Determination of lawasone and paraphenylenediamine in henna tattoos and hair dyes through UPLC-PDA

Introduction: For centuries, henna with its active substance lawsone has been used in the Arab and Hindu cultures as a hair dye or as expression of body art by applying it on the hands, feet, and body. This form of pure or red henna with lawsone as active ingredient is potentially genotoxic whereas the temporary black henna tattoo has been reported to cause allergic skin reactions due to the presence of the skin sensitizer paraphenylenediamine (PPD). Aim: To develop and validate a fast UPLC-PDA method to simultaneously determine lawsone and PPD in henna tattoos and hair dyes with the purpose to evaluate their potential risk for the consumers. Material and methods: Extraction of the target molecules is performed by adding the extraction solvent MeOH to the henna sample. Hereafter, the sample undergoes ultrasonification, centrifugation and filtration before analysis with the UPLC-PDA device. A simple C18-column is used and reverse phase chromatography with a final flow of 0,3 mL/min is performed. The conducted methods are standard calibration, standard addition, Youden calibration and combining two SAC with different sample weights. Results: Applying a standard calibration method resulted in low recovery for lawsone (74,2 %). Various attempts such as an additional ultra-sonification step, extraction in three steps or extraction solvent change over resulted in optimal conditions for the method to undergo method validation. Unfortunately, due to the occurrence of peak splitting and shoulder formation and the reoccurrence of low recoveries for lawsone and PPD, no method validation could be conducted. Due to the occurrence of matrix adsorption effect, a standard addition method was performed whereby the matrix effect was, however, not eliminated. Therefore, another method to determine the sample composition was approached, namely combining SAC and YC or combining two SAC with different sample weights. When comparing the calibration lines of SAC and SAC’, two non parallel lines were obtained, indicating that the matrix effect was not constant and can be considered as an incorrigible error. Conclusion: Due to the matrix interference that is considered as an incorrigible error, the method is not developed or validated. In the future, the analyst should try to identify the interferent and develop a method that results in separate signals for the interferent and the analyte.