Infrared spectral libraries

Chen, C.-S. Li, Y. Brown, C.W. Searching a mid-infrared spectral library of solids and liquids with spectra of mixtures. Vibr. Spectrosc. 1997, 8, 9-17. 

Gerhausser, C.I. Kovar, K.A. Strategies for constructing near-infrared spectral libraries for the identification of drug substances. Appl. Spectrosc. 1998, 51, 1504-1510. 

Sharpe, S., et al.. Creation of 0.10 cm resolution, quantitative, infrared spectral libraries for gas samples. Vibrational Spectroscopy-Based Sensor Systems, Proceedings of SPIE, vol. 4577,12-24(2001)... 

Searching spectral libraries may involve the use of inverted lists. These consist of each characteristic absorption band or emission line along with a list of corresponding numbered library spectra that include that particular band or line. A list for the spectrum of an unknown analyte can then be rapidly checked against the library lists. An example of part of an inverted list for an infrared spectral library is shown in Figure 1. It includes spectrum No. 66 among those listed with an absorbance band at 1220 cm and spectrum No. 105 among those listed with an absorbance band at 2730 cm . ... 

Fig, 1, Part of an inverted list for an infrared spectral library. 

In this experiment you will be given two unknown organic liquids to attempt to identify by infrared spectrometry. For one of the unknowns you will be given its molecular formula. The other must be identified by matching its infrared spectrum to a spectrum in a reference catalog of spectra (sometimes called a spectral library). 

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 collaboration with the Joint Committee on Atomic and Molecular Physical Data (JCAMP), are digitized and made available (64). Almost 25,000 ir spectra are available on the SDBS system developed by the NCLI as described. A project was initiated at the University of California, Riverside, in 1986 for the construction of a database of digitized ffir spectra. The team involved also developed algorithms for spectra evaluation (75). Other sources of spectral libraries include Sprouse Scientific, Aston Scientific, and the American Society for Testing and Materials (ASTM). 

In the field of CWC-related analysis, the chemicals should be identified by comparing their spectra to spectral libraries or to spectra measured from authentic chemicals. In infrared spectroscopy of CWC-related chemicals, the spectral interpretation is not enough for unambiguous identification, but it is an important tool in the structural elucidation of unknown chemicals. 

In the FTIR analysis of the chemicals related to the CWC, the spectral libraries are essential. For the purposes of the CWC, there has to be a reference spectrum for identification. If there is no infrared reference spectrum available, the identification cannot be accepted unless a reference... 

Searching the spectrum of an unknown chemical against a spectral library is a routine method used to identify chemicals. Most of the commercial infrared instruments include library search software that has several search algorithms to choose from. The search algorithm can sometimes have a strong effect on the library search result. This is due to the different ways the actual comparison between the spectra is done. Especially when the library and the unknown spectra have been measured differently (e.g. using solid KBr disk and cryodeposition GC/FTIR), the... 

Gas chromatography (GC) with an infrared (IR) detector was introduced as a method to detect volatile radiolytic products, some of which were hypothesized to be responsible for the bad smells emanating from irradiated drugs. Thiocyanic acid was held responsible, for example, for the sulfurous smell in irradiated ampicillin. The head-space (HS) injection technique for GC and the on-line MS detection allowed new approaches to detect radiosterilization [12]. Many volatile radiolytic products were identified from the mass spectral libraries. Some ofthe compounds identified such as aldehydes, esters and sulfides were quite malodorous. A few of the volatile radiolytic products came from the degradation of drug molecules by the ionizing radiation, whereas residual solvents played a key role in the formation of other volatile radiolytic products. 

RDF descriptors exhibit a series of unique properties that correlate well with the similarity of structure models. Thus, it would be possible to retrieve a similar molecular model from a descriptor database by selecting the most similar descriptor. It sounds strange to use again a database retrieval method to elucidate the structure, and the question lies at hand Why not directly use an infrared spectra database The answer is simple. Spectral library identification is extremely limited with respect to about 28 million chemical compounds reported in the literature and only about 150,000 spectra available in the largest commercial database. However, in most cases scientists work in a well-defined area of structural chemistry. Structure identification can then be restricted to special databases that already exist. The advantage of the prediction of a descriptor and a subsequent search in a descriptor database is that we can enhance the descriptor database easily with any arbitrary compound, whether or not a corresponding spectrum exists. Thus, the structure space can be enhanced arbitrarily, or extrapolated, whereas the spectrum space is limited. 

Peak identification is based on the comparison of normalized spectra representative for the peak with spectra of one or several standard compounds run in the same separation system and stored in a spectral library [107,116]. This approach is less powerful than for mass or infrared spectral searches due to the rather broad and featureless bands that typify absorption spectra. Absorption spectra of similar compounds and compounds with a chromophore well separated from the variation in molecular structure are often virtually identical. Also, spectral changes dependent on the experimental conditions (pH, mobile phase composition, temperature, etc.) occur frequently. For this reason user prepared local libraries tend to predominate over general libraries, in contrast to common practices in infrared and mass spectral searches. A favorable spectral match for an absorption spectrum by itself is not acceptable for absolute identification. 

Infrared and mass spectrometers provide complementary information highly desirable for identification of unknown compounds. Mass spectral libraries are significantly larger than those available for infrared spectra, so the main function of infrared information... 

The infrared spectra of paints are dominated by the polymeric binder bands, but additives such as calcium carbonate and titanium dioxide can produce bands of significant intensity in the 1500-1400 cm region and in the region below 800 cm respectively. There are a number of spectral libraries available that may be used as reference sources for the identification of paints and coatings [22, 23]. 

Various infrared spectral databases or libraries are available, which contain collections of the infrared spectra of a number of specific chemical species. Spectral search or data retrieval is a technique enabling one to identify a material of unknown origin by comparing its spectrum with library spectra, or to make a guess at the chemical structure of the unknown material from the similarity of its spectmm to some library spectra. 

Visually comparing unknown and reference spectra to each other to aid in interpretation is part of infrared spectroscopy. In the days before personal computers, collections of reference spectra called spectral libraries were plotted on paper and... 

Spectral Library Spectrai Libraries A collection of known infrared spectra stored together to make it easier to compare them to unknown spectra. Spectral libraries can come in paper or digital form. 

Spectroscopic analysis of ethanol-soluble portion This is usually performed by infrared spectroscopy. If the spectroscopist is experienced with these products, and if the spectral library is adequate, this step will tell the nature of the surfactant and indicate what other components are present in the ethanol-solubles. Since this fraction is usually a mixture, spectral interpretation is far from trivial. Mass spectrometry is also frequently applied to qualitative analysis of the ethanol-solubles. Experience is necessary, since ionization is quite dependent on the surfactant type (9). 

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