[Determination of 40 dyes in oxidative hair dye products by high performance liquid chromatography]

Oxidative hair dye products have always been one of the key concerns in cosmetic supervision. The various aromatic amine and phenol dyes used in such products have different degrees of sensitization and toxicities. Therefore, it is necessary to establish a rapid and accurate method for the determination of various dyes. A high performance liquid chromatography (HPLC) method was developed for the determination of 40 dyes in oxidative hair dye products, and the method was optimized in terms of mobile phase type, column temperature, detection wavelength, and extraction solvent concentration. The sample pretreatment method was as follows: weighed 0.5 g sample accurately, added to 10 mL of sodium bisulfite solution containing 70% ethanol, extracted by ultrasonication for 15 min, added to 25 mL of the sodium bisulfite solution. Chromatographic separation was carried out on a Waters Atlantis^® T3 MV Kit column (250 mm×4.6 mm, 5 μm) by gradient elution. To protect the column, the sample solution was filtered using a syringe filter with a 0.45-μm membrane before injection. The mobile phase was 0.02 mol/L ammonium acetate aqueous solution (containing 4% acetonitrile) and acetonitrile. The column temperature was varied between 30 ℃ and 35 ℃ during the separation. The dyes were detected using a photodiode array detector. The detection wavelength of 31 dyes was 235 nm, and that of the other nine dyes was 280 nm. The external standard method was used for quantitative analysis. The results showed that the 40 dyes could be separated well. All the dyes had good linearities in their own concentration ranges, with correlation coefficients (r) exceeding 0.999. The limits of detection (LODs) of the 40 dyes ranged from 5 to 168 μg/g, and the limits of quantification (LOQs) ranged from 16 to 504 μg/g. The average spiked recoveries at three levels (2.5, 5.0, and 10 mg/g) of the 40 dyes ranged from 81.4% to 109.6%, with relative standard deviations (RSDs) less than 5%. The stability of each dye in the standard solutions was good within 24 h, with RSDs ranging from 0.2% to 2.2%. To demonstrate the applicability of the method, 12 batches of commercial oxidative hair dye products from different manufacturers were analyzed. In total, 24 kinds of dyes were detected in the 12 batches of samples, and the contents of these dyes ranged from 0.01% to 2.83%. The method greatly increased the types of dyes detected by a single chromatography step, especially the permitted dyes (36 types). Compared with the standard method of Safety and Technical Standards for Cosmetics (2015 edition), this method replenished 13 permitted dyes: 1-hydroxyethyl 4,5-diaminopyrazole sulfate, hydroxyethyl-p-phenylenediaminesulfate, tetraaminopyrimidine sulfate, 2,6-dihydroxyethylaminotoluene, 2-amino-6-chloro-4-nitrophenol, 2-methyl-5-hydroxyethylaminophenol, 3-nitro-p-hydroxyethylaminophenol, 4-hydroxypropylamino-3-nitrophenol, 5-amino-4-chloro-o-cresol, 5-amino-6-chloro-o-cresol, HC yellow No. 2, hydroxybenzomorpholine, and hydroxyethyl-2-nitro-p-toluidine. The sensitivity and accuracy of the results could ensure and the detection efficiency could be improved through validation of the method. The developed method is suitable for the determination of various dyes in oxidative hair dye products and can provide an effective technical means for the supervision of such products.