Chemical fingerprints

The parent ion usually breaks apart into a collection of smaller pieces, many of which are also positively charged. The masses of these fragments provide a chemical fingerprint that indicates how the atoms in a molecule are connected together. A relatively simple example is the mass spectmm of methane, shown in the figure. There are peaks at mass numbers 16, 15, 14, 13, 12, and 1. Nearly all hydrogen atoms have. <4 = 1, and nearly all carbon atoms have A = 12, so these peaks can be identified as CH4 ,... 

To detect adulteration of wine. Bums et al. (2002) found that the ratios of acetylated to p-coumaroylated conjugates of nine characteristic anthocyanins served as useful parameters to determine grape cultivars for a type of wine. Our laboratory utilized mid-infrared spectroscopy combined with multivariate analysis to provide spectral signature profiles that allowed the chemically based classification of antho-cyanin-containing fruits juices and produced distinctive and reproducible chemical fingerprints, making it possible to discriminate different juices. " This new application of ATR-FTIR to detect adulteration in anthocyanin-containing juices and foods may be an effective and efficient method for manufacturers to assure product quality and authenticity. 

The pragmatic beauty of the chemical fingerprint is that the more common features of two molecules that there are, the more common bits are set. The mathematic approach used to translate the fingerprint comparison data into a measure of similarity tunes the molecular comparison [5]. The Tanimoto similarity index works well when a relatively sparse fingerprint is used and when the molecules to be compared are broadly comparable in size and complexity [5]. If the nature of the molecules or the comparison desired is not adequately met by the Tanimoto index, multiple other indices are available to the researcher. For example, the Daylight software offers the user over ten similarity metrics, and the Pipeline Pilot as distributed offers at least three. Some of these metrics (e.g., Tversky, Cosine) offer better behavior if the query molecule is significantly smaller than the molecule compared to it. 

The emerging analytical technique of laser-induced breakdown spectroscopy (LIBS) is a simple atomic emission spectroscopy technique that has the potential for real-time man-portable chemical analysis in the field. Because LIBS is simultaneously sensitive to all elements, a single laser shot can be used to record the broadband emission spectra, which provides a chemical fingerprint of a material. 

On the other hand, there is considerable interest to quantify the similarities between different molecules, in particular, in pharmacology [7], For instance, the search for a new drug may include a comparative analysis of an active molecule with a large molecular library by using combinatorial chemistry. A computational comparison based on the similarity of empirical data (structural parameters, molecular surfaces, thermodynamical data, etc.) is often used as a prescreening. Because the DFT reactivity descriptors measure intrinsic properties of a molecular moiety, they are in fact chemical fingerprints of molecules. These descriptors establish a useful scale of similarity between the members of a large molecular family (see in particular Chapter 15) [18-21],... 

Determine the "chemical fingerprints" that identify the various waters. 

As discussed previously, military-grade TNT is not a pure material, containing additional nitroaromatic constituents at concentrations of up to several percent by mass [4], Some of these explosive-related compounds (ERCs) have been shown to be significant contributors to the chemical fingerprint of a landmine [5, 7], Of the ERCs found in TNT, those that are most prevalent in the headspace vapor of TNT include 2,4-DNT, 2,6-DNT, 1,3-dinitrobenzene (1,3-DNB), and... 

Liger-Belair, G., Cilindre, C., Gougeon, R., Lucio, M., Gebefiigi, I., Jeandet, P., and Schmitt-Kopplin, P. (2009a). Unraveling different chemical fingerprints between a champagne wine and its aerosols. Proc. Natl. Acad. Sci. USA 106,16545-16549. 

A chemical fingerprint is generated consisting of scission products, in the MS/MS instrument, characteristic of the compound of interest. The parent molecule has a MW of 403. In each case the same major fragments are observed masses 361,301,... 

FIGURE 2 GC-MS/MS chemical fingerprint (product ion spectrum) of (a) standard muramic acid (2ng total in sample) and (b) muramic acid isolated from dust. Medical samples appear similar. 

Analyses conducted at LBNL (41-42) on artifacts from on a multi-component site known as Waywaka in the town of Andahuaylas in the Department of Apurimac exhibited two chemical fingerprints rarely detected outside the Andahuaylas area. The chemical types were assigned the names Andahuaylas A and Andahuaylas B by Burger and Asaro who were strongly convinced that the sources were located in this region. 

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