This document covers instrumental analysis by elemental analyser-isotope ratio mass spectrometry (EA-IRMS) of food materials to determine C and/or N isotope ratios. The isotope ratios obtained by following this document are expressed as ´13C and/or ´15N values relative to international measurement standards. Sample preparation is not included within this document. It is assumed that the food sample has been pre-treated as necessary and homogenized. Similarly, the interpretation of the obtained isotope delta values is not covered by this document. Following this protocol will result only in isotope delta values for the sample materials. Solid and/or liquid sample materials can be analysed following this document. Although other instrumental techniques can be applied to determine ´13C and/or ´15N values in food materials, these other techniques are not covered by this document.