Surface fitting for calculating the second dimension retention index in comprehensive two-dimensional gas chromatography mass spectrometry

Md Aminul Islam Prodhan; Xinmin Yin; Seongho Kim; Craig McClain; Xiang Zhang

doi:10.1016/j.chroma.2018.01.049

Surface fitting for calculating the second dimension retention index in comprehensive two-dimensional gas chromatography mass spectrometry

J Chromatogr A. 2018 Mar 2:1539:62-70. doi: 10.1016/j.chroma.2018.01.049. Epub 2018 Jan 31.

Authors

Md Aminul Islam Prodhan¹, Xinmin Yin¹, Seongho Kim², Craig McClain³, Xiang Zhang⁴

Affiliations

¹ Department of Chemistry, University of Louisville, Louisville, KY 40208, USA; University of Louisville Alcohol Research Center, Louisville, KY 40208, USA; University of Louisville Hepatobiology & Toxicology Program, Louisville, KY 40208, USA; Center for Regulatory and Environmental Analytical Metabolomics, University of Louisville, Louisville, KY 40208, USA.
² Biostatistics Core, Karmanos Cancer Institute, Department of Oncology, School of Medicine, Wayne State University, Detroit, MI 48201, USA.
³ University of Louisville Alcohol Research Center, Louisville, KY 40208, USA; University of Louisville Hepatobiology & Toxicology Program, Louisville, KY 40208, USA; Department of Pharmacology & Toxicology, University of Louisville, Louisville, KY 40208, USA; Department of Medicine, University of Louisville, Louisville, KY 40208, USA; Robley Rex Louisville VAMC, Louisville, KY 40292, USA.
⁴ Department of Chemistry, University of Louisville, Louisville, KY 40208, USA; University of Louisville Alcohol Research Center, Louisville, KY 40208, USA; University of Louisville Hepatobiology & Toxicology Program, Louisville, KY 40208, USA; Center for Regulatory and Environmental Analytical Metabolomics, University of Louisville, Louisville, KY 40208, USA; Department of Pharmacology & Toxicology, University of Louisville, Louisville, KY 40208, USA. Electronic address: xiang.zhang@louisville.edu.

Abstract

Comprehensive two-dimensional gas chromatography mass spectrometry (GC × GC-MS) has been widely used for analysis of volatile compounds. However, the second dimension retention index (I) of each compound is not widely used to aid compound identification owing to the limited accuracy of I calculation. We report a surface fitting approach to the calculation of I using n-alkanes (C₇-C₃₀) as references, where the second dimension retention time (²t_R) and the second dimension column temperature (²T_e) formed the X-Y plane and the I was the Z-axis to form the I surface. Compared to the conventional approach for calculating I using isovolatility curves, the surface fitting approach eliminated the construction of isovolatility curves for the reference compounds and gives better reproducibility. The goodness of the proposed surface fitting achieved R² = 0.9999 and RMSE = 6.1 retention index units (iu). Ten-fold cross validation demonstrated the surface fitting approach had a good predictability with average R² = 0.9999 and RMSE = 6.6 iu. The developed method was also applied to calculate the second dimension retention indices of compound standards in two commercial mixtures MegaMix A and MegaMix B. The mean standard deviation of the calculated I was only 1.6 iu for compounds in MegaMix A and 3.4 iu for compounds in MegaMix B. Compared with the literature results, the small value of standard deviation in the calculated retention index using surface fitting method shows that the surface fitting method has less measurement variability than the conventional isovolatility curve approach.

Keywords: GC × GC–MS; Retention index calculation; Second dimension retention index; Surface fitting.

MeSH terms

Alkanes / chemistry
Chemistry Techniques, Analytical / methods*
Gas Chromatography-Mass Spectrometry*
Models, Chemical
Reproducibility of Results
Temperature
Volatile Organic Compounds / chemistry

Substances

Alkanes
Volatile Organic Compounds

Abstract

MeSH terms

Substances

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