Guidelines for Sample Preparation and Stable Isotope Analysis of Food for Traceability Studies

ABSTRACT Stable isotope analysis is a powerful and increasingly applied tool for food traceability, enabling high‐confidence determination of origin, production practices, and authenticity. This guideline provides practical recommendations for the preparation and analysis of solid and liquid food samples using stable isotope techniques. Carbon, nitrogen, and sulfur isotopes are typically measured using elemental analysis coupled with isotope ratio mass spectrometry (EA‐IRMS), whereas hydrogen and oxygen isotopes due to their volatility and exchangeability are best analyzed using high‐temperature conversion elemental analysis (HTEA‐IRMS). Emphasis is placed on harmonized protocols for sample preparation, including drying, encapsulation, and homogenization, and on the use of internationally recognized isotope reference scales: Vienna Pee Dee belemnite (VPDB) for carbon, atmospheric air (AIR) for nitrogen, Vienna standard mean ocean water (VSMOW) for hydrogen and oxygen, and Vienna Canyon Diablo troilite (V‐CDT) for sulfur. Best practices for selecting and applying certified reference materials, multipoint normalization, correcting for instrument linearity, and uncertainty propagation using regression approaches are discussed. Quality control measures—such as blanks, replicates, and matrix‐matched standards—are essential to ensure reproducibility and interlaboratory comparability. These guidelines aim to standardize stable isotope methodology in food science and support users in producing accurate, defensible, and globally comparable isotopic data.