Effects of amine additives on the resolution of antipsychotic and antidepressant drugs on a cyanoalkyl HPLC column

The separation of basic antidepressant and antipsychotic drugs on a cyanoalkyl-bonded silica column has been studied to determine the effects on peak retention, symmetry, efficiency, and resolution of six different amine mobile-phase additives. The amines - ammonia, n-butylamine, triethylamine, N,N-diisopropylethylamine, N,N-dimethylbutylamine and N,N-dimethyloctylamine - were, except for N,N-diisoprspylethylamine, chosen because of their widespread use for improvement of peak symmetry in chromatographic methods; N,N-diisopropylethylamine was included as an example of a sterically hindered amine to see if the stereochemistry around the nitrogen atom is an important consideration in the selection of an additive. This study shows that a gain in symmetry and efficiency is accompanied by loss of resolution. The results obtained also indicate that one type of amine additive should be used when symmetry and efficiency are most important and another when resolution is paramount.