Determination of noradrenaline and dopamine in Chinese herbal extracts from Portulaca oleracea L. by high-performance liquid chromatography

A simple, rapid and accurate high-performance liquid chromatographic (HPLC) technique coupled with photodiode array (PDA) detection was developed for the simultaneous determination of noradrenaline (NA) and dopamine (DA) in Chinese herbal plant extracts from the different parts of Portulaca oleracea L. The effects of various parameters, such as sodium dodecyl sulfate (SDS) concentration, pH value and proportion of methanol on chromatographic behavior of the analytes (NA and DA) were investigated. Separation of NA and DA was achieved within 10 min by a mobile phase consisting of 70% (v/v) methanol and 0.02 M potassium dihydrogen phosphate solution, which contained 30 mM SDS and was adjusted to pH 3.0 with H3PO4. NA and DA showed good linear relationships in the range of 0.004–6.00 μg and 0.011–8.25 μg respectively. The correlation coefficients of the calibration curve for the analytes exceeded 0.999. The detection limits for NA and DA were 0.40 ng and 0.55 ng, at a signal-to-noise ratio of 3, respectively. Moreover, the optimized HPLC method was employed to analyze three different parts of Portulaca oleracea L.