Headspace sampling static

Prom the experimental point of view the static headspace sampling technique is very simple. The sample, either solid or liquid, is placed in a glass vial of appropriate size and closed with a Teflon-lined silicone septum. The 1 is carefully... 

In static headspace sampling [301,302] the polymer is heated in a septum-capped vial for a time sufficient for the solid and vapour phases to reach equilibrium (typically 2 hours). The headspace is then sampled (either manually or automatically) for GC analysis, often followed by FID or NPD detection. Headspace sampling is a very effective method for maintaining a clean chromatographic system. Changing equilibrium temperature and time, and the volumes present in the headspace vial can influence the sensitivity of the static headspace system. SHS-GC-MS is capable of analysing volatile compounds in full scan with ppb level... 

Cummins, T.M., Robbins, G.A., Henebry, B.J., Goad, C.R., Gilbert, E.J., Miller, M.E., and Stuart, J.D. A water extraction, static headspace sampling, gas chromatographic method to determine MTBE in heating oil and diesel fuel. Environ. Sci. Technol, 35(6) 1202-1208, 2001. 

The highly volatile odorants are not detected or are underestimated when the screening method is applied to an aroma extract. These compounds are lost when the extract is concentrated or they are masked in the gas chromatogram by the solvent peak. To overcome this limitation, the screening has to be completed by GC-O of static headspace samples (GCOH Fig. 16.3) [59-61]. 

Table 16.5 Gas chromatography-olfactometry of static headspace samples of parsley leaves [31] ...

A substantial amount of information on volatiles can be obtained with less than 30 g of each of these samples in a direct DHS/GC/MS analysis. DHS operation sweeps volatile flavors from the surface of food samples in a similar way as we sniff for the volatile flavors of a food. DHS does not require high sampling temperature or solvent for extraction and may be considered as a lcw-artifact arcma sampling technique. The concentrating effect of DHS provides better sensitivity than static headspace sampling. Techniques such as GC-coupled aroma perception and GC/MS identification can be used to complement other approaches in improvement of flavor quality of a variety of products. 

Despite the utility of these techniques, a distinct disadvantage is that very low concentration components may be masked by higher concentration interferants in such cases, devices based on thermal desorption (absorbent packing, static headspace sampling, cryogenic trapping) may prove useful. 

SPME can also be used to extract target analytes from food and drug samples. Thus, it has been employed for the extraction of caffeine from coffee and tea [225], and for that of volatile impurities in drugs. Headspace SPME has also been tested for flavour analysis in foods. Thus, the SPME/GC/TOF-MS tandem was successfully used for the rapid analysis of volatile flavour compounds in apple fruit. The sample (300-450 g of apple) was subjected to static headspace sampling for 4 6 h in order to allow the volatiles... 

Guth, H., Grosch, W. (1993) Identification of potent odorants in static headspace samples of green and black tea powders on the basis of aroma extract dilution analysis (AEDA). Flavour Fragrance J. 8, 173-178... 

Mulligan, K.J. 1995. Acqueous alkylation of anions for static headspace sampling with analysis by capillary gas chromatography mass spectrometry. Journal of Microcolumn Separations 7 567-573. 

Figure 8.1 Chromatogram of ethyl chloride (retention time 1.22 min) and internal standard n-propanol (retention time 1.96 min.) on an Rtx-BACl column (30 mx 0.32 mm i.d., 1.8 pm). Static headspace sampling following a 5-min equilibration time at 70 °C and isothermal GC separation at 45 °C for 3.5-min. Note that ethyl chloride and ethanol have the same retention time.

Figure 21.6 Static headspace. Sample vial in a state of equilibrium. The state of equilibrium is under the control of two factors K = Cj/Cg and /3= In addition to routine single...

Eight different lime and lemon flavor formulations were provided by a commercial flavor company (Table I). Six replicas of each flavor were analyzed using 7.5 uL aliquots. The aliquots were placed in 10 mL vials which were crimped and equilibrated for 15 minutes at 60 °C before static headspace sampling. The headspace parameters were 15 min incubation, 65 °C syringe, 0.75 min flushing of syringe after injection, cycle time of 4 min. Two mL were filled and injected at a 250 uL/s. There is no column for a separation prior to the mass selective detector (MSD), the entire headspace of each sample is introduced into the MSD. 

The sample cell or vessel is usually made of stainless steel or some other inert material and ranges in size from 150 /i,L to 50 mL. It is most important that the sample vessels are rated for the maximum working pressure of the system. Cell designs are either of a flow-through (dynamic) or headspace sampling (static) type. Flow-through cells enable the SF to continuously pass through the sample. Static headspace sample cells enable the SF to surround the sample while the headspace above the sample is with-... 

Trace environmental quantitative analysis (TEQA) utilizes various determinative teehniques (Chapter 4) in combination with various sample prep techniques (Chapter 3). In this appendix, one specific trace analysis using static headspace sampling automatically coupled to capillary gas chromatography with element specific detection is described. LSQUARES is a computer program developed by the author in BASIC and is used in the quantitative analysis discussed below. The actual program written in GWBASIC is also listed after illustrating its use in TEQA. 

Fig-1 EOS835 electronic nose (left) equipped with static headspace sampling unit HT200H (right)... 

Fig. 2. Static headspace sampling of insect volatiles with a SPME device.

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. 

Fig. 1 Comparison of dynamic, static, and SPME headspace sampling, (a) Dynamic headspace sampling uses a sorbent or cold trap to concentrate volatile analytes before analysis by the GC. (b) Static headspace sampling uses direct transfer of a volume of gas from the headspace above the heated sample vial directly to the GC for analysis. Injection designs are illustrated in Fig. 2. (c) SPME headspace sampling uses a fiber support with solid-phase coating. The fiber is placed in the headspace and reaches equilibrium with the headspace volatile analytes. The SPME fiber is transferred by means of a syringe and thermally desorbed in the injector of the GC for analysis.

Automated headspace systems have been offered by several manufacturers for many years, including Thermo Electron Corporation (San Jose, California, U.S.A.), PerkinElmer (Wellesley, Massachusetts, U.S.A.), Tekmar (Mason, Ohio, U.S.A.), and Agilent Technologies (Palo Alto, California, U.S.A.). There are essentially three injection techniques for static headspace sampling gas-tight syringe, balanced-pressure, and pressure-loop injection (Eig. 2). All these techniques are used on commercial headspace systems and are described. 

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