Hi folks

Mario, my guess is you've read that Methacarn should be made
up freshly and so you're doing it on a small scale in a
plastic (polystyrene) tube [e.g. a clear (not translucent)
graduated 15ml conical tube] AND you're putting the chloroform
in first.  Result: plastic dissolved in chloroform which then
precipitates when diluted with the other components in which
it is not soluble (...or maybe you are storing your chloroform
in such plastic, with the same result, or pipeting it with a
disposable, polystyrene pipet).  Do you see any sign of
crazing or etching of the tube/pipet afterwards?

The solution could be as simple as adding the chloroform last,
but try using polypropylene tubes instead, or better still, a
small glass measuring cylinder and/or glass pipet.

Cheers!
-David
===================================================
David A. Wright, PhD
Section of Neurosurgery
University of Chicago

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