412 J. Sep. Sci. 2014, 37, 412–418 Enrico Veschetti 1 Mario Vincenzo Russo 2 1 Istituto Superiore di Sanit ` a, Dipartimento Ambiente e connessa Prevenzione Primaria, Rome, Italy 2 Universit ` a degli Studi del Molise, Dipartimento Agricoltura, Ambiente e Alimenti (DiAAA), Campobasso, Italy Received September 21, 2013 Revised November 08, 2013 Accepted November 23, 2013 Research Article GC models for separation optimization in pressure-tunable tandem capillary columns operated isothermally Part 2: Control experiments using a new capillary column interface In the previous part of this study, a significant improvement of the fundamental relation- ships that control GC resolution in a pressure-tunable assembly operating in isothermal conditions inside a single oven was made. A theoretical approach for the correct choice of the working temperature was proposed for the first time. In this second part of our report, a new interfacing device has been proposed for a rapid and reliable alignment of the two columns at the midpoint junction. Moreover, the results of a series of experimental tests have confirmed the validity of the proposed mathematical models. Keywords: Capillary column interface / Control experiments / Selectivity tuning / Tandem column chromatography DOI 10.1002/jssc.201301045  Additional supporting information may be found in the online version of this article at the publisher’s web-site 1 Introduction High-resolution GC of complex mixtures involves a prelim- inary optimization of the experimental conditions that will be applied during the following analytical determination. In particular, the efficiency, selectivity, and capacity factor of the GC column are the parameters that must be carefully assessed and improved in order to ensure the complete sepa- ration of the relevant chromatographic peaks. For many years the resolution of retained compounds, whose separation is little affected by their capacity factors, was optimized almost exclusively by increasing the number of theoretical plates. On the contrary, the adjustment of column selectivity was mostly neglected although its influence on resolution is far more important than a drastic increase in column efficiency. In the most recent decades, a number of strategies have been de- veloped to adjust column selectivity to the needs of a specific critical separation. In particular, pressure tuning at the serial connection of two chromatographic columns has provided the most elegant and versatile solution. A comprehensive description of these methods was given in the first part of this report on our research [1] in which we improved the mathematical model on multichromatographic systems that operate in the isothermal mode by describing, inter alia, an original approach to select the optimal column temperature. Correspondence: Professor Mario Vincenzo Russo, Dipartimento Agricoltura, Ambiente e Alimenti (DiAAA), Universit ` a degli Studi del Molise, via De Sanctis, Campobasso 86100, Italy E-mail: mvrusso@unimol.it Fax: +39-0874-404652 In this work, which represents the second part of our study, the results of experimental tests planned to check the validity of the proposed model are shown and discussed. The experimental activity was preceded by the design and imple- mentation of an appropriate device to interface the two chro- matographic columns to be placed in series. The new device made it possible to solve the following problems described by other authors: installation difficulties and irreproducible alignment of the two columns at the midpoint junction, which are responsible for extracolumn effects, loss of resolution, and peak tailing as well as the detection of “ghost peaks” associated with the release of contaminants from seals. In the third part of our study, which will be published in the near future, the mathematical approach described in Ref. [1] will be applied to the prediction of the operating tem- peratures that enable the achievement of the best possible chromatographic resolution of test solutions containing lin- ear and branched hydrocarbons, halogenated organics, and organic solvents. 2 Materials and methods 2.1 Numbering, symbols, and acronyms Equation numbering, mathematical symbols and acronyms employed below are those defined in Ref. [1]. New equations introduced in this work are numbered in consecutive order with the last equation derived in Ref. [1]. A synoptic list of the symbols and equations cited or introduced in this article is provided in Supporting Information Tables S1 and S2. C  2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com