External standards calibration,
based on peak areas, was used for quantification. For each
analyte, six working standard solutions (0.05, 1, 2, 3, 4 and 5 lg/
ml were used to construct calibration curves using the least
squares method. Internal standard recovery was used to correct
sample carotenoid mass fraction. All standard solutions were
stored at 70 C under nitrogen and in the dark. On each occasion
of analysis, stock standard solutions were prepared from the solid
standards, and individual working solutions of each carotenoid injected
onto the HPLC system to verify purity and mass
concentration.