Headspace concentrating

Novotny, M., Lee, M.L. and Battle, K.D. (1974) Analytical aspects of the chromatographic headspace concentration methods using a porous polymer. Chromatographia 7, 333-338. 

Bartelt, R.J. Calibration of a commercial solid-phase microextraction device for measnring headspace concentrations of organic volatiles. Anal. Chem., 69(3) 364-372, 1997. 

Sampling is difficult because the vapor pressures for most explosives are very low. For example, the room temperature equilibrium headspace concentration of RDX in air is about 10 pptv (parts per trillion by volume). Collection of vapor is further compounded for explosives that are bound in matrices and wrappers and/or are concealed in wrappings or baggage. The prospects for trace detection of explosives are considered to be better when sampling objects for explosives contamination in the form of particles and residue. 

A simple method for assessing lipid oxidation is measuring the headspace concentration of hexanal by capillary GLC. Also, the total volatiles appearing in the chromatogram up to hexanal can be taken as oxidation index. The method was applied to determine the amounts of lipid peroxides present in rat liver cells. Enhancement of the hexanal concentration can be achieved on adding ascorbic acid (22), that reduces Fe(ni) present in the matrix to Fe(II), which catalyzes decomposition of hydroperoxides to aldehydes. Significant correlations are found between hexanal concentrations and various oxidation indices, such as TBARS (Section IV.D.2)" . ... 

The four key features of PTR-MS can be summarised as follows. First, it is fast. Time dependent variations of headspace profiles can be monitored with a time resolution of better than 1 s. Second, the volatile compounds do not experience any work-up or thermal stress, and very little fragmentation is induced by the ionisation step hence, measured mass spectral profiles closely reflect genuine headspace distributions. Third, measured mass spectral intensities can be directly related to absolute headspace concentrations, without calibration or use of standards. Finally, it is not invasive and the process under investigation is not affected by the measurements. All these features make PTR-MS a particularly suitable method to investigate fast dynamic process. 

Aerojet (fine chemicals division now acquired by AMPAC) also has reported technology to prepare and use diazomethane on large scale from the reaction of NaOH with N-methyl-N-nitrosamine. This process differs for the Phoenix process in that relatively large amounts of a low-boiling volatile solvent, diethyl ether, are uhlized to limit bulk liquid temperatures and minimize headspace concentrations of diazomethane [22]. 

Dalla Rosa, M., Pittia, P., and Nicoli, M.C. 1992. Influence of water activity on headspace concentration of volatiles over model and food systems. Ital. 1 Food Sci. 4 421-432. 

Zhu, J., Li, H., Korchinski, M. and Fellin, P. (2005) Prediction of initial emission rates of 2-butoxyethanol from consumer products using equilibrium headspace concentrations an appliacation of the vapor pressure and boundary layer (VB) model. Environmental Science and Technology, 39, 8214-19. 

J. Zechman, S. Aldinger, and J. LaBows, Jr., Characterization of pathogenic bacteria by automated headspace concentration—gas chromatography, J. Chromatogr., 377 49-57 (1986). 

The volatile constituents of canned Black Perigord Truffles (Tuber Melanosporum) were analysed by dynamic headspace concentration gas chromatography - mass spectrometry. A total of 36 compounds were identified and described for the first time as canned black truffle aroma constituents. The modification of flavor and the possible formation of the compounds due to the heating treatment are discussed. 

In summary, headspace concentration method is the usual way of analyzing the odor quality of packaging materials and has been shown to give reliable data which can be correlated with sensory evaluation data. Oven-heated microwavable packaging materials may pose a special flavor problem in the food consumed. 

Ethylene and carbon dioxide are produced by the plant cells in the culture and their respective headspace concentrations increase in the stoppered flasks. As expected, oxygen consumption by the cells results in reduction of the head-space composition. Specific 02 consumption rate and biomass accumulation curves as a function of time are presented in Fig. 2. The biomass accumulated at a rate of approximately 0.05 gdw 1 1 h the average specific 02 consumption rate calculated as 0.05 mmol gih v h The same data plotted as specific 02 con-... 

Fig. 1. Headspace concentrations of oxygen, carbon dioxide and ethylene from type a cultures of A. annua as a function of culture age. Ethylene ( ) carbon dioxide (a) oxygen ( )...

Fig. 3. Specific oxygen consumption rate (g 02 gdw h ) of A. annua from type a cultures as a function of oxygen headspace concentration...

