Continuous mass spectrometric techniques

Utilizing the continuous mass spectrometric techniques developed by Arnot and co-workers and Hornbeck and Molnar in which reaction identification is made from considerations of the appearance potentials of the product ions and from the effects of electron energy, pressure, and repeller potential on product-ion intensity, homonuclear associative ionization reactions have been reported in helium, " in neon, "- " " i46A9,5o,52-si,62) krypton,< " " - " > in... 

Speleothem frequency distributions have provided a useful tool for broad comparisons, but they suffer from the problem of biased sampling strategies and low resolution at times of known abrupt change. The increased precision afforded by mass-spectrometric techniques will result in fewer studies using this approach to assess of growth frequency and, more often, records of continuous deposition and growth rate studies will be graphically illustrated. 

As mentioned above in the context of the analysis of hgnin degradation products, gas chro-matography/mass spectrometry and related methods have been developed as extremely powerful tools for the identification of phenolic compounds. Use of high-pressure liquid chromatography in combination with mass spectrometry adds to the analytical arsenal with respect to the detection of polar, non-volatile compounds but, in particular, the advent of modem ionization techniques, such as ESI and MALDI mass spectrometry, have continued to broaden the analytically governable field of organic chemistry. The latter methods diminish the need of derivatization of polar phenolics to increase the volatility of the analyte. In this section, a more or less arbitrary selection of examples for the application of mass spectrometric techniques in analytical chemistry is added to the cases already discussed above in the context of gas-phase ion chemistry. 

Drift velocity measurements of ions formed by an electron pulse of sec duration convinced Hornbeck that the molecular ions Hc2, Nc2, and Ar2 were not formed by collision of an atom in a metastable state with a ground-state atom, as had been proposed by Arnot and M Ewen In confirmation of this conclusion, Hombeck and Molnar " reported a mass spectrometric study of molecular ion formation in the noble gases. This mass spectrometric technique, which may be called single-chamber, continuous mass spectrometry, was the same as employed by Arnot and M Ewen and by many workers in more recent times. 

Mass Spectrometer. The mass spectrometer is the principal analytical tool of direct process control for the estimation of tritium. Gas samples are taken from several process points and analy2ed rapidly and continually to ensure proper operation of the system. Mass spectrometry is particularly useful in the detection of diatomic hydrogen species such as HD, HT, and DT. Mass spectrometric detection of helium-3 formed by radioactive decay of tritium is still another way to detect low levels of tritium (65). Accelerator mass spectroscopy (ams) has also been used for the detection of tritium and carbon-14 at extremely low levels. The principal appHcation of ams as of this writing has been in archeology and the geosciences, but this technique is expected to faciUtate the use of tritium in biomedical research, various clinical appHcations, and in environmental investigations (66). 

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... 

Various analytical methods have made quantum leaps in the last decade, not least on account of superior computing facilities which have revolutionised both data acquisition and data evaluation. Major developments have centred around mass spectrometry (as an ensemble of techniques), which now has become a staple tool in polymer/additive analysis, as illustrated in Chapters 6 and 7 and Section 8.5. The impact of mass spectrometry on polymer/additive analysis in 1990 was quite insignificant [100], but meanwhile this situation has changed completely. Initially, mass spectrometrists have driven the application of MS to polymer/additive analysis. With the recent, user-friendly mass spectrometers, additive specialists may do the job and run LC-PB-MS or LC-API-MS. The constant drive in industry to increase speed will undoubtedly continuously stimulate industrial analytical scientists to improve their mass-spectrometric methods. 

In a well-equipped laboratory it is mandatory that these three techniques be coupled with a mass spectrometric detector in order to achieve a combination of resolution of mixtures, positive identification of separated organics and the high sensitivity that is essential when dealing with environmental samples. The penetration of mass spectrometers in recent years is indicated by the fact that of the 50 types of organic compound that have been determined by gas chromatography in 21 cases mass spectrometric detection is discussed. This trend will, no doubt, continue. 

In summary, the use of mass spectrometric methods, combined with various approaches to vaporizing and ionizing the particles, is gaining increasing popularity and interest for the analysis of continuous sources of particles or single particles. The problem of quantification of the components seen by single-particle laser ionization techniques remains to be solved. On the other hand, the vaporization approaches can provide quantitative data on some volatile and semivolatile components but cannot measure the nonvolatile species and, at present, do not provide a full mass spectrum for a single particle. 

FAB and LSIMS are matrix-mediated desorption techniques that use energetic particle bombardment to simultaneously ionize samples like carotenoids and transfer them to the gas phase for mass spectrometric analysis. Molecular ions and/or protonated molecules are usually abundant and fragmentation is minimal. Tandem mass spectrometry with collision-induced dissociation (CID) may be used to produce abundant structurally significant fragment ions from molecular ion precursors (formed using FAB or any suitable ionization technique) for additional characterization and identification of chlorophylls and their derivatives. Continuous-flow FAB/LSIMS may be interfaced to an HPLC system for high-throughput flow-injection analysis or on-line LC/MS. 

Mass spectrometric measurements using hydrogen gas are prepared from the sample by fractionation free techniques. Water is converted into H2 gas by being passed over uranium metal at 750 °C as a continuous method,or by being reacted with heated zinc shot or melted in a Pyrex or quartz tube at approximately 450 °C as a batch method. " ... 

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