Which method does NOT remove volatile impurities during purification?

Distillation is a process specifically designed for separating components in a mixture based on differences in their boiling points, and it effectively removes volatile impurities by converting the liquid to vapor and then condensing it back to liquid. This process takes advantage of the fact that volatile substances will evaporate, leaving behind less volatile impurities.

In contrast, filtration is a physical separation method that allows only certain sized particles to pass through, which means it cannot effectively separate substances based on volatility. Similarly, while deionization is a process used to remove ionic impurities from water, it does not address volatile substances. Reverse osmosis is also a filtration method that can remove various contaminants, including some volatile impurities, but it is not specifically designed for that purpose.

Thus, since distillation is effective at removing volatile impurities, it cannot be the correct choice for the method that does NOT remove them, reinforcing the understanding of each method's specific applications and limitations in purification processes.