Polymeric Pseudostationary Phases Research Articles

Comparison of a polymeric pseudostationary phase in EKC with ODS stationary phase in RP-HPLC.

Poly(stearyl methacrylate-co-methacrylic acid) (P(SMA-co-MAA)) was induced as pseudostationary phase (PSP) in electrokinetic chromatography (EKC). The n-octadecyl groups in SMA were the same as that in octadecylsilane (ODS) C18 column. Thus, the present work focused on the comparison of selectivity between polymeric PSP and ODS stationary phase (SP), and the effect of organic modifiers on the selectivity of polymeric PSP and ODS SP. 1-butanol could directly interacted with PSP as a Class I modifier, and improved both of the methylene selectivity and polar group selectivity. When the analysis times were similar, the polymeric PSP exhibited better methylene selectivity and polar group selectivity. Although the hydrophobic groups were similar, the substituted benzenes elution order was different between polymeric PSP and ODS SP. Linear solvation energy relationships (LSER) model analysis found that polymeric PSP and ODS SP exhibited two same key factors in selectivity: hydrophobic interaction and hydrogen bonding acidity. But polymeric PSP exhibited relatively strong n- and π-electrons interaction to the analytes.

Determination of phthalates in food packing materials by electrokinetic chromatography with polymeric pseudostationary phase

Polymeric pseudostationary phase (PSP), formed by random copolymer poly (stearyl methacrylate-co-methacrylic acid) (P(SMA-co-MAA)), was used in electrokinetic chromatography (EKC) to separate 15 kinds of phthalates (PAEs). The organic solvent modifier is a key factor for the separation of PAEs. Without organic solvents, only four kinds of PAEs with smaller molecular weight could be separated in the running buffer containing 1% P(SMA-co-MAA). The other eleven kinds of PAEs with larger molecular weight could be separated within 25min by adding 40% (v/v) methanol and 2% (v/v) 1-butanol in the running buffer. The linear ranges of 15 kinds of PAEs were between 2 and 200mg/L, and the limit of detection based on the ratio of signal to noise of 3 were between 1 and 3mg/L. The method was applied to determination of PAEs in 6 kinds of food packing materials. The recoveries were between 81% and 118% with the RSD less than 4%.

Physicochemical and chromatographic characteristics of random amphiphilic copolymer aggregation in electrokinetic chromatography

The random amphiphilic polymeric aggregation, self-assembled from poly (methyl methacrylate-co-methacrylic acid) (P(MMA-co-MAA)), was explored as a novel pseudostationary phase (PSP) in electrokinetic chromatography (EKC) in our previous report. This work focused on physicochemical characteristics and PSP performances of the polymeric aggregations. The physicochemical characteristics of polymeric aggregations, including critical aggregation concentration (CAC), zeta potential, hydrodynamic diameter, and micropolarity were determined. Experimental results showed that polymeric aggregations had much lower CAC, which decreased the usage of copolymer in EKC, weakened ionic strength and shortened analysis time. The monomer molar ratio of the copolymer was a key factor for physicochemical characteristics and PSP performances of the polymeric aggregations. With the increase of the hydrophobic monomer molar ratio, CAC, micropolarity and dimension of polymeric aggregation decreased significantly while zeta potentials were similar. Correspondingly, separation window enlarged and methylene selectivity evaluated with six kinds of n-alkylphenone homologous series enhanced. Linear solvation energy relationships (LSER) analysis found that hydrophobic interaction is the most important interaction between analytes and polymeric PSPs. Compared with SDS micelle, polymeric aggregations owned more types of interactions, such as stronger hydrogen bonding and relative larger dipole interaction, which provided a bigger adjustment room to improve PSP selectivity.

Retention behavior and selectivity of a latex nanoparticle pseudostationary phase for electrokinetic chromatography

The retention characteristics and separation selectivity of a novel latex nanoparticle (NP) pseudostationary phase (PSP) for electrokinetic chromatography have been characterized. The anionic NPs have very low or no affinity for cationic solutes, but show significant interactions and retention based on hydrophobic interactions. Retention factors of alkyl-phenyl ketones increase linearly with the concentration of the NPs and have zero or near zero y-intercepts as expected for electrokinetic chromatography with non-micellar PSPs. The retention factors of these solutes and representative pharmaceuticals decrease logarithmically with increases in the concentration of ACN in the background electrolyte, as expected for reversed-phase retention. Linear solvation energy relationship analysis indicates that the NPs are less cohesive than would be expected for polymeric PSPs with similar structure but that the overall separation selectivity can be expected to be similar to polymer PSPs with similar backbone chemistry. The results indicate that the hydrophobic core of the NPs is non-cohesive and is highly accessible to solutes, whereas the ionic head groups are not as accessible and do not contribute substantially to retention or selectivity.

