Analysis of lichen phenolics as environmental stress indicators by liquid chromatography coupled to mass spectrometric and UV-VIS diode array detectors

Abstract

Lichens that are under environmental stress undergo changes in their metabolism and biochemistry. The most interesting compounds that are involved in this response are the lichen phenolics. Changes in the relative amounts of these compounds might indicate differing levels of environmental stress, such as ultraviolet light exposure and ground level ozone. Semi-quantitative analysis of dried and ground lichen samples was performed on an Agilent 1100 series LC-MS using reversed phase liquid chromatography with ESI-MS and UV diode array detection. -- Cladina mitis and Cladina rangiferina exposed to differing exposures of ultraviolet light were obtained from Ontario. Usnea dasypoga and Bryoria trichodes were collected from different sites with varying ground level ozone exposure in New Brunswick. Changes in the relative amounts of lichen phenolics such as usnic acid, atranorin and fumarprotocetraric acid were of interest as these compounds have demonstrated ultraviolet absorption in the UV-B wavelengths and/or antioxidant properties. These compounds may be involved in a defensive response of the lichen to environmental stress. -- A method of analysis was developed that requires neither a chemical derivatization step nor a pre-concentration step. This method improvement simplifies the analytical method, shortens analysis times and removes the necessity for the use of toxic reagents. These improvements increase the viability of this method for use as a future pollution monitor in rural and undeveloped areas.