Susceptibility Plugs with Methanol

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Dear All,

	We have just taken delivery of a 3 mm probe, and want to extend our
low-concentration work from LC-NMR to this configuration.  We've always done
well by 5 mm Shigemi tubes, and were keen to try the equivalent for 3 mm
tubes:  Wilmad/Doty Susceptibility Plugs.   We have used the plugs made from
G-10 (Wilmad PN SP-PR-G-3 and Doty 99851).

	We use LC-NMR grade methanol, which we find to be very clean,
chemically.  We "conditioned" the G-10 plugs & positioning rod with soaks
and washes in ethanol and methanol.  

	The problem is that we see a LOT of chemical interference leeching
from the plugs/positioning rod.  On a ca. 5 ug solute sample, the
contaminating peaks would be _much_ more intense than the solute.  And
there's a wide range of crap coming off the plugs:  we see the biggest peaks
at 1.3 and 4.6 ppm, but less intense contamination giving rise to peaks at
0.9, 1.6, ca. 2, ca. 3, ca. 7, and 8 ppm

	Has anyone out there had similar experience?  Have you found good
cleaning conditions?  Any experience would be appreciated.

Thanks a lot,
	Mike

PS   I am not aware of anyone making Shigemi-type tubes (all glass
construction) at 3 mm.    M.

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