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Rocchi S.,National Research Council Italy | Fanali S.,National Research Council Italy | Farkas T.,Phenomenex Inc. | Chankvetadze B.,Tbilisi State University
Journal of Chromatography A | Year: 2014

In this study the separation performance of various chiral stationary phases (CSPs) made of polysaccharide-based chiral selectors coated onto superficially porous (core-shell or fused-core) silica supports were evaluated. The CSPs obtained by coating of various amounts of chiral selector (1-5%) onto supports of various pore size (100 and 300. Å) were studied. Their evaluation was pursued in both chiral nano-liquid chromatography (nano-LC) and chiral capillary electrochromatography (CEC). Among the goals of this study was to re-examine our previous unexpected finding of better performance of superficially porous CSP under CEC conditions compared to nano-LC conditions for a new set of chiral compounds, as well as to study the effect of varying the chiral selector content and nominal pore size of supporting silica on the performance of core-shell silica-based polysaccharide-type CSPs. Based on the results of this study it can be seen that CSPs based on superficially porous silica can successfully be used for the separation of enantiomers in both nano-LC and CEC mode. Only a slight advantage of CEC over nano-LC mode was observed in this study from the viewpoint of plate numbers, especially at higher mobile phase flow rates. It must also be noted that the optimal theoretical plate height is still too high and further optimization of superficially porous CSPs is necessary for both nano-LC and CEC applications. © 2014 Elsevier B.V. Source


Lomsadze K.,Tbilisi State University | Jibuti G.,Tbilisi State University | Farkas T.,Phenomenex Inc. | Chankvetadze B.,Tbilisi State University
Journal of Chromatography A | Year: 2012

This article reports comparative high-performance liquid chromatographic separations of enantiomers with chiral stationary phases (CSPs) prepared by coating cellulose tris(4-chloro-3-methylphenylcarbamate) on totally porous and on core-shell type silica of comparable particle diameter. Several interesting observations were made: (1) the selectivity of separation was higher on core-shell type CSP compared to totally porous CSP at comparable content of chiral selector (polysaccharide derivative); (2) much flatter dependence of plate height on the mobile phase flow rate was observed for columns packet with CSP prepared with core-shell silica compared to the ones packed with CSPs prepared with totally porous particles; (3) at low mobile phase flow rates core-shell CSP provided lower resolving ability compared to a commercially available CSP having four times higher content of chiral selector along with higher retention of chiral analytes. However, at high flow rates core-shell type CSP performed similarly or better than the commercial column in regards of plate count (N) and peak resolution (Rs) per column length and within a given total analysis time. The advantage of CSP prepared with core-shell silica is obvious from the viewpoint of plate numbers and resolution calculated per unit time (i.e. speed of analysis). © 2012. Source


Fanali S.,National Research Council Italy | D'Orazio G.,National Research Council Italy | Farkas T.,Phenomenex Inc. | Chankvetadze B.,Tbilisi State University
Journal of Chromatography A | Year: 2012

In this study two types of silica particles, one fully porous and the other superficial porous (core-shell or fused-core) were modified with a polysaccharide-type chiral selector and evaluated for the separation of enantiomers in nano-liquid chromatography (nano-LC) and capillary electrochromatography (CEC). The major goal of this project was to critically evaluate the contribution of the "flow through particles" to enhancing peak efficiency in CEC compared to nano-LC. The better performance of fused-core silica particles compared with silica particles of comparable size but having through pores questions the previous assumption that "flow through particles" is the major contributor to enhancing peak efficiencies observed in CEC. In addition, based on the results of this study it is suggested that contrary to previous reports on core-shell particles behaving poorly in narrow bore columns, these materials are quite suitable for CEC, at least in capillary columns of 100 μm I.D. © 2012 Elsevier B.V. Source


Mosiashvili L.,Tbilisi State University | Chankvetadze L.,Tbilisi State University | Farkas T.,Phenomenex Inc. | Chankvetadze B.,Tbilisi State University
Journal of Chromatography A | Year: 2013

This article reports the systematic study of the effect of basic and acidic additives on HPLC separation of enantiomers of some basic chiral drugs on polysaccharide-based chiral columns under polar organic mobile-phase conditions. In contrary to generally accepted opinion that the basic additives improve the separation of enantiomers of basic compounds, the multiple scenarios were observed including the increase, decrease, disappearance and appearance of separation, as well as the reversal of the enantiomer elution order of studied basic compounds induced by the acidic additives. These effects were observed on most of the studied 6 chiral columns in 2-propanol and acetonitrile as mobile phases and diethylamine as a basic additive. As acidic additives formic acid was used systematically and acetic acid and trifluoroacetic acid were applied for comparative purposes. This study illustrates that the minor acidic additives to the mobile phase can be used as for the adjustment of separation selectivity and the enantiomer elution order of basic compounds, as well as for study of chiral recognition mechanisms with polysaccharide-based chiral stationary phases. © 2013 Elsevier B.V. Source


Matarashvili I.,Tbilisi State University | Chankvetadze L.,Tbilisi State University | Fanali S.,National Research Council Italy | Farkas T.,Phenomenex Inc. | Chankvetadze B.,Tbilisi State University
Journal of Separation Science | Year: 2013

The separation of enantiomers of ten chiral arylpropionic acid derivatives was studied on six different polysaccharide-based chiral HPLC columns with various normal-phase eluents. Along with the successful separation of analyte enantiomers, the emphasis of this study was on the effect of the chiral selector and mobile phase composition as well as of the separation temperature on the elution order of enantiomers. The interesting phenomena of reversal of enantiomer elution order function of the polysaccharide backbone (cellulose or amylose), type of derivative (carbamate or benzoate), nature and position of the substituent(s) in the phenylcarbamate moiety, the polar modifier of the mobile phase (ethanol or 2-propanol), its content in the mobile phase, and separation temperature were investigated. In addition, an unusual increase in retention with increasing temperature was observed for some arylpropionic acid derivatives. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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