Peak capacity multidimensional chromatography

Elution with salt pulses A multiple step elution is performed by the introduction of, for example, 5%, 10%, 25%, 50%, and 100% of 1.5 M sodium chloride in 19 mM phosphate buffer (pH 2.5) containing 5% methanol. Each step is for 10 min and run at 0.5 mL/min. This elution method compromises analytical system dimensionality, as the peak capacity of the ion-exchange chromatography (IEX) step is equal at most to the number of salt steps. However, in the second dimension only one or two columns are needed and there is no particular limitation in the second dimension separation time as peptides are eluted in portions in a controlled manner. However, the number of salt steps is limited by the total analysis time. In this case the multidimensional system is relatively simple. 

At least two driving forces have contributed to the recent increased use and development of multidimensional liquid chromatography (MDLC). These include the high resolution and peak capacity needed for proteomics studies and the independent size and chemical structure selectivity for resolving industrial polymers. In this regard, separation science focuses on a system approach to separation as individual columns can contribute only part of the separation task and must be incorporated into a larger separation system for a more in-depth analytical scheme. 

Multidimensional chromatography separations are currently one of the most promising and powerful methods for the fractionation and characterization of complex sample mixtures in different property coordinates. This technique combines extraordinary resolution and peak capacity with flexibility, and it overcomes the limitations of any given single chromatographic method. This is the ideal basis for the identiflcation and quantification of major compounds and by-products, which might adversely affect product properties if not detected in time. 

Coupled-column separations or multidimensional chromatography can be considered as a sample preparation form, as one column is used to derive fractions for the second column. It provides a two dimensional separation in which sample substances are distributed over a retention plane formed by the operation of two independent columns. This type of two dimensional based separation method is more powerful than a single dimensional based one. A retention plane has more peak capacity than a retention line and so can accommodate much more complex mixtures. Component identification is more reliable because each substance has two identifying retention measures rather than one. These type of combinations offer high selectivity and high sensitivity, and could be used with less expensive and more robust detectors (e.g., flame ionization). ... 

The one dimensional GC technique cannot always provide sufficient separation of all components of plant volatiles. In order to enhance peak capacity, multidimensional gas chromatography can be used. Marriott ShelHe (2002) define multidimensional analysis in chromatography as any technique that combines two or more distinct separation/ analysis steps. The first dimensional separation is based on separation by boiling px)int in a nonpolar column. The second dimensional separation is based on sepjaration by polarity using a polar column. The inclusion of this makes this overall a two dimensional chromatogram... 

At present, most multidimensional chromatography methods are two-dimensional, composed of two one-dimensional systems coupled together. It is foreseeable that these two-dimensional technologies will proceed to three-dimensional systems and beyond. As the number of dimensions increases, and peak capacity further expands, more specific and unambiguous information is gained from each dimension, resulting in superior sample characterization possibilities. It can be predicted that in the future one-dimensional chromatographic analyses of complex samples will be redundant, replaced with faster and more efficient multidimensional methods. 

Multidimensional chromatography is a very attractive technique for the analysis of complex mixtures where a mono-dimensional separation cannot be sufficient to resolve all the components of interest. Obvious advantages are the higher peak capacity and resolution offered by these systems. Typically, one part of the chromatogram from the first column is transferred to another column via a suitable interface. 

Multidimensional chromatography tackles the root cause of limited chromatographic resolution by vastly improving the peak capacity, this being the product of the peak capacities, ft, of the individual chromatographic separations (Eq. 1) ... 

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