Fast combustion digestion for determination of halogens in makeup for eye region by ion chromatography

Halogen determination in cosmetics is challenging due to the relatively high complexity, consisting of water and solvent-based ingredients, waxes, resins, inorganic compounds, and colorants. These analytes may also form volatile species during the sample preparation step. Most studies focus on metal determination in cosmetic products, typically using acid digestion methods, which are unsuitable for the determination of halogens. Alternative extraction methods have been used, but they do not ensure full analyte recovery. Thus, there is a clear need for suitable methods for this purpose. The present study introduces a novel multielement method for halogen determination in eyelash mascara and liquid eyeliner.

Combining a single and effective sample preparation method by microwave-induced combustion (MIC) and ion chromatography with conductivity detection coupled to mass spectrometry (IC-CD-MS), it was possible to determine Br, Cl, F, and I. Using the optimized conditions (500 mg of sample, 50 mmol L^-1 NH₄OH as absorbing solution, and 5 min reflux), recoveries for all analytes ranged from 90 to 109% in both recovery tests (using standard solutions and certified reference materials). Suitable precision (RSD < 10 %) and low limits of detection (Cl: 10 mg kg^-1; F: 3 mg kg^-1 using conductivity detection, and Br: 1 mg kg^-1; I: 0.1 mg kg^-1 using mass spectrometry detection) were achieved. The analysis of eyelash mascaras and liquid eyeliners revealed significant variation for the concentration of Br (< 1 to 91 mg kg^-1), Cl(< 10 to 9760 mg kg^-1), F (< 3 to 1130 mg kg^-1), and I (< 0.1 to 40 mg kg^-1).

This study pioneers the combination of MIC and IC-CD-MS for determining halogen in semi-solid cosmetics, offering advantages such as lower volume of reagents and high efficiency of digestion with virtually no interferences. These conditions allowed the analysis of eyelash mascaras and liquid eyeliners from diverse origins, colors, and brands, highlighting the need for accurate quality control in cosmetics, particularly in the assessment of these "unconventional" elements.