betadex and benzylamine

The electrokinetic chromatographic (EKC) separation of a series of aromatic bases was achieved utilising an electrolyte system comprising an anionic soluble polymer (polyvinylsulfonic acid, PVS) and a neutral beta-cyclodextrin (beta-CD) as pseudo-stationary phases. The separation mechanism was based on a combination of electrophoresis, ion-exchange interactions with PVS, and hydrophobic interactions with beta-CD. The extent of each chromatographic interaction was independently variable, allowing for control of the separation selectivity of the system. The ion-exchange and the hydrophobic interactions could be varied by changing the PVS and the beta-CD concentrations, respectively. Additionally, mobilities of the bases could be controlled by varying pH, due to their large range of pKa values. The separation system was very robust with reproducibility of migration times being <2% RSD. The two-dimensional parameter space defined by the two variables, [beta-CD] and %PVS, was modelled using a physical model derived from first principles. This model gave very good correlation between predicted and observed mobilities (r2=0.999) for the 13 aromatic bases and parameters derived from the model agreed with the expected ion-exchange and hydrophobic character of each analyte. The complexity of the mathematical model was increased to include pH and this three-dimensional system was modelled successfully using an artificial neural network (ANN). Optimisation of both the two-dimensional and three-dimensional systems was achieved using the normalised resolution product and minimum resolution criteria. An example of using the ANN to predict conditions needed to obtain a separation with a desired migration order between two of the analytes is also shown.

Topics: Amines; Aniline Compounds; Benzylamines; beta-Cyclodextrins; Chromatography; Chromatography, Ion Exchange; Cyclodextrins; Electrophoresis, Capillary; Hydrogen-Ion Concentration; Mathematics; Neural Networks, Computer; Polyvinyls; Pyridines; Reproducibility of Results; Sensitivity and Specificity; Sulfonic Acids

Capillary zone electrophoresis (CZE) methods with indirect absorbance detection for analyzing mixtures of alpha-, beta-, and gamma-cyclodextrins (CDs) and their derivatives have been developed. Benzylamine, salicylic, sorbic, or 1-naphthylacetic acid (NAA) was utilized as background electrolyte (BGE) and absorbance provider. Separation of alpha-, beta-, and gamma-CD could be achieved in less than 18 min when the CZE was run in 2 mM NAA or 5 mM sorbate solution (pH 12.2) and detected by indirect absorbance at 222 or 254 nm, respectively. Mixtures of alpha- and beta-CDs, and dimethyl- and trimethyl-derivatives of beta-CD could also be analyzed by CZE, using 50 mM salicylic acid or benzylamine solution (pH 6.0) as BGE with indirect absorbance detection at 230 and 210 nm, respectively. CZE methods for determining the inclusion complex formation constants of various CDs for salicylic acid or benzylamine with either direct or indirect absorbance detection have also been developed. The formation constants of salicylate are in the range from ca. 8 +/- 0.3 mole-1 for the complex with alpha-CD to ca. 99 +/- 2 molarity-1 for the complex with methyl-beta-CD. The detection limits (determined at a signal-to-noise ratio of 3) for the NAA and the salicylate system are ca. 0.1 mM and 1 mM, respectively.

Topics: alpha-Cyclodextrins; Benzylamines; beta-Cyclodextrins; Cyclodextrins; Electrolytes; Electrophoresis, Capillary; gamma-Cyclodextrins; Naphthaleneacetic Acids; Salicylates; Salicylic Acid; Sorbic Acid