Migration time shift

The final obstacles remaining were migration time shifts and/or spikes in approximately 20% of any 10 consecutive injections of the same rMAb sample. Figure 8 shows typical spike peaks observed in the electropherograms of injections 1, 4, and 9 of the same rMAb samples... 

Since ACE is based mostly on the calculation of migration-time shifts of analytes upon addition of an interaction partner, migration-time reproducibility is extremely important. If the calculation is based on mobilities, this problem is certainly reduced. However, stable buffer electrolyte conditions are mandatory, which may be critical in sheath flow setups. 

Identification problems arise when the identity of a species is determined solely by retention times in a low-resolving separation system. More-dimensional analysis with different and independent methods is again the best solution. Capillary electrophoresis offers a fast and useful tool in this field (Michalke 1996), but specific problems (e.g., migration time shifts) must be taken into consideration. Standard addition procedures are therefore required. Precautions are also necessary concerning species altera-... 

Affinity capillary electrophoresis (ACE), reviewed by Shimura and Kasai,42 is a method for studying receptor-ligand binding in free solution using CE. The technique depends upon a shift in the electrophoretic mobility of the receptor upon complexation with a charged ligand. Pure receptor preparations or accurate concentration values are not required because only migration times are measured. 

Different migration times, poor peak shape, incorrect selectivity Peak shifting Poor sensitivity Leak error, no data acquired Inaccurate migration times... 

Note that the migration time of the IS does not change when the run buffer pH is varied however, shifts in mobility and resolution of the glycoprotein isoforms become apparent. 

In the example in Fig. 1, a mixture of anions is analyzed in a Tris-acetate buffer of pH 8. A 2% change in zeta-potential, from -50 to -51 mV, results in a dramatic shift in migration time of peaks with longer migration times. 

Preprocessing procedures are focused on improving the characteristics of CE data before proceeding with resolution and quantification tasks (16). Variations in the migration time of electrophoretic peak, often around l%-2%, may be responsible for data desynchronization and lost of trilinearity. Peak shifting... 

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