Posted by anne on Saturday, October 15, 2011 at 1:03am.
Hi,
Please advise on the following: -
A procedure for the determination of Impurities A & B in a compound says to use a 4.6 x 150mm x 3um column (stationary phase: octadecylsilyl silica gel).
The relative retention time with reference to the Principal Peak is: -
1) about 0.2 for Impurity A
2) about 0.3 for Impurity B
Principal Peak Retention Time is about 25min.
If I use a 4.6 x 100mm x 2.7um column (same stationary phase),
will the relative retention times of Impurities A & B still be 0.2 & 0.3 with reference to the main peak?
I did a run using the shorter column with smaller particle size and the relative retention times with reference to the Principal Peak are: -
1) Impurity A: 0.18
2) Impurity B:0.16
The resolution is good for the peaks.
Can you comment if results are acceptable?
To determine if the results are acceptable, we need to consider the changes in the relative retention times when using a different column. In this case, you switched from a 4.6 x 150mm x 3um column to a 4.6 x 100mm x 2.7um column, both with the same stationary phase (octadecylsilyl silica gel).
The relative retention time is the ratio of the retention time of a peak to the retention time of the Principal Peak. In this case, the relative retention times for Impurities A and B were initially reported as 0.2 and 0.3, respectively, with reference to the Principal Peak (which has a retention time of 25 minutes).
When you used the shorter column with smaller particle size, the relative retention times for Impurities A and B changed to 0.18 and 0.16, respectively.
In general, changes in column dimensions and particle sizes can affect the separation efficiency and retention times of peaks in chromatography. However, a small change in relative retention times, like the ones you observed, may still be acceptable if the resolution between the peaks remains good.
Resolution is a measure of how well two adjacent peaks are separated from each other. It is calculated as the difference in retention times divided by the sum of the peak widths. If the resolution is still good for Impurities A and B after switching to the shorter column, it suggests that the peaks are sufficiently separated and the quality of the separation is acceptable.
Therefore, based on the information provided, it seems that the results obtained with the shorter column are acceptable as long as the resolution between the peaks is good.