Micellar Electrokinetic Chromatography

The resolution equation for MEKC is identical to eqns [3] and [4] but contains an additional term, (tM/tMC)/[1 + (tM/tMC)k1], to account for the limited elution range (all solutes must elute between the retention time of an unretained solute, tM, and a solute

Time (min)

Figure 16 Separation of aromatic compounds by MEKC using a 65 cm (effective length 50 cm) x 50 ^m i.d. fused silica capillary and a mobile phase containing 30mmolL~1 sodium dodecyl sulfate and 50mmolL~1 sodium phosphate/100 mmol L~1 sodium borate buffer (pH = 7) at a field strength of 15 kV. (Reproduced with permission from Terabe S (1989) Trends in Analytical Chemistry 8: 129, copyright © Elsevier Science B.V.)

totally retained by the micelles, tMC; see Figure 16). The intrinsic efficiency of MEKC is much higher than column liquid chromatography, and optimization of the separation factor depends on a different set of parameters (changing surfactant type, use of additives, etc). Large values of the retention factor are unfavourable for obtaining high resolution since the additional term added to the resolution equation tends to zero at high k values. The optimum value of k for maximum resolution is around 0.8-5, corresponding to (tM/tMC)1/2. The retention factor is usually optimized by changing the surfactant concentration.

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