Simultaneous analysis of carbon and nitrogen isotope ratios by SIMS was applied for the first-time to a natural diamond from the Kelsey Lake kimberlite, State Line Distinct, Colorado (UWD-1). This
in situ procedure is faster, reduces sample size for analysis, and measures both isotope ratios from a single ~ 10 μm diameter pit, a critical advantage for zoned diamonds. The carbon isotope ratio (expressed as δ
13C
VPDB) of the bulk UWD-1 crystal, determined by the conventional combustion method in the present study, is -5.9‰ ± 0.2‰ (VPDB, 2
s). Nitrogen mass fraction ([N]) and isotope ratio (expressed as δ
15N
Air) were determined by stepwise combustion and gas-source mass-spectrometry, resulting in 553 ± 64 μg g
-1 and -6.7‰ ± 1.1‰ (Air, 2
s), respectively. Secondary ions of
12C
2-,
12C
13C
-,
12C
14N
-, and
12C
15N
- were simultaneously measured by SIMS using three Faraday cups and one electron multiplier. The spot-to-spot reproducibility of δ
13C and δ
15N values for the UWD-1 (178 spots on sixteen chips, 10 μm spots), were 0.3‰ and 1.6‰, respectively (2
s). While
12C
14N
-/
12C
2- ratios, which are an indicator for [N], varied up to 12% among these sixteen chips, such variation did not correlate with either δ
13C or δ
15N values. We propose that UWD-1 is a suitable reference sample for microscale
in situ analysis of δ
13C and δ
15N values in diamond samples.
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