Fig. 6. Ethylene and methyl jasmonate (MJ) interaction when MJ is supplied as ethanolic solution to the suspension cell cultures of T. cuspidata. All cultures were exposed to 10% (v/v) oxygen, 0.5% (v/v) carbon dioxide and designated headspace concentrations of ethylene. A 0 ppm B 5 ppm C 10 ppm. 0 pM MJ ( ) 10 pM MJ ( ) 100 pM MJ (a). Reprinted with the permission of the American Chemical Society and the American Institute of Chemical Engineers [27]...

Data from the stoppered culture tests was also used to determine the effect of declining 02 concentration on the rate of metabolism of the cells. The specific 02 consumption rate was determined to depend linearly upon the 02 concentration throughout the range of headspace concentrations measured (0-31 %). This seems to contradict the experience of other researchers [31-33, 50], who report saturation kinetics in plant cell cultures whenever 02 concentration exceeded 4-5% (gas phase). In the stoppered culture tests, at the same time 02 concentration declined, C02 and C2H4 concentrations increased. Other unidentified compounds may also have been produced. The declining rate of metabolism observed may have been caused by conditions other than declining oxygen. 

McNeal TP, Nyman PJ, Diachenko GW, et al. 1993. Survey of benzene in foods by using headspace concentration techniques and capillary gas chromatography. Journal of AOAC International 76 1213-1219. 

Keenaghan, J. Meyers, M.C. "Analysis of Volatile Organics in Foods and Beverages by Headspace Concentration-GC/MS" presented at the 34th Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy Atlantic City, N.J. March, 1984. 

Flores, M., Gianelli, M.P., Perez-Juan, M., and Toldra, F. (2007). Headspace concentration of selected dry-eured aroma eompounds in model systems as affected by curing agents. Food... 

Some static headspace methods do not require an external calibration and are based on measurements performed at thermodynamic equilibrium between liquid and gas phase. In the phase ratio variation method (PRV) described by Ettre and Collaborators (1993), the partition coefficient calculation is based on the fact that the headspace concentration changes as a function of the phase volume ratio (gas and liquid phases), while the partition coefficient remains constant. This method has been recently applied to study the interactions between aroma compounds and macromolecules in different food systems (Savary et al. 2006, 2007) but so far not to the wine. 

Aznar et al. (2004) used static headspace-APCI-MS to study the release of volatiles from water and hydroalcoholic systems (12 vol.%). They found a decrease in the headspace concentration of volatile compounds with an increase in the log P values (hydrophobicity values) until log P = 3. Nevertheless, for very non-polar compounds (log P > 3), they did not find this trend this could be due to changes in hydrophobic interactions in the solution. 

Table n. Percentage decrease in headspace concentration of aroma compound... 

Aroma compound logP % decrease in headspace concentration... 

The present investigation used a headspace concentration c illary gas chronatogrcphic technique with nitrogen- hoephorus detection. Advantages of this technique are that the procedure was rapid (about 30 minutes), potential for artifact formaticn is minimized and sanple requirsonents are email (15 ml). 

Compound Air Concentration (pptv) 1 S/N, Air Seawater Headspace Concentration (pptv) S/N, Seawater... 

The headspace concentration is reported because reliable Henry s constants are not available to calculate concentration. 

Fig. 5.21 Effect of edible oil on the vapour pressure of selected flavouring substances [52]. RVP (= relative vapour pressure) is the headspace concentration of a flavouring substance over a model system containing water, emusifier and oil divided by its headspace concentration above a system containing only water and emulsifier...

The way in which an oil is distributed physically in an aqueous phase can affect the headspace concentration of flavouring substances. In the case of dimethyl sulphide, a higher concentration of flavouring substance is needed in the oil-in-water emulsion to achieve the concentration in the gas phase which is measured above the non-emulsi-fied system (Fig. 5.22A). This points to an adsorption of the dimethyl sulphide on the boundary surfaces or to some other type of interaction. In the case of allyl mustard oil, a higher concentration is measured in the headspace of the emulsion than in that of non-emulsified system (Fig. 5.22B). Apparently the mustard oil has little or no affinity with the boundary surfaces. 

Fig. 5.22 Influence of the lipid phase on the headspace concentration of (A) dimethyl sulphide and (B) allyl mustard oil ( A = water, O - oil, o = emulsion, = water and oil not emulsified) [32]...

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