I'm running a reversed phase method with SIR detection on a tandem quadrapole. A colleague ran another analysis on the same instrument, with the same column right before we started to notice the change in the peak areas. The second injection of the standard always gives me a higher peak area.
Hello Michael, That is not a problem that means still have some carry over in you system. In order to avoid this, you have to run black after each injection to clear your system.
Try it and let me know you feedback!!!
You have not validated the method for robustness! I doubt the SST (system suitability) met the minimum 2.0% criteria.
Yes, carry over is the most likely reason. Failure to properly flush and then re-equilibrate the column after each analysis is the other common reason.
This could also be caused by using a poorly developed method which does not fully retain, then elute all compounds from the column during the analysis time. Problems occur when the mobile phase is not strong enough or if a gradient, does not go to a high enough concentration AND hold there for a long enough time to elute everything off.
Sample/Std concentration also effects retention time (which, depending on integration parameters, can effect total area). As you increase concentration, the peak's get wider. This will shift the Rt out a bit and must be accounted for when setting up the Rt windows for each std. Make sure you inject the SAME volume for each sample/std. Use the correct procedure of injecting the same volume each time, not different volumes for each sample to "create" different stds. The concentration should vary, not the volume.
Dear Sir. Concerning your question about the variation of standard peak areas with the increase of concentration . There are many different reasons. Nearly every part of the instrument can conceivably contribution to changes in peak area: injector and its type, air bubbles in sample, cleaned syringe, temperature changes, flow rate and detector . The following below links may help you in your analysis:
http://www.waters.com/webassets/cms/library/docs/wa20769.pdf
https://www.shimadzu.eu/sites/default/files/Tips_for_practical_HPLC_analysis-Separation_Know-how.pdf
Thanks
In addition to above mentioned answer, you may add an internal standard with respect to which you may record the relative retention time. Hope it will solve your problem.
Mass spectrometry analysis for quantitation needs saturation of detector, injecting 10 to 20 injection for detector saturation before analysis could definitely solve your problem.
Hi there,
I am also facing similar problem for my standard solution in LC-Q-TOF. In subsequent 4 injections, I have got the following area.
1. 18410
2. 50832
3. 163790
4. 164210
I am injecting 10 uL in a gradient system and RT is 3.85 min. My target compound is dissolved in ACN. My mobile phase, A: 0.1% Formic acid, B: ACN. Stop time: 8 min and Post time 10 min.
Thanks in advance for your suggestions.