Originally Posted by Burnt Toast
Skip the aspirin step because it is old tech. Back in the day, it was used as an interferant for only one type of test: the first-generation EMIT screen. Since then, a second-gen EMIT (aka EMIT II) was introduced to counter the interference issues caused by aspirin. As a result, the first-gen EMIT is seldom used anymore (if, at all).
The proper vitamin to use for urine color is B2 (Riboflavin). But keep in mind that creatinine and specific gravity checks have become SOP in recent years, making sample color the least aspect in determining an overly diluted sample. Even samples with a nice yellow color to them can still fall below acceptable limits for creatinine and SG, thus resulting in a "too-dilute" ruling.