How does one prepare standards for headspace gas chromatography?

In summary, the conversation discusses the need to measure trichloroethylene (TCE) in water samples using headspace gas chromatography. It is mentioned that standard solutions are necessary for creating a standard curve for concentration vs area. The process of preparing these standard solutions is questioned, specifically how the change in concentration of TCE in the liquid phase after equilibrium would affect the gas sample reading on the GC. The question of whether the samples and standards should be treated the same is also raised, with the comparison of a 1 ppm TCE standard and an environmental sample.
  • #1
Baho Ilok
47
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TL;DR Summary
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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  • #2
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?
 

1. How do I determine the appropriate concentration for my standards?

The concentration of your standards will depend on the specific compounds you are analyzing and the sensitivity of your gas chromatography instrument. It is important to consult the literature or consult with experienced colleagues to determine appropriate concentrations for your standards.

2. What is the best way to prepare my standards for headspace gas chromatography?

The most common method for preparing standards for headspace gas chromatography is to accurately weigh the pure compound and dilute it in a solvent to the desired concentration. Alternatively, you can purchase pre-made standards from a reputable supplier.

3. How should I store my standards for headspace gas chromatography?

Standards for headspace gas chromatography should be stored in a sealed container, away from light and heat. It is best to prepare fresh standards before each analysis, but if this is not possible, they should be stored in a cool, dark place and used within a few weeks.

4. Can I use a mixture of compounds as a standard for headspace gas chromatography?

Yes, you can use a mixture of compounds as a standard for headspace gas chromatography. However, it is important to ensure that the concentrations of each compound in the mixture are accurately known and that the compounds do not interact with each other in the headspace or during analysis.

5. How often should I run standards during my headspace gas chromatography analysis?

Standards should be run at the beginning and end of each batch of samples, as well as periodically throughout the analysis to ensure the instrument is performing accurately. It is also important to run a standard with a concentration similar to that of your samples to ensure accurate quantification.

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