Computer programs, library search

The reproducibility and reliability of RIs makes it possible to create RI libraries and the identification can be achieved without authentic reference chemicals. The reliability and simplicity of RI monitoring is increased significantly by using a computer program that searches for the RI pattern, calculates the RIs for all peaks in the chromatogram, and then compares the indices with the library data. In addition to the identification of target chemicals, RIs can also be used to locate the interesting peaks between different kinds of GC-based analytical techniques (65). In this way, it is possible to ensure that all GC-based techniques used for identification focus on the same peaks even in samples with a complex mixture of chemicals. 

The use of computer programs to predict spectra from a knowledge of the molecular structure of the sample is still in its infancy. However, although a fair amount of work still needs to be done, there is no doubt that this type of approach will be of great importance to the analysts of the future. Certainly, the experience of a spectroscopist in the characterisation of infrared and Raman spectra will be essential for many years to come, just as is the ability of computer programs to search through libraries of spectra to find the best match to a sample s spectrum. 

Solvents and their impurities represent a wide class of compound types therefore, a discussion of common mass spectral features is meaningless. However, most of the mass spectra are listed in computer library search programs and The Eight Peak Index. ... 

The best-known and the most commonly used hyphenated method is GC-MS more specifically, and most commonly, capillary column GC combined with quadrupole MS. This type of instrumentation is controlled by computer and data collected and analyzed by dedicated computer programs. The mass spectra produced by the analytes can be compared to those in a library of mass spectra of known compounds using a computer search algorithm. The computer program finds known compounds that best match the spectra of the analytes of interest. 

With regard to computer programming, the optimum seeking methods should be written separately and stored as a library program for repetitive use. The main program reads the input data, calls the search routine, performs any noniterative calculations, and handles the output. The calculation of iterative state variables and the calculation of the objective function should be performed within function subprograms. 

Library Search Routines To aid in the identification of hydrocarbons, computer programs are being developed for comparing unknown spectra to libraries of known compounds. As an example, a sample of 2-hexadecanol was compared to a library of over 100 compounds. The library search identified 2-hexadecanol as the... 

Three different approaches have been used for computer-assisted interpretations of chemical data. 1. Heuristic methods try to formulate computer programs working in a similar way as a chemist would solve the problem. 2. Retrieval methods have been successfully used for library search (an unknown spectrum is compared with a spectral library). 3. Pattern recognition methods are especially useful for the classification of objects (substances, materials) into discrete classes on the basis of measured features. A set of characteristic features (e.g. a spectrum) of an object is considered as an abstract pattern that contains information about a not directly measurable property (e.g. molecular structure or biological activity) of the object. Pure pattern recognition methods try to find relationships between the pattern and the "obscure property" without using chemical knowledge or chemical prejudices. 

Woodruff and co-workers introduced the expert system PAIRS [67], a program that is able to analyze IR spectra in the same manner as a spectroscopist would. Chalmers and co-workers [68] used an approach for automated interpretation of Fourier Transform Raman spectra of complex polymers. Andreev and Argirov developed the expert system EXPIRS [69] for the interpretation of IR spectra. EXPIRS provides a hierarchical organization of the characteristic groups that are recognized by peak detection in discrete ames. Penchev et al. [70] recently introduced a computer system that performs searches in spectral libraries and systematic analysis of mixture spectra. It is able to classify IR spectra with the aid of linear discriminant analysis, artificial neural networks, and the method of fe-nearest neighbors. 

Decades of combined spectral and chemistry expertise have led to vast collections of searchable user databases containing over 300 000 UV, IR, Raman and NMR spectra, covering pure compounds, a broad range of commercial products and special libraries for applications in polymer chemistry (cf. Section 1.4.3). Spectral libraries are now on the hard disks of computers. Interpretation of spectra is frequently made only by computer-aided search for the nearest match in a digitised library. The spectroscopic literature has been used to establish computer-driven assignment programs (artificial intelligence). 

Gas Chromatography-Mass Spectrometry. A Finnigan 4500/Incos instrument with a 30-m X 0.32-mm i.d. capillary column coated with SP-B-5 was used. The GC parameters were as follows injector, 270 °C column oven temperature programmed, 50 °C (0.1 min, hold) 15 °C/min to 100 °C, 5 °C/min to 270 °C internal standard, anthracene-djo helium flow, 3.0 mL/min sample size, 3.0 /xL. MS conditions were as follows El, 70 eV scan (m/z), 35-650 daltons source temperature, 250 °C filament current, 0.5 A sensitivity, 10-8 A/V. (NOTE When the name of a compound is followed by (confirmed) , it means that the standard material was analyzed for confirmation under conditions identical to those of the sample when the name is followed by (tentative) , it means that the mass fragmentography showed the best fit (>80 ) based on the National Bureau of Standards [NBS] library computer search.)... 

The basic ILLINET Online Network (Illinois Online Network) was used as the major computer-assisted information retrieval program. Within this network IBIS (Illinois Bibliographic Information Service), which provides abstracts taken from journal articles published from 1991 through December 1993, and CARL UnCover (Colorado Alliance of Research Libraries), which provides titles to journal articles published in 1988 through December 1993, afforded much of the current and recent information reported on here. Abstracts of the pertinent literature published from 1982 through mid-1993 were also obtained directly from CA (Chemical Abstracts). It is hoped that the overlap provided this way assures the broadest retrieval of published results. All of these sources were searched by means of the following key words ... 

---