Volatile compounds quantitation

Thin-layer chromatography Gas chromatography High-performance liquid chromatography Differential rates of migration of analytes through a stationary phase by movement of a liquid or gaseous mobile phase Qualitative analysis of mixtures Quantitative and qualitative determination of volatile compounds Quantitative and qualitative determination of nonvolatile compounds... 

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 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 ... 

Nijssen, L. M., Ed., Volatile Compounds in Food, Qualitative and Quantitative Data, 7th Edition, Division for Nutrition and Food Research TNO, Institute CIVO— Analysis TNO, Zeist, The Netherlands, 1996. 

While the earlier studies in chemical ecology of mammals were preoccupied with relatively gross measurements (e.g., presence or absence of a chemi-cal/pheromone in an olfactory stimulus), the new quantitative capabilities make it now imperative to evaluate more accurately the volatile compound ratios or patterns under different biological circumstances. 

Novotny, M.V., Soini, H.A., Koyama, S., Wiesler, D., Bruce, K.E. and Penn, D.J. (2007) Chemical identification of MHC-influenced volatile compounds in mouse urine. I Quantitative proportions of major chemosignals. J. Chem. Ecol. 33, 417—434. 

Extracts collected from reproductive females and boars contained on average more compounds than those from non-reproductive females (106, 125 and 61 respectively). There were a range of volatile compounds although there were many at a high molecular weight. A quantitative analysis of the compounds present in more than 50% of the animals per type revealed a high similarity between the compounds found in reproductive females and boars. Two major compounds of all extracts have a retention time of 8.45-8.51 (RI = 800) and 14.93-14.95 (RI = 992). 

Data have been analyzed from a multivariate point of view. In this way the cooperative effects of the different materials is studied and the characteristics of each sensor are easily compared with those of the other sensors. PLS was used as a regression method for calculating the capability of the set of sensors to discriminate between the volatile compounds. Volatile compounds were checked at different concentrations in order to evaluate the response of sensors in a wide concentration range. Nevertheless, the concentration variation tends to shadow the reaction of sensors with analytes, since the sensor response contains both qualitative (sensor analyte interaction) and quantitative (analyte concentration) information. In order to remove the quantitative information, data have been normalized using the linear normalization discussed in section 3. 

The analysis of organosulphur compounds has been greatly facilitated by the flame photometric detector [2], Volatile compounds can be separated by a glass capillary chromatographic column and the effluent split to a flame ionization detector and a flame photometric detector. The flame photometric detector response is proportional to [S2] [3-6]. The selectivity and enhanced sensitivity of the flame photometric detector for sulphur permits quantitation of organosulphur compounds at relatively low concentrations in complex organic mixtures. The flame ionization detector trace allows the organosulphur compounds to be referenced to the more abundant aliphatic and/or polynuclear aromatic hydrocarbons. 

Based on the quantitative determination of pentadecane it was calculated that—with a sample load of about 200pg—alkanes are detected by this screening method if their concentration is 5ppm or more. It is obvious that highly volatile compounds when present as such (e.g. dioxane) cannot be measured quantitatively because considerable losses of such components occur during the evaporation of the suspension liquid from the pyrolysis wire when it is prepared. Quantities measured for such compounds must therefore be considered as minimum values. 

Current EPA analytical methods do not allow for the complete speciation of the various hydrocarbon compounds. EPA Methods 418.1 and 8015 provide the total amount of petroleum hydrocarbons present. However, only concentrations within a limited hydrocarbon range are applicable to those particular methods. Volatile compounds are usually lost, and samples are typically quantitated against a known hydrocarbon mixture and not the specific hydrocarbon compounds of concern or the petroleum product released. By conducting EPA Method 8015 (Modified) using a gas chromatograph fitted with a capillary column instead of the standard, hand-packed column, additional separation of various fuel-ranged hydrocarbons can be achieved. 

Readily volatile compounds cannot, as a rule, be tested in this way. As described in the method for the quantitative determination of sulphur, they are heated in a sealed tube to about 200°-300° with fuming nitric acid, and the solution produced is diluted with water and tested for sulphuric acid with barium chloride. 

