Static Headspace Sampling

If a complex material, such as a piece of food, is placed into a sealed vessel and allowed to stand, some of the more volatile compounds in the sample matrix will leave the sample and pass into the headspace around it. If the concentration of such a compound reaches about 1 ppm in the headspace, then it may be assayed by a simple injection of an aliquot of the atmosphere in the vessel. How much compound enters the headspace depends on several factors, including the amount of it in the original sample, the volatility of the compound, the solubility of that compound in the sample matrix, the temperature of the vessel, and how long the sample has been inside the vessel. The concentration of the analyte in the heads-pace also depends, of course, on the volume of the vessel being used. At equilibrium, the amount of compound A that has escaped from the sample matrix and exists in the surrounding atmosphere is just the total amount of A minus the amount still in the matrix:

Headspace ^Total ^Matrix and the partition coefficient is just:

K _ AHeadspace

AMatrix

The amount of A that actually gets into the gas chromatograph depends on what portion of the total headspace is injected:

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