Chromatography Forum

Hello,
I am moving from vials to 96-well plate format for GCMS assays. This is not really high-throughput, but for the convenience (i.e. speed and accuracy) of transferring samples from a 96-well extraction format to a matching plate rather than into individual glass vials. GCMS runtimes are about 30 min so this means 96 samples in 48h. The sample matrix is chloroform, so I am looking for minimal evaporation in 48h on the autosampler (CTC, no cooler, just at RT = 20 degreesC), and also minimal extractables.

What I have tested to date are pp plates with either heat-sealing mats or press-on pp caps. The heat-sealing mats have a terrible extractable profile, whereas the press-on pp caps have a cleaner profile similar to glass vials (with our usual PTFE-silicone-PTFE crimp-caps). However, there is an unacceptable evaporative loss from both - the press-ons lose everything (100 microlitres sample) in a few hours and the heat-sealed mats in 24-48 hours. Our std crimp-sealed glass vials don't lose anything for weeks at RT.

Can anyone offer advice on the best sealing mat/plate combination solution for this setup? I know there are PTFE-faced silicone mats on the market that will probably give a cleaner extractable profile, but their ability to minimize evaporation of an organic solvent like chloroform is an unknown. I don't want to go down the route of microvials with crimp-caps in a 96-plate format, as the time taken to prep and seal such a format defeats the object of moving away from standard vials.

thanks
Tony

Tony,



Does the loss happen when you put the well plate on the instrument tray holder or when you leave it on a bench overnight?

If the loss is because of the heat from the GC you can try to move your tray holder as far as possible from the inlet and the oven.

If you have a CTC you can normally place the trays where you want.
On my Agilent system (6890+5975) I have the tray holder on the right just above the keyboard. The heat there should be minimal.


Best wishes,

bhuvfe

Evaporation is from the autosampler tray system, but as you suggested the tray is already in an optimized position with minimal heat input from the GC. To be honest, the loss occurs on the bench or on the tray holder; this is slowed down only by refrigeration (which is not possible with our current tray options).

I am really looking for the best possible 96-well (1mL or 500µL)/sealing mat combination that will work with chloroform, so that I get minimal evaporation and extractables over 48h.

thanks
Tony