Chromatography Forum

Hi,

So… sorry again, naïve question -

I have a new Shimadzu HPLC MS. I put a new C18 with a column guard in it today for its first ever runs and flushed it for an hour with H2O 95 / MeCN 5 / 0.1% HCOOH diverting it to the waste directly rather than to the MS.

I did a few injection of 1mg/mL of p-BrPhNH2 (injecting 10uL… I guess it’s too much maybe…) and the signal isn’t amazing. My background noise is quite high when I scan form m/z 100 to 450.

I especially have a large leak at m/z 100.

Any clue what I could do? Maybe flush with 95 ACN / 5H2O for a bit?

Thanks!

K!

Hi Kevin,

1 mg/ml is a lot for an MS - I would suggest betwenn 1 - 10 µg/ml for a scan. Although there are substances that do not ionize very well. Organic amines should be sensitive in positive mode.

In the range below 120 u you get peaks from your solvents and acids, Start your scan at 120 or 125 if possible.

Optimize the source temperatures.

Check the correct depth of the ESI-needle and optimze the horizontal position.

Check with reserpine if the instruments meets Shimadzu's specs.

ACN ist not always the best organic for MS work. In my experience MeOH is better most of the time (and cheaper).

If you suspect that your instrument is dirty, try flushing with ACN/IPA.

Best regards,
Hartmut

Thanks a lot!

Indeed it seems that having flushed the column with ACN and injecting less did the work.

Is MeOH better? We have a dual ionisation source (DUIS) and I wasn't sure, Shimadzu did say that ACN was fine (I know that apparently it's not fine at all in APCI!).

As above, I always flush a new column with high organic phase prior to using it, just to remove any organics that might have contaminated it during packing.