Fast mass spectrometry

The coupling of a shock tube to the ion source of a fast recording mass spectrometer and sampling from the reflected shock zone has been utilized to study diatomic dissociation. The rate of disappearance of the parent m/e peak is measured by taking mass spectra at specific time intervals, typically every 25 psec over a 0.5 msec observation period with 

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Hsieh, Y., Fukuda, E., Wingate, J., and Korfmacher, W. A. (2006). Fast mass spectrometry-based methodologies for pharmaceutical analyses. Comb. Chem. High Throughput Screening 9 3-8. 

Fast-Atom Bombardment (FAB) and Liquid-Phase Secondary Ion Mass Spectrometry (LSIMS) Ionization... 

A big step forward came with the discovery that bombardment of a liquid target surface by abeam of fast atoms caused continuous desorption of ions that were characteristic of the liquid. Where this liquid consisted of a sample substance dissolved in a solvent of low volatility (a matrix), both positive and negative molecular or quasi-molecular ions characteristic of the sample were produced. The process quickly became known by the acronym FAB (fast-atom bombardment) and for its then-fabulous results on substances that had hitherto proved intractable. Later, it was found that a primary incident beam of fast ions could be used instead, and a more generally descriptive term, LSIMS (liquid secondary ion mass spectrometry) has come into use. However, note that purists still regard and refer to both FAB and LSIMS as simply facets of the original SIMS. In practice, any of the acronyms can be used, but FAB and LSIMS are more descriptive when referring to the primary atom or ion beam. 

The basic principles of fast-atom bombardment (FAB) and liquid-phase secondary ion mass spectrometry (LSIMS) are discussed only briefly here because a fuller description appears in Chapter 4. This chapter focuses on the use of FAB/LSIMS as part of an interface between a liquid chromatograph (LC) and a mass spectrometer (MS), although some theory is presented. 

FAB has evolved, and fast atoms are being replaced by fast ions, such as cesium (Cs+). This variation is called liquid secondary ion mass spectrometry (LSIMS) because the sample solution affords the secondary ion beam while the bombarding ions constitute the primary beam. Spectra... 

Most of the previous discussion has concerned addition. Subtraction in binary is very similar, but multiplication is awkward (try it ). For this reason it is quicker for a computer to multiply by carrying out a series of additions. Multiplying 3x5 becomes adding 5 -(- 5 -(- 5. Because each addition is very fast, the time taken for even a large multiplication is very little and still appears instantaneous to us. Only with very large computations does this speed become obvious enough to merit special computers, more powerful than the ones being considered here for use in mass spectrometry. Finally, division is very similar to multiplication, except that a series of subtractions is carried out instead of additions. 

In the case of fast ions, the terminology of secondary ion emission mass spectrometry (SIMS) is more obvious in that a primary incident beam of ions onto a target releases secondary ions after impact. 

The term liquid secondary ion mass spectrometry (LSIMS) is sometimes used synonymously with FAB and is preferred by some as being more descriptive, since FAB could apply to bombardment of solid or liquid surfaces and does not indicate the types of secondaries investigated. In practice, little confusion is likely to result from using either term. Strictly, LSIMS can refer to the use of fast ions (FIB). 

After acceleration through an electric field, ions pass (drift) along a straight length of analyzer under vacuum and reach a detector after a time that depends on the square root of their m/z values. The mass spectrum is a record of the abundances of ions and the times (converted to m/z) they have taken to traverse the analyzer. TOP mass spectrometry is valuable for its fast response time, especially for substances of high mass that have been ionized or selected in pulses. 

Desorption ionization (DI). General term to encompass the various procedures (e.g., secondary ion mass spectrometry, fast-atom bombardment, californium fission fragment desorption, thermal desorption) in which ions are generated directly from a solid or liquid sample by energy input. Experimental conditions must be clearly stated. 

Caprioli, R.M., Continuous-Flow Fast Atom Bombardment Mass Spectrometry, Wiley, New York, 1990. 

Mass spectral analysis of quaternary ammonium compounds can be achieved by fast-atom bombardment (fab) ms (189,190). This technique rehes on bombarding a solution of the molecule, usually in glycerol [56-81-5] or y -nitroben2yl alcohol [619-25-0], with argon and detecting the parent cation plus a proton (MH ). A more recent technique has been reported (191), in which information on the stmcture of the quaternary compounds is obtained indirectly through cluster-ion formation detected via Hquid secondary ion mass spectrometry (Isims) experiments. 

The analysis of penicillins by mass spectrometry (qv) has developed with the advent of novel techniques such as fast atom bombardment. The use of soft ionization techniques has enabled the analysis of thermally labile nonvolatile compounds. These techniques have proven extremely valuable in providing abundant molecular weight information from underivatized penicillins, both as free acids and as metal salts (15). 

One of the reasons for lack offlterature was probably because environmental analysis depends heavily on gas chromatography/mass spectrometry, which is not suitable for most dyes because of their lack of volatility (254). However, significant progress is being made in analyzing nonvolatile dyes by newer mass spectral methods such as fast atom bombardment (EAB), desorption chemical ionization, thermospray ionization, etc. 

FABMS Fast-atom bombardment mass spectrometry... 

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