Use of Large Volume Sample Stacking for Improving Limits of Detection in the Capillary Electrophoretic Determination of Selected Cations

Abstract

On-capillary large volume sample stacking in capillary electrophoresis, with hydrodynamic injections of up to 300 s, can be used to significantly improve the LOD of selected cationic basic drugs and metal chelates by up to two orders of magnitude. This technique can be used to lower the LOD for a basic drug such as clenbuterol down to 3.2 × 10 ^{- 8} mol dm ^{- 3} for a 240 s injection from a value of 2.3 × 10 ^{- 6} mol dm ^{- 3} for conventional CZE using a 3 s hydrodynamic injection. Cobalt, as its cationic 5-Br-PADAP chelate, can be determined down to an LOD of 5.0 × 10 ^{- 8} mol dm ^{- 3} for a 300 s hydrodynamic injection as compared with an LOD of 5.0 × 10 ^{- 7} mol dm ^{- 3} for a 30 s hydrodynamic injection. This technique for such cations requires the use of the electroosmotic flow modifier cetyltrimethylammonium bromide for sample solvent removal during stacking. The cations are then determined at a UV/VIS detector after polarity switching.