ISSN 1061-9348, Journal of Analytical Chemistry, 2012, Vol. 67, No. 4, pp. 378–385. © Pleiades Publishing, Ltd., 2012. 378 1 The displacement of chemical species in free fluid electrolyte under the effect of an electric field, known as electrophoresis, has been the topic of computer simulation for more than 25 years. During these years a unified mathematical model for all modes of electro- phoresis was developed. The modeling started from the relatively simple system and later it was generalized to multi-component systems and macromolecules [1]. Capillary electrophoresis (CE) is a useful, sensitive and efficient analytical method for ionic species. Although absolute sensitivity of CE is very high, its analytical reproducibility due to irregular concentra- tion depends on the sample. That is, the migration time of sample species may change, depending on the conditions of the system [2]. Although the CE system seems very simple, it could be very complex in the sense that the electric field in the capillary might be easily disturbed by sam- ple injection. It was reported that the electrophoretic dispersion was caused by the oscillation in the electric 1 The article is published in the original. field. In fact, if the electric field was accurately con- stant throughout the process, the separation occurred would be idealistic. Therefore, the time and location dependence of the electric field is very significant in CE, but detailed studies on the behavior of CE electric field are very scarce [3]. Computer simulation may be helpful in order to consider what would happen in the capillary during the separation and what factors could possibly improve the separation quality. Several researches were per- formed for modeling and simulation of CE, and non- linear partial differential equations (PDE) were numerically solved in an unsteady state [2–9]. However, the simulations have some difficulties such as numerical instability [2]. Despite step increas- ing, upstream term uses and coefficient rearrangement are some useful methods to solve these difficulties. Taking into account the above problems in CE sim- ulation, this paper proposes a modified method to sti- fle instability. In this work, main variables were rear- ranged, two basis cases were defined for total mobility, Separation and Detection of Lanthanides by Capillary Electrophoresis 1 A. Nilchi a , M. Edalat b , M. Taghiof a, b , and S. Rasouli Garmarodi a a Nuclear Science and Technology Research Institute, P. O. Box 11365/8486, Tehran, Iran b Department of Chemical Engineering, Faculty of Sciences, Tehran University, Tehran, Iran Received July 13, 2010; in final form, April 27, 2011 Abstract—Due to the importance of application of lanthanides in various industries especially the nuclear ones, and the advantages of capillary electrophoresis method in separation of metal cations, this research was carried out in order to investigate the separation potential of lanthanides using capillary electrophoresis via simulation method at laboratory scale. Since the properties of various types of lanthanides are very similar, the separation of lanthanides using the usual approaches was not possible. Thus, the separation of lanthanides was devised upon partial, competing complexation in order to differentiate their properties. Salicylic acid was firstly used as the primary UV-absorbing ligand, whereas formic, acetic, lactic, tartaric and citric acids, which showed no absorption in UV-spectrum and had weaker complexes in comparison to salicylic acid, were used as auxiliary ligands. Upon the results of spectrometry, the wave length of 210 nm was selected for detecting lanthanides. The properties and stability of lanthanides were examined and furthermore acetic and citric ac- ids were selected as auxiliary ligands. The simulation was carried out with respect to the transport phenomena in the unsteady state. The ion species dissociation was found to be directly dependent upon the concentra- tion, and was also used in complexation. The results of simulation showed that the diffusion control of H + and homogenizing electrical field promoted separation quality. The separation conditions were optimized by using the simulation results as well as the tests obtained. In order to optimize the experimental conditions, variable factors such as voltage, injection time, pH, temperature and ionic strength were examined. Also, methanol was used as dissolving modifier as well as noise reducer on the base line. Sodium nitrate was used as ionic strength controller and sucrose for increasing viscosity which optimized separation quality. Keywords: capillary electrophoresis, lanthanides, electrical field, simulation, ionic strength, pH. DOI: 10.1134/S1061934812040156 ARTICLES