Repeatability Issues, Pesticide Residue Analysis, LC MS/MS

[BHolmes]

I am trying to QC a set of new calibration standards on our Waters Acquity UPLC Xevo TQ-S and the repeatability is terrible. I am 95% sure that the poor repeatability is a result of the uncontrolled room temperature - we had a power surge that blew out half the building , thankfully instruments are ok but the AC is dead

Here is the sample sequence I ran with %relative stdev for each set of triplicate injections in ()
4x cond
3x Std 1 (3.7%RSD)
1x MeOH blank
3x Std 2 (14.9%RSD)
1x MeOH blank
3x Std 3 (10.7%RSD)
1x MeOH blank
3x Std 4 (5.4%RSD)
1x MeOH blank

I have not pulled the room temperature data for when this sequence was running, but I do know that it was not controlled. Could there be any other reasons why I'm seeing this fluctuation from good to bad to good?

any thoughts/comments appreciated....

[BHolmes]

I was able to pull the room temp data, it only changed by less than 5degC throughout the entire run. I'm now working with manufacturers technical support on troubleshooting the issue. Right now we are focusing on UPLC portion, let you all know how it goes.

[yellaiah2013]

I am also faced the temperature problem on waters insttument.
If the temperature is stable waters instrument gives good reproducibility.
Whatever the temperature try to keep constant

[richiekichi]

Hi there,

Sorry to post to an older topic.

I also experience extremely poor repeatability with our Quattro Premier XE instruments on hotter days. Our lab temperature increases from about 20 to 35 on days when the outside temperature is 40 deg C.

I'd expect there to be retention time shifts but how do such fluctuations effect the mass spectrometer? I would have thought any changes would be with the quadrupoles and detector rather than at the source.

Happy New Year by the way. Hope you all had a good Christmas!

[richiekichi]

Just to answer my own question, I just had a couple of people from Waters over.

They confirmed that you can expect to see mass drift with large differences in temperature. Electronics operating outside their optimum I suppose. Their suggestion, for us, was to have a hot weather method. Or get better air conditioning.

So there you go. It is very likely you will experience repeatability issues if you cannot maintain the room temperature.

[Alp]

Glad you found the problem.

One would think that the "mass drift" would remain constant if the temp does not fluctuate between injections and that the error would be repeatable if the room stayed at say 5 degrees above where it usually does.


Had you not solved the issue, my first question would be
1. Are you using an internal standard that would compensate for sampling errors?

2. Have you inspected your autosampler syringe and switch valve for wear?

Alp

[kerri]

To add to Alp's questions (had the issue not been solved), I would change the Purge solution and then prime the needle 50 times to make sure there are no bubbles in the needle meter.

K

[BHolmes]

To end this discussion I thought an update was necessary. The room temperature situation has been fixed, but we were still not getting the precision we needed. We now purge both eluent lines and prime sample syringe before each run, this drastically improved precision within a single run. At a minimum, we purge for 1-2 min at 3mL/min and prime 1-2 cycles. Hope this helps others experiencing the same issues.