Evaluation of drug extraction procedures from urine.

Radioactive methadone, phenytoin, phenobarbital, and diazepam were easily and efficiently removed from human urine samples by adsorption on C18 bonded silica phases. These techniques were simpler than conventional extractions at pH 9.3 or 5.2 with dichloromethane, XAD-2 and methanol, or Celite 560 and dichloromethane.