Preconcentration will only give precise results for quantitative work if the initial extraction technique gives high, or at least known and reproducible, recoveries of the desired compounds from the initial sample. As typically, several cycles are needed, and the solvent containing the extracted compounds must be concentrated to a small volume. This is normally carried out by evaporation under reduced pressure. Volatile compounds may be lost in this procedure. However, for many applications the compounds of interest... 

Unsaturated fatty acids also seem to undergo oxidative breakdown during cooking. The volatile compounds found in cooked products are generally the same as in the raw product. Frequently there are, however, quantitative differences between the cooked and the raw product. Flowever, not much is known about the thermal fatty acid breakdown, but possibly it involves decomposition of already formed hydroperoxides in the raw product and/or oxidation of already formed volatile compounds. For example, l-octen-3-ol occurs in raw cut mushroom, whereas l-octen-3-one cannot be detected. On the other hand, l-octen-3-one is found in relatively large amounts in cooked mushroom [26]. 

Nijssen LM, Visscher CA, Maarse H, Willemsens LC, Boelsens MH (1996) (eds) Volatile compounds in food qualitative and quantitative data. 7th edn. TNO Nutrition and Food Research Institute, Zeist... 

The study of the parfait method reported here shows that it does not recover all classes of trace contaminants in water with equal efficiency. Volatile compounds are readily lost in this method. Contamination of eluates during elution of the ion-exchange beds is also a major problem. Even if this contamination were acceptable, the elution of these beds is not complete, as illustrated by the behavior of trimesic acid and glycine. Porous Teflon, on the other hand, offers a means to quantitatively and cleanly recover a set of water contaminants, albeit a set that was not the primary objective of the original parfait method. 

Splitless injection is required for very dilute solutions. It offers high resolution but is poor for quantitative analysis because less volatile compounds can be lost during injection. It is better than split injection for compounds of moderate thermal stability because the injection temperature is lower. Splitless injection introduces sample onto the column slowly, so solvent trapping or cold trapping is required. Therefore, splitless injection cannot be used for isothermal chromatography. Samples containing less than 100 ppm of each analyte can be analyzed with a column fdm thickness < 1 p.m with splitless injection. Samples containing 100-1 000 ppm of each analyte require a column film thickness 1 p.m. 

An extensive list of volatile compounds in apples and other fruits was included in a review by Nursten (222). White (223) reported that the principal components of the aroma of apples were alcohols (92% ) methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-l-propa-nol, 2-methyl-l-butanol, and 1-hexanol. The other constituents included 6% carbonyl compounds and 2% esters. Later, MacGregor et al. (224) tentatively identified 30 volatile components of McIntosh apple juice including four aldehydes, one ketone, 11 alcohols, 10 esters, and four fatty acids. The major organic volatiles in several different extractants of Delicious apple essence were identified and quantitatively estimated by Schultz et al. (225). They reported from sensory tests that low molecular weight alcohols contributed little to apple aroma. Flath et al. (226) identified... 

Concentration can be performed under a gentle stream of inert gas or with a micro-concentration apparatus (e.g., Kudema-Danish sample concentrator, Supelco, or microconcentrator). This step generates volatile losses (mainly very volatile compounds that have a boiling point lower than the solvent) and will modify the quantitative ratio. 

Chaintreau, A., Grade, A., and Munoz-Box, R. 1995. Determination of partition coefficients and quantitation of headspace volatile compounds. Anal. Chem. 67 3300-3304. 

Maarse, H. and Visscher, C.A. 1989. Citrus fruits. Products 5. In Volatile Compounds in Food. Quantitative and Qualitative Data, TNO-CIVO, pp. 35-99. Food Analysis Institute, Ziest, The Netherlands. 

Quantitative Detection of Vapors from Low Volatility Compounds , USP 3883739 (1975) 105) L. Elias M. Krzymien, Methods of Evaluating the Sensitivity of Explosives Vapor Detectors , Lab Tech Rept LTR-VA, Natl Res Council, Canada (1975) 106) T. Kraziejko,... 

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