How does one prepare standards for headspace gas chromatography?

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Baho Ilok
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How exactly do you prepare the standard solutions?
I need to measure trichloroethylene (TCE) in water samples using headspace gas chromatography. Obviously, I will need a set of standard solutions to make a standard curve for concentration vs area. How exactly do you prepare the standard solutions? What I don't understand is that, say I prepare a solution containing 1 ppm TCE in water in a Teflon-sealed vial. After equilibrium between liquid phase and gas phase, the concentration of TCE in the liquid phase would have changed. So if I take a gas sample from the headspace and feed it to the GC, that reading would correspond to that new concentration of TCE. So how do you measure that?
 

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Will you treat your samples and your standards the same? Wouldn’t a sample of 1 ppm TCE standard behave exactly as an environmental sample?