The Sensitivity of Gas Chromatography-Headspace Solid Phase Microextraction in Relationship with Relative Volatility of Volatile Organic Compounds

Abstract

In order to explore the analytical performance of Headspace-Solid-phase Microextraction (HS-SPME), the sensitivity of gas chromatography (GC)-Mass Spectrometry (MS) determinations was examined in terms of calibration slopes, that is, response factor values of selected volatile organic compounds (VOC). The HS-SPME was applied to extract two kinds of gaseous VOC analytes, namely group I (methyl ethyl ketone, isobutyl alcohol, methyl isobutyl ketone, and butyl acetate, all having high water solubility) and group II (benzene, toluene, styrene, and xylene, all having moderate water solubility) from water solutions. The results, derived by both external and internal calibration, were then evaluated by considering headspace sample volume and solute volatility. In the case of solutes consisting of group I, sensitivity seems to increase with increasing HS size, although there are no such discernible patterns for group II solutes. The observed relative patterns in extraction efficiency may be accounted for by the differences in intermolecular forces present between the compounds of groups I and II and the possible effects of diffusion kinetics of the VOCs to the SPME fiber or competitive adsorption between different VOCs. As such, sensitivity of HS-SPME is tightly affected by the air-water partitioning properties of the target compounds and the response of SPME to such properties.

Keywords:

• Environmental air samples
• Gas chromatography with mass spectrometry
• Odorants
• Solid phase microextraction
• Volatile organic compounds

Acknowledgments

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Education, Science, and Technology (MEST) (No. 2009-0093848).

Notes

^a Acronyms for nine compounds used in this study.

^b Source (R. Sander, 1999): H = C_gas/C_aq (dimensionless constant at 25°C).

^c All compounds except order nos. 2 and 5 are newly added as criteria offensive odorants for the malodor regulation purpose by the Korean Ministry of Environment (KMOE) from the year 2008.

^d Source http://www.inchem.org/documents/icsc/icsc/

^e Source http://www.eugris.info/FurtherDescription.asp?e=6&Ca=2&Cy=0&T=Benzene,%20toluene,%20ethylbenzene,%20and%20xylene

^f Source http://elmhurst.edu/~chm/vchembook/213organicfcgp.html

^a Three individual sets of calibration were performed by using a head-space volume of 30, 35, and 38 mL, respectively, with 10, 20, 40, and 100 ng µL⁻¹of liquid standard.

^b The initial quantities of VOC added into deionized water are used to draw curves between the mass in ng (x-axis) and peak area.

^c The quantities of VOC partitioned into each HS are used for regression analyses.

^d Results of simple normalization of slope-to-slope values for Equil (and aqueous (aq) calibration).

^a The results shown in terms of external calibration (Table 2) are also expressed as internal calibration.

^b Internal calibration results with mesitylene (M).

^c Internal calibration results with benzene-d₆ (B-d₆).

^d Normalized slope values for internal calibration made by mesitylene (M).

^e Normalized slope values for internal calibration made by benzene-d₆ (B-d₆).