2.7. Accuracy/recovery and precision
Accuracy/recoverywas determined by a comparison between
the theoretical concentrations of standard ascorbic acid added to
topical formulations analyte-free and those obtained within the
chromatographic analysis. Replicates of three for each concentration
were used and mobile phase was employed as solvent.
Precision, calculated as relative standard deviation (R.S.D.,
%), was obtained in two levels: intra- (10 injections/day, for 3
days) and inter-days (one injection/day, for 6 days).
Approximately 50 mg of nicotinic acid; 50, 150 and 250 mg
of topical formulations analyte-free; and 5, 15 and 25 mg of
standard ascorbic acid were weighed precisely and dissolved,
separately, in 50mL of the mobile phase, with subsequently
mixing. Samples were centrifuged at 3000 rpm for 5 min at room
temperature (24.0±2.0 ◦C). Supernatants were discarded.
To achieve accuracy/recovery, aliquots of samples were
diluted to final concentrations of 2.0, 6.0 and 10.0 gmL−1 of
standard ascorbic acid and 20.0 gmL−1 of nicotinic acid on the
mobile phase. To obtain intra- and inter-run precision, samples
were diluted to final concentration of ascorbic acid of 6.0, and
20.0gmL−1 of nicotinic acid [21,24–27].