A novel high-temperature combustion interface for compound-specific stable isotope analysis of carbon and nitrogen via high-performance liquid chromatography/isotope ratio mass spectrometry

Abstract

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 system reported 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.