Separation and determination of protocatechuic aldehyde and protocatechuic acid in Salivia miltorrhrza by capillary electrophoresis with amperometric detection

Capillary electrophoresis with amperometric detection was applied to separate and determine protocatechuic aldehyde and protocatechuic acid in Salivia miltorrhrza preparations. The electrode used was a 0.3 mm diameter carbon disk electrode fixed in a wall-jet with amperometric detection. Under the optimum conditions, the two analytes were separated completely within 8 min. Excellent linearity was obtained in the concentration ranges of 0.25–100.0 µg ml⁻¹ and 0.50–100.0 µg ml⁻¹ for protocatechuic aldehyde and protocatechuic acid, respectively. The detection limits were 0.10 µg ml⁻¹ of protocatechuic aldehyde and 0.25 µg ml⁻¹ of protocatechuic acid, which were found to be lower than those of other methods that determine protocatechuic aldehyde (3,4-dihydroxybenzaldehyde) and protocatechuic acid (3,4-dihydrobenzoic acid) simultaneously. The mean recoveries of protocatechuic aldehyde and protocatechuic acid were 97.4% and 103.3%. This method has been successfully applied to monitor these two components in real samples such as Salivia miltorrhrza and its two traditional Chinese medicinal preparations.