Chromatography Forum

Recently my lab has run into an odd problem on our Shimadzu LC-MS:
We would run a few blanks to see if there are any contamination peaks and found that while the first blank would appear clean, the following blanks would contain a particular analyte (which we often find in our samples) at a low concentration - throwing off our quantification on SIM and MRM.

We tried washing it over the weekend with a blank using an isocratic solvent we know the analyte dissolves well in (70:24:6 of MeOH:Acetonitrile:H2O with 0.03% Formic).

Despite the wash, we still see the same problem.

Unfortunately - it might have been due to overloading the column with sample, however we have changed to two columns thus far and found similar findings.

I believe blanks have nothing to do with injection needles or valves (took a look at https://hplctips.blogspot.com/2015/02/c ... on-in.html from a previous forum).

We've also tried cleaning the source needle on the mass spec but found no difference.

Any ideas of what could be happening for those who know the machinery better that I may?

Any chance that it's coming in with the mobile phase (e,g., via contaminated glassware)?

It can be from vials.

Does your autosampler have a NEEDLE WASH?

Recently my lab has run into an odd problem on our Shimadzu LC-MS:
We would run a few blanks to see if there are any contamination peaks and found that while the first blank would appear clean, the following blanks would contain a particular analyte (which we often find in our samples) at a low concentration - throwing off our quantification on SIM and MRM.

We tried washing it over the weekend with a blank using an isocratic solvent we know the analyte dissolves well in (70:24:6 of MeOH:Acetonitrile:H2O with 0.03% Formic).

Despite the wash, we still see the same problem.

Unfortunately - it might have been due to overloading the column with sample, however we have changed to two columns thus far and found similar findings.

I believe blanks have nothing to do with injection needles or valves (took a look at https://hplctips.blogspot.com/2015/02/c ... on-in.html from a previous forum).

We've also tried cleaning the source needle on the mass spec but found no difference.

Any ideas of what could be happening for those who know the machinery better that I may?

Have you tried running the gradient without injection (set vial No. to -1)? Do you still see a peak?
If yes, you can rule out the sampler. One possibility is PEEK-tubing in the system, especially the long one from the column to the MS. Try to recplace it with a SS-tubing.