CARBON REDUCTION AS A SAFE, SIMPLE, AND RAPID TECHNIQUE FOR δ18O ANALYSIS OF SILICATES AND OXIDES

Stable oxygen isotope analyses of silicates and oxides are utilized in a variety of research, but have generally been limited because these analyses require the use of extremely hazardous reagents, and also a very high level of operator skill and training. In addition, sample throughput is generally relatively slow (~25 minutes/sample), thereby limiting the development of large databases such as are common for carbonate or water analyses. A novel continuous-flow very high-temperature elemental analyzer – mass spec (high-T EA-MS) technique has been developed to perform δ¹⁸O analyses of quartz and other minerals that normally require fluorination. This technique is relatively simple, straightforward, rapid, and most importantly, eliminates the need for hazardous fluorinating reagents. Samples are reacted at temperatures up to 3000°C in a stream of helium in the presence of graphite, using a graphite-electrode furnace (otherwise known as inert gas fusion analysis) to produce CO gas which is analyzed for δ¹⁸O by continuous-flow mass spectrometry. Sample run times approach 10 minutes per analysis in manual mode. Although no attempts have yet been made to automate the technique, it appears amenable to doing so. Results to date yield an excellent correlation between δ¹⁸O analyses of SiO₂ performed by the new high-T EA-MS technique vs. a laser fluorination technique. δ¹⁸O analyses performed by both techniques have comparable uncertainties of approximately ±0.15‰ (1σ). Preliminary results from other minerals (e.g., zircon, feldspar, etc.) indicate that reactions for these minerals is also quantitative and yield data equivalent to fluorination. Method development continues, particularly the application of the new technique to analyze additional silicate and oxide minerals.