Liquid Chromatography coupled to Isotope Ratio Mass Spectrometry of Selected Polar Compounds

The analysis of light stable isotopes of organic compounds is nowadays a common tool in almost all fields of science. Geochemistry, archeology, product authenticity and ecology are only a few examples of the applicability of isotope ratio mass spectrometry. In this context it can answer questions regarding the botanical or synthetical origin of a sample constituent or help to reveal reaction mechanisms. However, due to several instrumental challenges there is still a need for analytical methods to determine compound-specific isotope ratios of thermolabile and non-volatile substances. Hence, many compound classes have not yet been studied using isotope ratio techniques. Thus, the work presented herewith focuses on the development of liquid chromatographic methods which can be used in combination with isotope ratio mass spectrometry. As analytes several sulfonamide drugs, trimethoprim and the herbicide glyphosate along with its metabolite aminomethylphosphonic acid were chosen. The developed methods were used to study environmentally relevant degradation mechanisms of these compounds. In the first part of the work, a high temperature liquid chromatography method was developed for the analysis of sulfadiazine, sulfathiazole, sulfametazine, sulfamethoxazole and trimethoprim. By the application of a high temperature gradient to a pure aqueous eluent for separation, all these compounds were fully resolved from each other on an octadecyl stationary phase. The lowest amounts necessary for a precise carbon isotopic analysis varied between 0.3 to 0.5 µg on column depending on the investigated substance. A repeatable offset of isotope ratios of 1.6 to 3.6 ‰ on the δ-scale has been observed and a careful investigation revealed an incomplete conversion of the analytes to the measured gas CO2 causing this offset. Additionally, it could be shown that the observed offsets could be corrected to obtain unbiased isotopic signatures. The applicability of the method was shown by the analysis of pharmaceutical products containing ...