LCGC The Peak - April 2008 - (Page 12)

12 THE PEAK APRIL 2008 Figure 3: Schematic illustration of the peak capacity in comprehensive twodimensional chromatography. In this example, the peak capacity in the first dimension is 32 (vertical direction; gradient-elution conditions) and that in the second dimension is 10 (vertical direction; isocratic conditions), resulting in a total peak capacity of 320. ogous series in one-dimensional chromatography), it is usually not realistic when the separation of very complex mixtures with GC GC or LC LC is considered. Nevertheless, peak capacity is a very useful measure to indicate the quality of a separation system. The higher the peak capacity, the greater the separation potential. The peak capacity in isocratic and in gradient-elution liquid chromatography can be estimated using conventional and moreoriginal concepts (8–10). As a rough summary, one-dimensional LC allows the separation of 50 or perhaps 100 (equally resolved) peaks in one experiment. Using gradient elution this number might be increased to hundreds and it can even exceed 500 (11). To get to these high numbers, (very) slow gradients are used. Working at very high pressures, elevated temperatures, or with the best available (long and efficient) monolithic columns all help (12). For example, raising the maximum pressure from 400 to 1000 bar (from 40 to 100 MPa) can enhance the peak capacity by some 20%. However, all these important (and welcome) developments in LC do not result in a quantum leap in the available peak capacity. In contrast, such a great leap forward can be realistically expected from LC LC. Key to this treasure is that the peak capacities in the two dimensions can be multiplied (Figure 3). A realistic estimate for the peak capacity in the first dimension (slow separation) is a few hundred; a realistic number for the (fast) second dimension is between 10 and 20. The result is a peak capacity in the thousands, which can be achieved with standard commercially available columns and instruments (13).

Table of Contents Feed for the Digital Edition of LCGC The Peak - April 2008

LCGC The Peak - April 2008 Contents LC3LC: Comprehensive Two-Dimensional Liquid Chromatography Split Injections in Gas Chromatography: How to Reduce Inlet Discrimination A Simple and Solvent-Free Method for Determining Tetracyclines in Prawns Industry News Events Education

LCGC The Peak - April 2008

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