Optimization via liquid phase mixtures in capillary gas chromatography

Takeoka, Gary R.; Richard, Hoogenboom; Mehran, M.; Jennings, Walter

doi:10.1002/jhrc.1240060306

Cited by 31 publications

(6 citation statements)

References 8 publications

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“…All these difficulties have encouraged experts to find out pioneering solutions. Two different approaches were initially proposed: the capillary column was coated with an homogeneous mixture of stationary phases ; two or more capillary columns with different stationary phases were connected in series . …”

Section: Introductionmentioning

confidence: 99%

GC models for separation optimization in pressure-tuneable tandem capillary columns operated isothermally. Part 1: Theoretical aspects

et al. 2013

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GC column selectivity can be continuously adapted to suit analytical needs using a flow-tuneable tandem system. Its application for the separation of complex mixtures requires a deep understanding of the theory in this area. Although a number of researchers have developed specific models, a general and exhaustive theory is still missing. In this paper, we have made an implementation of pre-existing models on tandem-column assemblies operated isothermally. In particular, we have investigated the effect of column length and diameter, phase thickness, and oven temperature on chromatographic parameters, such as capacity factor, selectivity, and intrinsic resolution. A new approach for the correct choice of the working temperature has been proposed.

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Section: Introductionmentioning

confidence: 99%

GC models for separation optimization in pressure-tuneable tandem capillary columns operated isothermally. Part 1: Theoretical aspects

et al. 2013

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“…The present model's lack of restriction on column geometry and composition uniformity suggests that one could very accurately predict (and optimize) analyte behavior on serially coupled capillary columns (47)(48)(49)(50)(51)(52)(53) provided that the effects of the pressure gradient on retention and zone broadening are accounted for. The model's lack of restriction on temperature isotropy could be used to include temperature gradients down the column (54).…”

Section: Methodsmentioning

confidence: 99%

Simulation of gas chromatographic retention and peak width using thermodynamic retention indexes

Dose¹

1987

Anal. Chem.

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The computational simulation of tsinperatursprogrammed gas Chromatographic behavlor of two serles of analytes Is Investigated. The approach presented accounts for both retention-time and peak-width behavlor over diverse temperature programs. The effect of the temperature dependence of carrier gas vlscoslty Is Included In the treatment. Sbnulatlon accuracies are generally 1 % for retention and 10-15 % for peak widths. The isothermal retention t h e data used as input of the simuiatlon are most conveniently reduced to two thennodynamlc quantltles AS, and AHv whkh are proposed as a new class of retention Indexes.Simulation of gas chromatographic behavior has been reported under three general approaches. Classical or semiclassical theoretical treatments (1-5) describe the dependence of separation efficiency of unspecified analytes on changes in column length (6, 7) and cross-section (8,9), carrier pressure (IO), and instrumental inefficiency (11). These treatments do not attempt to simulate particular separations but result in requirements on those that do. A second approach adjusts isothermal retention times (12)(13)(14) or retention indexes (15-23) for oven temperature changes, generally using semiempirical or linear extrapolative methods which predict retention behavior over a limited range of available conditions. The present work follows the third approach, the simulation, whether thermodynamic or empirical, of physical and chemical processes occurring in the instrument (24-31). This approach, while computationally demanding, should afford simulation of specific separation processes and their results over a very wide range of conditions. The degree of success of properly applied, thermodynamically based direct simulation reflects the accuracy of current chromatographic theory.In this work, isothermal data were used to perform temperature-programmed experiments off-line, that is, on a computer rather than on a chromatograph. The accuracy of this method for two classes of analytes is demonstrated. The degree of reproducibility allows relatively small effects such as carrier-gas-viscosity temperature dependence to be verified and included in the treatment. EXPERIMENTAL SECTIONApparatus. Chromatograms were obtained on two Hewlett-Packard 5890A gas chromatographs with electron-capture detection. Temperatures from the chromatographs' controllers were used directly. No corrections for heating lag time (28) were applied to this capillary system. Organochlorine pesticides (OCPs) were eluted from a 30-m, 0.32 mm i.d. DB-17 capillary column (J&W Scientific) of f i l m thickness 0.25 wm. Nitroaromatic (NA) analytes were eluted from a 30-m, 0.53 mm i.d. DB-210+ column (J&W) of film thickness 1.0 pm. Helium was used as carrier for all experiments.Procedures. Peak retention times were measured at the detector signal maximum as indicated by the Hewlett-Packard 3392A integrator. One-day retention time reproducibility was to 0.01 YO, multiday reproducibilities were to 0.05%, and multiday reproducibilities of retention time ratios...

