reproducibility problems

[firework1]

What is the typical of %RSD of three triplicate injections from the same sample vial? I am using a Thermo TSQ Quantum LC/MS instrument. I tried to make a standard curve using internal standard. However, the peak area ratio of three replicate (from the same vial, just injected three times successively) was not consistent, the %RSD was 3% to 5%. What is the typical %RSD in similar cases? What are the possible reasons for this? Thanks a lot.

[sam.pedraglio]

It's quite dependent from your injection and pumping system.
We work with a Waters UPLC and we'd obtain reproducibility around 0.5-1%.

[firework1]

thanks for your reply. Do you think the reproducibility has anything to do with the quality of tuning?

[JJG]

I would say that the HPLC should perform in the <1-2% RSD range of injection reproducibilty. I would calculate this from an n=6 injections though. You should probably take into consideration you're using an LC-MS, so I would not expect to get the exact same reproducibility. This is based on a neat sample too. I don't know if your samples are extracted from something or analyzed neat. If your samples are extracted, I would not be concerned with 3-5% RSD. I can't tell if your issues are from tuning since I don't know enough information on your method.

Do you notice a trend with your sample injections? Does your peak area continue to increase, or decrease? How about retention time? Is the ratio of internal standard area to analyte area proportional?

[shahis77]

for HPLC it is 2 or less than 2 % but in case of LCMS/MS it depends on your QA department I mean the STP it can vary from 5 to even 15 %.