Factors That Influence Mobility,Resolution and Selectivity in Capi&l-lary zone electrophoresis. II. The Role of the Buffers& Cation

Abstract

The effect of the buffer cation on mobility, resolution and selectivity in capillary zone electrophoresis was investigated. The results show that mobility times of analyte increased with increasing cation size Cs⁺Rb⁺K⁺Na⁺Li⁺. The increase in mobility times was verified by measuring the electroosmotic flows of benzene, mesityl oxide and guanosine in the five alkali buffers. The results show that electroosmotic flows of the three above markers decreased as the cation size increased. The separation of a test mixture of nine dansylated amino acids was better when 0.1 H cesium acetate solution was used rather than lithium acetate. Also, there was no change in the order of elution of the solutes in the test mixture in the five acetate solutions having the same pH and concentration. It was observed that at the same applied voltage (20 kV) the resulting current increased as the atomic weight of the cation increased, which is expected based on charge/size distribution.     

Studies with the Selectrode: Determination of Oxalate Ion Activity

Abstract

A solid state oxalate sensor is reported utilizing a commercial ion-selective electrode, the Selectrode^TM. Comparative measurements in aqueous solution of similar carboxylate ions and common inorganic anions, indicates appreciabl'e selectivity for oxalate. The Selectrode^TM was activated with a mixture of silver sulphide, lead sulphide, and lead oxalate.     

Calorimetric Investigation of the Complexation of Didodecylcalix[4]arene-crown-6 with Alkali Metal and Ammonium Cations in Acetonitrile

Abstract

The Cs⁺ selectivity of some calix-crown ligands makes them excellent candidates for use in separation systems such as liquid membranes. Separation performance can be understood and predicted from thermodynamic data for cation complexation. We have therefore determined the log K, ΔH and ΔS for the interaction of Na⁺, K⁺, Rb⁺, Cs⁺ and NH₄ ⁺ with didodecyl-calix[4]arene-crown-6 in acetonitrile at 25°C by titration calorimetry. The ligand is strongly selective for Cs⁺, and the selectivity trend results entirely from the enthalpy contribution, with entropy effects opposing the trend. These results are discussed in light of some corresponding data obtained by other researchers with similar ligands.     

Computer-Assisted Optimization of pH and Ion Concentration Selectivity in HPLC Using a Mixture Design Simplex Method

Abstract

A computer-assisted mixture design simplex method is presented for optimization of two-factor (pH and ion concentration) simultaneous selectivity for the optimal separation in reversed-phase HPLC. The method is based on two-factor selectivity rectangle concept with a special polynomial estimated from nine preliminary runs. Then connect to general simplex method for optimization. Double criteria simulation system (DCSS) is established for the measurement of chromatographic performance by this method. The validity of the optimization strategy is proved by applying it to an actual mixture and as compared with the general simplex method about thirty eight experiments can be omitted.     

The Al3+ Sensitivity of Chitosan-Silk Fibroin Complex Membrane on Swelling and Its Application on Chemical Valve for the Separation of Isopropanol-Water Mixture

Abstract

A novel natural biopolymer complex membrane, namely, a crosslinked chitosan-silk fibroin complex membrane (semi-IPN membrane) was prepared. The complex membranes manifested a good ion sensitivity when swelled in AlCl₃ aqueous solutions with different concentrations. According to its different swelling values with different Al³⁺ concentrations, the complex membrane could act as a chemical valve to control the flux of isopropanol-water mixture when separated by pervaporation. The pervaporation results indicated that the flux also showed an ion sensitivity when the Al³⁺ content in the feed was changed. In the meantime, the ion sensitivity of the flux expressed the same tendency as that of the swelling ratio. In addition, the flux of isopropanol-water mixture was significantly improved while the high selectivity was maintained when suitable amount of AlCl₃ was added to the feed.     

