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- Posts: 2
- Joined: Tue Apr 08, 2014 9:59 pm
Hi to all forum members,
My name is Dan and this is my first post on the forum. I have a long experience in quantitative LC-MS and have been using both Agilent and Sciex systems. Currently, we are running targeted metabolic profiling on Sciex 5500 QTrap coupled to 2 x Agilent 1260 pumps. Unfortunately, we are having a lot of problems with our 5500 machine. The first one that we purchased worked OK for about a year, but as the time was progressing we were having more and more problems. At the end, Sciex could not fix the problems, so they gave us another new unit. The new machine worked great for about 4-5 months, but then started to give us a lot of problems (poor reproducibility, CAD gas bouncing around, sudden lost of signal, etc). As someone who has a lot of both practical and theoretical knowledge of MS (got my PhD from Purdue working on the development of triple-quads), I run some tests to figure out why we are having the problem, and everything points out to electronics. One of our methods runs in positive mode and has 62 MRMs. We run in parallel both, regular MRM as well as scheduled MRM. Bingo, scheduled MRM did not generate improvement in the signal. Here is a very interesting finding:
If we place few same MRMs in the method with the same optimized parameters (CE, DP), we noticed that the same MRMs can produce 5-40% different signal. Even if we place two same MRMs next to each other, the signal might still be different. We have delay time of 5 ms (according to Sciex that's plenty time for electronics to stabilize). In our regular MRM, dwell time is 5 ms. In scheduled MRM, it is anywhere between 5 to 20 ms. The problem is present in both, scheduled and non-scheduled MRM. We also tasted this on two other 5500 machines and found the same problem.
Has anyone else noticed the same problem? Has anyone else experienced that the instrument over time decreases signal and no meter what service is done, the signal never gets back near where it was when the machine was new?
Cheers,
Dan
My name is Dan and this is my first post on the forum. I have a long experience in quantitative LC-MS and have been using both Agilent and Sciex systems. Currently, we are running targeted metabolic profiling on Sciex 5500 QTrap coupled to 2 x Agilent 1260 pumps. Unfortunately, we are having a lot of problems with our 5500 machine. The first one that we purchased worked OK for about a year, but as the time was progressing we were having more and more problems. At the end, Sciex could not fix the problems, so they gave us another new unit. The new machine worked great for about 4-5 months, but then started to give us a lot of problems (poor reproducibility, CAD gas bouncing around, sudden lost of signal, etc). As someone who has a lot of both practical and theoretical knowledge of MS (got my PhD from Purdue working on the development of triple-quads), I run some tests to figure out why we are having the problem, and everything points out to electronics. One of our methods runs in positive mode and has 62 MRMs. We run in parallel both, regular MRM as well as scheduled MRM. Bingo, scheduled MRM did not generate improvement in the signal. Here is a very interesting finding:
If we place few same MRMs in the method with the same optimized parameters (CE, DP), we noticed that the same MRMs can produce 5-40% different signal. Even if we place two same MRMs next to each other, the signal might still be different. We have delay time of 5 ms (according to Sciex that's plenty time for electronics to stabilize). In our regular MRM, dwell time is 5 ms. In scheduled MRM, it is anywhere between 5 to 20 ms. The problem is present in both, scheduled and non-scheduled MRM. We also tasted this on two other 5500 machines and found the same problem.
Has anyone else noticed the same problem? Has anyone else experienced that the instrument over time decreases signal and no meter what service is done, the signal never gets back near where it was when the machine was new?
Cheers,
Dan
