Gradient elution continuous

The design procedure described above will, in theory, be applicable only to samples that are separated by isocratic development. Under gradient elution conditions the (k ) value of each solute is continually changing, together with the viscosity of the... 

The device for continuous gradient elution in horizontal chamber described by Nyiredy [15] and presented in the preceding text, (Figure 6.10) seems to be a very interesting solution both for analytical and preparative applications. 

Gradient elution is a procedure whereby the conditions under which the sample is eluted are progressively varied throughout the separation so as to speed up the process. This can be achieved by altering the composition of the mobile phase or increasing the temperature or flow rate. The effect is to elute components more rapidly in the latter stages and sharpen their elution profiles. Stepwise elution is a similar procedure in which elution conditions are changed at predetermined times rather than continuously. 

Step 4 Clean autosampler sample loop and trap column 2 using 90% organic solvent from pumps 1 and 2 and then condition trap column 2 and sample loop with 95 to 100% water from pump 1. Continue to run gradient elution of sample from trap column 1 and analytical column using pumps 3 and 4 until the end. Switching valve A = on switching valve B = off. 

Control of the vaporization process, i.e. the temperature of the capillary, is of crucial importance. Optimum performance is obtained with around 95% vaporization of the liquid stream. Too much heat results in vaporization occurring within the capillary with deposition of analyte and, if operation of the interface under these conditions is continued for any length of time, blockage of the capillary. On the other hand, if insufficient heat is applied to the capillary, vaporization does not occur and liquid flows from it and no spray is obtained. The optimum temperature is dependent on a number of parameters, among the most important being the composition of the mobile phase and its flow rate. Good temperature control is therefore required to obtain the best conditions when gradient elution is employed. 

For the implementation of techniques such as step-elution, gradient-elution, displacement-elution, as well as for the wash and sanitation steps needed for ion exchange chromatography and continuous downstream processing in general. 

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