Dear Anonymous,
I would guess that the solvent you are using, 50% ACN, is not dissolving the
peptides you have presumably formed. You don't say exactly how you treated
the sample after you extracted it from the gel, but if you then removed the
SDS, those very hydrophobic peptides probably fell out of solution. Try
dissolving your matrix in a stronger solvent, maybe 2-propanol, or
chloroform:MeOH:water in the ratio 2:5:2. The resulting solution will
probably spread alot on the target surface, but it might give you a signal.
Arnie Falick
Applied Biosystems
FalickAM@appliedbiosystems.com
----- Original Message -----
Subject: MS: Whitish substance on Maldi Sample (fwd)
> I am working on membrane proteins and I have tried to:
>
> i.) collect the trypsin digest solution (after in-gel trypsin digest)
> directly for Maldi MS analysis with the use of alpha-cyanohydroxycinnamic
> acid as the matrix. I found that upon mixing the sample solution and the
> matrix - a fine whitish powdery layer is formed together with the
crystals.
>
>
> ii.) do in-gel trypsin digest with the addition of excess buffer so that
the
> trypsin solution would not dry up overnight in the 37C incubator. The
next
> morning, there was still trypsin digestion left and I added 0.1%TFA/50%
> acetonotrile to the samples followed by sonication. I found the whitish
> layer too in these samples after spotting them onto Maldi Sample plate.
>
> Both batches of samples yield no results. I am wondering if anybody has
> come across such situations and can give explanation to this.
>
>
> Thanks in advance!
>
>
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