While working on method development and simultaneous determination of two drugs, we have experienced that peaks of the plasma appear in between the peaks of two drugs. The retention time of the first drug was 2.69, while plasma peaks appeared between 3.3 to 3.7 min however, the retention time of the second drug was about 6.692 min. one drug was eluted earlier than the plasma and the second drug was eluted after the plasma. Is there any issue in acceptance of such method?
Dear John R Carney
Can you explain the ESI/MRM?
I just want to confirm that by using reverse phase high-performance liquid chromatography (RP-HPLC), the appearance of plasma peak after one of the two drugs and before the second drug is acceptable or not?
No. As long as these peaks are well separated from this other peak and does not interfere.
Dear can you suggest me any references in support of such reports???
Not really. However, you can check the FDA's 1994 (caution pre-internet!) 'Guide on chromatographic separations' and www.chromacademy.com for current resolution equations.
Sometime unwanted peaks came because of method and system suitability,might be impurity. Better run a blank preparation,it will confirm from where this unwanted peak came,If it present in blank run then no need to worry this method can be justified otherwise method need to be changed.
As per my experimental experience, it is surely possible. The main concern is the effect of the matrix. Another point to be noted is that the first peak is coming out very early and it will be highly affected by the matrix in your case plasma, hence unsuitable for developing the bioanalytical protocol. As such a normal RHPLC protocol will not work, u also need to add an internal standard to maintain the integrity of the data. Furthermore, plasma peaks will not be stable so I don't think they will remain in the same place throughout the analysis.
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