Abstract
Resolution in micellar electrokinetic chromatography is highly complex and describes a non-linear function of the experimental variables. Four experimental variables; the surfactant concentration, the percentage of organic modifier, the applied temperature and the ionic strength of the buffer were studied via response surface modelling and related to resolution, retention factor and migration time window utilizing partial least-square regression. The effect of acetonitrile on the separation performance between enkephalin-related peptides was studied at four different domains, 0–5, 5–10, 10–15 and 15–20% (v/v), while keeping the other variables at constant intervals. Determination of the critical micellar concentration for sodium dodecyl sulfate, showed that micelles were formed even at high levels of acetonitrile and temperature. Principal component analysis of the responses revealed that the different parameters such as efficiency, migration time window and retention factor exert strong influence on the resolution, and could not be independently controlled. Furthermore the results revealed very different influence of the experimental variables in each domain and the effect of acetonitrile was highly non-linear and dependent on the temperature used. The resolution increased by increasing the temperature and acetonitrile in the low level domain, while it decreased in the high level domain. There seems to be a change in the thermodynamics of the system at high levels of acetonitrile, since increased temperature resulted in higher association of the peptides to the micelles.
Published Version
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