My extracted GC sample (in ethyl acetate) has some residual water in it, which I want to remove before GC injection. I will be using calcium sulphate, but I am not getting any clear protocol for this, as to how much to add in small sample volume of 100 microlitre and how to process it after the addition.
I would assume that your GC sample is in organic solvent, e.g. acetone, toluene, or hexane. The easy way is to add Magnesium sulfate into the sample, spin, and centrifuge or filter. This is very commone for QuEChERS method (google QuEChERS for more info). We use this method to determine pesticides in produce. MgSO4 is very effective to absorb water from organic solvent than NaSO4. However, it does not hurt to try NaSO4 as well (you need to dry it in the oven to eliminate water residue in NaSO4 before use).
Yes exactly as said earlier by Chamkasem, pass your sample from bed of Na2SO4.
Deffinitley with Na2SO4 or MgSO4, probably the best way to do it is before concentration step, whole extract is filtered through layer of mentioned sulfates and then you shold proceede to cocncentration step.
Agree with the others. As far as the amount of sulfate compound added, unless you are going to be running lots and lots of samples and want to make it efficient (then you may have to play around with the amounts and test it), I doubt it matters if you add too much Na2SO4 if you don't know how much water is in there. Just be sure to get rid of it before introducing it to the GC.
I made thousands of small mini-columns in Pasteur pipets: a twist of glass fiber, then anhydrous MgSulfate, then 5 cm of silica gel. Addition of the entire sample followed by 1 ml of analytical n-hexane gave a dry sample for concentration and GC-MS. This should work just fine with other anhydrous solvents like Et OAc, as the sample should not have to be dried further.
I have a concern of addition silica gel to the mix, please check that it does not retain your analytes.
I also agreed with the previous comments. You can easily remove water by pass your sample over Sodium sulfite (Na2SO3) either on a glass column or even on a glass funnel.
Thanks for the great suggestions. I read that MgSO4 is not compatible with ethyl acetate, so I can not use it. I am planning to use CaSO4. Anybody has any experience with it ? Also, how much you generally add in small volumes like 0.1 ml of sample.
when u put ur sample in a micro tube u will get both layers separate so by doing this u get separate it try this in market there are available micro tubes for HPLC that might be help u
I am a lazy chemist 1) do the easy one first with less step e.g. use dispersive SPE with sodium sulfate, centrifuge, and done no filtration 2) use what works before don't reinvent the wheel (use sodium sulfate, don't bother to try calcium sulfate). At the end of the day, you still have check the recovery of your analyte with the method you decide to use.
You can remove the water with nitrogen. If your solvent evaporates also, just dissolve again in the quantity of this that you want. In that way, you are not going to lose any sample.
Simply you can dry 0.1 mL of water samples using a gentle stream of nitrogen, and then reconstitute with 0.1 mL methanol before performing GC analysis.
I usually use anhydrous sodium sulphate (Na2SO4 ) or anhydrous magnesium sulphate( MgSO4 ) for removing the water from organic extract before analysis by GC
Hemraj Rimal Do you have any suggestions for using anhydrous magnesium sulphate for removing the trace water from my organic phase. My sample is viscous and has no major solvent.
Hello Jomin,
I used anhydrous magnesium sulphate mostly during the removal of water. sometimes I also use the lyophilization method for the substrate like flavonoids.
If your sample has no major solvent I will suggest using lyophilization.
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