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 whether the relative retention times of Impurities A and B will remain at 0.2 and 0.3, respectively, when using a 4.6 x 100mm x 2.7um column instead of a 4.6 x 150mm x 3um column, we need to consider the effect of column dimensions on the retention behavior.
The relative retention time (RRT) is defined as the ratio of the retention time of the impurity to the retention time of the principal peak. RRT is influenced by various factors, including the column length and the particle size of the stationary phase.
When the column length is decreased (e.g., from 150mm to 100mm) while keeping the particle size and stationary phase constant, the retention times of all compounds tend to decrease. This is because the shorter column allows for faster elution of the compounds.
Moreover, when the particle size is decreased (e.g., from 3um to 2.7um), the retention times also decrease. Smaller particles provide greater surface area for interactions between the analytes and the stationary phase, leading to faster elution.
Therefore, it is expected that the retention times of Impurities A and B will be reduced when using a shorter column and a smaller particle size. This explains the observed RRT values of 0.18 for Impurity A and 0.16 for Impurity B, which are smaller than the RRT values obtained with the original column.
In terms of the acceptability of the results, it depends on the specific acceptance criteria set for the determination of Impurities A and B. If the method allows for a certain range of variation in the RRT values, and the observed values fall within that range, then the results can be considered acceptable. The good resolution of the peaks, as mentioned, is also a positive indication.
However, it is important to refer to the method validation requirements or guidelines provided in the procedure to assess if the observed RRT values meet the acceptance criteria. If there are no specific criteria mentioned, it may be necessary to consult with the method developer or determine the acceptable range through method validation experiments.