Chemical ionization sources, mass

The term nebulizer is used generally as a description for any spraying device, such as the hair spray mentioned above. It is normally applied to any means of forming an aerosol spray in which a volume of liquid is broken into a mist of vapor and small droplets and possibly even solid matter. There is a variety of nebulizer designs for transporting a solution of analyte in droplet form to a plasma torch in ICP/MS and to the inlet/ionization sources used in electrospray and mass spectrometry (ES/MS) and atmospheric-pressure chemical ionization and mass spectrometry (APCI/MS). 

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). 

Van Breemen, R.B. et al.. Liquid chromatography/mass spectrometry of carotenoids using atmospheric pressure chemical ionization, J. Mass Spectrom., 31, 975, 1996. Tian, Q., Duncan C.J.G., and Schwartz S. J., Atmospheric pressure chemical ionization mass spectrometry and in-source fragmentation of lutein esters, J. Mass Spectrom., 38, 990, 2003. 

Wu, H.-F. Lin, Y.-P. Determination of the Sensitivity of an External Source Ion Trap Tandem Mass Spectrometer Using Dimethyl Ether Chemical Ionization. J. Mass Spectrom. 1999,54,1283-1285. 

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. 

The following discussion will be concerned primarily with applications of the ms/ms technique in the synfuel area. Attempts will be made to illustrate the unique capabilities of the ms/ms analysis with examples taken from our work on coal liquefaction products. Figure 5 shows the positive ion chemical ionization (PCI) mass spectrum of the coal liquid in question (SRC II mid heavy distillate, total bottoms). This spectrum is actually the normalized sum of approximately 500 individual mass spectra taken while the SRC II was thermally vaporized from a solids probe into the source of a mass spectrometer, and represents the molecular weight profile of this distillate fraction. Since isobutane Cl gives to a first approximation only protonated molecular ions (and no fragment ions), the peaks represent the individual components in the SRC II arranged incrementally by molecular weight. 

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... 

Finally, the desorption chemical ionization (DCI) mass spectra of several synthetic nucleosides, mostly in the pyrimidine series, have been recorded. The potential application of protonated or cationized (NH4 ) molecular ions and bases for the detection of these nucleosides has been demonstrated. One of the important features of these spectra is the presence of [ B + H ] and/or [B -f- NHJ ions, which confirms the previously described general fragmentation scheme. In desorption chemical ionization studies (which describe in-beam experiments in a Cl source), the desorption of intact molecules, followed by ionization, is often confused with the desorption of preformed ions. Slow hydrolysis within a Cl source leads to intense ions (e.g., [BH]" ) such as those observed for nucleosides, as well as for intact DNA. ... 

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-... 

Siegel, M.M. Tabei, K. Lambert, R Candela, L. Zoltan, B. Evaluation of a Dual Electrospray lonizafion/AtmosphericPressure Chemical Ionization Source at Low Flow Rates for the Analysis of Both Highly and Weakly Polar Compounds, /. Am. Soc. Mass Spectrom. 9(11), 1196-1203 (1998). 

Atmospheric pressure chemical ionization uses an atmospheric pressure ionization interface. The interface is similar to that used for ESI, but a corona discharge is used to ionize the analyte in an atmospheric pressure region. (Note This is different than the chemical ionization source described in Chapter 20 for GC-MS.) The gas-phase ionization of less polar analytes is more efficient than with ESI, but the mass range is hmited to about 2000 daltons. ESI and APCI are complementary. APCI has largely replaced thermal ionization as an interface in commercial instraments. 

Figure 8.16. TG-MS with a chemical ionization source as described by Bamngarmer and Nachbaur (74). 1, thermobalance 2. furnace 3,3-way valve 4. reaction gas cylinder 5. rotary-pumps 6, coupling line 7. quadrupole mass spectrometer 8. Cl-ion source 9. metering valve 10, ionization gauge 11, analyzer diffusion pump 12. Cl diffusion pump.

When the device is operated as a mass spectrometer, ions produced by an electron-impact or chemical ionization source are admitted through a grid in the upper end cap. The ionization source is pulsed so as to create a burst of ions. The ions over a large mass range of interest are trapped simultaneously. The ion trap can store ions for relatively long times, up to l.o minutes for some stable ions. A technique called mns.s-.te/ct/ri C ejeaion is then used to sequentially eject the trapped ions in order of ma,ss by increasing the radio-frequency... 

All mass spectra were recorded using a Hewlett-Packard 5985B mass spectrometer equipped with a dual electron impact/chemical ionization source including negative ion capability. The source temperature was 125QC, filament emission current was 300 uA, and electron energy was 230 ev. The interface between the GC and MS was a glass-lined stainless steel transfer line. Methane was used both for carrier gas and as the chemical ionization reactant gas. A methane flow of 11.5 mL/min. resulted in an ion source pressure of 0.5 torr. 

A functionally similar dissociation method, electron transfer dissociation (ETD) was more recently reported (32), specifically for use on QIT instruments, although it is also beginning to be adapted to other mass analyzers. ETD is accomplished by electron transfer to the analyte from a negatively charged species that is produced in a chemical ionization source and directed into the region where the analyte ions are trapped. For peptides and proteins, it produces spectra that... 

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