High‐temperature reversed‐phase liquid chromatography coupled to isotope ratio mass spectrometry

Abstract

Compound-specific isotope analysis (CSIA) by liquid chromatography coupled to isotope ratio mass spectrometry (LC/IRMS) has until now been based on ion-exchange separation. In this work, high-temperature reversed-phase liquid chromatography was coupled to, and for the first time carefully evaluated for, isotope ratio mass spectrometry (HT-LC/IRMS) with four different stationary phases. Under isothermal and temperature gradient conditions, the column bleed of XBridge C(18) (up to 180 °C), Acquity C(18) (up to 200 °C), Triart C(18) (up to 150 °C), and Zirchrom PBD (up to 150 °C) had no influence on the precision and accuracy of δ(13) C measurements, demonstrating the suitability of these columns for HT-LC/IRMS analysis. Increasing the temperature during the LC/IRMS analysis of caffeine on two C(18) columns was observed to result in shortened analysis time. The detection limit of HT-RPLC/IRMS obtained for caffeine was 30 mg L(-1) (corresponding to 12.4 nmol carbon on-column). Temperature-programmed LC/IRMS (i) accomplished complete separation of a mixture of caffeine derivatives and a mixture of phenols and (ii) did not affect the precision and accuracy of δ(13)C measurements compared with flow injection analysis without a column. With temperature-programmed LC/IRMS, some compounds that coelute at room temperature could be baseline resolved and analyzed for their individual δ(13)C values, leading to an important extension of the application range of CSIA.

A novel high‐temperature combustion based system for stable isotope analysis of dissolved organic carbon in aqueous samples. I: development and validation

“…Barbituric acid, melamine and humic acid were analyzed as model compounds that are resistant to oxidation, and thus potentially affecting DOC and SI analyses . We found a recovery rate of ≥99%, proving complete oxidation.…”

Reference materials selection for the stable carbon isotope analysis of dissolved carbon using a wet oxidation system

“…However, note that these highly oxidative conditions may significantly reduce the lifetime of the filament in the mass spectrometer. This problem can be reduced by using an oxygen scrubber online directly from the helium stream with the sample before it is introduced into the ion source of the mass spectrometer …”

“…This problem can be reduced by using an oxygen scrubber online directly from the helium stream with the sample before it is introduced into the ion source of the mass spectrometer. 13,23 For all analyses, the same concentrations of reagents were used:…”

Current challenges in compound-specific stable isotope analysis of environmental organic contaminants

“…As a first example Godin et al used temperatures up to 170°C to separate hydrosoluble fatty acids and phenolic acids via a very hydrophobic porous graphitic carbon column [130]. Because commercially available columns often do not support these temperatures [130], Zhang et al investigated four different stationary phases and showed that under isothermal and temperature gradient conditions, column bleed had no effect on the precision and accuracy of d 13 C values [131]. These results are promising for compound-specific isotope analysis of polar organic contaminants by hightemperature LC-IRMS.…”