Demonstrated in this study is that without pretreatment and preconcentratio
n nanomolar-level catecholamines in human urine samples can be quantitative
ly determined with ease by utilizing capillary electrophoresis coupled with
amperometric detection. The detector employs a parallel-opposed dual-elect
rode scheme assembled with an on-capillary electrode and a disk electrode a
nd takes advantage of the redox cycling of analytes between the two working
electrodes to improve the limit of detection. The matrix effect of urine s
amples significantly decreases the detection sensitivity from that obtained
in standard solutions. Therefore, calibration curves derived from standard
solutions cannot be used in quantitative determination of catecholamines.
Methods of standard addition and internal standard have been studied. The r
esults suggest that isoproterenol is a good internal standard to facilitate
the measurements of dopamine, epinephrine, and norepinephrine in human uri
ne samples. (C) 2001 Elsevier Science B.V. All rights reserved.