Headspace sampling dynamic

Dynamic headspace sampling employs the continuous removal of... 

Gas phase stripping (purge-and-trap) techniques can iaq>rove the yield of organic volatiles from water or biological fluids by facilitating the transfer of volatiles from the liquid to the gas phase it is also more suitable than dynamic headspace sampling when the sample volume is restricted (320 23,347-351). Tbe technique is used routinely in many laboratorl B for the analysis... 

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. 

Static headspace may also be carried out by substituting the heating step by a microwave treatment. In this procedure the material is immersed in a solvent that is transparent to microwaves relative to the sample in order to impart most, if not all, of the microwave energy to the sample [208]. Another configuration of MAP gas-phase extraction relates to dynamic headspace sampling. 

Figure G1.2.2 Typical set-up for dynamic headspace sampling using a volatile adsorbent trap.

A number of different set-ups can be used. Figure G 1.2.2 shows one possible set-up of dynamic headspace trapping. Normally, the vessel contains the food product, an inlet for nitrogen gas, and an outlet connected to the trap. The inlet could be directed through the liquid food, often called purge-and-trap, or above the food, often called dynamic headspace sampling. 

J., Gonzalez-Castro, M.J., De La Cruz Garcia, C. Determination of volatile 4.36 components in fresh, frozen, and freeze-dried Padron-type peppers by gas chromatography-mass spectrometry using dynamic headspace sampling and 4.37 microwave desorption. J. Chromatogr. 

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. 

This paper discusses initial results obtained fran analysis of the volatile components of the tail meat and the hepatopancreas of boiled crayfish and the volatile caiponents fran pasteurized crafcmeat samples using a procedure of combined dynamic headspace sampling, capillary column gas chromatography and mass spectrometry. 

Hernandez and Rutledge (1994a) used dynamic headspace sampling to analyse cocoa mass from 13 geographical locations at different roasting... 

Of these methods, dynamic headspace sampling is probably the least well known, yet it has a number of advantages over other techniques in use. 

Figure 2. Apparatus for dynamic headspace sampling of volatiles, released from intact apples. 1 = high purity purge air, 2 dessicators, 3 = thermostated waterbath (18°C), 4 = fine metering valve, 5 = Tenax adsorber, 6 = flow meter, 7 = wet-testmeter.

Aroma development In ripening apples is dependent on a number of external and Internal factors. Dynamic headspace sampling of the volatiles from intact fruits, followed by high resolution gas chromatography or g.c.-m.s. anlysis is a convenient procedure for the study of these factors. 

The volatiles of fresh pineapple (Ananas comosus [L] Merr.) crown, pulp and intact fmit were studied by capillary gas chromatography and capillary gas chromatography-mass spectrometry. The fnjit was sampled using dynamic headspace sampling and vacuum steam distillation-extraction. Analyses showed that the crown contains Cg aldehydes and alcohols while the pulp and intact fruit are characterized by a diverse assortment of esters, h rocarbons, alcohols and carbonyl compounds. Odor unit values, calculated from odor threshold and concentration data, indicate that the following compounds are important contributors to fresh pineapple aroma 2,5-dimethyl-4-hydroxy-3(2H)-furanone, methyl 2-methybutanoate, ethyl 2-methylbutanoate, ethyl acetate, ethyl hexanoate, ethyl butanoate, ethyl 2-methylpropanoate, methyl hexanoate and methyl butanoate. 

Dynamic Headspace Sampling. The crown, intact fmit and blended pulp volatiles were isolated using dynamic headspace sampling. 

The volatiles of the crown, pulp and whole intact fni it were examined by dynamic headspace sampling using a procedure developed in our laboratory (1 ). The method uses a fast flow of sweeping gas (3L/min) onto large Tenax traps. 

Figure 2. Capillary gas chromatogram of blended pineapple pulp volatiles obtained by dynamic headspace sampling. Temperature programmed from SOX (4 min isothermal) to 180X at 2X/min on a 60m X 0.32 mm i.d. DB-WAX column. The peak numbers correspond to the numbers in Table II.

The vacuum SDE method confirmed the presence of nearly all of the constituents identified using dynamic headspace sampling and revealed many additional compounds. The method was more effective in extracting the less volatile const rtuents such as long chain esters. In contrast to the previous runs this sample was chromatographed on a nonpolar DB-1 column. The constituents identified in the pulp sample prepared by vacuum SDE are listed in Table VI. The %area values should be considered as only approximate since known pineapple constituents such as ethyl acetate, methyl propanoate, methyl 2-methylpropanoate, ethyl propanoate, ethanol, propyl acetate, and ethyl 2-methylpropanoate co-elute with the solvent peaks and hence could not be included in the quantitation. 

Headspace sampling is usually employed to identify the volatile constituents of a complex matrix without actually taking a sample of the material itself. There are three variations of the technique (a) static head-space sampling, (b) dynamic headspace sampling, and (c) purge and trapping. 

Gas Chromatography-Olfactometry of Decreasing Dynamic Headspace Samples (GCO-DHS)... 

Another configuration of MAP gas-phase extraction relates to dynamic headspace sampling, often referred to as purge and trap sampling. The container can be fitted with an aperture enclosing a trap, or a sorbent, cooled by some common means. This allows the application of a prolonged, low-power irradiation, or of a multi-pulse irradiation of the sample, thus providing a means to extract all of the volatile analytes from the matrix. The contents of the trap can then be transferred (by elution for a chemical or sorbent trap, or by thermal desorption for a cold trap) to an analytical instrument, such as a... 

Figure 1 Release rates of the major lerpenes from intact flowering Arahidopsis Col plants and parts of these plants determined by dynamic headspace sampling. Inflorescences are the main source of conslitiilive terpenc emission.

The coupling of a pervaporator to a gas chromatograph is one of the most promising uses of pervaporation and is worth a more detailed discussion, because of the advantages that pervaporation presents as compared with both static and dynamic headspace sampling techniques. In the static approach, the sample is placed in a closed chamber and heated until the volatile compoimds in the headspace reach the equilibrium with the sample. Then, part of... 

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