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Registervariation in response of the analyte and internal standard [Bioanalytics]
Dear Hale,
I can see two different reasons for this problem, in addition to the one mentioned by Helmut, but there may be some others:
- one common problem with LC/MS/MS can be the need to condition the ion source to obtain a stable signal. You may need a number of injections from plasma samples before your signal stabilises. Sometimes it is just half a dozen, but it may happen that you need 20 or 30 injections. Injecting mobile phase regularly doesn't really solve the issue, you rather need to inject some plasma blanks before your samples. If you are in this situation you probably see a trend towards a decrease or increase in the signal of the internal standard over time in the run. It may not be that clear if the IS is not affected much but the analyte is. You may be able to explore this by repeated injections of a QC sample in a run and monitoring the response of the analyte and IS.
- another possibility is the accumulation of phospholipids on the column, which can then "bleed" out of the column in an erratic way, leading to matrix effects issues. Variations in retention times can sometimes also be seen due to this accumulation, which modifies the polarity of the stationary phase. Possible solutions are a better sample clean-up, or use of a mobile phase gradient to clean the column between two injections (will not take longer than your injections of mobile phase).
Regards
Ohlbe
❝ I have response variation problem. When injections made from same vial
❝ responses of the analyte and IS changes but not with same proportion.
❝ Also after every six injections in a batch mobile phase is injected four
❝ times and results get better with this procedure.
I can see two different reasons for this problem, in addition to the one mentioned by Helmut, but there may be some others:
- one common problem with LC/MS/MS can be the need to condition the ion source to obtain a stable signal. You may need a number of injections from plasma samples before your signal stabilises. Sometimes it is just half a dozen, but it may happen that you need 20 or 30 injections. Injecting mobile phase regularly doesn't really solve the issue, you rather need to inject some plasma blanks before your samples. If you are in this situation you probably see a trend towards a decrease or increase in the signal of the internal standard over time in the run. It may not be that clear if the IS is not affected much but the analyte is. You may be able to explore this by repeated injections of a QC sample in a run and monitoring the response of the analyte and IS.
- another possibility is the accumulation of phospholipids on the column, which can then "bleed" out of the column in an erratic way, leading to matrix effects issues. Variations in retention times can sometimes also be seen due to this accumulation, which modifies the polarity of the stationary phase. Possible solutions are a better sample clean-up, or use of a mobile phase gradient to clean the column between two injections (will not take longer than your injections of mobile phase).
Regards
Ohlbe
—
Regards
Ohlbe
Regards
Ohlbe
Complete thread:
- variation in response of the analyte and internal standard haydonat 2011-01-13 10:27
![[Mix]](https://static.bebac.at/img/mix.png "open in Mix view")
- variation in response of the analyte and internal standard Helmut 2011-01-13 17:08
- variation in response of the analyte and internal standard haydonat 2011-01-15 15:16
- variation in response of the analyte and internal standard Ohlbe 2011-01-15 23:09
- variation in response of the analyte and internal standard haydonat 2011-01-15 15:16
- variation in response of the analyte and internal standardOhlbe 2011-01-13 19:14
- variation in response of the analyte and internal standard haydonat 2011-01-15 15:22
- variation in response of the analyte and internal standard NewInPK 2011-02-01 18:32
- variation in response of the analyte and internal standard Ohlbe 2011-02-02 10:22
- variation in response of the analyte and internal standard Helmut 2011-01-13 17:08
Ing. Helmut Schütz