RATIONALE: In aqueous samples compound-specific stable isotope analysis (CSIA) plays an important role. No direct method (without sample preparation) for stable nitrogen isotope analysis (δ15N SIA) of non-volatile compounds is known yet. The development of a novel HPLC/IRMS interface based on high-temperature combustion (HTC) for both δ13C and δ15N CSIA and its proof of principle are described in this study. METHODS: To hyphenate high-performance liquid chromatography (HPLC) with isotope ratio mass spectrometry (IRMS) a modified high-temperature combustion total organic carbon analyzer (HTC TOC) was used. A system to handle a continuously large amount of water (three-step drying system), favorable carrier and reaction gas mix and flow, an efficient high-temperature-based oxidation and subsequent reduction system and a collimated beam transfer system were the main requirements to achieve the necessary performance. RESULTS: The proof of principle with caffeine solutions of the system succeeded. In this initial testing, both δ13C and δ15N values of tested compounds were determined with precision and trueness of ≤0.5‰. Further tests resulted in lower working limit values of 3.5 μgC for δ13C SIA and 20 μgN for δ15N SIA, considering an accuracy of ±0.5‰as acceptable. CONCLUSIONS: The development of a novel HPLC/IRMS interface resulted in the first systemreported to be suitable for both δ13C and δ15N direct CSIA of non-volatile compounds. This highly efficient system will probably open up new possibilities in SIA-based research fields.
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