Repeatability and reproducibility were estimated by regression analysis,
and they were expressed as RSD (%) of the molar absorption coefficient. The molar absorption coefficients were e 5 (2.3 6 0.2) 3 103, (2.2 6 0.1) 3 103, and(2.1 6 0.1) 3 103 M21 cm21 with an RSD of 5.0, 4.9, and
4.5% in each occasion.