Computers, mass spectral data processing

A modem mass spectrometer is generally equipped with an on-line computer that can be used to collect, process, and display the mass spectral data. In addition, the computer often has one or more spectral libraries included in its memory. In some cases the instrument is equipped with libraries... 

In the second system, the computer is programmed to follow very similar reasoning processes to the mass spectroscopist by making available to it the extensive body of knowledge currently known about mass spectral behaviour [60,61]. The reduction of the latter to a computer programme represents considerable effort and requires up-dating as further MS data becomes available. 

The interpretation of spectroscopic data for the identification and structure elucidation of organic compounds is largely an empirical process and relies heavily on the use of previously accumulated reference data. Compilation of computer-readable spectroscopic data bases is nowadays feasible because most commercially available spectrometers have small built-in computers for the digital acquisition of measured spectroscopic data they are also equipped with a suitable mass storage device to store spectra or selected spectral data, or they provide the facility to transfer the recorded spectra to a more powerful external computer. If the computer-readable spectroscopic data are suitably organized, the analyst is provided with a very powerful tool for the identification of a compound, a group of compounds or a structure by means of suitable software, thereby avoiding the slow and tedious manual work otherwise involved [67,69]. 

Hewlett-Packard Mass Selective Detector (MSD)(HP 5971A). The ion source was run in the El mode at 170 °C using an ionisation energy of 70 eV. The scan rate was 0.9 scans/sec. Data from the MSD was stored and processed using a Hewlett-Packard Vectra QS20 computer installed with Mustang software and the Wiley Mass Spectral Library. Kovats indices were calculated against extemd hydrocarbon standards. Concentrations were determined from the internal standard, butyl hexanoate, and are not corrected for detector response. 

To record a mass spectrum it is necessary to introduce a sample into the ion source of a mass spectrometer, to ionize sample molecules (to obtain positive or negative ions), to separate these ions according to their mass-to-charge ratio (m/z) and to record the quantity of ions of each m/z. A computer controls all the operations and helps to process the data. It makes it possible to get any format of a spectrum, to achieve subtraction or averaging of spectra, and to carry out a library search using spectral libraries. A principal scheme of a mass spectrometer is represented in Fig. 5.2. To resolve more complex tasks (e.g., direct analysis of a mixture) tandem mass spectrometry (see below and Chapter 3) may be applied. 

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