“…Two certified standards of known isotopic composition were used to quality control samples, coumarin (δ 18 O-VSMOW =15.83‰, δ 2 H VSMOW =62.56‰) and glucose penta-acetate (δ 18 O-VSMOW =23.94‰, δ 2 H VSMOW =−98.48‰), which have been calibrated against internationally recognised reference materials by Iso-Analytical (Sandbach, Cheshire, UK). Polyethylene (IAEA-CH-7) was also used for quality assurance purposes [9][10][11][12]. The principle was to use span standards which cover the range expected from the samples analysed.…”