Determination and evaluation of gas holdup time with the quadratic equation model and comparison with nonlinear models for isothermal gas chromatography

Gas holdup time (t(M)) is a basic parameter in isothermal gas chromatography (GC). Determination and evaluation of t(M) and retention behaviors of n-alkanes under isothermal GC conditions have been extensively studied since the 1950s, but still remains unresolved. The difference equation (DE) model [J. Chromatogr. A 1260: 215-223] reveals retention behaviors of n-alkanes excluding t(M), while the quadratic equation (QE) model [J. Chromatogr. A 1260: 224-231] including t(M) is suitable for applications. In the present study, t(M) values were calculated with the QE model, which is referred to as t(MT), evaluated and compared with other three typical nonlinear models. The QE model gives an accurate estimation of t(M) in isothermal GC. The t(MT) values are highly accurate, stable, and easy to calculate and use. There is only one t(MT) value at each GC condition. The proper classification of t(M) values can clarify their disagreement and facilitate GC retention data standardization for which t(MT) values are promising reference t(M) values. (C) 2013 Elsevier B.V. All rights reserved.