Gas chromatographic-mass spectrometric analysis of the lipid layer of human skin. The express approach and its application prospects

The development of new methods for the analysis of chemical markers in biological fluids is an urgent area of research, because it is focused on solving socially significant tasks related to healthcare, chemical safety of the population, and countering terrorism. In this regard, new methods for the analysis of metabolites and exogenous substances in the body using alternative biological fluids available for non-invasive sampling are being actively studied and developed. In this paper, the authors present the results of developing and testing an approach for express determination of micro concentrations of volatile organic substances in the lipid layer of human skin by gas chromatography/mass-spectrometry (GC/MS) using a simple procedure of non-invasive sampling without a sample preparation stage. Samples of the lipid layer were collected using adhesion arising from mechanical contact of a metal carrier made of a piece of wire with the skin’s surface, and were analyzed without any additional sample preparation. A field chromatograph-mass-spectrometer with a custom made attachment for introducing samples with flash thermal desorption, previously designed by the authors, was employed for performing analyses. The qualitative composition of trace impurities in the lipid layer of the skin was characterized in the samples collected from 25 donors during the approbation of the method; identified impurities included technological additives to common plastics, psychoactive substances, medicines. It was shown that the impact of sample size variability during sampling on the repeatability of analytical results can be significantly reduced by using one of the main matrix components (e.g., squalene, oleic or palmitic acid) as an internal standard. The analysis time, including sample preparation, did not exceed 15 minutes. The feasibility of using the proposed approach for therapeutic drug monitoring with a 5-minute analysis frequency was demonstrated using caffeine as an example. An increase in caffeine content in the skin lipid layer (relative to oleic acid) in the range of 0.02 % to 2 % was experimentally observed after consumption of caffeine; the pattern of concentration changes differs significantly for different modes of consumption.