Headspace analysis automated methods

For analysis of free compounds, the headspace analysis with a multiphase fiber is even more interesting and less time-consuming. This approach can replace the majority of the quantification of free compounds measured by SPE techniques, considering also the possibility of the sampling automation using a GC-MS system which can be coupled to a statistical treatment of fragments abundance (Kinton et al., 2003 Cozzolino et al., 2006). Moreover, HS-SPME/GC-MS is a very effective and efficient method to analyze specific compounds present in trace levels at about ppt level, because they can be better and selectively enriched in the headspace. This method is employed nowadays to quantify some important and peculiar sensory compounds such as ethyl and vinylphenols, pyrazines, cork off-flavour substances (TCA, etc.) and other contaminants such as geosmine (Riu et al., 2002 Chatonnet et al., 2006) and, as shown below, sulphur volatiles. 

Norman KNT. 1991. A rapid method for the determination of liquid fumigant residues in food commodities using automated headspace analysis. Pestic Sci 33 23-34. 

Volatiles are usually analyzed by the use of purge and trap (which is an EPA-approved technique ), stripping, and headspace (HS) analysis. These methods either require expensive instmmentation or are not sufficiently sensitive. Nonvolatiles are analyzed primarily by means of LEE (also an EPA-approved technique) and SPE. These methods are generally time consuming, difficult to automate, and use expensive high-purity toxic organic solvents. 

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 ... 

Stuart et al. [ 184] studied the analysis of volatile organic compounds in soil using an automated static headspace method. Recoveries increased in the or-... 

Static headspace extraction is also known as equilibrium headspace extraction or simply as headspace. It is one of the most common techniques for the quantitative and qualitative analysis of volatile organic compounds from a variety of matrices. This technique has been available for over 30 years [9], so the instrumentation is both mature and reliable. With the current availability of computer-controlled instrumentation, automated analysis with accurate control of all instrument parameters has become routine. The method of extraction is straightforward A sample, either solid or liquid, is placed in a headspace autosampler (HSAS) vial, typically 10 or 20 mL, and the volatile analytes diffuse into the headspace of the vial as shown in Figure 4.1. Once the concentration of the analyte in the headspace of the vial reaches equilibrium with the concentration in the sample matrix, a portion of the headspace is swept into a gas chromatograph for analysis. This can be done by either manual injection as shown in Figure 4.1 or by use of an autosampler. 

A method for the automated analysis of volatile flavor compounds in foods is described. Volatile compounds are removed from the sample and concentrated via the dynamic headspace technique, with subsequent separation and detection by capillary column gas chromatography. With this method, detection limits of low ppb levels are obtainable with good reproducibility. This method has experienced rapid growth in recent years, and is now in routine use in a number of laboratories. 

Headspace is useful for the trace analysis of compounds having a high affinity for the fiber phase and that can be enriched in the HS of the sample. The use of a multiphase fiber is a very interesting and low time-consuming approach. It also considers the possibility of sampling automation using a GC/MS system coupled with a statistical method for treatment of fragment abundance (Kinton et al., 2003 Cozzolino et al.,2006). 

In the dynamic headspace method, the sample is put in a thermal desorption unit in order to desorb the RS a continuous flow of a carrier gas pushes the RS into a trapping system which is refrigerated and where they are accumulated prior to analysis. Then the RS are rapidly desorbed by rapid heating and carried onto the column via the carrier gas. There are different ways to apply this technique. The arrangement when purge gas passes through the sample is often called the purge and trap technique (some other equipment uses the acronym DCI (desorption, concentration, injection)). This method is particularly useful for very low concentrations of RS as the total amount of a substance is extracted and can be applied directly to powders without need to dissolve them. The main drawback is that the dynamic headspace methods are not readily automated. ... 

Headspace sampling methods prior to capillary gas chromatography are widely used for the determination of volatile compounds present in very different types of samples. An automated and rapid system for determination of volatiles from yoghurt was developed. Thirty-five volatile organic compounds(VOCs) were identified in PS cups used for yoghurt packaging and 42 VOCs from yoghurt samples. Quantitative analysis of styrene in several samples from the Spanish retail market was carried out. 16 refs. 

The most popular cleanup method now is headspace GC or headspace GC-MS, which permits automated analysis of dozens of samples and standards in a single campaign. Vacuum distillation is at least as sensitive and accurate as headspace GC, but only a few samples and standards can be analyzed in a day. A number of liquid-liquid and liquid-solid extraction methods have been proposed to isolate 1,4-dioxane from surfactants prior to GC determination, but recovery varies with each matrix (55). The purge-and-trap methods used in environmental analysis are rarely applied to analysis of surfactants, since the impurities of interest are not readily adsorbed from the purge gas stream. In order to gain the high sensitivity of electron capture detection, ethylene oxide may be stripped and converted to ethylene iodohydrin before GC analysis (59). Detection limits in the low parts per billion range are claimed for this technique. 

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