Isotope reference · free tool

Isotope standards conversion

Bring a δ value measured against one standard onto the scale of another, using the published offsets between the two: the page gives the converted value, its propagated uncertainty and the source of each offset. When no published calibration links two standards, it says so and computes nothing.

Free, no accountEvery offset sourcedUpdated with the Atlas

Convert a value Browse published offsets

For each conversion

The converted value, from the exact formula, with its difference from the additive approximation.
The propagated uncertainty, in your convention, 1σ or 2σ, and the share of each term.
The source of each offset, with its full reference and DOI.
Validity conditions: lot or bottle, natural material used as a reference, change of isotope ratio.
A reasoned refusal when an offset is missing or was published without an uncertainty.

Converter

Bring a value from one standard to another

Choose the system, your isotope ratio and the two standards. Each measured lot or bottle is a separate entry: pick the one you use.

Isotope system

Your system is not listed? Systems without calibration

Measured ratio

Defaults to the ratio of the published calibrations.

Source standard

Target standard

Measured value

Uncertainty

Convention

Without a value, the page gives the offset between the two standards.

The converter needs JavaScript.

Method

What the calculation does

A published calibration, or nothing

The name of a standard says nothing about its composition. Two bottles of SPEX PLSN5 tin solution carrying the same lot number were measured 0.26 ‰ apart in δ122/118Sn, while lots of the same maker's CLSN2 range are identical to each other (Meister et al., 2026).

The page therefore links two standards only through measured and published offsets, each referred to the scale zero of its system. Without a published offset, it gives no value.

The exact formula

δ_B = (δ_A + a + δ_A·a/1000 − b) / (1 + b/1000)

a and b are the values of standards A and B on the common scale. This is the composition of isotope ratios, set out by Meister et al. (2026, equation 6). The usual additive form δ_A + a − b departs from it by about δ·a/1000: negligible for offsets of a few tenths of a per mil, noticeable for offsets of several per mil, as between V-PDB and V-SMOW.

The propagated uncertainty

u = √(u_measurement² + u_a² + u_b²)

Each uncertainty is brought to one standard deviation: a published 2SD or 2SE is halved, an expanded uncertainty divided by its coverage factor k. It is weighted by the derivative of the exact formula, then returned in your convention.

The two offsets are treated as independent; when they come from the same study, the uncertainty is probably overestimated. A reproducibility 2SD is read as two standard deviations, the usual reading, which remains narrower than a full calibration uncertainty.

Changing isotope ratio

(1 + δ_j/1000) = (1 + δ_i/1000)^β, β = ln(m_j/m_j′) / ln(m_i/m_i′)

If you measure another ratio than the calibrations, 122Sn/118Sn instead of 124Sn/116Sn for instance, the offsets between standards are carried over with the mass-dependent fractionation law (Wombacher and Rehkämper, 2004), exponential or equilibrium. Only those offsets are transformed, never your value: a mass-independent anomaly it may carry, such as Δ199Hg or Δ33S, stays intact. The page shows what the other law would give.

References: Meister, A.C.E. et al. (2026). A Common Reference Material for Mass-Dependent Sn Isotope Compositions: An Inter-Laboratory Calibration Approach. Geostandards and Geoanalytical Research, 50(2), 341-367. doi:10.1111/ggr.70035. Wombacher, F. and Rehkämper, M. (2004). Problems and Suggestions Concerning the Notation of Cadmium Stable Isotope Compositions and the Use of Reference Materials. Geostandards and Geoanalytical Research, 28(1), 173-178. doi:10.1111/j.1751-908x.2004.tb01054.x.

Published offsets

The standards, one by one

Each standard with its value on the scale of its system's zero, the uncertainty as published and the source. Notes on each standard are in French.

Systems and standards with no conversion offered

These systems and standards appear in Atlas records, but no published offset links them to another standard in the database: the page offers no conversion for them. Radiogenic ratios (lead, strontium, neodymium, osmium) call for a different approach, renormalisation to the reference value of the standard.

Frequently asked questions

Converting between standards

Can a value be converted between two standards without a published calibration?

No. The name of a standard says nothing about its isotopic composition: two bottles of SPEX PLSN5 tin solution carrying the same lot number were measured 0.26 ‰ apart in δ122/118Sn (Meister et al., 2026). The page links two standards only through measured and published offsets; when none exists, it says so and computes nothing.

Which formula does the page use?

The exact composition of ratios: δ target = (δ + a + δ·a/1000 − b) / (1 + b/1000), where a and b are the values of the two standards on the common scale. The additive approximation δ + a − b is given as well, with its difference from the exact formula.

How is the uncertainty propagated?

As the quadratic sum of your measurement uncertainty and those of the two published offsets, all brought to one standard deviation and returned in your convention, 1σ or 2σ. The two offsets are assumed independent, which usually overestimates the uncertainty when they come from the same study.

My standard is not listed: what can I do?

No published offset then links it to the scale in the database, and the page offers no conversion. Measuring a listed standard, or a shared reference material, in the same session gives the missing offset. If we have missed a published calibration, write to colin.ferrari@isofind.tech.

I measure δ122/118Sn and the database gives δ124/116Sn: is that a problem?

No. Choose your ratio in the converter: the offsets between standards are carried over with the mass-dependent fractionation law, and your value itself is not transformed. For tin, the inter-calibration of Meister et al. (2026) is published as δ122/118Sn; with the exponential law, the converter gives back the published values, to rounding.

Is the standards conversion free?

Yes, with no account. Atlas access adds conversion of a series of values, notation changes, renormalisation of a radiogenic ratio and export; the Atlas sample comparison brings published ranges to your standard by itself.

Cite this page

IsoFind. Isotope standards conversion. Ferrari, C. (ed.). https://www.isofind.tech/en/standards-conversion/ (accessed [date]).

Please also cite the publication behind each offset you use: the result copied from the converter lists the references.

From published values to your sample

Converting a single value is free. Inside the Atlas, the sample comparison brings published ranges to your standard by itself, and Atlas access adds batch conversion, notation changes and export.

Open IsoFind Atlas About the Atlas Isotope reference