Development of a generic flow injection analysis method for compounds with a secondary amine or amide function, using an experimental design approach I. Selection and evaluation of the FIA system parameters

A generic flow injection analysis (FIA) method to determine compounds with a secondary amine or an amide in their structure was developed. A first part of the development, namely the selection and evaluation of the FIA system, is described. A chemical reaction with sodium hypochlorite (NaOCl) first converts the secondary amine or the amide to a primary amine. This is followed by reaction of the primary amine with o-phthalaldehyde (OPA) and a thiol (N-acetylcysteine, NAC), to form a derivative which can be measured fluorimetrically. To investigate the influence of the different FIA system parameters on both the peak height and the residence time for a set of 28 pharmaceutical compounds, a half-fraction factorial design for five factors at two levels (2^5-1: resolution V=16 experiments) was executed. Effects on both responses were calculated. Since the peak height should be maximized and the residence time minimized, the Pareto optimality concept was applied to make an optimal compromise between both responses and to eventually select a generic FIA system.