Quantitative Analysis in Pharmaceutical Analysis - Chiral Separations by Capillary Electrophoresis - page 325

The calibration curve was obtained by plotting the concentration of d-dopa in the
test solution against the peak-area ratios of both enantiomers. The good calibration
data are demonstrated by the linear equation y = 0.1095 x + 0.0911 and showed a
linearity coni rmed by the coefi cient of determination r 2 = 0.9984 and the RSD
( y -mean) between 0.29% and 3.82%.
The precision and the accuracy of the method were investigated in a similar way
with respect to repeatability and intermediate precision or accuracy. Two different solu-
tions of 1.2 and 4.0 g/mL of d-dopa corresponding to the 0.12% and 0.40%, respec-

tively, in 1.0 mg/mL levodopa were prepared. Each solution was injected six times on
one day (intraday precision or accuracy) and on two different days, respectively (inter-
day precision or accuracy). The corrected peak area and the relative migration times
(RMT) as well as the accuracy values at the two concentration levels of d-dopa are
summarized in Table 11.2. The acceptable RSDs with respect to the RMTs were found
to be between 0.75% and 0.84% for intraday precision and between 0.53% and 0.90%
for interday precision in 2 days. In the case of the corrected peak area-ratio, RSDs for
the intraday precision were found to be in a range of 0.85% and 3.91% and for interday
precision between 1.75% and 3.77%. Thus, the method proved to be precise.
The data, being summarized in Table 11.2, also demonstrate acceptable accuracy
of the method. The highest RSD values for the interday and intraday accuracy were
found to be 3.77% and 3.91%, respectively, and, thus, within the required range of
±

μ

10% of the theoretical values of the concentration of minor component d-dopa.
The robustness of the method was checked with respect to the most critical
parameters such as variation of the applied voltage between −14 and −16 kV; the cap-
illary temperature ranging from 18°C to 22°C; the pH of the BGE between 2.4 and
2.6; the buffer concentration in a range of 18 and 22 mM; the chiral selector concen-
tration between 9.0 and 11.0 mM, considering corrected peak-area ratio, the RMT,
and the resolution factor ( R s ) of both enantiomers in the electropherogram. The solu-
tion containing 1.0 mg/mL of Levodopa spiked with 0.1% of d-dopa was analyzed

TABLE 11.2
Determination of D -Dopa in Levodopa: Intra- and Interday Precision of the
Corrected Peak Area Ratio and Relative Migration Times as well as the
Accuracy of the Method Tested at Two Different Concentration Levels

Conc. D -Dopa
( m g/mL)

Peak Area
Ratio

Accuracy
( m g/mL) (%) Day RSD (%) RMT RSD (%) RSD (%)

Interday precision Interday accuracy

1 1.2 0.221 3.18 0.638 0.90 1.20 100.08 3.18

4.0 0.503 1.75 0.638 0.53 4.02 100.62 1.75

2 1.2 0.223 2.52 0.629 0.78 1.21 101.15 2.52

4.0 0.510 3.77 0.639 0.55 4.08 101.99 3.77

Intraday precision Intraday accuracy

1.2 0.218 0.85 0.623 0.84 1.18 98.64 0.85

4.0 0.505 3.91 0.632 0.75 4.04 101.06 3.91