Ionization, chemical source

A further important property of the two instruments concerns the nature of any ion sources used with them. Magnetic-sector instruments work best with a continuous ion beam produced with an electron ionization or chemical ionization source. Sources that produce pulses of ions, such as with laser desorption or radioactive (Californium) sources, are not compatible with the need for a continuous beam. However, these pulsed sources are ideal for the TOF analyzer because, in such a system, ions of all m/z values must begin their flight to the ion detector at the same instant in... 

Although the conventional mass spectra of the five C- nitro derivatives of indazole are nearly identical, the corresponding metastable peak shapes associated with the loss of NO-can be used to differentiate the five isomers (790MS114). The protonation and ethylation occurring in a methane chemical ionization source have been studied for a variety of aromatic amines, including indazoles (80OMS144). As in solution (Section 4.04.2.1.3), the N-2 atom is the more basic and the more nucleophilic (Scheme 5). 

Chemical Ionization Source Combination Gas Chromatography/Chemical... 

Figur 9.7 Schematic diagram of a high flow rate interface for direct fluid introduction into a modified chemical ionization source for SFC/MS. (Reproduced with permission from ref. 83. Copyright American Chemical Society).

Allene Radical Cations. The bimolecular reactivity of the radical reactions of allene and propyne has been a longstanding matter of interest. Myher and Harrison179 studied the ion/molecule reactions of ionized C3H4 with the respective neutral precursor in a medium-pressure chemical ionization source. CsH7+ ions were found to be amongst... 

Fig. 1.12 Atmospheric pressure chemical ionization source. A Analyte.

Gallagher, R. T Balogh, M. P. Davey, P. Jackson, M. R. Sinclair, L Southern, L. J. Combined electrospray ionization-atmospheric pressure chemical ionization source for use in high-throughput LC-MS applications. Anal. Chem. 2003, 75, 973-977. 

Figure 3. Mechanisms for positive ion formation in a chemical ionization source...

Aqueous solutions of ammonium sulfate and ammonium bisulfate were deposited on Fluoropore filters, placed in the direct insertion probe, and analyzed in the chemical ionization mode (H2O reagent) gas. The samples were heated from 100°C to 330 C at 15 C/minute. No sample ions were observed under these anlaysis conditions, even when several micrograms of ammonium salts were analyzed. The thermal decomposition of ammonium salts of sulfate has been the subject of many studies. (29,30) Some pathways include sulfuric acid production at one stage of the decomposition while others suggest ammonia, SO2 and SO3 are the products. None of these accurately simulate the conditions (temperature, pressure, gas flow) present in our chemical ionization source. However, no sulfuric acid ions (H3SO4+, etc.) were ob-served... 

Schwarz and coworkers have used the technique of neutralization-reionization mass spectrometry (NRMS) to structurally characterize numerous elusive silicon-containing molecules of interstellar interest342. The identification of HNSi was supported by ab initio calculations. The radical ion [HNSi] + was produced from N2 and SiH3I in the chemical ionization source of the mass spectrometer. 

The chemical ionization mass spectrum of cimetidine and the major fragmentation ions are presented in Figure 8 and Table 4. The spectrum was obtained using a Finnigan lYbdel 3200 quadrupole mass spectrometer fitted with a chemical ionization source. The sample, applied to the probe from an acetone solution, was introduced via the direct inlet system. Methane was used as the reactant gas. 

Mass spectrometry has proved highly suitable for the elucidation of chemical structures and sensitivity. It is thus an invaluable tool for resolving extremely complex natural mixtures. Thus, on-line coupled SFE-MS constitutes a rapid, reliable choice for the determination of mycotoxins in wheat, which possess a high toxicological interest. For example, an SF extractor coupled to an MS chemical ionization source provided limits of detection in the picogram range for diacetoxyscirpenol and toxin T-2 [122]. Used in tandem with chemical ionization-collision induced dissociation MS-MS, SFE has also enabled the rapid detection and identification of species without the need for complete extraction [131],... 

Pyrolysis-direct chemical ionization mass spectrometry ( r-DCI-MS) was recently introduced as a pyrolysis technique for the characterization of complex macromolecular samples and for the analysis of biopolymers. This technique does not require special pyrolysis equipment and can be performed with an instrument which is equipped with a chemical ionization source and a standard DCI probe, which consists of an extended wire used to introduce the sample material directly into the chemical ionization plasma. An important characteristic of this technique is the pyrolysis... 

FIGURE 13. (a) CID spectrum of protonated aniline (m/z 94) generated in ESI conditions (20 eV collision energy) and (b) low energy CID spectrum of protonated aniline generated in a chemical ionization source... 

ANI, and consequently that the condensed-phase ANI protonation mainly occurs at the nitrogen atom, at variance with the gas-phase process (which occurs in the chemical ionization source, vide supra). Moreover, use of the tabulated heats of formation of NH3 (— 46 kJ mol-1), C6H5+ (1127 kJmor1), H" (218 kJmor1) andC6H5NH2,+ (829 kJ mol ) allows one to estimate that the H" loss requires about 34 kJ mol 1 less energy than the NH3 loss. This demonstrates that the relative abundances of the m/z 93 and 77 peaks also depend on the corresponding frequency factors. 

The Finnigan chemical ionization source was modified by the addition of two cartridge heaters. Eluate entered the source through a heated 1/2" probe and excess solvent was removed by a mechanical vacuum pump connected directly opposite the eluate entrance. The interface consisted of 1 meter deactivated silica capillary tubing (ID, 60 OD, 0.008"), led from the outlet of microbore column and threaded through the probe. The probe design has been previously described (26). For all analyses, the probe was operated at 240 C and the source at 250 C. The analyzer pressure was 10 b torr. 

Figure 7-S Schematics of (A) eiectrospray and (B) atmospheric pressure chemical ionization sources. Note the different points where ionization occurs, as described in the text.

N-C Hj-morphine as internal standard. The internal standard was added to 10 ml urine, the urine buffered to pH 8.5 and extracted with chloroform isopropanol (4 1). The extraction residue was trimethylsilylated by adding 25 ul of N,0-bis(trimethylsilylJacetamide and heating at 60°C for about 1 h. About 2 ul was analyzed on a 3 % 0V-17 column at 230°C coupled direct to a Finnegan 1015 quadrupole mass spectrometer equipped with a chemical ionization source, which was operated at an ionizing energy of 100 eV, an ion repeller voltage of 0 V and a filament emission of 300 uA. The mass spectrometer was interfaced with a System Indus-... 

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