A New Approach for the Determination of Trace Heavy Metals in Hair Dyeing Cosmetics

Abstract

Although hair does not have a vital function in humans, it is an essential body component that affects appearance and self-confidence for both men and women. Cosmetic application using chemicals to change hair color is called "hair coloring". There are many different natural and synthetic products used for hair coloring. Many different heavy metal salts are added to increase the color performances of hair dyes or as impurities. Since the harmful effects of heavy metals on human health are known, it is vital to determine the amount of heavy metals in hair dyeing products. The flame atomic absorption spectroscopy (FAAS) method is a fast, practical, and economical method that is widely used to determine heavy metals. However, it is insufficient to determine the ppb and sub-ppb concentrations directly. In addition, the complex matrices of the analyzed samples also cause difficulties in the analysis. For these reasons, separation and/or preconcentration step is needed to increase sensitivity before analysis by FAAS. In this thesis, ultrasound assisted-deep eutectic solvent based-dispersive liquid-phase microextraction (DES-UA-LPME) was developed, and the determination of ii trace elements was carried out by flame atomic absorption spectrometry (FAAS). For this purpose, deep eutectic solvent (DES) prepared from choline chloride (ChCl), and phenol (Ph) as extraction solvent, dithizone as a complexing agent, and THF as aprotic solvent were used. All parameters affecting the extraction efficiency such as pH, DES volume and composition, extraction time, dithizone amount were optimized. As a result of the optimization studies, when pH is 6.0, dithizone (3x10-3 M) volume is 500 μL, DES (ChCl: Ph) mole ratio is 1:3, DES volume is 1 mL, ultrasound application time is 3 minutes, and centrifugation time is 4 minutes, the extraction takes place with the highest efficiency. Under optimum conditions, for Cd(II), Cu(II), Pb(II), and Ni(II), the enhancement factor (EF) of 57, 50, 92, and 58, the limit of detection (LOD) of 0.7, 1.4, 2.3 and 0.8 μg L-1, the limit of quantitation (LOQ) of 2.3, 4.7, 7.6 and 2.5 μg L-1, the relative standard deviation (n= 10) of 2.3, 1.8, 1.7 and 2.7, were calculated, respectively. After optimizing the experimental conditions and evaluating the analytical features, the method was applied to hair dyes and henna samples from different brands and origins. As a result of the experiments, high recovery values were obtained with high sensitivity and accuracy, away from the matrix effect. The amounts in the selected samples are between 0.12 and 2.66 μg g-1 for Cd, 0.73 and 7.07 μg g-1 for Cu, 3.58 and 15.60 μg g-1 for Pb and 1.16 and 7.36 μg g-1 for Ni.