# Determination of gas-liquid partition coefficients by automatic equilibrium headspace-gas chromatography utilizing the phase ratio variation method

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## Summary

The new phase ratio variation method is described which represents a convenient way for the determination of gas-liquid partition coefficients for practical purposes, utilizing equilibrium headspace-gas chromatography (EHS-GC). This method is based on the relationship between reciprocal peak area and the phase ratio in the vial containing the sample solution; it involves regression analysis of the EHS-GC measurements of a number of sample vials containing the same sample solution but with a wide variation of phase ratios. Examples are given for both aqueous systems and systems consisting of a stationary (liquid) phase used as the solvent; comparison of the measured values with results obtained by other methods shows satisfactory agreement. A critical discussion of the conditions influencing the accuracy of the analytical results is given.

## Key Words

Gas chromatography Equilibrium headspace sampling Partition coefficient determination Theory of chromatography## Acronyms and Symbols

- EHS
equilibrium headspace (sampling)

- GC
gas chromatography

- GLPC
gas-liquid partition chromatography

- HS
headspace (sampling)

- MHE
multiple headspace extraction

- VPC
vapor-phase calibration method for determination of the partition coefficient (EHS-GC)

- a
intercept of Eq. (20)

- a′
intercept of Eq. (27)

- a″
intercept of Eq. (30)

- A
peak area obtained when analyzing an aliquot of the gas phase (headspace) of the sample vial, in equilibrium with the sample (EHS-GC)

- A
_{1}, A_{2} peak area obtained in EHS-GC measurements corresponding to vials with respective phase ratios of β

_{1}and β_{2}- b
slope of Eq. (20)

- b′
slope of Eq. (27)

- b″
slope of Eq. (30)

- c
_{G}^{*} concentration of the analyte in the gas phase (headspace) of vial, at equilibrium (EHS)

- c
_{L}^{*} concentration of the analyte in the stationary (liquid) phase, at equilibrium

- c
_{M}^{*} concentration of the analyte in the mobile phase, at equilibrium

- c
_{S} concentration of the analyte in the original sample (solution) in the sample vial (EHS)

- c
_{S}^{*} concentration of the analyte in the sample phase (solution) in the sample vial, at equilibrium (EHS)

- f
_{i} proportionality factor

- j
carrier gas compressibility correction factor (GC)

- k
retention factor (capacity ratio) of the analyte

- K
partition coefficient (distribution constant) of the analyte

- m
_{L}^{*} amount of analyte present in the stationary (liquid) phase, at equilibrium

- m
_{M}^{*} amount of analyte present in the mobile phase, at equilibrium

- r
correlation coefficient of linear regression calculation

- r
_{c} inner radius of the chromatographic column

- t
_{M} hold-up time (retention time of a non-retained compound)

- t
_{R} retention time of the analyte

- t
_{R}^{′} adjusted retention time of the analyte

- T
absolute temperature

- V
_{G} volume of the gas phase in the column (GC); volume of the gas phase (the headspace) in the sample vial (EHS)

- V
_{L} volume of the stationary (liquid) phase in the chromatographic column

- V
_{M} volume of the mobile phase in a chromatographic column in general; gas hold-up volume (retention volume of a non-retained compound) in GC)

- V
_{R} retention volume of the analyte

- V
_{R}^{′} adjusted retention volume of the analyte

- V
_{S} volume of the sample solution introduced into the vial (EHS)

- V
_{V} total volume of the vial (EHS)

- W
_{L} amount of the stationary (liquid) phase in the column

- β
phase ratio of the chromatographic column (GC, LC); phase ratio of the sample vial (EHS)

- β
_{1}, β_{1} maximum and minimum phase ratio values of a series of sample vials containing the same sample solution but in different volumes (EHS-GC)

- π
_{L} density of the stationary (liquid) phase at column temperature

- Φ
_{S} sample phase fraction in the headspace vial (EHS)

- *
asterisk refers to equilibrium conditions

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## References

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