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Publication - Professor Richard Evershed

    Practical considerations in high-precision compound-specific radiocarbon analyses

    eliminating the effects of solvent and sample cross-contamination on accuracy and precision

    Citation

    Casanova, E, Knowles, T, Williams, C, Crump, M & Evershed, R, 2018, ‘Practical considerations in high-precision compound-specific radiocarbon analyses: eliminating the effects of solvent and sample cross-contamination on accuracy and precision’. Analytical Chemistry.

    Abstract

    Preparative capillary gas chromatography (pcGC) is widely used for the isolation of single compounds for radiocarbon determinations. While being effective at isolating compounds, there are still genuine concerns relating to contamination associated with the isolation procedure, such as incomplete removal of solvent used to recover isolated samples from the traps and cross-contamination, which can lead to erroneous 14C determinations. Herein we describe new approaches to identifying and removing these two sources of contamination. First, we replaced the common “U” trap design, which requires recovery of compounds using organic solvent, with a novel solventless trapping system (STS), consisting of a simple glass tube fitted with a glass wool plug, allowing the condensation of isolated compound in the wool and their solventless recovery by pushing the glass wool directly into a foil capsule for graphitization. With the STS trap, an average of 95.7 % of the isolated compound was recovered and contamination from column bleed was reduced. In addition, comparison of 14C determinations of fatty acid methyl ester (FAME) standards determined offline to those isolated by pcGC in STS traps showed excellent reproducibility and accuracy compared to those isolated using the traditional “U” traps. Second, “cold-spots” were identified on the instrument, i.e. the termini of capillaries in the preparative unit, which can be cleaned of compounds condensed from earlier runs using a heat gun. Our new procedure, incorporating these two modifications, was tested on archaeological fat hoards, producing 14C dates on isolated C16:0 and C18:0 fatty acids statistically consistent with the bulk dates of the archaeological material.

    Full details in the University publications repository