Recent progress in the use of ionic polymers as pseudostationary phases for electrokinetic chromatography

This review is an account of the development, utilization, and characterization of polymeric pseudostationary phases (PSPs) for EKC since the previous review in this series in 2007. Improvements in performance by means of new polymeric phases and modifications to previously reported materials are described. The use of EKC and spectroscopic studies to characterize the interactions between polymeric PSPs and analytes is discussed. The application of polymeric PSPs for techniques or approaches to which they provide particular advantages is reviewed. Chief among these is the application of polymeric PSPs for the combination of EKC with MS detection.

Electrokinetic chromatography with polymeric pseudostationary phases

Recent research and development efforts concerning polymeric pseudostationary phases (PSPs) for electrokinetic chromatography are reviewed. The introduction of new materials, characterization of structural effects on performance and selectivity, applications, and the use of polymeric PSPs with mass spectrometric detection are considered. Very interesting results concerning the effects of polymer structure have been reported. Significant developments have also been reported in the development of novel applications of polymeric PSPs, particularly for sample preconcentration using micellar affinity gradient focusing. The use of mass spectrometric detection with electrokinetic chromatography has seen significant development, and recent reports indicate that this is a robust and sensitive approach.

Recent progress in the use of ionic polymers as pseudostationary phases for EKC

This review concerns the introduction, characterization, and application of polymeric pseudostationary phases (PSPs) for EKC since 2004. Achiral and chiral polymers and separations are reviewed, as is the application of polymeric PSPs for the combination of EKC with mass spectrometric detection.

Cationic and perfluorinated polymeric pseudostationary phases for electrokinetic chromatography

Separation selectivity in electrokinetic chromatography (EKC) is directly affected by the chemistry and solvent characteristics of the pseudostationary phase (PSP). The chemical selectivity of micellar PSPs has been previously demonstrated to vary significantly between anionic and cationic surfactants as well as between hydrocarbon and fluorocarbon surfactants. Polymeric PSPs have also been demonstrated to provide unique selectivity. In the current study, four cationic polymeric pseudo-stationary phases, two of which have perfluorinated pendant groups, are introduced and characterized as PSPs in EKC. Their performance and selectivity is compared to conventional micellar PSPs with similar structure. The solvation characteristics and selectivity of the four polymers most closely resemble those observed for cationic micelles. The polymers are all more cohesive and more polar than their hydrocarbon micellar counterparts. The fluorocarbon PSPs did show preferential interaction with fluorocarbon solutes, were somewhat more cohesive, and were stronger hydrogen bond donors. However, the presence of fluorocarbon moieties did not have as dramatic an effect on selectivity as was observed and published previously for fluorocarbon micelles. This may result from the selectivity being dominated by the presence of the cationic head groups or from the fluorocarbon character of the pendant groups being moderated by the presence of hydrocarbon functionality on the polymer backbones.

Performance and selectivity of polymeric pseudostationary phases for the electrokinetic separation of amino acid derivatives and peptides

Two polymeric pseudostationary phases, one an acrylamide polymer and the second a siloxane polymer, have been investigated for the separation of naphthalene-2,3-dicarboxaldehyde (NDA)-derivatized amino acids and small peptides. The dervatized amino acids were detected by UV absorbance and laser-induced fluorescence (LIF) detection. The polymers provided very high efficiency and good selectivity for the separation of the amino acids. The separation selectivity using the polymers was significantly different from that of SDS micelles, and there were subtle differences in selectivities between the polymers. Although very good detection limits were obtained with LIF detection, a significant background signal was observed when the polymers were not washed to remove fluorescent impurities. The polymers did not separate the peptides very well. It is postulated that the fixed covalent structure of the polymers prevents them from interacting strongly or efficiently with the peptides, which are large in relation to the analytes typically separated by electrokinetic chromatography using polymers.

Conformational effects on the performance and selectivity of a polymeric pseudostationary phase in electrokinetic chromatography.

The effect of the conformation of a polymeric pseudostationary phase on performance and selectivity in electrokinetic chromatography was studied using an amphiphilic pH-responsive polymer that forms compact intramolecular aggregates (unimer micelles) at low pH and a more open conformation at high pH. The change in conformation was found to affect the electrophoretic mobility, retention, selectivity, and separation efficiency. The low-pH conformer has higher electrophoretic mobility and greater affinity for most solutes. The unimer micelle conformation was also found to provide a solvation environment more like that of micelles and other amphiphilic self-associative polymers studied previously. It was not possible to fully characterize the effect of conformation on efficiency, but very hydrophobic solutes with long alkyl chains appeared to migrate with better efficiency when the unimer micelle conformation was employed. The results imply that polymers with a carefully optimized lipophilic-hydrophilic balance that allow self-association will perform better as pseudostationary phases. In addition, the results show that electrokinetic chromatography is a useful method for determining the changes in solvation environment provided by stimuli-responsive polymers with changes in the conditions.

