Detection of drugs using XAD-2 resin. I:Choice of resin, chromatographic conditions, and recovery studies.

Amberlite XAD-2, a nonionic polystyrene divinylbenzene resin, was first used for the analysis of drugs in urine and a number of reports have described the development at optimal conditions for extraction, including type of resin columns, pH conditions, and eluting solvents. XAD-4 and XAD-7 resins were compared to the similarly structured XAD-2 resin and no significant advantage over the XAD-2 resin for drug screening was observed. A quantity of 5 to 6 g of resin was found to have sufficient capacity for the extraction of 200 ml of pentobarbital solution (1 mg/100ml). A column flow rate of approximately 15 ml/min (gravitational flow) was sufficient for analysis and slower rates were not more efficient. A mixture of ethyl acetate and 1,2-dichloroethane (3:2) was found to give best overall recovery (66 to 94%) of drugs, the resulting extracts being reasonably free of interfering substances. A pH value of 8.5 is recommended as optimum for comprehensive analysis of acidic and basic drugs. Recovery studies were conducted on spiked samples to determine drug losses occuring during various steps in the XAD-2 extraction procedure for four acidic (amobarbital, secobarbital, pentobarbital, and phenobarbital) and four basic (morphine, codeine, meperidine, and methadone) drugs. A relatively small amount (0 to 5%) of the drugs was not adsorbed by the resin and amounts varying from 6 to 40% failed to be desorbed by the eluting solvent. Additional losses occurred during the removal and analysis of TLC spots. Recovery of drugs from aqueous solutions analyzed with the XAD-2 resin were compared to recoveries reported in the literature with other XAD-2 resin methods for the extraction of drugs from urine. Recovery of phenobarbital, morphine, and codeine improved by 4 to 23% while recoveries of amobarbital, pentobarbital, secobarbital, methadone, and meperidine were 4 to 28% less efficient when compared to literature data.