What does an HPLC assay for procainamide suggest if the internal standard peak for sample 1 is 15% greater than sample 2?

The suggestion that less recovery from sample 2 occurred in the extraction step is correct. In HPLC (High-Performance Liquid Chromatography), the internal standard is used to normalize the results of the assay to account for variation in sample preparation, injection volume, and other analytical factors. If the internal standard peak area in sample 1 is 15% greater than that in sample 2, it strongly indicates that the conditions or the processes used to prepare or extract sample 2 were less effective than those for sample 1.

This difference can arise from several factors related specifically to the extraction process, such as incomplete extraction of procainamide or a loss of the analyte during sample preparation for sample 2. Therefore, observing a reduced internal standard peak area in sample 2 suggests that the proper amount of analyte did not reach the HPLC system, leading to a skewed comparison.

The other options relate to potential analytical variations or experimental conditions that do not directly explain the disparity in the internal standard peak area. For example, the column pressure change could affect retention times or the resolution of the peaks but would not specifically account for a significant difference in internal standard peaks. Similarly, changes in pH might alter the retention or separation of the analy