Identification of mass spectra by computer-searching a file of known spectra

Abstract

petroleum-based materials. The standard deviation for precision based on the pooled data is 0.02 % hydrogen. DISCUSSIONThe apparatus has been in continuous routine service for over a year without combustion mishaps. Because of the availability of other methods for analyzing volatile samples, we have used this method only for samples boiling above 200 °C, and weighed the samples in open porcelain boats. The use of ampoules (7) to contain the samples would undoubtedly extend the method to lower-boiling materials. Although the apparatus as described is suitable only for hydrogen determinations, simple modifications would permit carbon determinations also. This would require, for example, attaching to the water absorbers two additional aluminum absorbers, the first containing manganese dioxide to absorb nitrogen oxides (7, 3) and the second containing Ascarite to(3) R. Belcher and G. Ingram, Anal. Chim. Acta, 4, 401 (1950). collect the carbon dioxide. A coating of Teflon (Du Pont) or similar material sprayed on the inside surface of the absorber tube would be necessary to prevent reaction between aluminum and the alkaline Ascarite. The approximate cost of parts needed to construct the apparatus is $1000. The estimated cost of materials and reagents is $1.00 per analysis, assuming replacement of the combustion tube and packing after 60 analyses and no recovery of reagents.By dovetailing combustion and purging operations, one operator can perform seven analyses in an 8-hour day. The construction of a dual apparatus with automatic cycle timers to control the rate of heating and the changes in gas flow should permit 14 analyses per day per operator.

An approach to the isotypical and solid solution problems in multiphase X-ray analysis

“…In particular, by choosing a form that represents the shifts to be expected if a unit cell were to be isotropically expanded or contracted, phases isotypical with the unknown phase can be located. Gas chromatographic and mass spectrometric data-base search programs designed with similar capabilities have been in use for about ten years (Hertz, Hites & Biemann, 1971). In order to look for isotypical matches to an unknown, an ISOSEARCH command was added to SANDMAN.…”

Organic Compounds in Urban Atmospheres: A Review of Distribution, Collection and Analysis

“…They all basically consist of the same programs for processing and searching data files. 63 -361 ' 362 The commercial systems are also similar. Most systems have the capability of plotting mass spectra with optional background deletion, scale expansion and scan summing, plotting of total ion current traces and mass chromatograms for GC/MS analyses, listing of prominent ions, and optionally data file searching.…”

A new matching algorithm for high resolution mass spectra

“…The aim of spectrum evaluation can be either the identification of a compound (assuming a reference spectrum is already available) or the interpretation of spectral data in terms of the unknown chemical structure or comparing spectra of complex mixtures. Identification is most efficiently performed by library search methods based on spectral similarities [1][2][3][4][5][6]; there are a number of MS databases and powerful software products offered which are routinely used for this purpose. Most of these methods (if not all) are focused on libraries containing mass spectra of pure compounds, but there should be no reason not to store and retrieve complex mass spectra by these library search products [7].…”

“…In the mass spectroscopic literature, a long list of methods for library construction and search has been proposed since the beginning of the 1970s. Stein and Scott [4] reviewed these and compared and tested five of the most popular algorithms proposed in the literature for library searchingincluding those implemented in many instrument software packages: Probability based matching (PBM) [8], Hertz similarity index [3], Euclidean distance (L 2 -norm), dot-product, and absolute value distance. The best performance was achieved with the dot-product function, which measures the cosine of the angle be-tween spectra.…”