Standardization lecture

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• standards from the IAEA may come as two types: those that are set to exact values, so do not have any error associated with them (e.g. VSMOW, VPDB), and others that have an uncertainty associated with them. These latter will introduce additional uncertainty into our measurements. • in the case of nitrogen there exist no standards from the IAEA that are set to any values by definition. The nitrogen data in our lab is calibrated against two IAEA standards: USGS25 (ammonium sulphate) δ 15 N = -30.4‰ ± 0.4‰ AIR, and IAEA-305A (also ammonium sulphate) δ 15 N = 39.8‰ ± 0.25‰ AIR. We must keep these uncertainties in mind when we report the overall uncertainty for our samples. The total uncertainty is a combination of machine uncertainty (precision) and standard uncertainty (accuracy).
• there are other factors that can contribute to the quality of isotopic measurements. One extremely important one is homogeneity. This has two facets to it: (1) is your sample really a true representation of what you want to measure; and (2) is your sample well mixed so that if I take a small portion of it to measure it will agree with other analyses from that same batch of sample. Our overall precision can quickly be destroyed from a poorly homogenized sample, and the accuracy we may think we’ve obtained may be incorrect due to a poorly chosen sample (i.e. the sample does not reflect its source).
Page 1 and 2: Isotope Ratio Standardization
Page 3 and 4: • we’ve seen in class that wate
Page 5 and 6: • we generally use a two point ca
Page 7 and 8: • but these original batches were
Page 9 and 10: Uncertainty In Isotope Ratio Measur
Page 11 and 12: • mass spectrometers are used to
Page 13 and 14: • when we make our measurements w
Page 15: • standards from the IAEA may com
Page 19 and 20: • Note: many isotope laboratories
Page 21 and 22: Sample Calculation
Page 23 and 24: • Given Info from Analysis (which
Page 25 and 26: Step 1 Subtract backgrounds from si
Page 27 and 28: Step 4 Apply Boato equation to calc
Page 29 and 30: Step 5 Craig 17 O Correction δ 13
Page 31 and 32: Get lost.

Standardization lecture

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