Headspace equilibrium

C, headspace equilibrium-GC, at different solute concn 0.48-19.1 mg/L, measured temp range... 

ICN humic acid, ICN HA coated A1203, headspace equilibrium, Garbarnini Lion 1985)... 

It is possible to conduct calibration according to the admixture method in conjunction with this technique if the organic impurities can be recognized on the basis of the gas chromatogram. Equal quantities of water are measured into similarly shaped glass vessels so that the same size of gas space relative to the water volume is present in all calibration samples. Increasing quantities of the suspected substances are then measured into the water in correspondingly low concentrations, and headspace equilibrium is established, as in the analysis of the sample. In the case of fuel... 

For the samples under analysis, the headspace equilibrium is established at, for example, 20 C, 30 C or 50 C. The water sample may either be shaken by hand and then headspace equilibrium is established at various temperatures, or a mechanical shaker may be used for a defined period, following which headspace equilibrium is established at the specified temperature. Next withdraw various volumes of gas (1 to 5 ml) with a gas... 

There are two basic principal methods of headspace analysis in polymers. In one method a solution of the polymer is examined, in the other method solid polymer is examined directly. When working with polymer solutions, headspace equilibrium is more readily obtained than the solid approach and the calibration procedure is simplified. 

The solution headspace approach is applicable to a much wider range of samples than the solid approach. When working with sample solutions, headspace equilibrium is more readily attained and the calibration procedure is simplified. The sensitivity of the solution method depends upon the vapor pressure of the constituent to be analysed and its solubility in the solvent phase. Vinyl chloride, butadiene, and acrylonitrile, are readily transferred from polymer solutions into the headspace by heating to 90 °C. The headspace/solution partitioning for these constituents is not appreciably affected by changes in the solvent phase (namely, addition of water) since the more volatile materials favonr the headspace at 90 °C. Less volatile monomers such as styrene (bp = 145 "C) and 2-ethylhexyl acrylate (bp = 214 °C) may not be determined using headspace techniques with the same sensitivities realised for the more volatile monomers. By altering the composition of the solvent phase to decrease the monomer solubility, the equilibrium monomer concentration in the headspace can be increased. This resulted in a dramatic increase in the detection sensitivity for styrene and 2-ethylhexyl acrylate. 

Headspace methods have a second disadvantage in that it is difficult to do quantitative studies using them. The analytical data one obtains reflects the amount of an aroma constituent in the headspace. As was discussed earlier, the relationship between concentration in the headspace (equilibrium or nonequilibrium) vs. the food can be very complex and must be determined experimentally. 

Table 1 Headspace Equilibrium of d-Limonene with 100 pm Polydimethyl Siloxane and 50/30-pm Divinylbenzene/Carboxen/Polydimethyl Siloxane Fibers ...

Figure 1 Headspace equilibrium time for d-limonene in water (12 ppm) and 11.8 °Brix, 10% suspended pulp orange juice (200 ppm). Sample (125 mL) in 250-mL capped (Teflon septa) bottle held up to 18 hr at 26°C. Fiber (100 pm PDMS) contact with sample headspace for 1 min. PDMS, polydimethyl siloxane., water , juice.

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