Are the asserted advantages of organic solvents in capillary electrophoresis real? A critical discussion

Abstract

Are the asserted advantages of organic solvents in capillary electrophoresis real? A critical discussionBackground electrolytes (BGEs) prepared in pure organic solvents are common alternatives to aqueous BGEs in capillary electrophoresis. Several general advantages of organic solvents over water have been asserted in the literature, namely (i) organic solvents increase the separation selectivity; (ii) organic solvents increase the separation efficiency; (iii) high separation voltages and/or high BGE ionic strengths can be used in organic solvents due to lower electric current compared to water. Related assumptions are that (iv) due to higher field strengths applicable in organic solvents the analysis time is shorter than in aqueous BGEs, and (v) the solubility and/or stability of components (either analytes or BGE chemicals) is higher/better in organic solvents. In the present work, these asserted advantages were critically evaluated based on the physical principles of ion transport and zone dispersion in solution. The result was that many of the above-mentioned general advantages are overestimated or even inexistent; often they have no fundamental basis.

Reproducible and efficient separation of aggregatable zein proteins by CZE using a volatile background electrolyte

“…For small ions, it has already been shown that the inverse of the effective mobility, assuming fully charged species, depends linearly on t/eZ, where Z, t and e are the solvent viscosity, the Debye dielectric relaxation time and the permittivity, respectively [34,35]. However, such general equation does not apply to proteins, since the ACN content will modify not only the pK a of the various acidic and basic sites [36] but will also modify the 3-D structure of the zein proteins [37,38] and thus their electrophoretic mobilities.…”

Development of HPLC and NACE methods for the simultaneous determination of benzoic and sorbic acids in sour snap beans containing oil

“…In NACE, the organic solvent and the electrolyte are the two important parameters for tuning the mobility of EOF (m eof ) and the effective mobility (m ep ), as well as selectivity and resolution [17][18][19]. MeOH, EtOH, and ACN are widely used as the organic media in NACE [20][21][22], and NH 4 Ac [20][21][22] and Tris [23] are commonly used as special buffering group and electrolyte in both CE and NACE.…”

“…However, MEKC featured some defects such as the longer migration time and complicated BGE composition. Nonaqueous CE (NACE), as an important CE separation mode, is performed in the BGE with an organic solvent medium, it can improve the preservative's solubility, the stability of EOF, the separation resolution, and the reproducibility of the method, due to the presence of the great difference of physicochemical properties between organic and water solvent [17][18][19]. Thus, the aims of the present work are as follows: (i) to develop a practical extraction and cleanup procedure prior to the analysis of BA and SA; (ii) to develop both practical HPLC and NACE methods for the measurement of BA and SA, and (iii) to determine BA and SA in sour snap beans containing oil, using the developed methods.…”

Development of a NACE method for simultaneous measurement of three adenosine monophosphate isomers in biomimicking prebiotic synthesis without sample pretreatment

“…NACE, as an important CE separation mode, is performed in the BGE with an organic solvent medium. It can improve the separation resolution and the reproducibility of the method, due to the great difference in physicochemical properties between organic and water solvent [42,43]. However, the analysis for nucleotides (especially for AMP isomers) has not been extensively documented by NACE.…”

“…Among these methods, HPLC is most widely used, due to its high separation performance, for the determination of nucleotides in many different samples [22][23][24][25][26][27][28][29][30][31]. As an alterative method, CE has been widely utilized in the nucleotide analysis in recent years [32][33][34][35][36][37][38][39][40][41][42] due to CE having many advantages over the traditional HPLC. Therefore, in this paper, we try to develop a practical CE method for the simultaneous measurement of three AMP isomers in the biomimicking prebiotic synthesis samples.…”