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- Posts: 4
- Joined: Fri May 24, 2019 7:19 am
I am writing to you for advice, because I have a problem with LC-MS/MS.
My equipment:
HPLC - Agilent 1200 series, column Agilent Zorbax XDB C18 150x4.6 mm, flow 0.5 mL/min, injection volume is 10 uL,
eluent A - water, eluent B - methanol (both with 5mM ammonium acetate).
Mass spectrometer - AB Sciex 3200 QTRAP with ESI source.
I am analyzing pesticide residues and for some time I have very poor repeatability.
I inject 6 times pesticide mix standard in pure solvent (concentration 100 ng/ml) from the same vial.
For some analytes the RSD% is 1-5% but for others RSD > 20%.
The ion source, orifice plate are cleaned.
Some time ago an ion source temperature error message appeared. The message said that the set temperature of 600’C is not reached. The service technician from the spectrometer stated that the heaters in the ion source are in poor condition and would be replaced (upgrade to the new type od heaters) Unfortunately after upgrade, sometimes an ion source temperature error message still appears. I lowered the temperature of the source to 500'C and the error no longer appears but still repeatability of pesticide standards are very poor.
Is it possible that the ion source works in an unstable way and hence the lack of repeatability of peak area fields? Even though at 500'C the message about ion source temperature error does not appear anymore?
It is necessary to optimize again all of the MRM pairs, because we upgrade the heaters?
Or it is necessary to calibrate mass spectrometer by PPGs?
Maybe ion source works unstable, because still is something wrong with temperature?
Best regards
Marcin from Poland