Mass spectrometry conventional

In conventional mass spectrometry with electric and magnetic sectors arranged in-hne (see Chapter 26), an ion beam consists of a stream of ions of all m/z values, which is separated into individual m/z values by the magnetic sector before being collected by single-point or multipoint detectors (see Chapters 28 and 29). 

It is recommended that the convention used by Budzikiewicz, Djerassi, and Williams (Mass Spectrometry of Organic Compounds, Holden-Day, 1967, p. 2) be followed in referring to a-cleavage as fission of a bond originating at an atom which is adjacent to the one assumed to bear the charge the definition of p-, y-, then follows automatically. The process ... 

The conventional method for quantitative analysis of galHum in aqueous media is atomic absorption spectroscopy (qv). High purity metallic galHum is characteri2ed by trace impurity analysis using spark source (15) or glow discharge mass spectrometry (qv) (16). 

Inductively coupled plasma-mass spectrometry (ICP-MS) is a multielement analytical method with detection limits which are, for many trace elements, including the rare earth elements, better than those of most conventional techniques. With increasing availability of ICP-MS instalments in geological laboratories this method has been established as the most prominent technique for the determination of a large number of minor and trace elements in geological samples. 

The abundance of a trace element is often too small to be accurately quantihed using conventional analytical methods such as ion chromatography or mass spectrometry. It is possible, however, to precisely determine very low concentrations of a constituent by measuring its radioactive decay properties. In order to understand how U-Th series radionuclides can provide such low-level tracer information, a brief review of the basic principles of radioactive decay and the application of these radionuclides as geochronological tools is useful. " The U-Th decay series together consist of 36 radionuclides that are isotopes (same atomic number, Z, different atomic mass, M) of 10 distinct elements (Figure 1). Some of these are very short-lived (tj j 1 -nd are thus not directly useful as marine tracers. It is the other radioisotopes with half-lives greater than 1 day that are most useful and are the focus of this chapter. 

The mass spectrometry of diazo compounds was reviewed by Zeller (1983) and by Lebedev (1991). It is difficult to record mass spectra of diazonium salts using conventional techniques. With the water thermospray method, however, Schmelzeisen-Redeker et al. (1985) observed the diazonium ion and various fragments such as [Ar+ - N2 + 2H]+ and [Ar + N2 + H20]+. Ambroz et al. (1988) applied the fast atom bombardment (FAB) technique using a 3-nitrobenzylalcohol matrix. Peaks for ArNJ, Ar+, and [M + ArN2]+ and further peaks due to solvated ions were found. 

Verification of the molecular weight of thiirene dioxides by mass spectrometry, employing the conventional electron-impact (El) ionization method, has been unsuccessful due to the absence or insignificant intensity of molecular ion peaks in their mass spectra. The base peak is rather characteristic, however, and corresponds to the formation of the disubstituted acetylene ion by loss of sulfur dioxide91 (equation 3). 

Similarly, the thermal sensitivity of sulfur allotropes makes mass spectrometry of elemental sulfur and sulfur-rich compounds difficult especially with the conventional electron impact ionization. Nevertheless, valuable information has been obtained by this technique also. 

Cl is an efficient, and relatively mild, method of ionization which takes place at a relatively high pressure, when compared to other methods of ionization used in mass spectrometry. The kinetics of the ion-molecule reactions involved would suggest that ultimate sensitivity should be obtained when ionization takes place at atmospheric pressure. It is not possible, however, to use the conventional source of electrons, a heated metallic filament, to effect the initial ionization of a reagent gas at such pressures, and an alternative, such as Ni, a emitter, or a corona discharge, must be employed. The corona discharge is used in commercially available APCI systems as it gives greater sensitivity and is less hazardous than the alternative. 

The application of a selective pyrolysis process to the recovery of chemicals from waste PU foam is described. The reaction conditions are controlled so that target products can be collected directly from the waste stream in high yields. Molecular beam mass spectrometry is used in small-scale experiments to analyse the reaction products in real time, enabling the effects of process parameters such as temperature, catalysts and co-reagents to be quickly screened. Fixed bed and fluidised bed reactors are used to provide products for conventional chemical analysis to determine material balances and to test the concept under larger scale conditions. Results are presented for the recycling of PU foams from vehicle seats and refrigerators. 12 refs. 

