Mass spectra during

Therefore, the information obtained, through onsite GC/MS analysis about the identity of compounds present in a sample should be restricted to chemicals relevant to the aim of the inspection. This is achieved by operating the instrument in a specially developed blinded mode, which shows neither the chromatogram nor mass spectra during or after the chromatographic run. Additionally, if the analysis is conducted in blinded mode, the only available postprocessing software is a specifically developed on-site version of AMDIS (Automated Mass Spectral Deconvolution and Identification System). This software works only with the OCAD, which contains only compounds relevant to the CWC thus, it reports exclusively the presence of compounds for which spectra are in this database library. 

Reconstruction of a gas release pattern which normalizes the largest gas release peak or region to 100 and indexes the mass spectra during the run. 

Gas chromatography-mass spectrometry (GC-MS) was performed with a Fin-nigan MAT (San Jose, CA) model 4021B quadrupole mass spectrometer interfaced to a Hewlett Packard 5890 GC equipped with an on-column injector. Mass spectra during GC-MS were obtained by chemical ionization with ammonia reagent gas at a source pressure of 0.3 torr. 

Repetitive Acquisition of Mass Spectra During Eiution... 

During the course of biochemical studies (138). the mass spectrum of 2-acetamidothiazole was recorded its main peaks are the molecular ion (m/e= 142, relative intensity = 26%) and fragments 100 (100), 58 (2. 5), and 43 (39). For 2-acetamido-5-bromothiazole the main peak results again from the loss of C2H2O by the molecular ion. 2-AcetyIacet-amido-4-methylthiazole (2S) exhibits significant loss of from the... 

At the end of this section, let us return briefly to the spectra shown in Fig. 3. Notice the structure in the mass spectrum of QoCa, between the completion of the first metal layer at 32 and the second at 104. This structure is identical in the fragmentation mass spectra of fullerenes covered with Ca and with Sr. It is reminiscent of the subshell structure of pure Ca clusters. The subshells could be correlated with the formation of stable islands during the growth of the individual shells[10,l 1]. The sublayer structure we observe here may also give some clue to the building process of these layers. However, the data is presently insufficient to allow stable islands to be identified with certainty. 

One of the major limitations of FI is that the excess energy imparted to the analyte molecule during electron bombardment may bring about such rapid fragmentation that the molecular ion is not observed in the mass spectrum. Under... 

The flow rate of liquid in the HPLC-electrospray system is paramount in determining performance both from chromatographic and mass spectrometric perspectives. The flow rate affects both the size and size distribution of the droplets formed during the electrospray process (not all droplets are the same size) and, consequently, the number of charges on each droplet. This, as we will see later, has an effect on the appearance of the mass spectrum which is generated. It should also be noted that the smaller the diameter of the spraying capillary, then... 

Examination of the mass spectrum of P2VPY taken during the maximum decomposition rate reveals the major decomposition products as methylpyridine (93 a.m.u.), protonated vinyl pyridine (106 a.m.u.), and protonated dimer (211 a.m.u.) with ion ratios 74 100 59 respectively. Trimeric and tetrameric protonated species (316 and 421 a.m.u.) are also observed but in relatively small amounts. Protonated ions, rather than the simple monomers and dimers observed for the decomposition of poly(styrene) by MS11, may be created by a mechanism similar to that reported for the decomposition of 2-(4-heptyl)pyridine12 in the mass spectrometer. 

During a search for physiologically active compounds in South African plants, a new hasubanan ester acetal alkaloid, methylstephavanine (6), was isolated from Stephania abyssinica (19). The H-NMR spectrum of the new alkaloid 6 exhibited signals for one methylenedioxy, one N-methyl, and four methoxyl groups (19) (Table II). Its mass spectrum revealed the most abundant ion peak at m/z 229, indicating a close resemblance to the known hasubanan alkaloid, stephavanine (18). 

The central engine of this data workflow is the process of spectral deconvolution. During spectral deconvolution, sets of multiply charged ions associated with particular proteins are reduced to a simplified spectrum representing the neutral mass forms of those proteins. Our laboratory makes use of a maximum entropy-based approach to spectral deconvolution (Ferrige et al., 1992a and b) that attempts to identify the most likely distribution of neutral masses that accounts for all data within the m/z mass spectrum. With this approach, quantitative peak intensity information is retained from the source spectrum, and meaningful intensity differences can be obtained by comparison of LC/MS runs acquired and processed under similar conditions. 

If during the ionization the amount of energy deposited on the molecule is low, as occurs in soft techniques, i.e. Cl, ESI, DESI and MALDI, the mass spectrum is very simple. It is characterized by protonated/deprotonated molecules, and eventually few adduct ions but very few or no fragment ions. This implies that it is easy to obtain the molecular weight of the analyte under investigation, but structural information is missing. As an example, the ESI mass spectrum of a small molecule is reported in Figure 2.20. There are two main ions one at m/z 556 and another at m/z 578. As the mass spectrum has been obtained in positive... 

The general pattern of the mass spectrum and the presence of peaks at mlz 424, 426 and 442, attributed, respectively, to the molecular ions of lupeol, lupenone and betulin, suggest the presence of birch bark tar. This study provided the first evidence that birch bark tar was used for assembling bronze tools during the Iron Age in Europe. 

The MS detection system can be such that the full mass spectrum is observed (at least five peaks) or just selected ions monitored (SIM) with three or four identification points. For some analyses, it may be necessary to use MS-MS" techniques [8]. In LC-MS, it is important to make sure that ionization of the compounds of interest has been achieved. For all of these approaches, the criteria for matching of the analyte with the standard should be established during validation studies. 

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