The analysis of the samples was performed by the IRMS system (Isoprime100, connected to the elemental analyzer “vario PYRO cube”) of the Plant Production laboratory of the Department of Food Science and Technology at the University of Patras. This elemental analyzer operates with a combustion system for N, C and S analysis, providing content determination for these elements.

The combustion system consists of two reactors (combustion and reduction) and a system of two “purge and trap” columns (for SO₂ and CO₂). To avoid overlap of the Ν₂ peak with that of CO₂ in IRMS, a suitable column adsorbs the CO₂ and sends it for analysis after the Ν₂ elution. MS analysis provides isotopic ratio of N, C and S stable isotopes.

In the collected samples, stable isotopic ratio measurements were performed by mass spectrometry (Isotope Ratio Mass Spectrometry-IRMS). In particular, the ratio of stable isotopes ¹³C/¹²C, ¹⁵N/¹⁴N and ³⁴S/³²S was determined in each sample.