Gradient elution mixing devices

Kutter, J. P., Jacobson, S. C., and Ramsey, J. M. (1997). Integrated microchip device with electrokinetically controlled solvent mixing for isocratic and gradient elution in micellar electrokinetic chromatography. Anal. Chem. 69, 5165-5171. 

Since gradient elution was first used in chromatography, many more or less complex devices have been used. We shall describe first devices for mixing two... 

DuPont system when the Model 833 precision flow controller is coupled with the gradient elution accessory immediately after the pneumatic pump on solvent A line (Fig. 7). The air pressure is adjusted so that the flow-rate is kept constant. Also in the DuPont device, solvents that differ widely in viscosity can be difficult to mix and the shape of the gradient can be altered. 

Figure 21.21. Gradient devices used in liquid chromatography. A Simple mixing device for gradient elution, gradient formed on low-pressure side of pump. Ri is the flow rate of A into the flask. Ra is the flow rate of A + B to column. B Gradient profiles obtained from A. C Schematic for two-pump gradient chromatograph. Gradient formed on high-pressure side of pump.

The device described by Wieland and Determann [756] for gradient elution TLC (Fig. 44) appears very convenient and capable of extension. The gradient is produced here by running the liquid to be added from a burette or measuring pump through a capillary (3) into the circular chamber (6 cm diameter) where it is then mixed with the existing... 

Fig. 44. Device for gradient elution according to [756]. 1 perforated plate holding the TLC-plate 2 magnetic stirring bar for mixing S supply tube for the second solvent 4 overflow 5 narrow TLC-plate 6 start points...

Soczewinski and Matysik (21) proposed a simple device, without a magnetic mixer, coupled with a horizontal sandwich chamber. The device consists of two vessels with two solvents, which mix spontaneously owing to density differences of the solvents and formation of molecular complexes (e.g., chloroform-ethyl acetate). They have also shown (22) that stepwise gradient elution can be easily performed in a sandwich chamber with a glass distributor (41,47) (Fig. 5). Matysik and Soczewinski (23) also described a device that is a modification of the system introduced by Niederwieser et al. (7,43,44). 

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