Factors Affecting Quantitative Electrokinetic Injections from Submicroliter Conductive Vials in Capillary Electrophoresis

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Abstract
The factors influencing quantitative electrokinetic injections in capillary electrophoresis for custom 340-nL, 10̄-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.