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Blumberg L.M.,Fast GC Consulting
Journal of Chromatography A | Year: 2011

Earlier introduced metrics of separation performance are described in a systematic way. After providing the definitions of the metrics suitable for a broad variety of applications, the study focuses on static analyses (isothermal GC, isocratic LC, etc.) and their general separation performance. Statistically expected number of resolved (adequately separated) single-component peaks is treated as the ultimate metric of general separation performance of chromatographic analysis. That number depends on the peak capacity of the analysis and the number of components in a test mixture. The peak capacity, in turn, depends on the separation capacity of a column and the lowest separation required by the data-analysis system for resolving poorly separated peaks. The separation capacity is a special case of a broader metric of the separation measure which is a function of column efficiency, solute separability, and the level of the solute interaction with a column stationary phase. The formulae for theoretical prediction of all these metrics for arbitrary pairs of peaks in static analyses are derived. To provide a better insight into the basic metrics of the separation performance, additional metrics such as the solute discrimination (relative difference in solute velocities), utilization of separability (solute discrimination per unit of their separability), specific separation (the separation per unit of separability), and others are defined and found for static analyses. © 2011 Elsevier B.V.

Metrics of separation performance described in Part 1 of this series were applied here to theoretical evaluation of performance of a heating ramp in temperature-programmed GC. As in Part 1, the dependence of the separation (Δs) of two arbitrarily spaced peaks (the number of σ-slots between them) on operational parameters of GC analysis was treated here as the main building block for construction of other performance metrics. Simple expressions describing Δs of two peaks eluting during isobaric linear heating ramp and dependence of Δs on the heating rate, on column efficiency and on the peak spacing were derived. The use of dimensionless heating rate and other dimensionless operational parameters made these expressions universally suitable for different column dimensions, heating rates, carrier gas types, flow rates, etc. The use of dimensionless parameters also made it possible to express Δs as a simple function of the earlier introduced chromatographically meaningful characteristic parameters of thermodynamics of solute-column interactions. The expressions for Δs developed here, together with the ones described in Part 1 were used for theoretical prediction of total separation capacity (s c), total peak capacity (n c), and total number of resolved peaks in temperature-programmed analysis controlled by a balanced temperature program consisting of a linear heating ramp preceded by specially designed balanced temperature plateau. A numerical example of these parameters for a particular column, heating rate, carrier gas, and its flow rate is also provided. It has been shown that n c obtainable in temperature-programmed analysis is 2-3 times larger than that obtainable in equally long isothermal analysis using the same column and gas. Comparison of this improvement with potentially more than an order of magnitude larger peak capacity of GC×GC has been discussed. Also described are the speed of analysis (the number of σ-slots per unit of time), and other characteristics of the separation performance of a heating ramp. In many respects, metric Δs is similar to the widely known metric of resolution (R s). Advantages of Δs over R s as a metric of the separation performance, as well as the advantages of other metrics utilized here over their widely known counterparts are discussed. © 2012 Elsevier B.V.

Klee M.S.,Agilent Technologies | Blumberg L.M.,Fast GC Consulting
Journal of Chromatography A | Year: 2010

Flow modulation of methane-doped carrier gas is used to visualize the second dimension hold-up time in GC × GC continuously throughout the run. This provides an internal reference of hold-up time and presents a straightforward means of examining retention in each dimension of GC × GC. Retention factors on similar and dissimilar column pairs are examined. Stationary phase bleed is shown to be retained by the second dimension column. © 2010 Elsevier B.V.

Bicchi C.,University of Turin | Blumberg L.,Fast GC Consulting | Cagliero C.,University of Turin | Cordero C.,University of Turin | And 2 more authors.
Journal of Chromatography A | Year: 2010

The study aimed to find the best trade-off between separation of the most critical peak pair and analysis time, in enantioselective GC-FID and GC-MS analysis of lavender essential oil, using the GC method-translation approach. Analysis conditions were first optimized for conventional 25 m × 0.25 mm inner diameter (dc) column coated with 6I-VII-O-tert-butyldimethylsilyl-2I-VII-3I-VII-O-ethyl-β-cyclodextrin (CD) as chiral stationary phase (CSP) diluted at 30% in PS086 (polymethylphenylpolysiloxane, 15% phenyl), starting from routine analysis. The optimal multi-rate temperature program for a pre-set column pressure was determined and then used to find the pressures producing the efficiency-optimized flow (EOF) and speed-optimized flow (SOF). This method was transferred to a shorter narrow-bore (NB) column (11 m × 0.10 mm) using method-translation software, keeping peak elution order and separation. Optimization of the enantioselective GC method with the translation approach markedly reduced the analysis time of the lavender essential oil, from about 87 min with the routine method to 40 min with an optimal multi-rate temperature program and initial flow with a conventional inner diameter column, and to 15 min with FID as detector or 13.5 min with MS with a corresponding narrow-bore column, while keeping enantiomer separation and efficiency. © 2010 Elsevier B.V. All rights reserved.

Blumberg L.,Fast GC Consulting | Klee M.S.,Agilent Technologies
Journal of Chromatography A | Year: 2010

Multidimensional (MD) separations, especially comprehensive two-dimensional (2D) separations such as comprehensive 2D LC (LC × LC), and comprehensive 2D GC (GC × GC), are potentially powerful separation techniques. It is important to have a clear definition of MD techniques to better understand the scope and boundaries of the subject. Widely accepted definitions of MD Separations have their roots in the definition proposed by Giddings. Giddings also added several comments that clarified the scope of his definition. However, some researchers extend Giddings' definitions beyond their intended scope. Doing so disqualifies such comprehensive 2D techniques as LC × LC, GC × GC and 2D TLC from being considered as 2D techniques. In other instances, extended treatment of Giddings' definition is used as a basis to justify design-parameters of comprehensive 2D separations despite the fact that these parameters lead to sub-optimal implementations. We believe that the shortcomings in the definition and its popular interpretations are serious enough to warrant attention, especially by those interested in designing optimal instrumentation for MD separations like comprehensive 2D GC. After discussion of the weaknesses in the currently used definitions, we propose to define n-dimensional analysis as one that generates n-dimensional displacement information. We believe that this definition captures the spirit of Giddings' definition while avoiding the problems associated with its popular interpretations. © 2009 Elsevier B.V. All rights reserved.

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