Role of counter-ions in background electrolyte for the analysis of cationgenic weak electrolytes and amino acids in neutral aqueous solutions by capillary electrophoresis with electrokinetic injection.

We elucidated theoretically and experimentally that counter-ions in background electrolyte (BGE) play a role of booster for electrokinetic injection (EKI) for the determination of cationgenic weak electrolytes and amino acids in neutral aqueous solutions using capillary electrophoresis (CE). The pH change in the sample solution caused by the migration of counter-ions resulted in the increase of analyte mobility and hence the increase of the amount of analyte injected into the capillary. This type of EKI was named as counter-ion boosted EKI. Using the counter-ion boosted EKI-capillary zone electrophoresis (CZE), the limit of detections (LODs, S/N=3) for creatinine (4.8nM) and l-histidine (9.0nM) were lowest ever achieved by CE with UV detection. The RSDs (n=3) of the migration time for creatinine and l-histidine were obtained as 0.35% and 0.34%, for peak areas of 13% and 12%, and for peak heights of 12% and 8.5%, respectively. The concentrations of creatinine and l-histidine in a urine sample obtained by the proposed method were within those reported with a good recovery.