Continuous‐flow δ¹⁸O measurements: new approach to standardization, high‐temperature thermodynamic and sulfate analysis

Abstract

The continuous-flow method for the determination of the O-isotope composition of solid samples has significant advantages over off-line extraction methods, but the problem has arisen of the standardization of results that has only partially been resolved by the use of water standards. We propose a new approach to standardization that uses carbothermic reduction of calcium carbonate standards catalyzed by high-purity AgCl. Analytical accuracy, precision, variance homogeneity and long-term stability are proven. Preliminary data on the barium sulfate delta18O analyses are reported, with a closer look at the different results obtained by off-line and on-line methods on intercomparison standards NBS-127 and MSS3.

Controls on the abiotic exchange between aqueous sulfate and water under laboratory conditions

“…TC/EA measurements have reported relatively poor external precision for nitrates, sulfates, and phosphates, and can vary from 0.1‰ (1σ) to 0.6‰ (1σ) within the same laboratory (Vennemann et al 2002;Boschetti and Iacumin 2005). The 1σ analytical error reported here (0.4‰) is consistent with this range, especially as we report the standard deviation of δ 18 O SO4 on duplicate or triplicate (rather than quadruple) measurements.…”

“…The 1σ analytical error reported here (0.4‰) is consistent with this range, especially as we report the standard deviation of δ 18 O SO4 on duplicate or triplicate (rather than quadruple) measurements. There are several hypotheses for the variable performance of the TC/EA-CFIRMS (continuous flow isotope ratio mass spectrometry), including memory effects resulting from oxygen isotope exchange between newly generated CO and residual BaO from previous samples during subsequent sample analyses (Boschetti and Iacumin 2005). The buildup of memory effects was mitigated in our analytical setup by running a blank sample every ~ 12 samples.…”

“…Variations in the height of the crucible result in a greatly decreased CO yield (to a 7 5% yield- Boschetti and Iacumin 2005). This is unlikely to be problematic in the TC/EA setup used in this study, where the packing depth has been optimized over years of analyses.…”

A review on useful concepts for stable isotope of oxygen in phosphate (δ18Op) extraction, purification and analysis of freshwater samples and other potential phosphate sources

“…Resins used in this study are normally neutralized with sodium chloride and decomposed by incineration. Aqueous waste from the resin is normally neutralized and Functions of the typical components of the reduction tube and impurity trap [3,14,30,31].…”

“…Simple conversion equation is shown below [30] O from Ag 3 PO 4 s ð Þ þ C s ð Þ←→CO g ð Þ þ residuals s; l; g ð Þ An impurity trap is also attached to the instrument before passing through the GC column to remove residual gases.…”