By Anonymous on Wednesday, October 1, 2003 - 11:14 am:
I did SPE of human urine samples. The final eluant was 0.2 N HCl in methanol/acetonitrile. After evaporating at 45C for about 25 minutes under nitrogen, I saw some brown/black residue left. I suspect that it was from decomposition of acetonitrile under very acidic conditions. Has anyone got an idea what it is?
Thanks!
By A.Mouse on Wednesday, October 1, 2003 - 08:20 pm:
How do you know it was not from the urine or the SPE cartridge? Did you do a blank extraction doing exactly what you did, but without loading urine, just loading water? Did you add 0.2 N HCL to the urine and then evaporate this to dryness? Of course, you can also take methanol and acetonitril, add 0,2N HCl and see if you get brown stuff.