I used 3-HPA as matrix (10mg/mL in 50% ACN water solution with 1 mg/mL ammonium citrate dibasic) , and the sample (~60 pmol, 30-mer, and 10 of 30 were phosphorothioated ,~ 9.4 kDa) was analyzed in Shimazu Maldi 8020 positive mode (linear). The oligmer was desalted by a 3k cut-off ultrafiltration tube (3 times) before analysis.
When the laser energy reached 90, the peaks of 3-HPA appeared, but there were no signal around 8 kDa-10 kDa, even noise;
and I countinued to raise up the laser energy to 120, the noise came out but still no spetra of the DNA sample.
Did my DNA samples still have salts that affect the ionization? Please help me. Thanks
I have never used MS for DNA, so forgive my question: can you produce positive ions from DNA, despite all the negative phosphate groups? Perhaps negative ion mode would be better?
Hi,
I agree with Engelbert Buxbaum you should try to shoot on your sample in negative mode.
Is the cristallisation is similar of what you get for other samples in this matrix?
Best,
Sébastien
Sébastien Brûlé
Thanks for your reply! The dried samples on the plate were indeed a little bit different from other samples, that is, the samples trended to crystallize more at the edge of drops though there were still a thin film in the middle. But I tried to focus the laser shot on the edge of the dried drop, where white crystals stacked a lot. Still only noise.
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