The analyte must be converted into a volatile compound suitable for mass-spectrometric analysis. Procedures for C, N, and O follow those developed for conventional organic microanalysis— oxidation of organic C to COj, reduction of organic N to N2, and conversion of O2 into CO or COj. In most procedures, cryogenic purification of the products is carried out before mass spectrometry, and both off-line and on-line procedures have been developed. 

The method for chloroacetanilide soil metabolites in water determines concentrations of ethanesulfonic acid (ESA) and oxanilic acid (OXA) metabolites of alachlor, acetochlor, and metolachlor in surface water and groundwater samples by direct aqueous injection LC/MS/MS. After injection, compounds are separated by reversed-phase HPLC and introduced into the mass spectrometer with a TurboIonSpray atmospheric pressure ionization (API) interface. Using direct aqueous injection without prior SPE and/or concentration minimizes losses and greatly simplifies the analytical procedure. Standard addition experiments can be used to check for matrix effects. With multiple-reaction monitoring in the negative electrospray ionization mode, LC/MS/MS provides superior specificity and sensitivity compared with conventional liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/ultraviolet detection (LC/UV), and the need for a confirmatory method is eliminated. In summary,... 

LC/MS/MS. LC/MS/MS is used for separation and quantitation of the metabolites. Using multiple reaction monitoring (MRM) in the negative ion electrospray ionization (ESI) mode, LC/MS/MS gives superior specificity and sensitivity to conventional liquid chromatography/mass spectrometry (LC/MS) techniques. The improved specificity eliminates interferences typically found in LC/MS or liquid chro-matography/ultraviolet (LC/UV) analyses. Data acquisition is accomplished with a data system that provides complete instmment control of the mass spectrometer. 

Carburization of rhenium filaments has been used to optimize Th and Pa ionization efficiency for TIMS analysis on single filaments (Esat 1995). ReC has a greater work function than Re metal, and elemental oxidation state is maintained in the reduced or metal state by the presence of carbon in the filament. Using this method and a mass spectrometer with improved ion optics, Esat (1995) was able to improve Th transmission and ionization efficiency by about a factor of 30 over conventional methods. Using more conventional mass spectrometry, Murrell et al. (personal communication) were able to improve ionization efficiency for Pa and Th by a factor of 5-10 over conventional graphite sandwich loads on Re filaments (Goldstein et al. 1989 Pickett et al. 1994). For Pa analysis, one drawback is that Pa and U ionization commonly overlap using this... 

Conventional calibration MDRD equation [used only with those creatinine methods that have not been recalibrated to be traceable to isotope dilution mass spectrometry (IDMS)]... 

In ToF-MS, the ion source is pulsed to create packets of ions. In the conventional procedure, the system waits for all the ions in a packet to reach the detector before injecting the next packet of ions. Complications arise when ToF-MS is coupled to a continuous ion source. Such coupling is therefore often accomplished by the orthogonal extraction approach, in which a segment of the ion stream is accelerated orthogonally by a push-out pulse. However, in this process, up to 95 % of the information contained in the ion steam is lost. Recently, Hadamard transform time-of-flight mass spectrometry (HT-ToFMS) was developed to couple continuous ion... 

This chapter deals mainly with (multi)hyphenated techniques comprising wet sample preparation steps (e.g. SFE, SPE) and/or separation techniques (GC, SFC, HPLC, SEC, TLC, CE). Other hyphenated techniques involve thermal-spectroscopic and gas or heat extraction methods (TG, TD, HS, Py, LD, etc.). Also, spectroscopic couplings (e.g. LIBS-LIF) are of interest. Hyphenation of UV spectroscopy and mass spectrometry forms the family of laser mass-spectrometric (LAMS) methods, such as REMPI-ToFMS and MALDI-ToFMS. In REMPI-ToFMS the connecting element between UV spectroscopy and mass spectrometry is laser-induced REMPI ionisation. An intermediate state of the molecule of interest is selectively excited by absorption of a laser photon (the wavelength of a tuneable laser is set in resonance with the transition). The excited molecules are subsequently ionised by absorption of an additional laser photon. Therefore the ionisation selectivity is introduced by the resonance absorption of the first photon, i.e. by UV spectroscopy. However, conventional UV spectra of polyatomic molecules exhibit relatively broad and continuous spectral features, allowing only a medium selectivity. Supersonic jet cooling of the sample molecules (to 5-50 K) reduces the line width of their... 

---