Static headspace extraction quantitative techniques

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. 

The four most common approaches to quantitative static headspace gas chromatography calibration are external standard, internal standard, standard addition and multiple headspace extraction (MHE). The choice of technique depends on the type of sample being analyzed (Slack et al, 2003). 

Static HSGC has been used extensively for the determination of VHC in oils, lipids and fatty foods (Fig. 3.15). Quantitation of VHC by an electron-capture detector provides the means to achieve superb detection limits. In aqueous foods the limit of detection has been reported to be 1 ppb, whereas in fatty foods it has been reported to be in the 10-50 ppm range (Entz and Hollifield, 1982). With a multiple headspace extraction technique the detection limits for VHC in butter are even lower (1-5 ppb) (Uhler and Miller, 1988). The absolute detection limit for perchloroethylene in olive oil has been found to be 1 pg (Van Rillaer and Beernaert, 1989). A method for the determination of VHC in olive oil by packed column HSGC is described in EC Regulation 2568/91 (CEC, 1991). Precision data of a capillary column... 

Validation of a SPME method for target analytes should be performed using standard reference materials with similar matrix, when available. Another possible and frequently used way is validation of a SPME method against well-accepted extraction techniques, such as purge-and trap [13,25,46] or static head-space [46]. Several interlaboratory studies demonstrated that SPME is a reliable technique for the quantitative analysis of volatile organic compounds [46] and pesticides in water samples [47 48]. We have validated our SPME-GC-MS method for the determination of nitrous oxide in urine by means of the comparison with static headspace [33]. 

Static headsp>ace extraction, also known as equilibrium headsp>ace extraction, is one of the techniques used for qualitative and quantitative analysis of volatile substances in the forensic field, in this technique the sample is placed in a closed vial, the volatile analytes disseminate into the headspace of the vial (figure 1), once equilibrium is reached between the analyte concentration in the headspace and the analyte concentration in the sample, a portion of the headspace is taken and injected into the gas chromatograph this can be done manually or with an autosampler, this process will be usually carried out at a pressure and temperature above ambient conditions (Slack et al., 2003). 

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