Determination of oxidative hair dyes using miniaturized extraction techniques and gas chromatography-tandem mass spectrometry

Three methodologies based on miniaturized solvent extraction: vortex extraction (VE), ultrasound-assisted extraction (UAE), and matrix solid-phase dispersion (MSPD), were optimized for the gas chromatography-tandem mass spectrometry analysis of seven regulated oxidative hair dyes, including some of the most frequently used sensitizers in hair products (resorcinol, RL; 1-naphthol, 1NL), as well as their banned isomers (hydroquinone, HQ; 2-naphthol, 2NL). The use of MS/MS in combination with GC is a valuable approach that had not been applied before in the analysis of the considered compounds in hair dyes formulations. Parameters influencing the extraction efficiency were optimized for the three sample preparation techniques employing real sample. 0.1 g of sample and 1 mL of organic solvent were used in all cases, which reduced the solvent consumption compared to other methods proposed in literature. Under the optimal selected conditions, three methods were validated. Good linearity (R2 ≥ 0.991, %RSD ≤ 10) was achieved in a broad range of concentrations. In general, quantitative recoveries were obtained in real samples spiked at low, medium and high concentration levels using the three extraction techniques (ranged from 71.4 to 118% with exceptions). Good method precision (%RSD ≤ 14) and LOQ ≤ 0.13 μg g− 1 were achieved in all cases. Results demonstrated that the three methods could be implemented indistinctly. In the commercial hair dye formulations analyzed, all investigated compounds but 2-naphtol were found. Thus, hydroquinone, one of the banned hair dyes according to EU Cosmetic Directive, was evidenced in at least one formulation.