[rjb]

Hi,

As part of one of my process flows, I extract my sample from a solid substrate using around 200µL of ACN (which works well as an extraction solvent) which then goes through a syringe filter into a 300µL microvial. I blow this down to dryness under nitrogen allowing me to carry out solvent exchange, meaning that I can reconstitute in a run solvent that performs a lot better with my GC setup than ACN. To maximise sample concentration, I typically reconstitute using either 10 or 20µL of run solvent, but because of the low volumes, it worries me that I'm not getting the best out of my process.

As things stand, I typically slowly pipette the new solvent into the microvial making sure that the tiny volume of solvent comes into contact with as much of the glass surface as possible. I then vortex and spin down to bring my sample to the bottom of the vial.

Firstly, is there a better way that any of you clever folk can think of doing this? Sadly the solvent volume is not something I can increase.

Secondly, as the solvent evaporates under blowdown, is most of the analyte likely to remain in the diminishing volume of solvent where it eventually ends up in the very bottom of the microvial when the solvent finally evaporates away, or is is likely to form a layer on the glass of the vial like an invisible tide mark? I guess this will depends upon the properties of the glass and of the analytes, but your gut feeling would be most welcome.

Kind Regards

R

[marquis]

Is there any way you can spike the sample to get recovery calculations?

That way you could at least figure out how good your process is. 

[rjb]

Thanks Marquis,

I didn't spot your reply so apologies for non-response - I wasn't being wilfully ignorant!
The good thing is that I know my starting concentration and am now running a positive control at various stages, so have implemented your suggestion to some extent. Several of my analytes are a nice yellow colour and when concentrated during blowdown become visible at the bottom of the vial (with no obvious colouration on the vial sides) which I suspect answers the question I posed at the end of my initial post. Thought it worth noting this for posterity.

Thanks

R