291 METHOD FOR SIMULTANEOUS QUANTITATION OF RESORCINOL The method precision and interday precision were evaluated on the basis of relative standard deviation (RSD) values for resorcinol, p-phenylenediamine, and m-aminophenol and were found to be in the range 0.6% to 1.4%. As the RSD values were 2%, the developed method was found to be precise. The accuracy of the method showed acceptable recoveries in the range of 99% to 101%. Robustness of the method was studied by making deliberate changes in the chromatographic conditions like flow rate (±0.2 mL min−1), wavelength (λ ± 5 nm), mobile phase composition (hexane-1-sulfonic acid ±5 mL), and pH. The results of robustness study of the developed method were validated by change in flow rate, change in λ, and change in mobile phase ratio, and the %RSD of those variations were 2. Figure 3. Chromatograms of (A) standard, (B) Godrej Expert, and (C) Garnier Color Naturals. AU: arbitrary units MAP, m-aminophenol PPD, p-phenylenediamine.

292 JOURNAL OF COSMETIC SCIENCE Table II Validation Parameters of Proposed Method Parameters RES PPD MAP Linearity, µg mL−1 10–150 10–150 10–150 Correlation coefficient 0.9993 0.9990 0.9997 Precision (i) Method precision 0.760 0.898 1.657 (ii) Intermediate precision 1.820 1.238 1.636 (iii) System precision 0.360 1.490 1.349 Accuracy, %recovery 50 100.4 99.6 100.1 100 100.5 100.4 99.9 150 100.4 100.6 100.8 Assay, %101.2 100.1 100.3 Purity angle threshold angle Peak pure Peak pure Peak pure Solution stability up to 24 h Yes Yes Yes %RSD 1.33 1.23 1.19 Robustness, %RSD RSD 2% in modified condition Complies Complies Complies Mobile phase ratio plus 0.18 0.13 0.10 Mobile phase ratio minus 0.21 0.07 0.14 Flow plus 0.38 0.51 0.25 Flow minus 0.76 0.52 0.09 pH plus 1.55 1.52 0.53 pH minus 1.33 1.97 1.23 λ plus 1.21 1.46 1.27 λ minus 1.61 1.37 1.48 MAP: m-aminophenol PPD: p-phenylenediamine RES: resorcinol RSD: relative standard deviation. Figure 4. Calibration curves of (A) resorcinol, (B) p-phenylenediamine, and (C) m-aminophenol.