Screening for drug abuse: use of NaCl to increase drug recovery from papers coated with ion-exchange resin.

Use of papers loaded with ion-exchange resins to adsorb drugs from urine specimens resulted in large losses during the procedure. The first step, removal of drugs from urine specimens, was 25-85% efficient. The second step, elution of drugs from paper for further processing, was approximately 40-70% complete. The efficiency of the first step was decreased and the efficiency of the second step was increased by addition of NaCl, except in the case of barbiturates. Presence of salt during elution increased the yield of dihydromorphine by 20%, of methadone by 16%, of amphetamine by 34%, and of chlorpromazine by 40%, but did not enhance the yield of pentobarbital. Overall recovery rates were: 51% for the opiates, 57% for methadone, 72% for a phenothiazine tranquillizer, but only 35% for amphetamine and 15% for a barbiturate.