Programmed-temperature gas chromatographic (GC) retention information is difficult to share because it depends on so many experimental factors that vary among laboratories. Though linear retention indexing cannot properly account for experimental differences, retention times can be accurately calculated, or "projected", from shared isothermal retention vs. temperature (. T) relationships, but only if the temperature program and hold-up time vs. T profile produced by a GC is known with great precision. The effort required to measure these profiles were previously impractical, but we recently showed that they can be easily back-calculated from the programmed-temperature retention times of a set of 25 n-alkanes using open-source software at www.retentionprediction.org/gc. In a multi-lab study, the approach was shown to account for both intentional and unintentional differences in the temperature programs, flow rates, and inlet pressures produced by the GCs. Here, we tested 16 other experimental factors and found that only 5 could reduce accuracy in retention projections: injection history, exposure to very high levels of oxygen at high temperature, a very low transfer line temperature, an overloaded column, and a very short column (≤15. m). We find that the retention projection methodology acts as a hybrid of conventional retention projection and retention indexing, drawing on the advantages of both; it properly accounts for a wide range of experimental conditions while accommodating the effects of experimental factors not properly taken into account in the calculations. Finally, we developed a four-step protocol to efficiently troubleshoot a GC system after it is found to be yielding inaccurate retention projections.
Bibliographical noteFunding Information:
We thank Jerry D. Cohen (University of Minnesota) for helpful discussions and a thoughtful review of this manuscript. We also thank the National Institutes of Health [R01GM098290], the National Science Foundation [IOS-0923960 and MCB-0725149], the Minnesota Agricultural Experiment Station, the Gordon and Margaret Bailey Endowment for Environmental Horticulture, and the Charles J. Brand endowment for financial support, and we thank Agilent Technologies for generously donating the GC columns used in this work.
© 2014 Elsevier B.V.
Copyright 2015 Elsevier B.V., All rights reserved.
- Compound identification
- Gas chromatography-mass spectrometry
- Instrument non-idealities
- Programmed-temperature retention from isothermal retention
- Retention prediction
- Retention projection