Recent developments in capillary electrokinetic chromatography with replaceable charged pseudostationary phases or additives.

Although electrochromatography in packed beds or monolithic columns has gained enormous interest, techniques based on charged pseudostationary phases like micelles are of high practical importance in electrically driven separation science. However, nonmicellar alternatives, e.g., using charged soluble polymers or smaller additives are still attractive, as they allow high concentrations of organic solvents, and their application is not limited by the critical micellar concentration. This review discusses the developments in the field of electrokinetic chromatography with these additives in the last three years, covering ionic polymeric pseudostationary phases, dendrimers and so-called micelle polymers, but also small molecules which implement separation selectivity due to their specific interaction with the analytes.

Ionenes acting as pseudostationary phases in capillary electrokinetic chromatography

Ionenes are used as polymeric pseudostationary phases in capillary electrokinetic chromatography. These polymers are composed of charged ammonium moieties interconnected with aliphatic carbohydrate chains and/or aromatic rings within the molecule. The effect of the ionene structure and its concentration in the background electrolyte on migration and separation of analytes was examined. The investigated systems were shown to be suitable for the separation of uncharged analytes possessing hydrophobic or aromatic groups.

High‐speed separations by electrokinetic chromatography using polymeric pseudostationary phases

High-speed separations of hydrophobic solutes by capillary-based electrokinetic chromatography (EKC) are reported in this short communication with analysis speed comparable to that of high-speed capillary electrochromatography (CEC). Polymeric pseudostationary phases can provide highly efficient separations of hydrophobic solutes in the presence of high concentration of organic solvents, and some of them have low electrical conductivity compared with sodium dodecyl sulfate micelles, so that a high electric field can be used without a significant loss of efficiency or resolution. Using poly(sodium 2-acrylamido-2-methylpropane sulfonate-co-dihydrocholesteryl acrylate) as the pseudostationary phase on a capillary column of 31 cm total length (23 cm effective length) and under an electric field strength of 962 V/cm, a separation of 12 out of 15 polycyclic aromatic hydrocarbons (PAHs) was achieved within 138 seconds. The RSD of retention times were less than 1.5% (n = 25).

High-speed separations by electrokinetic chromatography using polymeric pseudostationary phases

High-speed separations by electrokinetic chromatography using polymeric pseudostationary phases

Effect of pendent group structures on the chemical selectivity and performance of sulfonated copolymers as novel pseudophases in electrokinetic chromatography.

Amphiphilic copolymers of 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) with dihydrocholesteryl acrylate (pDHCHAt) or tert-octyl acrylamide (ptOAm) as comonomers were synthesized, characterized and used as new polymeric pseudostationary phases in electrokinetic chromatography. High-efficiency separations with theoretical plates around 500,000 to 870,000/m were achieved. Linear solvation energy relationships analysis of 20 solutes was performed to investigate the retention mechanism. Polycyclic aromatic hydrocarbons (PAHs) were separated under 30% v/v acetonitrile. The separation of nine aromatic model solutes by pDHCHAt showed significantly different selectivity from that of sodium dodecyl sulfate. Although only minor difference in selectivity was found for small aromatic compounds on pDHCHAt and poly(AMPS-lauryl acrylate), significantly different retention mechanism was found for PAHs and n-dodecanophenone comparing both copolymers. Significant chemical selectivity difference was found for selected small aromatic compounds on ptOAm and poly(AMPS-stearyl acrylamide).

On-column sample preconcentration in electrokinetic chromatography by sweeping with polymeric pseudo-stationary phases

This paper demonstrates in a practical manner the on-column preconcentration of hydrophobic solutes, such as quinine, alkyl phenones, and progesterone, by the sweeping mechanism using polymeric surfactants with highly acidic ionic head groups. The sulfonated and sulfated copolymers used showed high electrophoretic mobilities, high solubility, and good stability in organiclaqueous solutions with low pH values. More than 1000-fold increase in signal was observed for quinine, heptanophenone, and progesterone using sweeping in reversed-flow electrokinetic chromatography at low pH. The detection limit of quinine can be lower than 42 ppb (ng/mL) using a diode array UV detector. Quinine, a cationic hydrophobic solute with a relatively high retention factor, can be concentrated 5800 to 10,000-fold and separated from other hydrophobic solutes using a separation buffer containing a relatively high concentration of organic modifier. Under these conditions, detection of 12.5 ppb of quinine with a signal-to-noise ratio of 15 is achieved. The retention times and peak heights of hydrophobic solutes are shown to be reproducible.

