ethanol vs methanol as a solvent

[piggie1230]

So I’m supposed to be extracting experimental residues from pottery (archaeologist here)

I was using dichloromethane, but I’ve realized it’s old and decided I would rather use chloroform-methanol. Except we don’t have methanol. My advisor uses ethanol for his pollen extractions instead of methanol--I don’t think they’re interchangable but he seemed hesitant to go get methanol, and I figured I could use the dichloromethane. Here we are 9 pm and I’m wanting the methanol.

So. How long is dichloromethane good for? If it’s started to decompose (it reacted with sodium bicarbonate, so I get the impression it is) is it useless for my extractions?

Can I use chloroform-ethanol? What would be the main differences between the chloroform-ethanol and chloroform-methanol?

[Don_Hilton]

If the dichloromethane has decomposed and has been stored similarly to the chloroform, expect that the chloroform has decomposed as well. If the dichloromethane reacted with bicarbonate it is really bad. Stored correctly dichlormethane should last many months, if not several years.

There is a significant difference between ethanol and methanol in polarity. Is it significant enough to make a difference in what you are doing? It all depends on what you are doing. Some things that are soluble in chloroform/methanol may be less soluble in chloroform/ethanol.

Also ethanol for the laboratory is often denatured (to keep people from drinking it), which means it has other compunds in it. These may or may not make a difference in what you are doing.