Comparison between isotope ratio mass spectrometry (IRMS) and cavity ring‐down spectroscopy (CRDS) for analysing the carbon isotope ratio and detection of adulteration in coconut water

Summary This study investigated the carbon isotope ratio (¹³C/¹²C, δ 13 C in unit of parts per thousand or per mill, ‰) of different coconut water samples using elemental analysis isotope ratio mass spectrometry (EA‐IRMS) and combustion module cavity ring‐down spectroscopy (CM‐CRDS). Natural coconut water from young coconuts from 12 provinces in Thailand ( n = 94), adulterated coconut water containing three sweeteners (sucrose, glucose and fructose) at different concentrations and eight brands of commercial coconut water were analysed. The δ 13 C of all samples were not significantly different ( P > 0.05) between the EA‐IRMS and CM‐CRDS analyses. The natural coconut water (C3 plant) had δ 13 C ranging from −21.58‰ to −27.79‰ (mean −24.64 ± 0.91‰). Three sweeteners (C4 plant) contained δ 13 C between −11.46‰ to −13.16‰. The use of δ 13 C determination can detect adulteration of a singular extraneous sweetener (either glucose or sucrose) down to a level of 2% of adulteration. For the detected δ 13 C values of commercial products labelled as ‘no added sugar’, about 50% of products were adulterated. This study demonstrates that CM‐CRDS can be used as an alternative analytical platform to EA‐IRMS for detecting adulterated products, especially coconut water.