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“…Takeoka et al [2], in fact, used open tube columns differing substantially in diameter. This further complicates the issue since values of P are dramatically affected in such circumstances, and equation (7) is invalid.…”

Section: (7)mentioning

confidence: 98%

Compressibility effects in the optimization of serially connected gas chromatographic capillary columns by the window diagram technique

Purnell

Williams

1983

J. High Resol. Chromatogr.

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Serially coupled capillary columns Window diagram Optimization CompressibilityIn two recent publications, Jennings and his collaborators [1,2] 41,to the operation of serially connected pairs of gas chromatographic columns. In both publications they conclude that the method provides only a first approximation which has to be followed by empirical adjustment for best results. This view, as we will show elsewhere [5], is entirely incorrect and reflects major errors in their approach. The first, in the theoretical extension offered by lngraham, Shoemaker, and Jennings [l], is an algebraic errorwhich leads to a totally incorrect equation forthe calculation of column lengths. The second, is that these authors, as also did Jakeoka, Richard, Mehran, and Jennings [2], totally ignored the effect of carrier gas compressibility in their theory. It is with this latter point that we deal here.The very earliest publication in elution gas chromatography [6] established that retention volume is influenced by the inletloutlet pressure ratio. We had assumed that, in the light of the work of Hildebrand and Reilley in 1964 [7] and, more recently of Buys and Smuts [8], it has been widely appreciated that in serial columns of differing composition, so too is relative retention. Thus, in operating a two column serial system, say A and B, the relative retention of any pair of solutes depends upon whether A or B is at the inlet end. In both the publications referred to [1,2] such variation of relative retention was observed and led these authors to propose the rather remarkable explanation that: "Because the carrier gas velocity is lower than the average at the inlet end, and higher than the average at the outlet end, solutes encounter (per unit length of column) more solubility sites at the inlet end, and fewer solubility sites at the outlet end, than would be expected". If this were true, the concepts of both compressibility corrected and specific retention volume for single substrate columns would obviously be meaningless. Although the basic theory for coupled columns of equal gas permeability and porosity has been presented earlier [7,8] we present here a new version because it is both simpler and free of earlier assumptions.We designate the column at the inlet end of the pair F, and that at theoutlet end B,with Foperatingoverthepressuredroppi topand B over the drop p to po. The James-Martin compressibility corrections are jF over F and j B over B.The total dead time t d (unretained solute) is, in termsof the column lengths, LF and LB, given by L No ---where u is the velocity at p and j is the compressibility correction from pi to po which should be the same whicheverway around the column system is operated.The retention time of a retained solute, t R is, correspondingly, given by LB (1 + ke') whence, the fully corrected retention time, t'R, is given by

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Optimization via liquid phase mixtures in capillary gas chromatography

Cited by 31 publications

References 8 publications

GC models for separation optimization in pressure-tuneable tandem capillary columns operated isothermally. Part 1: Theoretical aspects

GC models for separation optimization in pressure-tuneable tandem capillary columns operated isothermally. Part 1: Theoretical aspects

Simulation of gas chromatographic retention and peak width using thermodynamic retention indexes

Compressibility effects in the optimization of serially connected gas chromatographic capillary columns by the window diagram technique

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