Spectra libraries

Figure 5.6 Successful transformation of Aeromonas hydrophila raw spectra A acquired on day 27 to new locations a (relationship indicated with a dotted arrow) near an A. hydrophila day 1 library spectrum C using another day 27 bacterium, E. coli 1090 D as reference compared to its own day 1 E. coli 1090 Library spectrum L (relationship indicated with a solid arrow).

Figure 9 ATR infrared spectra for the normal (top) and non-melt (middle) areas of the injection-molded sheet and a library spectrum for a polycaprolactone (bottom).

Figure 11 shows the ATR-FTIR spectrum acquired from the surface of the white-colored paint sample after the paint had been dried. Figure 12 shows the closest spectral library database matches obtained Figure 13 compares the spectrum of the surface of the white-colored paint sample with that of a reference library spectrum of a vinyl toluene-modified alkyd. The binder from the dried... 

Figures 61 and 62 show the ATR-FTIR spectra recorded from areas C and D, respectively, from the cross-section of catheter sample 2. The infrared spectra from both areas, C and D, are spectrally matched closest by a library spectrum of a polyethylene. (Both the recorded spectra show weak additional absorption bands in the region 1,700-1,500 cm-1.) The ATR-FTIR spectrum recorded from...

Figure 69 ATR-FTIR spectrum of the heat seal surface of the good white film (top), the heat seal surface of the bad white film (middle), and the library spectrum of an ethylene/ vinyl acetate copolymer (bottom). 

Figure 69 shows the ATR-FTIR spectra of the inside heat seal layer of the white film from both the "good" and "bad" packages. A library spectrum of an EVA copolymer is also shown for comparison. The heat seal layer is identified as EVA, based on the position of peaks in the sample spectra compared to the library EVA spectrum. The heat seal layer appears to have a lower vinyl acetate content compared to the library spectrum, which was acquired from a 14% vinyl acetate copolymer. There were no significant spectral differences between the spectra of the "good" and "bad" samples. 

FJciureJyT. (a) Mass spectrum at the top of the chromatographic peak (b) background spectrum (c) analyte spectrum after background subtraction (d) library spectrum of hexachlorobiphenyl (score 99%). 

FIGURE 8.11 The Direct-EI mass spectrum of lindane is shown in the upper trace, and it is compared with the standard NIST El library spectrum shown in the lower trace. 

Figure 6. Top, MS/MS fragment ion library spectrum of lactic acid standard and bottom, MS/MS fragment ion spectrum of lactic acid emanating from the hand.

Figure 10.11 Comparison of the mass spectra of a neroli oil peak (camphene) obtained by HPLC-HRGC-MS (a) and GC-MS (b) with a library spectrum of the same compound (c). Reprinted from Perfumer and Flavorist, 21, L. Mondello et al., On-line HPLC-HRGC in the analytical chemistry of citrus essential oils , pp. 25-49, 1996, with permission from Allured Publishing Corp.

The mass spectrum corresponding to this peak (Figure 6b) matches well with the spectrum obtained from the drug standard, and also with the (Wiley NBS) library spectrum. Using the accurate mass measurements obtained on the FTMS data, comparisons can be made between the standard and the unknown. Based on twelve... 

These spectra were converted from. ras to. abs files with no change in the Y-axis scale and then used to search Sadtler libraries of commercial material using Mattson First software with a correlation coefficient search algorithm which takes into account baseline drift and differences in scaling. As can be seen the sample spectrum and the library spectrum are usually quite similar. The library spectra shown here were the best hits in each of the searches with a search correlation coefficient of >0.9 with 1.0 representing a perfect match. 

During processing of the test run data (injection of OPCW test mixture) AMDIS is searching a small, dedicated Chemical Standards Library (ASCII file onsite.csl). This library contains only data and spectra of the 16 compounds contained in the OPCW test mixture (see Annex 2, Table 1). A compound in the test mixture is defined as detected if the net match factor of the compound spectrum compared with library spectrum is >85. This threshold of identification is fixed in the on-site version of AMDIS. 

Other reference substances are available and can be used as well. Sometimes the resonance of the actual solvent can serve as a reference. Preferably, the referencing method used for the sample should be the same as that used for the authentic reference sample (or library spectrum), or at least the scale... 

NMR spectral parameters, that is, chemical shift (8) and coupling constant (J), may be considerably affected by the sample condition, that is, solvent, pH, sample temperature, concentration, and choice of internal and/or external chemical shift references. Solvent and pH (in water/D20 samples) have the greatest effect. The sample condition should therefore be the same as or comparable to that used for the authentic reference chemical (or library spectrum) and the blank sample. 

The same original spectrum with a sloping background added is shown in Fig. 5-3. The second derivative with a 15-point smooth was calculated and is shown in the figure, where it is compared with the second derivative with a 15-point smooth of the original spectrum. The two derivatives are identical. This demonstrates the importance of derivatives in matching an unknown with a library spectrum. Frequently, real unknown samples can be plagued with... 

An example of search results is shown in Fig. 5-10. An unknown spectrum (ibuprofen tablet) is compared with three library spectra. The unknown and each of the library spectra were interpolated so that the number of frequencies, the first and last frequencies, and the frequency increment were identical for all the spectra. Next, the baseline minimum was subtracted from each of the spectra, and each of the spectra was normalized so that the total area was 1.0. Finally, the Euclidean distances and dot products were calculated using Eqs. (5-9) and (5-10), respectively. Library spectrum 3 had the smallest Euclidean distance and the largest dot product with the unknown spectrum. Spectrum 3 corresponds to pure ibuprofen powder, so the correct match was obtained. 

In the forward search, all of die ions in both the library spectrum and the unknown specdiun are used in the calculation of the fit factor, while in the reverse search only the ions in the library specdiun are used in this calculation. Forward searches work well only for pure compounds, while die reverse search is admirably suited for dealing widi die composite spectra fiom mixtures. 

Figure 5.6. Spectrum of Motrin obtained with a 785 nm laser, but not corrected for instrument response function (spectrum A). Spectrum B results from subtraction of a corrected library spectrum for ibuprofen from spectrum A. Residual ibuprofen features result from differences in relative intensity between the corrected and uncorrected spectra.

The dominant peak at c 28 minutes is PBO itself, whilst the other peaks are assumed to be impurities present from the manufacturing process. Many of these other peaks have been identified by the mass spectroinetric techniques employed in these studies, but the data are not considered relevant to the current discussion, ["he El mass spectrum of PBO [Pig- 6.2) is similar to the published library spectrum. The fragmentation pattern of PBO, and hence many of its degradation products, is unusual. Whilst the El spectrum shows a clear molecular ion rrs/z 338), the spectrum is dominated by the fragment ion at m/z 176, which has been attributed by previous workers Williams and Williamson, 1991) to the rearrange merit ion ... 

Figure 6 shows the complex mixture spectrum versus the 2CEES library spectrum on an expanded scale. The more intense transitions in the library are seen in the mixture spectrum. It is evident that the resolution of this technique makes it possible to extract single components analytically from a complex mixture as is necessary for this technique to be applied to the detection of chemical weapons in real (non-laboratory) settings. 

Figure 6 Comparison of the pure rotational spectrum (10,000 averages) of the CWA mixture of the four simulants combined into one sample cylinder (A) with the 2CEES library spectrum (B).

FIGURE 3 Electron impact spectrum of the unknown compound (top) and the library spectrum of I.Z-dimethylbenzene (bottom). 

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