where AH is the enthalpy of solution (or adsorption) from the mobile phase to the stationary phase.

Figure 1 for the general elution problem also shows values of k for different zones of the chromatogram. With low k values (k < 1) the peaks are eluted too rapidly and there is no time for separation. With high k values (k >10) elution times are long, the peaks are broad and the peaks are overresolved. This problem can be corrected using the technique of temperature programming. Assuming that this chromatogram was obtained isothermally at 100°C it would be possible to choose a lower starting temperature (say 50°C) and then raise the temperature to say 150°C over a given period of time. This would have the effect of increasing the k values for the early peaks and decreasing the k values for the later peaks, the object being to get all peaks in the optimum region 1 <k <10. Modern computer-controlled gas chromatographs have the facility to use isothermal periods and linear and nonlinear temperature programs with multiple ramps to giver better control over k values.

The retention equation also indicates that a similar effect could be achieved using the analagous technique of flow-programming and changing the carrier gas flow rate. However, increase in carrier gas flow rate gives an approximately linear effect whereas temperature programming has a logarithmic effect. In spite of this, flow programming finds a use in the separation of labile and temperature-sensitive samples where high temperatures are to be avoided.

A satisfactory separation is achieved when all three terms in the Purnell equation are optimized.

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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