Browsing by Subject "rotating sample platform"

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  • Kannela, Niina (Helsingfors universitet, 2013)
    Cortisol is a vital hormone for normal bodily functions. Both physical and mental stress, as well as many diseases like the Cushing syndrome are known to increase the human cortisol levels. These levels can be measured in many biological matrixes, such as saliva. Traditionally, these measurements have been done by using immunoassays or liquid chromatographic-mass spectrometric methods (LC-MS). However, in the last few years, ambient ionization techniques, which are quick and easy to use, have also proven suitable for quantitative analysis of compounds in biological matrixes. Thus, these techniques could offer an alternative to traditional methods in the analysis of cortisol from human saliva. The aim of this study was to investigate the suitability of desorption atmospheric pressure photoionization (DAPPI) for quantitative analysis of steroids in saliva. The investigated steroids were dehydroepiandrosterone (DHEA), cortisol and testosterone. Because of the low quantities of testosterone and DHEA in saliva, the study was mainly focused on cortisol analysis. In this study, the ionization mechanism for the steroids was observed to be proton transfer with every tested spray solvent (acetone, chlorobentzene and toluene). Even though the choice of spray solvent did not change the ionization mechanism, it affected the efficiency of ionization. In cortisol measurements acetone was observed to be the best solvent. The temperature of the microchip, as well as the UV-lamp used (dc- or rf-lamp), only affected the ionization slightly. In this study, measuring cortisol in non-pretreated saliva was not successful. However, solid phase extraction (SPE) method for the pretreatment of saliva was optimized with high recovery for cortisol (106 %). The detection limit for cortisol (50 nM) in water samples and the linear area of cortisol in both water and pretreated saliva samples (500 nM - 10 µM) were also determined. Poor repeatability of DAPPI-system was the main challenge in these measurements. The DAPPI-MS-method developed in this study is suitable for analyzing cortisol in pretreated saliva samples. However, without further development it is not sensitive enough to be used in quantitative analysis of cortisol in salivary levels.