Headspace analyzers dynamic

Uehori and co-workers (1987) developed a retention index in GC to screen and quantify volatile organic compounds in blood. A dynamic headspace analyzer and GC/FID with retention indices were employed for the detection of 1,1-dichloroethane at nanogram levels. Uehori and co-workers noted that this method is simple, reliable and requires little or no sample preparation. 

Dynamic headspace analyzer GC has been used for the analysis and identification of 1,1-dichloroethane in water and fish tissue (Comba and Kaiser 1983 Mehran et al. 1985, 1986 Otson and Williams 1982 Reinert et al. 1983 Trussell et al. 1983). The analytic sample is placed in a... 

Small solid seuaples can be analyzed directly by dynamic headspace sampling using a platinum coil and quartz crucible pyrolyzer and cold trap coupled to an open tubular column (341,369,379). This method has been used primarily for the analysis of mineral samples and of additives, catalysts and byproducts in finished polymers which yield unreliable results using conventional headspace techniques owing to the slow release of the volatiles to the headspace. At the higher temperatures (450-1000 C) available with the pyrolyzer the volatiles are more readily and completely removed from the sample providing for quantitative analysis. 

Some methods are available for determining -hexane in urine and tissues. A modified dynamic headspace extraction method for urine, mother s milk, and adipose tissue has been reported (Michael et al. 1980). Volatiles swept from the sample are analyzed by capillary GC/FID. Acceptable recovery was reported for model compounds detection limits were not reported (Michael et al. 1980). A solvent extraction procedure utilizing isotope dilution followed by GC/MS analysis has been reported for tissues (White et al. 1979). Recovery was good (104%) and detection limits are approximately 100 ng/mL (White etal. 1979). 

Dynamic headspace GC utilizes a constant purge of the sample with an ultra-high purity gas (i.e., helium). The purged volatiles are then adsorbed onto a trap, followed by heat desorption onto the GC for analysis. Either a flame ionization detector or mass selective detector can be used. The protocol presented here is designed to analyze a meat sample. 

In flavor analysis, the most frequent use of volatile traps is in analyzing the flavor compounds in foods using purge-and-trap or dynamic headspace, followed by GC-MS or GCO. Additionally, the traps can be used to measure static headspace and air-matrix partition coefficients where air is pushed out of an equilibrated cell containing the sample onto a volatile trap (Chaintreau et al., 1995). Volatile traps have been also used for flavor release measurements during eating (Linforth and Taylor, 1993) or simulated eating (Roberts and Acree, 1995). 

A first approach to analyze such volatiles is the application of the AEDA on extracts prepared by dynamic headspace extraction. An apparatus used for the extraction especially of solid foods is shown in Figure 5 [55]. The powdered material is placed into a rotating cylinder and the volatiles are continuously flushed onto a polymer material (Tenax( )) by using a stream of helium (1 L/min). After 3 hr the volatiles are desorbed from the polymer by elution with a small amount of diethyl ether and evaluated by AEDA after concentration. Since different yields may change the composition of the volatiles during headspace extraction [7], it is essential to sensorially evaluate the flavor of the extracts in comparison with the food flavor itself. The following examples show applications of this method on fresh and stored wheat bread crust [55] and on fresh rye bread crust [P. Schieberle and W. Grosch, unpublished results]. 

Louisiana crayfish (Procambarus clarkii) and blue crab (Callinectes sapidus) were analyzed for volatile flavor ccnponents. Dynamic headspace sampling, capillary column gas chromatography, mass spectrometry and chromatography-coupled aroma perception were used for characterization. 

Gas chromatographic (GC) methods have been used for determining volatile oxidation products. Static headspace, dynamic headspace or direct injection methods are the three commonly used approaches. These methods were compared in an analysis of volatile compounds in an oxidized soybean oil. It was found that each method produced significantly different GC profiles (Frankel 1985). The dynamic headspace and direct injection methods gave similar results, but the static headspace is more sensitive to low molecular weight compounds. Lee and co-workers (1995) developed a dynamic headspace procedure for isolating and analyzing the volatiles from oxidized soybean oil, and equations were derived from theoretical considerations that allowed the actual concentration of each flavor component to be calculated. 

If the components of interest in a solid or liquid sample are volatile, a good way to analyze them is to examine the concentration of these analytes in the gas phase above the matrix (headspace) when in a closed container, either by taking a sample directly from the gas phase or trapping and concentrating the gas prior to analysis. This type of extraction techniques are known as headspace analysis (Smith, 2003) the analysis and subsequent separation of volatile substances is normally carried out by the technique of gas chromatography, which is a mature technology, reliable and supported by a large body of work. The sample can be in contact and in equilibrium with the extractant gas (static or equilibrium headspace), or volatile compormds can be extracted by a steady stream of inert gas (dynamic headspace). 

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