Volatile compounds, analyses

Gaseous and volatile compound analysis is covered in Chapter 7. Since all MS systems ultimately require gas phase ions, such a topic is of high importance in inorganic as well as molecular MS analysis. The chapter is short, yet does cover sample preparation for volatiles as well as some important applications. This chapter is very well referenced. 

Chin, H. W., Bernhard, R. A., and Rosenberg, M. (1996). Solid phase microextraction for cheese volatile compound analysis. ]. Food Sci. 61,1118-1122. 

Sample Courier Service Volatile Compound Analysis ... 

A.D. Hewitt, Storage and Preservation of Soil Samples for Volatile Compound Analysis, USA Cold Regions Research and Engineering Laboratory, Special Report 99-5, [US Army Corps of Engineers, 1999a]. 

After mixing the contents, the tubes were tightly stoppered with Teflon-lined caps and kept at 4 C for 7, 14 or 21 days. All samples were made in duplicate. Otfier temperatures (25, 90 °C) were also tested. Samples were kept at -80 C until the volatile compound analysis (less than a month). 

Volatile Compound Analysis by Solid-Phase Microextraction-Gas Chromatography-Mass Spectrometry (SPME-GC-MS)... 

AOCS has a recommended practice (Cg 3-91) for assessing oil quality and stability (AOCS, 2005) for measuring primary and secondary oxidation products either directly or indirectly. For example, peroxide value analysis (AOCS method Cd 8-53) (AOCS, 2005) determines the hydroperoxide content and is a good analysis of primary oxidation products. To determine secondary oxidation products, the procedure recommends p-anisidine value (AOCS Method Cd 18-90, 2005) volatile comlb by gas chromatography (AOCS Method Cg 4-94, 2005) and flavor evaluation. (AOCS Method Cg 2-83, 2005). The anisidine value method determines the amounts of aldehydes, principally 2-alkenals and 2, 4-dienals, in oils. The volatile compound analysis method measures secondary oxidation products formed during the decomposition of fatty acids. These comlb can be primarily responsible for the flavors in oils. The... 

Krist, S., Unterweger, H., Bandion, R, and Buchbauer, G., Volatile compound analysis of SPME head-space and extract samples from roasted Italian chestnuts Castanea sativa Mill.) using GC-MS, Fur. Food Res. TechnoL, 219, 470-473, 2004. 

Major Volatile Compounds Analysis Produced from Mezcal Fermentation Using Gas Chromatography Equipped Headspace (GC-HS)... 

One of the major analytical problems with fruit and vegetable samples is the detection and identification of non-volatile organic compounds present in low concentration levels, as happens for most of the phytoalexins produced by plants. Mass spectrometry is widely used in the analysis of such compounds, providing exact mass identification. However, the difficulty with their unequivocal identification and quantitative detection lies in their volatilization into the gas phase prior to injection into the analyser. This constitutes particular problems for thermally labile samples, as they rapidly decompose upon heating. To circumvent this difficulty a wide range of techniques have been applied for non-volatile compound analysis, including FAB (Fast Atom Bombardment), FD (Field Desorption), LD (Laser Desorption), PD (Plasma Desorption) and SIMS (Secondary Ion Mass Spectrometry). Further details of laser desorption can be found in Section 28.7. 

The experiments were carried out on two different days using the same batch of popcorn, but freshly popped each time just before the experiment. The direct injection method results should represent the true nature of the sample as extracted by supercritical CO2. The aims of this experiment were to apply the use of the SFE SPME and SFE DI methods in volatile compound analysis for the first time and to evaluate the feasibility of using this technique for flavor analysis from difficult solid matrices using smaller sample quantities. 

Quantitative Calculations When needed, the relationship between the analyte and the analytical signal is given by the stoichiometry of any relevant reactions. Calculations are simplified, however, by applying the principle of conservation of mass. The most frequently encountered example of a direct volatilization gravimetric analysis is the determination of a compound s elemental composition. 

Gas chromatography (gc) has been used extensively to analyze phenoHc resins for unreacted phenol monomer as weU as certain two- and three-ring constituents in both novolak and resole resins (61). It is also used in monitoring the production processes of the monomers, eg, when phenol is alkylated with isobutylene to produce butylphenol. Usually, the phenoHc hydroxyl must be derivatized before analysis to provide a more volatile compound. The gc analysis of complex systems, such as resoles, provides distinct resolution of over 20 one- and two-ring compounds having various degrees of methylolation. In some cases, hemiformals may be detected if they have been properly capped (53). 

