Double-focusing Sector Instrument Research Articles

Sector instruments for chemical analysis and research

When the last chemical elements were successfully measured by mass spectrometry its use for the characterisation of isotopes declined, but its use for chemical analysis and research grew. This new field of activity was aided by the emergence of commercially manufactured sector mass spectrometers designed for the analysis of oil refinery gases. Although the 1940s saw the use of mass spectrometry dominated by the petroleum industry it also saw many developments in its application to chemical analysis. By the early 1950s heated inlet systems were allowing spectra of all kinds of volatile organic compounds to be obtained. The 1950s saw the development of accurate mass measurement of organic molecules as a means of determining their elemental composition. This led to a demand for higher resolution double focusing instruments. Two types of design competed for this application, each with their perceived advantages and disadvantages. It was another decade, following the application of computers to high throughput accurate mass measurement, before one of these came to dominate. Double focusing sector instruments also enhance the information afforded by “metastable” ions, allowing identification of precursor and product ions. This led to the developments of Collision Induced Decompositions, MIKES and “linked scans”. The mass range demanded of mass spectrometers jumped to new levels with the development of Fast Atom Bombardment (FAB). This led to new sector designs incorporating innovative new magnets. The success of FAB as a soft ionisation technique meant it produced little fragmentation and structural information. This led to a growth in the use of tandem MS/MS instrumentation as a tool for determining structures. This paper recounts these and many other developments which kept magnetic sectors at the centre of major new developments in mass spectrometry for chemical analysis and research for so long.

Electron monochromator-mass spectrometer instrument for negative ion analysis of electronegative compounds.

Electron monochromators designed for the production of low-energy electrons (0-15 eV) with nearly monoenergetic distributions have been available for many decades. The concept of adapting the electron monochromator as an ion source onto mass spectrometers for the purpose of electron capture negative ion-mass spectrometric (ECNI-MS) analyses is only now being realized. Two different analyzers, a quadrupole and a double focusing sector instrument, have recently been retrofitted with electron monochromators to test their utility as analytical instruments for the detection of environmental compounds and chemical agents. Electron energy scans of compounds in these classes reveal unique negative ion resonances, which can be used as an additional analytical dimension of information for compound identification and confirmation. Electron currents of 430 μA at 0.03 eV electron energy are now available from the electron monochromator, which will provide sufficient electron flux to meet modern standards for trace level analyses. The narrowest electron energy spread achieved has been ±0.07 eV (fwhm). The electron monochromator-mass spectrometer (EM-MS) instrument has been interfaced to a gas chromatograph (GC), and this system (GC/EM-MS) was used to record ion chromatograms of mixtures of polychlorinated compounds. Regioselective ion loss, resulting from dissociative electron capture by the parent molecule, is electron-energy dependent and can be monitored with the EM-MS instrument. Finally, positive ion spectra produced with monoenergetic electrons have also been recorded. © 1997 John Wiley & Sons, Inc.

Application of a new atmospheric pressure ionization source for double focusing sector instruments

In three application examples we demonstrate how the capabilities of a modern atmospheric pressure ionization (API) source, as a universal LC-MS coupling tool, are supplemented by the high mass resolution available on double focusing sector instruments. The examples include charge state determination in complex electrospray ionization-collisional induced dissociation (ESI-CID) spectra of multiply charged ions, mixture analysis of multicomponent samples without prior chromatographic separation, and very sensitive and highly specific detection of pesticides using atmospheric pressure chemical ionization (APCI).