Headspace analysis instrumentation

Headspace analysis (EPA 3810, 5021) also works well for analyzing volatile petroleum constituents in soil. In the test method, the soil is placed in a headspace vial and heated to drive out the volatiles from the sample into the headspace of the sample container. Salts can be added for more efficient release of the volatile compounds into the headspace. Similar to water headspace analysis, the soil headspace technique is useful when heavy oils and high analyte concentrations are present, which can severely contaminate purge-and-trap instrumentation. Detection limits are generally higher for headspace analysis than for purge-and-trap analysis. 

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). 

The common VOCs observed in the SPME-GC headspace analysis of the explosive samples were presented individually, and combined, to previously trained and certified explosive detection canines that previously had only encountered actual explosives in training and certification. Chemicals that illicit a response from certified explosive detection canines can be considered explosive odorants, whereas chemicals to which canines do not alert may be considered as inactive VOCs. It should be noted that an inactive VOC might still have the potential to enhance the response by a canine to known odorants. In addition, inactive VOCs for the canines tested might be odorants to other canines trained in different ways and with different target materials. Finally, inactive VOCs might be useful target vapor chemicals for instrumental detectors. 

Automated dedicated headspace GC instruments such as the Perkin Elmer HS40 can analyse up to 40 samples unattended and run continuously for 24 h. Temperature and pressure conditions are precisely controlled for each sample so that overall precision is better than 1%. Figure 5.15 includes examples of headspace analysis. A more complete discussion of applications of headspace analysis is given later in the chapter. 

Flavors are widely used in pharmaceutical solutions to mask drug bitterness. Zhu s group [48] has used an MOS electronic nose to perform headspace analysis of these formulations. The method was able to qualitatively distinguish six common flavors (raspberry, red berry, strawberry, pineapple, orange, and cherry) in placebo mixtures. The instrument was also able to identify unknown flavors. It was also indicated that the instrument could be used to identify different flavor raw materials. Moreover, the electronic nose was used for quantitative analysis of flavors in an oral solution. Data processing and identification were done by PCA, discriminant factorial analysis (DFA), and partial least squares. 

Headspace Technique. One of the most recent methods of flavor analysis which evolved with the development of sensitive gas chromatographic instrumentation is the headspace technique. Withycombe et al (19), gave an excellent description of headspace analysis. In this procedure volatiles in gaseous state that are in equilibrium over the food are analyzed. 

The volatile nature of ethanol makes it eminently suitable for headspace analysis. The principle on which the method is based is that of partition theory, i.e., that the concentration of a volatile species in the headspace above a solution is proportional to the concentration of that species in solution. Procedures based on this principle must therefore be classed as indirect , but nevertheless they have some advantages over direct methods, the most important being that the procedure separates volatile species from the numerous nonvolatile compounds commonly found in alcoholic beverages. As most sensors used in instrumentation for the determination of ethanol are at best semispecific and are usually oxidative in... 

See also Activation Analysis Neutron Activation. Atomic Absorption Spectrometry Principles and Instrumentation. Atomic Emission Spectrometry Principles and Instrumentation. Chromatography Overview Principles. Gas Chromatography Pyrolysis Mass Spectrometry. Headspace Analysis Static Purge and Trap. Infrared Spectroscopy Near-Infrared Industrial Applications. Liquid Chromatography Normal Phase Reversed Phase Size-Exclusion. Microscopy Techniques Scanning Electron Microscopy. Polymers Natural Rubber Synthetic. Process Analysis Chromatography. Sample Dissolution for Elemental Analysis Dry... 

Headspace GLC analysis is a method used to monitor a vapour over a polymeric matrix. It is a very effective technique, but may require more time and effort than direct injection. This method can be performed manually, when a vial containing the monomer is heated, an equilibrium is established, for volatile compounds between the sample and the headspace above it. Because no dissolution step is required, sample viscosity problems and loss of response due to dilution are eliminated. Automated headspace analysis units are available from instrument manufacturers, as well as multiple extraction systems. Any analytically useful headspace method must obey Henry s law ... 

Instrumentation for the determination of non-polymeric volatiles and water in polymers are discussed in Chapter 5 and include gas chromatography, high performance liquid chromatography, polarography, headspace analysis, headspace analysis - gas chromatography - mass spectrometry and purge and trap analysis. 

Figure 10 Raman spectra of various mixtures of nitrogen and oxygen obtained with the spectrograph in Figure 9. For the sake of clarity the spectra have been vertically displaced from one another. The N2 peak is on the right. Band intensity is essentially from the pure vibrational mode. The rotational-vibrational side bands form weak overlapped wings on either side of the main peaks. Reproduced with permission of the Society of Photo-Optical Instrumentation Engineers (SPIE) from Gilbert AS, Hobbs KW, Reeves AH and Jobson PP (1994) Automated headspace analysis for quality assurance of pharmaceutical vials by laser Raman spectroscopy. Proceedings of the SPIE - Society of Photo-Optical Instrumentation Engineers 2248 391-398.

PA Rodriguez, CR Culbertson. Quantitative headspace analysis of selected compounds in equilibrium with orange juice. In G Charalambous, G Inglett, eds. Instrumental Analysis of Foods, Vol. 2. New York Academic Press, 1983, pp 187-195. 

As discussed in Sec. II.B, any static headspace analysis can inject only a fraction of the compound of interest to the chromatograph, since the concentration in the headspace is in equilibrium with that still in the sample matrix, and only a portion of the headspace is withdrawn and transferred. Consequently, for very low levels of analyte concentration in the original sample material, static headspace techniques may lack the sensitivity required for the determination. Elevating the temperature of the sample generally increases the volatility of the analyte, but most static headspace instruments have the capability of heating samples only to about 150 = C. 

Other work on the topic of the spoilage of food, particularly fish quality and freshness, the volatile compound trimethylamine (TMA) is used as a marker. In fact, the odour of fish and the relevant chemicals is shown in Fig. 16.8. Traditionally headspace analysis is utilised and as pointed out by Nilsen et al. while such instruments with a high degree of automation are available for the trapping and... 

EXMAT - A Linked Network of Expert Systems for Materials Analysis. Seven individual expert systems comprise EXMAT (1) problem definition and analytical strategy (2) instrumental configuration and conditions (3) data generation (4) chemometric/search algorithms (5) results (6) interpretation (7) analytical goals. Dynamic headspace (DHS)/GC and pyrolysis GC (PGC)/concentrators... 

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