Volatiles, analysis

SFE-GC-MS is particularly useful for (semi)volatile analysis of thermo-labile compounds, which degrade at the higher temperatures used for HS-GC-MS. Vreuls et al. [303] have reported in-vial liquid-liquid extraction with subsequent large-volume on-column injection into GC-MS for the determination of organics in water samples. Automated in-vial LLE-GC-MS requires no sample preparation steps such as filtration or solvent evaporation. On-line SPE-GC-MS has been reported [304], Smart et al. [305] used thermal extraction-gas chromatography-ion trap mass spectrometry (TE-GC-MS) for direct analysis of TLC spots. Scraped-off material was gradually heated, and the analytes were thermally extracted. This thermal desorption method is milder than laser desorption, and allows analysis without extensive decomposition. 

EDXRA Energy-dispersive X-ray analysis EVA Evolved volatile analysis... 

The present study included the volatile analysis of 16 male and 15 female individuals from 10 different European Zoos. All animals were mature (aged 3-15 years). From these, 13 males and 10 females were sampled during both seasons (breeding and non-breeding season). 

The most difficult problem in flavour research is to interpret the results of the volatile analysis, which gives information on the identity and the quantity of the volatile compounds collected from a given product. Many volatile compounds are not flavour-active, i.e. they cannot be detected in the olfactory system, while others may even in trace amounts have significant effects on flavour owing to their low odour-threshold values that is defined as the minimum concentration needed to produce an olfactory response. Consequently, the most abundant volatiles are not necessarily the most important contributors to flavour. Much... 

N. (2004) Maturity discrimination of snake frmt (Salacca edulis Reinw.) cv. Pondoh based on volatiles analysis using an electronic nose device eqmpped with a sensor array and fingerprint mass spectrometry. Flavour Fragrance J. 19 44-50. 

Volatile constituents of fruits contribute to the flavor and aroma of wines, and their detection and levels have received considerable attention from many researchers. This is particularly true in recent years with the development of gas chromatography and mass spectrometry which have permitted accurate volatile analysis of fruits. 

Rancidity measurements are taken by determining the concentration of either the intermediate compounds, or the more stable end products. Peroxide values (PV), thiobarbituric acid (TBA) test, fatty acid analysis, GC volatile analysis, active oxygen method (AOM), and sensory analysis are just some of the methods currently used for this purpose. Peroxide values and TBA tests are two very common rancidity tests however, the actual point of rancidity is discretionary. Determinations based on intermediate compounds (PV) are limited because the same value can represent two different points on the rancidity curve, thus making interpretations difficult. For example, a low PV can represent a sample just starting to become rancid, as well as a sample that has developed an extreme rancid characteristic. The TBA test has similar limitations, in that TBA values are typically quadratic with increasing oxidation. Due to the stability of some of the end-products, headspace GC is a fast and reliable method for oxidation measurement. Headspace techniques include static, dynamic and solid-phase microextraction (SPME) methods. Hexanal, which is the end-product formed from the oxidation of Q-6 unsaturated fatty acids (linoleate), is often found to be a major compound in the volatile profile of food products, and is often chosen as an indicator of oxidation in meals, especially during the early oxidative changes (Shahidi, 1994). 

Comparison between 1 hr and 37 hr-heatings does not provide a consistent trend some volatiles remaining at the same level, while others increasing at different rates. To clarify the effect of heating time, a new experiment was conducted with more frequent measurements over a period of 5 days. Several samples of butteroil, 10 g each, were placed in special glass tubes to maintain a surface-to-volume ratio similar to that of the 350 g batches of the previous experiment. All samples were heated in the same 185 C oil bath, and tubes taken out for volatile analysis at specified intervals. 

Samples were reheated at full power for 1 minute in a microwave oven prior to proceeding with flavor volatile analysis (60 C internal temperature). A reproducibility study was carried out on 5 identical, 100 g samples that had been stored for 3 days after cooking, except that they were not reheated in the microwave prior to analysis. An ad hoc panel convened for these experiments consisted of two trained meat flavor panelists who scored the samples for characterization of MFD according to descriptive sensory methods described by Johnsen and Civille (12) and Love (13). The panelists were also active members of a twelve member descriptive sensory panel at the Center. Two duplicate repetitions were carried out for each experiment (4 samples studied). 

Volatile analysis by non-destructive headspace techniques Is also an Interesting tool for flavor formation studies e.g. by treatment of Intact apples with ester precursors (carboxylic acids, aldehydes, alcohols). 

The characterization of the physical and chemical changes that occur in montmorillonite/PDMS nanocomposite elastomers as they are thermally aged is reported. Broadband Dielectric Spectroscopy (BDS) was used to track changes in the physical interaction between the polymer and clay associated with increases in non-oxidative thermal stability (as determined by TGA). The evolution of volatile siloxane species from the elastomers was characterized with Thermal Volatilization Analysis (TVA). Results suggest that the improved thermal stability and the increases in polymer/clay association are a result of significant re-structuring of the polymer network. 

Tholl D, Boland W, Hansel A, Loreto F, Rose US, Schnitzler JP. Practical approaches to plant volatile analysis. Plant J. 2006 45 540-560. 

Thermal volatilization analysis (TVA) A pyrolysis technique in which the pressure of... 

Thermal volatilization analysis (TVA) of blends or mixtures of PP and poly(methyl methacrylate) (PMMA) reveals that the PMMA component tends to be stabilized and the PP destabilized. Pre-Irradlatlon of blends strongly suppresses the yield of monomeric methyl methacrylate but methyl methacrylate units appear In the chain fragment fraction. 

Figure 5 compares Thermal Volatilization Analysis (TVA) thermograms for unlrradlated and preirradiated polypropylene. The lack of coincidence of the traces In each thermogram Indicates a... 

Volatile Analysis. Volatile profiles of enzyme treated apple puree and ultrafiItered juice were obtained by gas liquid chromatography. 

Sample extracts may be concentrated by nitrogen evaporation. Turbovap concentrators direct a steam of nitrogen over the extract surface. Vessels are housed in a temperature-controlled water bath. Although some losses of volatiles occur, this technique is suited to semi-volatile analysis such as DRO. 

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