Factors affecting quantitative electrokinetic injections from submicroliter conductive vials in capillary electrophoresis

The factors influencing quantitative electrokinetic injections in capillary electrophoresis for custom 340-nL, 10-μL, and 110-μL stainless steel sample vials have been investigated using a six-analyte mixture containing catecholamines and indolamines. Deleterious sample degradation is increased with smaller sampling vials, decreased capillary-electrode distances, and increased current passed during the injection. Zero-voltage injections from the smallest vials also demonstrate additional injection discrepancies when compared to larger-volume bulk solution injections. These effects are in addition to the electrokinetic bias and complicate the selection of appropriate internal standards. For nanoliter-volume conductive vials, the injection process creates new species and eliminates other electroactive species to such an extent that quantitation becomes problematic.