Sample preparation in GC-HS

[Santosh Gandhi]

Hi,

I just want to know if it is necessary for the substance that is being analysed for residual solvents by GC-HS to be completely soluble in the dissolution solvent.What will be the drawbacks if there is no solubility.

[rb6banjo]

The major drawback that I see is that your sample/gas phase equilibrium could behave as an adsorption system. It can be very difficult to quantitate in these types of matrices. If the solid behaves like a liquid (highly plasticized pvc does this), then you can analyze the solid directly. If enough water can be added so that your system behaves well (a partition system), then you will be ok with the solid not dissolving.

If you're just starting, there's much work to be done. You need to investigate how much water to add. You don't want to dilute your analytes too much. How long it takes to reach equilibrium? If you add analyte to the system do you get back what you put in?

[Peter Apps]

An additional problem is that residual solvent that is trapped within the product particles does not get into the headspace, and analyte that is added to the samples to calibrate the peak area does not behave in the same way as the trapped analyte.

Peter

[chromatographer1]

You desire to measure all the solvent not part of it in your sample, correct?

If it is not released into the liquid from being trapped in the solid phase it can't enter into equilibrium with the headspace.

It is like depositing $100 into your bank and then getting a deposit slip for $65. You are getting cheated.

Sometimes, solvents can escape the solid matrix, but this could take weeks if not months, or even never.

The truth is always better than what is easy. Do it right, or why bother?

best wishes,

Rod