Estimation of high pressure liquid chromatographic retention indices of narcotic analgetics and related drugs.

A method for the prediction of the retention index of drugs on C18 reversed-phase columns was developed and then applied to a series of drugs that were structurally related to morphine and to a series related to fentanyl. The HPLC retention index (/) of the test compounds was estimated using the equation: / = 200 pi + /ref. where pi was the sum of the Hansch substituent constants for the compound, and /ref. was the index experimentally observed for the reference compound of the series. It was also found that the observed index could be used to assign the stereochemistry of the fentanyl analogues.