Mass Spectral Fingerprinting

Although the identification of VOCs may be necessary for certain applications, compound identification is not always required and a more holistic approach has its advantages. Simple VOC patterns, which we will refer to rather loosely as fingerprinting, together with appropriate statistical analysis, may provide more than sufficient information for certain analytical food applications. Comparison with other techniques, such as sensory analysis by a panel of human tasters, may also be valuable and provide confirmatory information when using PTR-MS for food analysis (the food s quality, origin, etc.). Examples where 

The types of statistieal analytical methods required in this application are often multivariate methods. These statistical procedures are called multivariate when the property being measured, for example, the location of the food, is being related to several variables (such as the signal levels in different miz channels) in the analysis. Multivariate statistical methods can be broadly divided into two types (1) unsupervised, which means that no a priori knowledge of the samples to be classified is required and (2) supervised, which requires a priori knowledge about the samples [18]. A good example of an unsupervised method is principal component analysis (PCA) [19-27], which looks for patterns in a block of data that depend on different variables. PCA provides a useful tool to explore and visualize information, and in particular to identify patterns in complex data, and it is therefore widely used. Applications of PCA in food science will be presented later in this chapter. 

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Jarman, K. H. Daly, D. S. Peterson, C. E. Saenz, A. J. Valentine, N. B. Wahl, K. L. Extracting and visualizing matrix-assisted laser desorption/ionization time-of-flight mass spectral fingerprints. Rapid Comm. Mass Spectrom. 1999, 13, 1586-1594. 

Despite the complexity of the chemical composition of the resinous materials, in a few minutes such techniques provide a mass spectral fingerprint, which highlights the compounds that are the main components in the sample. They avoid any sampling treatment before analysis. They have thus enabled diterpenoid resinous materials from Coniferae, and several triterpenoid materials to be clearly identified. In particular, the DE-MS technique is able to distinguish between different triterpenoid materials such as mastic resin, frankincense resin and birch bark tar. In fact, using PCA on DE-MS mass... 

Mass spectra of numerous single compounds are available in reference libraries. However these spectra have not always been obtained in the same conditions as those used in DE or DI EI-MS modes and the spectra of molecules of specific interest in the field of cultural heritage have not been systematically registered. It is thus of importance to achieve mass spectra on a set of standard molecular constituents in order to study their mass spectral fingerprint in detail before investigating the more complex mass spectra of multicomponent materials. 

All these results obtained on commercial pure molecular constituents may now be exploited for interpreting more complex mass spectral fingerprints achieved on natural substances. 

These results show that, depending on the lipid substances present in a sample, direct mass spectrometry may allow the identification of all the lipid substances present in a material, in particular when their mass spectral fingerprints do not overlap, or to determine the main molecular constituents still preserved in the sample. 

To date, the vast majority of applications of intact cell MALDI-TOF analyses have been to bacteria. However, preliminary extensions of the approaches used in bacteria have been applied to fungi. From the standpoint of the discovery of novel chemotypes via natural products, this is obviously a desirable step, but it is also clearly in its infancy. Two groups reported [36,37] the observation of relatively simple mass spectral fingerprints from the intact fungal tissue they analyzed. This application might have the advantage of simplified spectral comparisons, relative to those for bacteria, but also means that such comparisons would have fewer data points to support them. 

Using the mass spectrometry based chemsensor the entire headspace volatiles of each of the 8 flavor samples were sampled and a characteristic fingerprint mass spectrum was obtained. For example. Figures 1 and 2 represent the TIC and MS obtained for formulations 1 and 8 respectively. Inspection of these two figures indicates that each flavor sample has a characteristic mass spectrum. Similar results were observed with the mass spectrum from the rest of the flavors formulations. Even though the mass spectral fingerprints of the citrus oils were similar there were sublte differences in some ion ratios. 

Figure 3 contains the mass spectra line plot of all 8 formulations used for developing the chemometric models. These lineplots contain the mass spectral information in which a line connects the ions abundances. A closer look of the data is seen in the inset that shows how the different flavor samples have different ion abundance and therefore different mass spectral fingerprints. These... 

The mass spectrum of the corresponding trimethyl-silyl ether derivative is shown in Figure lb, and an important advantage of this derivatization is immediately apparent in the prominent [M —CH3] ion at m/z 173. This ion allows the estimation of the molecular weight of the derivative in cases where a molecular ion is absent. In addition, because the fragmentation pattern is characteristic of the molecule, it may be used as a mass spectral fingerprint to confirm the identity of the GC peak, and libraries of reference spectra are readily available. Trimethylsilylation is one of the most common derivatizations in GC-MS. Further details and examples are given later in the section on silylation. 

Hansen MAE, Smedsgaard J. Automated work-flow for processing high-resolution direct infusion electrospray ionization mass spectral fingerprints. Metabolomics 2007 3 41-54. 

In order to quantitatively intercompare mass spectral fingerprints produced by base-specific fragmentation, we formulated the scalar or inner product defined by Equation 4.1. We define a scalar product (often referred to as a dot product ) of two mass spectra as ... 

Fast and non-invasive analysis of VOCs has the potential to determine the quality and origin of wine. This is particularly important given the huge commercial market in wine and the potential for adulteration and production of fake products. Boscaini et al. were the first to use PTR-MS for the characterization of wine using direct headspace analysis and mass spectral fingerprints [53]. Owing to the high ethanol content of wine it was not possible... 

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