Highly Sensitive Method for Determination of Mineral Oil Aromatic Hydrocarbons in Cosmetics by Preparative Liquid Chromatography Combined with On-line Liquid Chromatography-Gas Chromatography

Mineral oil is an important ingredient in cosmetics, with its main component being mineral oil saturated hydrocarbons (MOSH). The presence of residual mineral oil aromatic hydrocarbons (MOAH) can pose health risks, thus drawing significant attention. However, the high proportion of MOSH makes the analysis of trace amount of MOAH in cosmetics very difficult, even with the use of on-line high performance liquid chromatography coupled with gas chromatography (LC-GC). In this study, a highly sensitive detection method for MOAH in cosmetics was established by combining preparative liquid chromatography (Prep-LC) with LC-GC. Firstly, ethanol and n-hexane were used for extraction, followed by addition of water to achieve phase separation and obtain the mineral oil extract. The extract was then subjected to pre-purification and injected into the Prep-LC separation. Prep-LC employed a pure silica gel column (250 mm x 10 mm, 5 mu m) with a mobile phase of n-hexane- dichloromethane binary solvent system. Through gradient elution, MOSH above 2 mg was separated and removed, resulting in the preparation of high purity MOAH. The MOAH prepared using Prep-LC was confirmed to be free from MOSH interference through LC-GC and comprehensive two-dimensional gas chromatography hyphened with time-of-flight mass spectrometry (GC x GC-TOFMS). Finally, the collected MOAH was concentrated and injected into LC-GC for quantification. Methodological investigation demonstrated that the quantitative limit of this method was 10 mg/kg, with recoveries of 82.0%-100.8% and RSD of 3.6%-7.3%. Using this method, 15 kinds of commercially available lipsticks and lip balms were tested, and MOAH was detected in four samples, with concentrations ranging from 204 to 1460 mg/kg. This study provided an accurate and reliable method for the routine detection of trace amounts of MOAH in cosmetics.