Static headspace extraction liquid sample matrices

The principles behind MAP liquid-phase and gas-phase extractions are fundamentally similar and rely on the use of microwaves to selectively apply energy to a matrix rather than to the environment surrounding it. MAP gas-phase extractions (MAP-HS) give better sensitivity than the conventional static headspace extraction method. MAP-HS may also be applied in dynamic applications. 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 [477]. 

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. 

Where A is the area of the chromatographic peak obtained for the analyte, is the concentration of analyte in the headspace, C° is the concentration of analyte in the liquid sample, K is the partition coefficient, and P is the ratio volume of the phases. The partition coefficient depends on the extraction temperature, while P is determined by the relative volume between the two phases In static headspace extraction the sensitivity depends on the solubility of the analyte in the matrix for analytes with a high partition coefficient, the most important parameter is the extraction temperature, since most of the analyte is in the liquid phase and it can only be passed into the headspace by heating the vial on the other hand, for analj es with low partition coefficients, they are already present in the headsp>aoe even without any heating, so in this case, the most important parameter is the volume relation between the phases. That is, increasing the extraction temperature is only effective in polar volatile analytes, while the sensitivity of non-pelar analytes remains essentially unchanged by the increase of the extraction temperature (Slack, et aL, 2003). 

Headspace Extraction Headspace (HS) extraction is a well-known method of sample preparation and is frequently used in many laboratories, especially in industrial applications. It involves a partitioning equilibrium between the gas phase and a sample (liquid or solid). In this technique, an aliquot of gas phase is sampled into GC. There are two types of analysis, static and d3Uiamic. In the static version, when the equilibrium is reached, the gas phase is injected into GC. In dynamic analysis, the volatiles are exhaustively extracted by the stream of gas. However, matrix effects result in decreased sensitivity for certain substances, especially polar and hydrophilic samples. A comprehensive book describing HS techniques was presented by Kolb [31]. 

Monomers are either gaseous or relatively volatile liquids and so GC and GC-MS based techniques are used to determine them in both the rubber compound and the food simulant/food product. To simplify the analysis, a static headspace sampler is often used to isolate the monomer from the sample matrix an extraction procedure often presenting chromatographic problems with the extraction solvent obscuring the analyte. 

The headspace technique, a static gas extraction method, is particularly suitable for the enrichment of volatile compounds. It enables the analysis of solid and liquid samples by direct sampling from the gas phase, and can be directly combined with gas chromatography. This principle is based on the distribution of analyte between the matrix and gas phase. It has been used successfully to determine volatile sulfur compounds from various matrices, such as wastewater, body fluids, plants, and animal fatty tissue. 

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). 

This term can be applied to a number of techniques including static headspace, purge and trap, and thermal desorption. All of these techniques involve the extraction of a gaseous component from a solid or liquid sample. Static headspace is usually a one step technique where the componait of interest is extracted from the sample held in a closed vessel usually at elevated temperatures and then injected onto the GC. Purge and trap is a multistep technique where the compound of interest is extracted into a matrix and then thermally desorbed onto the GC for analysis. SPME used in conjunction with GC analysis could be considered a purge and trap technique. In thermal desorption, the sample is heated r idly and isolated using a cryogenic trap with the compounds isolated thermally desorbed. 

In the static mode, the sample is placed into an extraction vessel, filled with a supercritical fluid at the appropriated temperature and pressure, and allowed to stand for a period. When the extraction is complete, the supercritical fluid is released through a trap to collect the analytes. Static extraction allows analytes with slow mass transfer time to be solvated by the SF. In addition, the use of a known concentration of modifier is possible by direct addition of the modifier to the extraction cell. The main limitation of static extraction is its inability to perform an exhaustive extraction. As in static headspace GC, and the traditional liqnid-liquid extraction, as a result of the equilibrium of the analyte between the matrix and SF, one extraction can not exhaustively extract the analyte from the matrix. Consequently, it is often necessary to perform multiple static extraction. The use of SFE has been decreasing over the years in part due to the growth of accelerated solvent extraction (ASE), which employs much of the same instrumentation and methodology of Sra. 

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