Analytical characteristics of the method.

aThe number of data for each calibration graph correspond to 8 different concentration levels, with three replicates for each level.
bThe standard deviation obtained from a series of 11 blanks solutions.
cLimit of detection calculated according to IUPAC definitions: 3S0/K, where K is the slope of the calibration graph.
dLimit of quantification calculated according to the IUPAC definition: 10S0/K.
eRelative standard deviation obtained from a series of 11standards each containing 0.50 µg ml−1berberine hydrochloride.