Secondary ion mass spectrometry for the determination of δ37Cl: Part I. Ion microprobe analysis of glasses and fluids

A detailed technique is presented for the determination of 37Cl/35Cl in natural glasses by Secondary Ion Mass Spectrometry (SIMS). This technique utilizes a large format high-resolution, high-transmission ion microprobe—the Cameca IMS 1270. teral spatial resolution achieved by the microprobe is 10–20 μm—providing the capability to measure δ37Cl in very small objects, such as igneous melt inclusions, or in fine-scale zoning in other natural glasses. An overall reproducibility of individual analyses better than 1.5‰ (2σ) is demonstrated for replicates of homogeneous glass reference material. This performance is achievable in samples with as little as 100–200 ppm total Cl. echnique has also been extended to the direct determination of 37Cl/35Cl in very small (1 μl) samples of natural fluids, containing only μg quantities of Cl. Using the simple approach of first integrating the dried fluids with graphite powder, these samples can also be analyzed with an overall reproducibility better than 1.5‰ (2σ). This latter procedure is particularly advantageous in cases where the available sample supply is severely limited in quantity.