Two Fairfax County convenience stores were snared in a undercover sting for selling too much of a strictly regulated stimulant used to make methamphetamine, police said Thursday.

Of the 51 Fairfax County stores where officers sought to buy ephedrine — a common ingredient in cold and diet pills — last month, only workers from One Stop Market on Richmond Highway in Alexandria and Texaco on Lee Highway in Fairfax violated Virginia’s year-old regulations on the sale of the chemical, police said.