RESUMEN
We determined δ11B values of green and roasted coffee beans from 20 locations worldwide and conducted laboratory experiments with the aim to investigate boron isotope fractionation during roasting. Authentic single origin roasted coffees were found to be isotopically lighter than their green bean counterparts, with an average difference of 1.5. This isotope fractionation can be explained as arising from partial dissociation of boric acid in capillary water of green beans, where 11B isotopes are preferentially partitioned into molecules of undissociated boric acid and are then volatised during roasting. However, boron isotope fractionation induced by roasting was significantly smaller than between-origin variations in δ11B values of green coffee beans that had the range of â¼54. This implies that δ11B isotopic composition of roasted coffee retains the geographical origin information within δ11B values of green beans when regional differences in boron isotopic composition of coffee are considered.
Asunto(s)
Coffea , Boro , Isótopos , Semillas , CalorRESUMEN
This article overviews recent developments in the use of multicollector inductively coupled plasma mass spectrometry (MC-ICPMS) in studies of mass-independent isotope chemistry of heavy elements. Origins of mass-independent isotope effects and their relevance to isotope ratio measurements by MC-ICPMS are briefly described. The extent to which these effects can affect instrumental mass bias in MC-ICPMS is critically discussed on the basis of the experimental observations. Furthermore, key findings reported in studies of mass-independent isotope fractionation (MIF) of mercury in the field of environmental sciences are reviewed. MIF of heavy elements is not only of interest from a fundamental point of view, but also provides scientists with a new and effective means of studying the biogeochemistry of these elements.