Preconcentration of aliphatic amines from water determined by capillary electrophoresis with indirect UV detection

Preconcentration methodology based on adsorption chromatographies for enriching aliphatic amines (C1 to C4 substituted primary, secondary, and tertiary) and alkanolamines in water was studied by free zone capillary electrophoresis (CZE) with indirect UV detection. The solid-phase extraction of amines from water (pH 5) as a preconcentration step was studied for ion exchange solid-phase extraction (SCX) cartridges, cation ion exchange extraction disks, and ion-pairing with C-18 extraction disks. In the course of the investigations, the electrophoretic properties of the amines was studied in some detail in order to optimize separations and detection limits. The indirect mode is particularly powerful in being able to detect primary through quarternary amines without derivatization. Mobilities of amines were correlated with their Stokes' radii. Increased selectivity for resolving closely related amines under CZE was explored using nonionic surfactants, pH adjustment, and optimized background electrolyte. Techniques were developed for obtaining stable baselines in the indirect detection mode. Linearity, sensitivity, and efficiency were explored for this mode of detection for a large set of amines.