Question

A recreational drug combination that is gaining popularity is ketamine and heroin. Given the data below, describe a solid phase extraction procedure for separating the two components.

Ketamine, pKa= 7.45

Heroin, pKa= 9.1

It is relevant to know that both molecules are relatively non-polar, with ketamine being the less polar of the two.

A complete answer will include: identification of the stationary phase relative polarity, all solvents, and the conditions for 1. loading the sample and 2. extracting the two drugs separately.

Answer 1

Since the two compunds are fairly non polar, it will be recommended to take polar stationary phase. So silica gel as stationary phase in column chromatography will be recommended.

Dissolve the compound mixture is minimum fairly polar solvent such as dichloromethane or ethyl acetate in an appropriate sized round bottom flask, then add just enough silica gel to completely cover the solvent and then dry the solvent over rotavap to predissolve compound ocer silica gel and then load it above the stationary phase in the column.

Using thin layered chromatography, determine the solvent system where you first add the solvent mixture of less polarity so that ketamine being the less polar compound moves as higher spot, but it's Rf value remains between 2.5 to 3.0. Further find the solvent system where the top spot moves higher and the lower spot of Heroin moves to Rf between 2.5 to 3.0.

Pass solvent system (mixture of petroleum ether and ethyl acetate) of lower polarity first as determined by tlc so that the top spot of ketamine is completely eluted and separated. After that, add the solvent system of higher polarity determined by tlc to elute cocaine. Collect them separately.