HV gYGV Y dY

where Tmax = xmax/w, is the dimensionless coordinate of the maximal concentration of the focused zone. R can be experimentally determined as the ratio of the retention volume (or the retention time) of an unretained sample component (equal to the volume of the channel) divided by the retention volume (retention time) of the retained sample component. The simple and known relationship between the X and the particle size make it possible to calculate the PSD from the experimental retention data.

Each fractionation is based on transport processes which lead to the formation of the concentration gradients. From the thermodynamic point of view, the general entropic tendency of a closed system is to erase such gradients by molecular motion. As a result, the spreading of the zones due to dispersion processes occurs. The zone spreading can be quantitatively described by the height equivalent to a theoretical plate H:

In a number of practical cases, the spreading function can be approximated by the normal Gaussian function. The application of the correction of an experimental fractogram is demonstrated in Figure 2.

The true PSD can be expressed as a number of the particles of a given diameter n; relative to the number of all the particles in the sample:

or as the mass of the particles mt of a given diameter ¿i relative to the total mass of the sample:

where VR is the retention volume and a is the standard deviation of the zone of uniform size particles. The elution curve (fractogram) of a polydisperse sample thus reflects the contribution of the spreading processes superposed over the fractionation according to the PSD.

In order to calculate a true PSD from the experimental raw fractogram, a correction for the zone i oo 0

The PSD can be used further to calculate various average particle sizes such as the mass average particle diameter:

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.

Get My Free Ebook


Post a comment