Mass negative mode

Description ring cleavage charge retained on nonreducing end infrequent pathway in the positive-ion mode, but a major pathway in the negative mode, because a stable, enolate anion results from loss of the enolic hydrogen atom ions are 42 mass units higher than those formed in Pathway C. 

The time-of-flight mass spectrometer was usually operated in the positive mode in order to detect the cationic sodium adducts of the analyte molecules. The anions of H-acidic substances were detected in the negative mode. This mode significantly enhanced the signals of acidic compounds, e.g. free fatty acids compared with ester signals in the mass spectra of beeswax and tung oil. 

Octadecyl sulfate sodium salt (Ci8H37-0-S03 Na+) was examined by laser desorption (LD) Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) in the negative mode resulting in [M - H] ions. Little fragmentation was observed under these conditions [28]. 

For comparison of the different ionisation methods and detection modes, the results obtained as FIA overview spectra are presented in Figs. 2.11.7 and 2.11.8. Reconstructed ion chromatograms (RIC) of APCI and ESI combined with selected mass traces of all LC separations and, in parallel, the selected standardised mass traces of the C42 and C14 homologues containing three ethoxy chain links recorded in the negative mode are presented in Fig. 2.11.9. These results again demonstrate the quite large variation in the ionisation efficiency of... 

A mixture of these fluorinated surfactants was separated according to the method applied by Popenoe et al. [52]. For ionisation and detection, ESI-MS in the negative mode was applied. The result of LC separation is presented in the RIC in Fig. 2.11.26(a). Some of the separated compounds in the TIC and mass traces could be identified as perfluoro alkylsulfonates and perfluoro alkylcarboxylates such as... 

Sulfosuccinates, as presented with their general structural formula in Fig. 2.11.33, are applied as surfactants for personal hygiene because of their hypoallergenic features. The sodium salt of the sulfosuccinate blend with the formula ROOC-CH-(SC>3 )-CH2-COOR Na+ (R = CsH-iy) was examined by APCI-FIA-MS in the positive and negative modes. The addition of an excess of ammonium acetate under FIA-APCI-MS(+) conditions resulted in [M — NH4]+ ions with mlz 440 while [M — H] ions with mlz 421, however, were observed in the negative APCI-FIA-MS mode (Fig. 2.11.34(a)). Only one type of ion could be observed in this industrial blend by FIA-MS. This purity could also be confirmed by APCI-LC-MS(-), as shown in the total ion current trace (cf. Fig. 2.11.34(b)), which is presented in combination with the averaged mass spectrum under the signal in the inset of Fig. 2.11.34(b) [22],... 

Busman M., Schey K.L., Oatis Jr. J.E., and Knapp D.R.J. (1996), Identification of phosphorylation sites in phosphopeptides by positive and negative mode electrospray ionization tandem mass spectrometry, J. Am. Soc. Mass Spectrom. 7, 243-249. 

HPLC - Beckman 125 binary gradient pumps, 168 diode-array detector, 507 autosampler MS - Ion-trap mass spectrometer Finnigan LCQ equipped by APCI (atmospheric pressure chemical ionization), data analyzed in negative mode, spectra confirming found compounds were obtained from tandem mass spectromectry (MS/MS). 

The optimization of the process in recent years, led to defined ion formation with solvent evaporation and complete desolvatation of analyte ions, which are then accelerated towards the mass separator. Analyte molecules often form multiply charged ions. ESI can be carried out both in positive and in negative mode. The sample introduction can be performed with microscale tips mainly made of fused silica capillaries, which are inexpensive and available in various sizes and geometric forms. Recently, nanospray technologies as microvariants of ESI with increased sensitivity were developed, which allowed the analysis of extremely small sample amounts [57]. 

Detection of the polyols is carried out on a Quattro Micro tandem mass spectrometer (Micromass) equipped with an electron ion spray source operating in the negative mode. The mass spectrometer parameters are as follows source temperature, 350°C cone voltage, 30 V collision energy, 10 eV. Detection of the polyols is performed by MRM. The MRM transition (Q1/Q3) settings for the different polyols are ... 

Unlike with GC-MS, quality criteria for identification of drug residues by LC-MS have not been yet defined within the European Union, but this is currently under review. Criteria for GC-MS stipulate the measurement of preferably at least four diagnostic ions. However, this is not always possible with LC-MS because most compounds will only produce an M ion in positive mode or a M ion in negative mode, with little fragmentation when using thermospray (TSP), electrospray (ESP), or atmospheric pressure chemical ionization (APCI). Even where the ions and ratios are in agreement, there will be still possibility of misidentification. For this reason, mass spectra data are often interpreted with additional supporting data such as the LC retention times, as, for example, in the LC-MS analysis of sulfadimethoxine and sulfadoxine that present identical mass spectra (24). 

TOFSIMS analysis. The positive and negative TOFSEMS spectra of the same films are shown in Fig. 2. It should be noted that these were acquired in the low mass resolution mode, hence the peak identification is not completely unequivocal in some cases. 

The TLC purified diphosphoryl lipid A fractions (TLC -3, -5, and -7) were analyzed by FAB mass spectrometry in the negative mode as previously described (23) and the results are shown in Table X. TLC-3 gave a molecular ion (M-H) at m/z 1796 TLC-5, m/z 1586 TLC-7, m/z 1360. As expected, these values were 80 amu or (P03H2 H) larger than those for the corresponding monophosphoryl lipid A s of the series as shown in Table VIII. These results established the structural relationship between the mono- and diphosphoryl lipid A s. 

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