Headspace Loss Calculator

When a sample bottle is sealed with even a few millilitres of trapped air, dissolved gases redistribute between the oil and the headspace until they reach thermodynamic equilibrium. The fraction that ends up in oil is governed by the Ostwald solubility coefficient and the volumes of the two phases — and the loss is selective, not uniform.

This tool implements the partition equation directly. Sample Volume is the total bottle capacity; the headspace $V_{G}$ is a sub-volume of it, and $V_{L} = Sample - V_{G}$ is the oil that remains. Adjust the controls below to see how much of each gas the lab actually sees at equilibrium, and where the diagnostic damage starts to show.

Gas species

Sample Volume — total bottle capacity100 mL

V_{G}

— air gap above the oil5.0 mL

V_{L}

—

V_{L} = Sample - V_{G}

95.0 mL

True concentration (μL/L)

Partition equation

f_{oil} = \frac{k _{O} \cdot V _{L}}{k _{O} \cdot V _{L} + V _{G}} = \frac{0.0556 \cdot 95.0}{0.0556 \cdot 95.0 + 5} = 0.5137

fraction in oil at equilibrium

f_{lost} = 1 - f_{oil} = 0.4863

fraction lost to headspace

H₂,

k_{O}

= 0.0556

True value

100.0 μL/L

Measured value

51.4 μL/L

-48.63 %

|Δ| > 5 % — fingerprint will shift across zone lines

k_{O}

values from IEC 60567:2023 Annex A Table A.1

k_{O}

values for the nine fault gases are taken from IEC 60567:2023 Annex A Table A.1. The partition equation follows the mass-conservation derivation in ASTM D3612-02 (Reapproved 2026), §27.1, equations (14)–(17); the equivalent back-correction form is given in IEC 60567:2023, Annex D.

Continue to the multi-gas Duval drift tool to see how a real fault fingerprint shifts across Triangle 1 and Pentagon Unified zones when multiple gases partition together.

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