ACS Analytical Chemistry Practice Exam 2026 – The Complete All-in-One Guide to Exam Success!

The concept being tested is how the separation factor, alpha, behaves in chromatography. Alpha is defined as the ratio of the retention factors of two solutes, specifically the more-retained one divided by the less-retained one: alpha = k2' / k1'. Since retention factors k' are nonnegative and, by definition, we compare the more-retained solute to the less-retained one, alpha cannot be less than 1. The smallest value occurs when both solutes have the same retention (k2' = k1'), giving alpha = 1. Values below 1 would imply the second compound is less retained than the first, which contradicts the usual labeling. A value like 2 is possible if the second solute is twice as retained as the first, but it is not the minimum. Therefore, the minimum possible alpha is 1.