Chromatographic methods peak capacity

The limitations of one-dimensional (ID) chromatography in the analysis of complex mixtures are even more evident if a statistical method of overlap (SMO) is applied. The work of Davis and Giddings (26), and of Guiochon and co-workers (27), recently summarized by Jorgenson and co-workers (28) and Bertsch (29), showed how peak capacity is only the maximum number of mixture constituents which a chromatographic system may resolve. Because the peaks will be randomly rather than evenly distributed, it is inevitable that some will overlap. In fact, an SMO approach can be used to show how the number of resolved simple peaks (5) is related to n and the actual number of components in the mixture (m) by the following ... 

A practical method for enhancing the peak capacity, and thus the resolution of analytes in multicomponent complex mixtures, can be achieved by changing the mode of the separation during the chromatographic analysis, employing a column switching system in order to optimize a separation. 

In a more recent work Ito [101] has described a simple and highly sensitive ion chromatographic method with ultraviolet detection for determining iodide in seawater. A high-capacity anion exchange resin with polystyrene-divinylbenzene matrix was used for both preconcentration and separation of iodide. Iodide in artificial seawater (salinity, 35 % ) was trapped quantitatively (98.8 0.6%) without peak broadening on a preconcentrator column and was separated with 0.35M sodium perchlorate+ 0.10M phosphate buffer (pH 6.1). On the other hand, the major anions in seawater, chloride and sulphate ions, were partially trapped (5-20%) and did not interfere in the determination of iodide. The detection limit for iodide was 0.2pg L 1 for 6mL of artificial seawater. This method was apphed to determination of iodide (ND-18.3pg L ) and total inorganic iodine (I +I03 -I, 50.0-52.7pg L 1) in seawater samples taken near Japan. 

For many chromatographic runs, especially with complex samples, resolution or peak capacity is inadequate for the desired separation. In these cases steps can be taken to improve resolution. These steps are described in this section. If resolution is already adequate, other steps can be taken to do the separation faster without losing resolution. Methods for increasing speed will be described in Section 12.S. 

Ideally, components that are not separated in the first separation step are resolved in the second. Peak capacity is the number of individual components that can be resolved by a separation method. A mathematical model shows that if the MD separations are orthogonal, then the total peak capacity is the product of the individual peak capacities of each dimension [14], Load capacity is defined as the maximum amount of material that can be run in a separation while maintaining chromatographic resolution. MD separations can be designed to significantly increase the load capacity in a first dimension to achieve enrichment of low-abundance or trace components in a peptide mixture, while the necessary peak capacity may be obtained in the second separation dimension [15]. 

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. 

Two-dimensional (2D) separation systems are of interest because of their increased peak capacity over one-dimensional separations. Microfabricated devices (microchips) are potentially useful for multidimensional separations because high-efficiency separations can be achieved and small sample volumes can be manipulated with minimal dead volumes between interconnecting channels. Various techniques may be adopted for the fabrication of chromatographic columns in microchips for p-CEC following integration with other orthogonal separation methods as well as sample pretreatment proaches for rapid, automated analysis of more complicated biosamples with possible coupling to mass spectrometric detection. 

Column effects. In order to establish optimal operating conditions, it is useful to consider the effects of system parameters on the resolution characteristics of an HDC system. HDC has been described as a chromatographic method with very low capacity but very high efiBciency. For example, the calibration curves show that the spectrum of sizes from less than 100 nm to greater than 300 nm is encompassed in less than about 5% of the column void volume. On the other hand, the theoretical plate count corresponding to the marker peak is typically in the range of several thousand per foot. Comparisons in terms of the specific resolution factor, enable a more precise analysis, since both the separation factor and peak dispersion are included in its definition. A simple form for the specific resolution between two particle populations of diameter Dpi and Dp2 is [11]. 

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