Peak Shape and Broadening

The variation of solute concentration in the stationary phase with solute concentration in the mobile phase, at constant temperature, is known as the sorption isotherm. Simple chromatographic theory assumes a linear isotherm relationship, i.e. the distribution coefficient is constant. Under these conditions the retention time is independent of sample concentration and the peak moves with a constant speed. Given a peak profile with plug-shape distribution on injection, this plug shape should be maintained as the peak passes through the column to emerge at the exit. However, because of longitudinal diffusion in the direction of flow, the peak takes on a Gaussian distribution. If the isotherm relationship is nonlinear (e.g. Langmuirian or anti-Langmuirian), the distribution coefficient is not constant but varies with solute concentration and there is a distribution of solute molecule velocities across the peak that is described as tailing or fronting. This relationship between isotherm shape and peak shape is illustrated in Figure 3.

The width of a chromatographic peak is a function of the column efficiency, expressed as the plate number (N), calculated from the following equations depending on the value used for the peak width (see Figure 2):

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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