Headspace sampling techniques dynamic

Headspace Sampling Technique. The method used a new gas chromatographic desorption - concentration - GC introduction device (D.C.I.) based on dynamic headspace analysis and available from Delsi Instruments (Paris, France). This apparatus made it possible to isolate volatiles from both solid and liquid samples (4). 

Before analysis, the bacterial cultures should be transferred into standard 20 ml headspace vials and sealed with PTFE-lined Teflon caps to equilibrate the headspace. Sample handling is a critical step affecting the analysis by E-nose. The quality of the analysis can be improved by adopting an appropriate sampling technique. To introduce the volatile compounds present in the headspace (HS) of the sample into the E-nose s detection system, several headspace sampling techniques have been used in E-nose. Typically, the methods of headspace sampling (Ayoko, 2004) include static headspace (SHS) technique, purge and trap (P T) technique, stir bar sorptive extraction (SBSE) technique, inside-needle dynamic... 

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... 

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 headspace sampling, (b) dynamic headspace sampling, and (c) purge and trapping. 

Callus cultures were established with three olive (Olea europaea L.) varieties using a method reported previously (2). Volatiles were collected from the olive cultures (20g) using dynamic headspace sampling techniques described previously (3). Analysis of volatiles was performed using an Automatic Thermal Desorption System linked to a Perkin Elmer Autosystem GC. Lipoxygenase (LOX) activity of the cultures was assayed routinely using an oxygen electrode. 

Heat extraction techniques for solid sample preparation in GC are static and dynamic headspace analysis (SHS, DHS, HS-SPME and HSSE), thermal desorption (TD-GC, TD-GC-MS), pyrolysis and thermochromatography. Nomenclature is not unambiguous as to DHS, TD and PT. The terminology purge-and-trap is usually preferred for the simplest dynamic technique in which it is not necessary to subject the sample to either solvents or elevated temperatures. Scheme 2.7 shows the family of headspace sampling techniques. Headspace sorptive extraction (HSSE) and HS-SPME represent high capacity static headspace. 

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. 

Dynamic headspace-extraction stripping and purge-and-trap methodology are used most often for determination of M-hcxanc in water and hazardous wastes. Dynamic headspace extraction techniques have been applied to water samples (Roberts and Burton 1994) and sediment (Bianchi et al. 1991). Detection limits of 0.5 g/L were reported for lake water (Roberts and Burton 1994) and 20 ng/kg (ppt) for sediment (Bianchi et al. 1991). Supercritical fluid extraction (SFE) is a relatively new technique that has been applied to -hcxane in soil (Yang et al. 1995). Membrane extraction of M-hexane from water samples has been developed to provide online, continuous monitoring (Wong et al. 1995 Xu and Mitra... 

The analyses of the flavour composition of yellow passion fruits were performed by four dilferent isolation techniques, namely vacuum headspace sampling (VHS), the dynamic headspace method, simultaneous distillation and extraction at atmospheric pressure, and simultaneous distillation and extraction under reduced pressure [62]. Significant differences were found not only in the chemical composition of the resultant extracts but also in their sensory properties. The most representative and typical extract was obtained by VHS. 

Hammers WE, Bosnian HFPM. 1986. Quantitative evaluation of a simple dynamic headspace analysis technique for non-polar pollutants in aqueous samples at the ng/kg level. J Chromatogr 360 425-432. 

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

A sampling technique known as headspace , of which there are two modes, static and dynamic, is very widespread in GC for the qualitative and even quantitative analyses of volatile constituents present in some samples (cf. Chapter 21). 

An essential oil (EO) is internationally defined as the product obtained by hydro-, steam-, or dry-distillation of a plant or of some of its parts, or by a suitable mechanical process without heating, as in the case of Citrus fruits (AFNOR, 1998 Council of Europe, 2010). Vacuum distUladon solvent extraction combined offline with distillation simultaneous distillation extraction supercritical fluid extraction microwave-assisted extraction and hydro-distiUation and static, dynamic, and high concentration capacity headspace sampling are other techniques used for extracting the volatile fraction from aromatic plants, although the products of these processes cannot be termed EOs (Faleiro and Miguel, 2013). 

Liquid-liquid extraction has a counterpart for the determination of VOCs in the technique known as static or equilibrium headspace sampling. The technique is most often combined with the determinative step and is often referred to as static headspace gas chromatography, abbreviated HS-GC. The principles that underlie this technique will be outlined in this section. The decision to measure VOCs in the environment by either HS or purge and trap (P T or dynamic headspace) represents one of the ongoing controversies in the field of TEQA. This author has worked in two different environmental laboratories in which one used P T as the predominant technique to determine VOCs in the environment and the other used HS-GC. 

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