Food matrix reference materials for hydrogen, carbon, nitrogen, oxygen, and sulfur stable isotope-ratio measurements: Collagens, flours, honeys, and vegetable oils - Schimmelmann, Arndt; Qi, Haiping; Dunn, Philip J.H.; Camin, Federica; Luana Bontempo; Potocnik, Doris; Ogrinc, Nives; Kelly, Simon; Carter, James; Abrahim, Aiman; Reid, Lauren; Coplen, Tyler (Journal of Agricultural and Food Chemistry, 2020)