop (Lolium perenne L.) based on gas chromatography in combination with hybrid quadrupole time-of-flight mass spectrometry. According to literatures published, a target analysis was performed by using retention index, accurate masses of characteristic ions and second-stage mass spectra (MS2 spectra). And a series of experiments showed that low electron impact energy was beneficial to the improvement of the abundances of low abundance molecular ion peak. peak was beneficial to qualitative analysis. Totally, 60 Enhancing the abundances of low abundance molecular ion volatile compounds were identified, the great majority cornpounds of which were benzeneacetaldehyde (14.8%), 2,5-dimethyl-pyrazine (9.6%), and hexanal (9.3%). Identification was complied by mass spectral search, retention index and accurate masses of characteristic ions. 相似文献