Evaluation of Cortisol Levels in Artificial Saliva by Paper Spray Mass Spectrometry

Abstract

Cortisol is a steroid hormone that has an important function in the regulation of many physiological and pathological processes, while its quantification in biological fluids may contribute to the diagnosis of numerous diseases. The objective of this study is to verify the use of paper spray mass spectrometry (PS-MS) to evaluate the levels of cortisol in artificial saliva. Therefore, mass spectra in the range of 100–800 m/z were acquired using a Thermo Fisher Scientific LCQ FLEET equipment equipped with a low-resolution Ion Trap mass analyzer. The presence of cortisol in artificial saliva samples was evaluated by the presence of ions 363, 385, 725 and 747 m/z, which are related to the cortisol molecule. The spectra of saliva with cortisol addition shows the presence of ions attributed to the presence of cortisol at different m/z ratios, which are not present in the spectra of pure saliva, pointing out the potential of these ions for monitoring cortisol levels. The Principal component analysis (PCA) showed groups of samples with and without cortisol addition. The loading plot explains the groups formed by the differences between m/z associated to cortisol molecule, confirming PCA analysis as a powerful qualitative method to assess cortisol levels in saliva. Finally, the ions selected to discriminate the groups formed in the PCA, named 363, 385 and 747 m/z, were suggested as markers for determining cortisol levels in saliva samples. The PS-MS showed to an efficient and promising technique to the determination of real-time salivary cortisol levels without using any sample preparation step. From a volume of only 5.0 µL of sample, placed directly on the sampler equipment, it was possible to obtain an identification of cortisol by analyzing the mass spectrum in approximately 45 s.