Hi, everyone!

I use SPE to clean up very polar drugs from human plasma. The final elution step uses 95% water/5% methanol as eluant. To achieve a reasonable recovery, I have to elute with 1 ml of the eluant in the final step ( for 3 ml cartridges). However, it takes 50 minutes to completely evaporate 1 ml water under a stream of nitrogen flow at 45 degrees celsius. Do you have any suggestions as to how to speed up the evaporation process? I can not accept higher temperature. Maybe a good choice is by adding aonther solvent to form azeotropes. I remember that water forms azeotrope with dichloromethane but I do not find anything relaterd to it in CRC Handbook. Any suggestions are highly appreciated and welcome.

You could concentrate the sample again on a second SPE cartridge (maybe even a smaller one) and then elute with methanol.
Alternatively, you could dilute the sample and inject directly. This depends on how much enrichment you currently need before you inject the sample into the HPLC. If you need to inject a large fraction of the sample, the dilution may not be practical, because it may take to long a time. It depends what you need to do.

If you have a rotary evaporator you can do this much more quickly, without the potential problem of gas peaks which we see frequently with N2 evap.You can use much higher temps than the 45 deg. if you don't evaporate to dryness (evaporation keeps the temp. down, inside).
The trouble with azeotropes is that you often loose the temp. advantage in the form of much higher volumes.

Hans