Hplc techniques are used to routinely separate and quantify less volatile compounds. The hplc columns used to affect this separation are selected based on the constituents of interest. They are typically reverse phase or anion exchange in nature. The constituents routinely assayed in this type of analysis are those high in molecular weight or low in volatility. Specific compounds of interest include wood sugars, vanillin, and tannin complexes. The most common types of hplc detectors employed in the analysis of distilled spirits are the refractive index detector and the ultraviolet detector. Additionally, the recent introduction of the photodiode array detector is making a significant impact in the analysis of distilled spirits. 

H. Marse, C. Visscher, L. WiUemsens, and M. H. Boelens, Volatile Compounds in Food Qualitative and Quantitative Data, Vol. II, TNO-CIVO, Food Analysis Institute, A. J. Zeist, The Nethedands, 1989, pp. 661—679. 

The hexafluoroacetone derivatives are highly volatile compounds. TTiey can therefore be-used for gas-chromatographic analysis of mixtures of a-amino and... 

The retention gap method (1, 2) represents the best approach in the case of qualitative and quantitative analysis of samples containing highly volatile compounds. The key feature of this technique is the introduction of the sample into the GC unit at a temperature below the boiling point of the LC eluent (corrected for the current inlet pressure), (see Eigure 2.2). This causes the sample vapour pressure to be below the carrier gas inlet pressure, and has two consequences, as follows ... 

GC using chiral columns coated with derivatized cyclodextrin is the analytical technique most frequently employed for the determination of the enantiomeric ratio of volatile compounds. Food products, as well as flavours and fragrances, are usually very complex matrices, so direct GC analysis of the enantiomeric ratio of certain components is usually difficult. Often, the components of interest are present in trace amounts and problems of peak overlap may occur. The literature reports many examples of the use of multidimensional gas chromatography with a combination of a non-chiral pre-column and a chiral analytical column for this type of analysis. 

Let us consider one other reaction of ethanol. If ethanol is heated with aqueous HBr, we find that a volatile compound is formed. This compound is only slightly soluble in water and it contains bromine its molecular formula is found by analysis and molecular weight determination to be C2HsBr (ethyl bromide, or bromoethane). With the aid of the bonding rules, we can see that there is only one possible structure for this compound. This result is verified by the fact that only one isomer of C2H6Br has ever been discovered. 

The particles then enter a conventional mass spectrometer source where they are vaporized prior to being ionized using electron impact or chemical ionization. As with other interfaces, this may cause problems during the analysis of thermally labile and highly in volatile compounds. 

Egan, H. Preussmann, R. Walker, E.A. Castegnaro, M. Wasserman, A.E. Eds. "Environmental Carcinogens Selected Methods of Analysis Vol. 1 - Analysis of Volatile Nitrosamines in Food." lARC Scientific Publications No. 18. International Agency for Research on Cancer Lyon, 1978. Walker, E.A. Griciute, L. Castegnaro, M. Borzsonyi, M., Eds. "N-Nitroso Compounds Analysis Formation and Occurrence" lARC Scientific Publications No. 31. International Agency for Research on Cancer Lyon, 1980. Hedler, L. Schurr, C. Marquadt, P. J. Am. Oil Chem. Soc. 1979, 681-684. 

For aerobic degradation, uptake of oxygen or the evolution of carbon dioxide is most widely used. Use of the concentration of dissolved organic carbon may present technical problems when particulate matter is present, though analysis of dissolved inorganic carbon in a closed system has been advocated (Birch and Fletcher 1991), and may simultaneously overcome problems with poorly soluble or volatile compounds. 

The analyte must be converted into a volatile compound suitable for mass-spectrometric analysis. Procedures for C, N, and O follow those developed for conventional organic microanalysis— oxidation of organic C to COj, reduction of organic N to N2, and conversion of O2 into CO or COj. In most procedures, cryogenic purification of the products is carried out before mass spectrometry, and both off-line and on-line procedures have been developed. 

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