Analyses – SwissSIMS

Ion probes allow three types of analyses, in any case in solid material:

Point analysis : a stationary or rastering primary beam is used to know the composition in a point with a spot size between 5-20µm
Depth profiling: the progressive erosion of the sample surface using a scan of a small surface (raster) allows monitoring of the variations of composition as a function of depth
Imaging : an image of either elemental or isotopic variations in composition with a spatial resolution of roughly 1µm — As CASA center is equipped with a NanoSIMS instrument with a high spatial resolution, by far higher than the SIMS, we usually do not do imaging.

The measurements accuracy allowed by the IMS 1280 HR can be as low as conventional bulk technique (e.g. 2SD for oxygen isotopes is 0.2-0.3‰).

Accurate isotopic analysis requires matching of the chemical matrix composition (to a few wt%) and the unknown sample, as well as a match of the structure. Chemical variations due to solid solutions, present in many glasses and crystals, requires a series of reference materials wich cover the range in composition to be analyzed (with respect to major elements).

SwissSIMS analytical portofolio:

Material	Elements/isotopes routinely analyzed
Quartz	d¹⁸O, d³⁰Si, traces elements (Li, Al, Ti, Fe)
Glass	d¹⁸O, d⁷Li, d¹¹B, d³⁰Si, d³⁷Cl, volatile contents, dD, Mg-Al isotopes
Biotite	d¹⁸O, volatile contents
Sulfure	D³⁴S, d⁵⁶Fe
Micas	d¹⁸O, OH
Feldspars	d¹⁸O
Graphite	d¹³C
Organic matter	d¹³C, D³³S
Apatite	d¹⁸O, d³⁷Cl, d³⁴S
Calcite, dolomite	d¹³C, d¹⁸O
Olivine	d¹⁸O, d⁵⁶Fe, Mg-Al isotopes
Diamonds	d¹³C
Zircon	d¹⁸O, U-Pb dating
Monazite	d¹⁸O, U-Pb dating
Tourmaline	d¹⁸O, d¹¹B
Garnet	d¹⁸O, d⁷Li

SwissSIMS precisions for regular (~10-15µm) spot size

δ⁷Li: ± 1‰ 2SD or better for [Li] > 20 ppm
δ¹¹B: ± 1‰ 2SD or better for [B] > 20 ppm; ± 0.3‰ 2SD in tourmaline
δ¹³C: ~ ± 1‰ 2SD
δ¹⁸O: ± 0.3‰ 2SD
δ³⁰Si: ± 0.3‰ 2SD
δ³⁴S: ± 0.3‰ 2SD
δ³⁷Cl: ± 0.4‰ 2SD for [Cl] > 100 ppm
δ⁵⁶Fe: ± 0.3‰ 2SD
Cl, F, H2O: F-H2O: 0.3 – 0.6% s.e., Cl: 1% s.e. (F-OH-rich minerals)
Trace elements: ~ ± 10 %