Combined ¹³C and ¹⁵N isotope analysis on small samples using a near-conventional elemental analyzer/isotope ratio mass spectrometer setup.

RATIONALE

A high sensitivity elemental analyzer/isotope ratio mass spectrometer setup was developed to allow analysis of (13)C and (15)N isotopic composition on microgram amounts of C and N, respectively.

METHODS

Increased sensitivity of a conventional elemental analyzer equipped with a low blank autosampler was obtained by decreased carrier gas flow of 35 mL/min. The diameters of the oxidation and reduction reactors and water trap were reduced to 7.8, 7.8 and 4 mm i.d., respectively, to obtain sharp sample peaks in the mass spectrometer. To increase the lifetime of the reduction reactor, a 1:1 He/O2 mixture was used as oxidizing agent in the elemental analyzer.

RESULTS

Sample amounts of 0.6 µg N and 1 µg C were sufficient for accurate isotopic analysis with <1 ‰ standard error after blank correction. One major advantage of the setup is the easy switching between conventional EA and μEA as only consumable parts need to be exchanged.

CONCLUSIONS

The proposed setup proved to be suitable to analyze minute amounts of C and N in one analytical run simultaneously.