35


also studied [16]. For the case of the first dimension increasing the λ decreases the crossover time from 3.89 min to 1.89 min (when λ is increased from 0.60 to 0.80).


The effect of the second dimension parameters that make up the 2 2treeq


tc (2


a decrease in the 2 the crossover time; 2


tg To re-write [16]: and


) on the crossover time are as follows: treeq tg


minimum (between 5-15 s) for crossover times between 1-10 min; shorter 2 more sensitive to the 2


tg treeq


crossover time with an increase of 2 Potts and Carr’s study [16], used the f1D


were


(faster increase in treeq


Neue et al. and Fairchild et al. [19,20] that showed the dependence of the 1


nc on 1 nc versus 2 tg tg


well as a fitting equation from the work of Huang [12] and Li [4] (2


to


) [16]. term


. As ) to derive


the crossover time (τ), for cases of severe first dimension under-sampling, with the aid of Solver function in Microsoft ExcelTM approximate:


(6) (8)


significantly reduced experienced a


Doing so allowed them to explore the effect of the 1


nc on the effective 2D peak capacity


which had little effect even in the case that the first dimension experienced severe under-sampling, in agreement to previous findings [4,21]. They recommend the use of Eq. (8) to calculate the crossover time and determine if any practical changes to the 1D or 2D method are worthwhile. Potts and Carr conclude that with future innovation to achieve faster first dimension sampling rates (decrease in 2 (fcoverage


tc ) and orthogonal separations approaching unity) would result in


a further decrease of the τ [16]. The peak capacity power of the LC × LC approach overtakes 1D methods at short analysis times, hence should be the technique of choice for complex separations demanding high-throughput, high-resolution analyses.


Additionally Potts and Carr created a new α parameter by lumping (2


tc, f1D, 2 nc


into a single parameter - α, shown in Eq. (7) [16]:


Table 1. Method development


2DLC related Topic


Review Method Development 2011 2011 2011 2011 2006 2005


Data processing


2013 2008 Year


2007 2008 2011


Title Main Author(s)


Fast, comprehensive two-dimensional liquid chromatography D.R. Stoll et al. Implementations of two-dimensional liquid chromatography G. Guiochon et al. H. Gu et al.


Peak capacity optimization in comprehensive two dimensional liquid chromatography: A practical approach


Effect of first dimension phase selectivity in online comprehensive two dimensional liquid chromatography (LCxLC)


Effects of first dimension eluent composition in two-dimen- sional liquid chromatography


Improving Peak Capacity in Fast Online Comprehensive Two-Dimensional Liquid Chromatography with Post-First-Dimension Flow Splitting


Perspectives on recent advances in the speed of high-performance liquid chromatography


A protocol for designing comprehensive two-dimensional liquid chromatography separation systems


Viscous fingering induced flow instability in multidimensional liquid chromatography


Data Processing for 2D-LC: where are we heading?


Recent advancements in comprehensive two-dimensional separations with chemometrics


H. Gu et al. X. Li, P.W. Carr M.R. Filgueira et al. P.W. Carr et al. Citations [Ref]


173 104 15


8 6 13 38 P.J. Schoenmakers et al. 77 K.J. Mayfield et al. P.G. Stevenson K.M Pierce et al. 32 - 93


1 a


15 18 17 b c d e f g and fcoverage ) 3. The LC × LC valve


All of the hyphenated LC x LC methods employ switching valves to allow the sample


(7) to be switched between the 1st and the 2nd


dimension columns. The switching valve can come in different configurations, comprising of 6, 8 and 10 ports, with the 2 position being the most popular for 2D LC. The valve itself has several components, with different manufacturers having slightly different designs; however, the basics of the valve design are that it comprises of three major components;


• Valve motor • Rotor • Stator


The rotor and stator can be made of different materials and careful choice of the material can significantly reduce the levels of carryover [23].


Chromatographers who are new to hyphenation often find the use of valves daunting as the amount of tubing seems to increase, however all LC systems already use valves to allow the sample to be introduced into the fluidic stream, and so understanding how a valve works and some of the limitations actually helps improve the understanding of a standard LC system.


There are many different configurations that chromatographers have employed for 2D and comprehensive 2D LCxLC separations, involving the use of a single valve or multiple valves. The increasing


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