Spectral files

The successful use of VIRS methods as research tools requires more than anything a published framework that will provide standards for the collection and interpretation of data, and accessible data libraries that can give examples for comparison and contrast. The spectral libraries used for mineral identification are in part public-domain, but much information remains tied to the instrument software and cannot readily be distributed. Differences in the formats used for spectral files in different libraries complicate their use in standard software and impedes information exchange. 

In the case where MS analytical data has been contributed in the other formats, it is prepared into a NIST MS Database, using the NIST MS Search program. This program is used to create MS spectral files from the following electronic formats JCAMP, NIST ASCH, AMDIS, and NIST MS Database. If the analytical data contains no chemical structure, the structure is created in ISIS Draw and then imported into the database as an MOL file. The information associated with the MS analytical data is handled by the NIST program. 

There are no comprehensive data files for CD spectra for standard reference materials (SRM) that compare with the exhaustive libraries which have been compiled for absorbance data in the electronic and vibrational spectroscopy ranges. Analysts are required to create their own CD spectral files using SRM prepared by the usual purveyors of fine chemicals. A significant problem with an SRM is that although it might meet the industry specifications for chemical purity, its enantiomeric purity is open to question. The few cases in which absolute enantiomeric purity might be assured involve natural products whose syntheses are under total enzymatic control. To prove 100% enantiomeric purity is beyond current capabilities. The problem is compounded even more with the risk that the material might racemize after its extraction from its natural environment. Therefore, it is not possible to assume absolute enantiomeric purity with firm conviction. 

Instrument companies have added spectral search systems as a spectrometer accessory for modest-sized files. The largest mass spectral files are accessible through the NIH-EPA Chemical Information System (CIS), and the largest IR on-line search system is available on Tymshare (196). 

In the second case, that is where the basic file is of documents organised on the basis of numeric data, the problems are somewhat different. The data in question are still most commonly the properties of compounds, and the most common function is where as user is seeking to use known properties to identify a compound, or where, by identifying a group of compounds with a common property, he seeks structure/property relationships. The basic file is therefore generally of structures, as for example the Sadtler spectral file mentioned above 29). However, in some cases the file may be... 

The spectral data were weight normalized to a sample weight of 2.00 mg with the scaling function In the arithmetic command according to the equation (FFA) (SCA) scaled spectrum. FFA Is the contents of spectral file A and SCA Is a scaling factor computed by multiplying the reciprocal of the sample weight by 2. 

From the information theory (Chapter 11.6.1) it is known that a signal contains most information if all possible values of the signal have equal probability. To generate pattern vectors with equally distributed features intensity levels must be created for each mass number. Each level should have the same probability in the spectral file. If there are k intensity levels and d mass numbers a set of (k-1)d threshold values must be stored for spectral preprocessing C250D. 

A computer file of about 19,000 peak wavenumbers and intensities, along with search software, is distributed by the Infrared Data Committee of Japan (IRDC). Donated spectra, which are evaluated by the Coblentz Society in coUaboration with the Joint Committee on Atomic and Molecular Physical Data (JCAMP), are digitized and made avaUable (64). Almost 25,000 ir spectra are avaUable on the SDBS system developed by the NCLl as described. A project was initiated at the University of California, Riverside, in 1986 for the constmction of a database of digitized ftir spectra. The team involved also developed algorithms for spectra evaluation (75). Other sources of spectral Hbraries include Sprouse Scientific, Aston Scientific, and the American Society for Testing and Materials (ASTM). 

Abstract A relatively small number of mammalian pheromones has been identified, in contrast to a plethora of known insect pheromones, but two remarkable Asian elephant/insect pheromonal linkages have been elucidated, namely, (Z)-7-dodecen-1-yl acetate and frontalin. In addition, behavioral bioassays have demonstrated the presence of a chemical signal in the urine of female African elephants around the time of ovulation. Our search for possible ovulatory pheromones in the headspace over female African elephant urine has revealed for the first time the presence of a number of known insect pheromones. This search has been facilitated by the use of a powerful new analytical technique, automated solid phase dynamic extraction (SPDE)/GC-MS, as well as by novel macros for enhanced and rapid comparison of multiple mass spectral data files from Agilent ChemStation . This chapter will focus on our methodologies and results, as well as on a comparison of SPDE and the more established techniques of solid phase microextraction (SPME) and stir bar sorptive extraction (SBSE). 

Of course one may employ automated library searches ( library percent reports ) to check for compound identities, but algorithms for library matching are not infallible, and mass spectral libraries are not exhaustive, thus some compounds of interest will likely not be identified. Additional dilemmas are presented by mere reliance on retention times and library percent reports to ascertain the presence of common or unique peaks from among multiple mass spectral data files. As illustrated in Table 2.1, the TICs from the GC-MS of urine from four elephants evidence a peak at essentially the same retention time, but the library search results are inconclusive as to their common identity or lack thereof. As will be seen below, our novel macros can assist in making such decisions for a large number of peaks. 

Macro FindPeak.mac automatically exports the mass spectral data, including ion masses and abundances for each peak in the gas chromatogram, to a. CSV (comma separated value) file. Each. CSV file contains MS data for one peak from the gas... 

McLafferty, F.W. Gohlke, R.S. Mass-Spectrometric Analysis Spectral-Data File Utilizing Machine Filing and Manual Searching. Anal. Chem. 1959, 31, 1160-1163. 

In the first phase, a data base is acquired from one of a variety of sources. Some of the CIS data bases have been developed specifically for the CIS, an example of this being the mass spectral data base (2). Others, such as the Cambridge Crystal File (4), are leased for use in the CIS and still others, such as the X-ray powder diffraction file (5), are operated within the CIS by their owners, in this case the )oint Committee on Powder Diffraction Standards. 

It is possible that the future may also see the use of digital calculators in qualitative spectrometric analyses. Various types of punched cards have been used as a method of recording spectral data on pure compounds. The purpose of these files is to facilitate the identification of spectral data on unknown substances. Their use in infrared analysis has been covered by Mecke and Schmid (M6), Keuntzel (K3), and Baker, Wright, and Opler (B2). The last named authors describe a file of 3150 spectra which was expected eventually to be expanded to include up to 10,000 spectra. Zemany (Zl) discussed the use of edge-notched cards in cataloging mass spectra and Matthews (M4) describes a similar application in connection with X-ray diffraction powder data. These two applications made use of only hand-sorting methods the files of Baker et al. were intended to be processed by machine. 

NRC-NBS (Creitz) File of Spectrograms. Issued by National Research Council-National Bureau of Standards Committee on Spectral Absorption Data, National Bureau of Standards, Washington 25, DC. Spectra presented on edge-punched cards. 

Additional files, FORMAT.TEMP, PULSEPROGRAM, VDLIST, TITLE, OUTD, PARAM.TXT, META and others may also be present if you have imported your NMR data directly from a Bruker spectrometer. These files contain additional information and settings initialized by the spectrometer operator and relate to the acquisition pulse program, lists of variable delays, spectrum title, the spectral layout and others and are non-essential for off-line data processing. 

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