APPLICATION OF PURPALD® FOR DETERMINATION OF CARBOXALDEHYDES 397 the blank solution. The infl uence of different solvents (methanol, ethanol, water, dioxane, and acetone) on Purpald® solution was studied. The aim was to choose one that does not change color of the blank solution, and the absorbance of this solution is low. The lowest absorbance value was measured for the sample diluted with water, so we used this solvent during the preparation of samples for calibration curve. However, satisfactory results were not achieved. The absorbance–concentration of the aldehyde relationship did not show the linear dependence. The reason could be the fact that water does not stop the derivatization reaction as opposed to organic solvents. Therefore, ethanol was chosen as the suitable solvent. The value of absorbance for the blank solution containing this sol- vent was lower than that for the sample diluted with methanol. The samples diluted with dioxane and acetone were strongly colored in purple and yellow, respectively. The method was validated on the basis of the following parameters: linearity, precision, solution stability, and accuracy. LINEARITY The working standard of aldehydes was obtained according to experimental part. The reaction mixture was incubated at room temperature for 45 min, the reaction was stopped by adding ethanol and the absorbance was measured at 538 nm. The reference cuvette contained identical concentration of sodium hydroxide and Purpald® solution. The anal- ysis showed that the absorbance obeys Beer’s law in the range of 2.5 × 10−5 to 3.0 × 10−4 mol·l-1 (0.250–3.00 μmol) for 3-cyclohexene-1-carboxaldehyde and 2.0 × 10−5–2.0 × 10−4 mol·l-1 (0.10–1.00 μmol) for hydroxyisohexyl 3-cyclohexene carboxaldehyde. Figure 5. The infl uence of sodium hydroxide solution concentration on the absorbance value caldehyde = 4.0 × 10−4 mol·l−1, cPurpald®=1.0 × 10−2 mol·l−1.
JOURNAL OF COSMETIC SCIENCE 398 A = 0.1355c 0.0017 for 3-cyclohexene-1-carboxaldehyde and A = 0.1525c 0.0489 for hydroxyisohexyl 3-cyclohexene carboxaldehyde were the equations achieved at the least squared regression, with A being the absorbance (AUS) and c the concentration of aldehyde (μmol·l-1). Standard curves consistently gave r2 values above 0.999 within a calibration range of the analyte. The molar absorptivity under our measuring conditions was calculated as 1.36 × 103 l·mol-1·cm-1 for 3-cyclohexene-1-carboxaldehyde and 1.52 × 103 l·mol-1·cm-1 for hydroxyisohexyl 3-cyclohexene carboxaldehyde, which was determined from the linear part of the aldehyde concentration. PRECISION AND ACCURACY The method was found to be highly precise (Table I). Intra-batch coeffi cient of variation at 2.5 × 10−5, 1.0 × 10−4, and 3.0 × 10−4 mol·l−1 (n = 6) was noted to vary between 2.8% and 3.4%. The precision and accuracy results based on absorbance ratios with good recov- eries were obtained. There were no signifi cant differences between the added amounts of aldehydes and the amounts found. INTERFERENCES Although all the aldehydes are potential interference in the determination of 3-cyclohexene carboxaldehydes by Purpald®, literature has shown that structural differences in the prod- ucts formed by different aldehydes lead to variations in their spectra (23,24). The impor- tant advantage of this reagent is its sensitiveness and specifi city for aldehydes. Purpald® Figure 6. The infl uence of Purpald® solution concentration on the absorbance value caldehyde=4.0 × 10−4 mol·l−1, cNaOH=1.0 mol·l−1.
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