| Hair dye is one of the most common cosmetics. Oxidation hair dye is the most widely used type of dyes because of its good dyeing effect,long maintaining time and wide range of their colors. The active ingredients of oxidation hair dyes are aniline and phenol substances,which may cause skin damage, cancer, and has genetic toxic effect on the individual, and will impair people’s health. As a result, the content of dyes in the oxidation hair dyes should be limited. Reverse-phase high-performance liquid chromatography is the most important method to determine the aniline and phenol substances because of its good resolution, fast analysis speed and high sensitivity. <Hygienic Standard for Cosmetics> of our country provide 93 dyes which are permitted to use temporarily and their limitation. But only 8 dyes have the Determination method which is using the HPLC. China Food and Drug Administration issue a method that determining 32 banned and restricted components in hair dyes, but the reproducibility and durability of this method is inferior,its sensitivity is low too. This paper was carried out to rebuild this method to meet the need of the hair dye determination.It has always been a difficult issue in RP-HPLC to separate the acidoid and alkaline substance. The acidoid and alkaline substance ionizein the mobile phase, while nearly no ionized components was reserved because of the sharply increase in the hydrophilcity of the ionized component. When the stationary phase and mobile phase was in partition equilibrium, their molecules and ions also reached ionization equilibrium.A slight p H value change could promote the change of ionization equilibrium and lead to the change of retention value. Therefore, the basic thought to change this problem is to estimate the pH range of mobile phase when the molecule was completely in a molecular state, and then divide the components with certain intersection in this range in one group,in this way, it not only could ensure the molecule is in a molecular state in ionization, but also ensures its durability and reproducibility. Generally when the alkaline substances such as aniline are in the molecular state,the solvents are also alkaline, while the bearable p H value of common C18 column is between 2 and 6, so distinguishingly bonded stationary phase column should be selected. Besides, the author also optimized the variety of buffer salt, the concentration of buffer salt, the extraction solvent and measurement wavelength,etc.A high performance liquid chromatography(HPLC) method was proposed for the determination of 32 components in hair dyes. The 32 components were divided into three groups according to the value of pKa of each component. The ZORBAX Extend C18(4.6 mm×250 mm, 5 μm)and the ZORBAX Bonus-RP C18(4.6 mm×250 mm, 5 μm) column were used. Methanol, acetonitrile and buffers which pH are equal to 7.0, 8.0and 9.0 respectively were used as the mobile phase. The flow rate was 1.0mL/min. The diode array detector was used and the detection wavelengths were 280, 230 and 250 nm. The linear range was from20μg/mL to200μg/mL with good relationship. Relative standard deviation of each component was lower than 3%. The RSDs of stability were lower than 5%. The recoveries in concentration state of 4, 10, 40mg/L werefrom 70% to 130%. The method was simple and specific with great repeatability and durability, and is suitable for the analysis of various hair dyes. |
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