Effect of pendant chain lengths and backbone functionalities on the chemical selectivity of sulfonated amphiphilic copolymers as pseudo-stationary phases in electrokinetic chromatography

Amphiphilic copolymers of AMPS (2-acrylamido-2-methyl-1-propanesulfonic acid) and hydrophobic monomers with various chemical structures were synthesized, characterized and used as novel electrokinetic chromatography polymeric pseudo-stationary phases, showing significant chemical selectivity differences from that of the conventional monomeric pseudo-stationary phase, sodium lauryl sulphate. Copolymers of AMPS and methacrylates with different pendant chain lengths (C 8, C 12 and C 18) were investigated and no significant difference in chemical selectivity was observed among them. However, the spacer bonding chemistry was shown to contribute to significant chemical selectivity difference, e.g. poly(AMPS–lauryl methacrylate) showed different chemical selectivity from poly(AMPS–lauryl methacrylamide). Linear solvation energy relationship analysis of 20 solutes by eight different polymeric pseudo-stationary phases was employed to investigate the solute molecule structural contributions to the retention. Hydrogen-bonding properties (described by system constants b and a) of poly(AMPS–alkyl methacrylamide) were found stronger than these of poly(AMPS–alkyl methacrylate).

Application of linear solvation energy relationships to polymeric pseudostationary phases in micellar electrokinetic chromatography.

Polymerized sodium 11-acrylamidoundecanoate (poly(Na 11-AAU)) was used as a pseudostationary phase (PSP) for micellar electrokinetic chromatography to separate uncharged compounds. The polymer PSP showed signifcantly different solute migration behaviors from conventional micelles including sodium dodecyl sulfate and poly (sodium 10-undecylenate), giving high separation efficiencies (>200000 theoretical plates/m). Linear solvation energy relationships were used to evaluate and characterize the chemical interactions that influence the retention behavior in the poly (Na 11-AAU) micellar system. It was found that the solute volume and solute hydrogen bond basicity mainly influenced the retention. The characteristic feature of the poly (Na 11-AAU) micellar system is that the micelle has a significantly higher capacity for dipole-dipole and dipole-induced dipole interactions as well as a slightly higher capacity for electron pair interactions than the aqueous phase. Due to its unique selectivity, the poly(Na 11-AAU) micellar system would become an attractive new option for selectivity optimization on methods development.

Synthesis and characterization of novel anionic siloxane polymers as pseudostationary phases for electrokinetic chromatography.

Four novel siloxane polymeric pseudostationary phases with three different ionic head groups have been synthesized and characterized for electrokinetic chromatography. Siloxane polymers are of interest in this application because of the wide range of chemistries that can be developed based on these backbones, including much of the chromatographic stationary phase chemistry developed in the last thirty years. All four of the siloxanes studied were synthesized by modification of a single methylhydrosiloxane polymer with highly acidic anionic functionalities. One of the siloxanes had both ionic groups and alkane chains attached to the siloxane backbone. The electrophoretic mobilities varied from being somewhat less than sodium dodecyl sulfate (SDS) to being much greater than SDS. The siloxanes substituted with ionic groups at all of the silicon sites showed significant nonequilibrium band broadening, severely limiting the efficiencies of these polymers. Substitution of 20% of the silicon sites with an alkyl group improved the efficiency of the separations and the peak symmetry. The chemical selectivities of the siloxane polymers are very different from SDS, but are similar to each other.

Polymeric and polymer-supported pseudostationary phases in micellar electrokinetic chromatography: performance and selectivity.

Several types of synthetic ionic polymers have been employed as pseudostationary phases in electrokinetic chromatography. The polymers have been shown to have some significant advantages and different chemical selectivity relative to conventional surfactant micelles. Polymeric phases are effective for the separation and analysis of hydrophobic and chiral compounds, and may be useful for the application of mass spectrometric detection. Additionally, the polymeric phases often demonstrate unique selectivity relative to micellar phases, and can be designed and synthesized to provide desired selectivity. This review covers efforts to develop and characterize the performance, characteristics, and selectivity of synthetic polymeric pseudostationary phases since their introduction in 1992. Some ideas for the future development of polymeric pseudostationary phases and the role they may play in electrokinetic separations are presented.