Preparation and Pervaporation Performances of PEA‐based Polyurethaneurea and Polyurethaneimide Membranes to Benzene/Cyclohexane Mixture

Pervaporation is promising in the separation of benzene/cyclohexane mixture for the petrochemical industry. Two kinds of pervaporation membrane materials, including PEA‐based polyurethaneurea (PUU) and polyurethaneimide (PUI), were successfully synthesized from the same soft segment of poly(ethylene adipate)diol (PEA) and different hard segments via a two‐step method. The hard segment of PUU was prepared from toluene diisocyanate (TDI) and 4,4′‐diaminodiphenyl methane (MDA), while that of PUI was from 4,4′‐methylene‐bis(phenylisocyanate) (MDI) and pyromellitic dianhydride (PMDA). The structures and properties of PUU and PUI were characterized by means of FT‐IR, DSC and TGA. During the pervaporation experiment, the PUI membranes had a flux of 12.13 kg µm m^?2 h^?1 and separation factor of 8.25, while the PUU membranes had a flux of 26.35 kg µm m^?2 h^?1 and separation factor of 6.29 for 50 wt% benzene in the benzene/cyclohexane mixture at 40°C. The effects of the structures of hard segments on pervaporation performances were discussed. The investigation of the relationship in molecular structure and PV performances will be helpful for the choice and design of membrane materials in the separation of benzene/cyclohexane mixture.     

Study on composite membranes with high selective permeance properties

Flavonoids are natural products having several biological and physiological properties depending upon their molecular configurations. Flavonoids with similar configuration cannot be separated by traditional separation method and membrane separation technology whose selectivity is lower. This work investigates composite membranes with structural and functional molecular recognition properties prepared according to molecular imprinted technology. Functional silica sol was synthesized by taking luteolin as the template (or imprinting) molecule, γ-aminopropyltriethoxysilane (γ-APTS) as the functional monomer, and tetraethoxysilane (TEOS) as the cross-linker. The resultant functional silica sol was coated on Al₂O₃ microporous substrate followed by the removal of the template molecule. Scanning electron microscope micrographs showed a 5 μm thickness composite membrane with uniformly distributed porosity. Steady state flux was reached at ∼70 min at 215 L m⁻² h⁻¹ for the composite membrane, while a lower value of 168 L m⁻² h⁻¹ was measured for the blank membrane (i.e. non-templated). Further, in an aqueous mixture containing similar template molecules, the selectivity factor of luteolin to rutin was 14.1, thus suggesting that the imprinting process allowed for preferential permeance and affinity selectivity to the template molecule (i.e. luteolin). These results strongly suggest the formation of cavities, which are joined by channels to deliver the percolative effect for the permeation of luteolin. In addition to structural formation, further site recognition properties were accomplished by the functional silica sol in the composite matrix by electrovalent bonds. Considering the percolative effect in tandem with electrovalent bonds and under the influence of a concentration gradient (i.e. driving force), a mechanism of molecular recognition was proposed based on the molecular bond, followed by bond cutting and jumping to another site to form another molecular bond. The preparation method of the composite membrane was applied to other template molecules, and the template molecules can selectively permeate the membrane. So the method was universal for other substance. So it made it possible for the separation of the natural products exactly and efficiently. At the same time, it had great potential for the resolution of the chiral drugs and the preparation of the new membrane reactor.     

Evaluation of novel dendrimer chiral stationary phases using HPLC

Summary The reversed phase chromatographic properties of the [G1]-L-glutamic and ethyl ester-AC-silica (1), [G2]-L-glutamic acid ethyl ester-AC-silica (2) and the [G1]-L-glutamic acidt-butyl ester-AC-silica (3) dendrimer stationary phases were evaluated. Initial studies involved the comparison between these phases with a classic reversed phase (i.e. ODS1) by the separation of a standard reversed phase test mixture composed of dimethylphthalate, nitrobenzene, anisole, diphenylamine and fluorene. Separations were achieved with comparable performance to those obtained with the conventional reversed phase (ODS1). However, it was apparent that the chromatographic selectivity exhibited by the dendrimer stationary phases was different from that of the ODS1 phase. On a per mole basis, the dendrimers exhibited similar (and sometimes greater) affinity for these analytes compared with the ODS1 ligand. Subsequent chromatographic experiments were conducted upon the dendrimer chiral stationary phases using chiral analytes under reversed phase and normal phase conditions. Chiral resolution was not observed.     

Fluorinated Porous Poly(spirobifluorene) Via Direct C‒H Arylation: Characterization,Porosity, and Gas Uptake

Considering intrinsic properties of conjugated polyfluorenes and special functions of porous polymers, synthesis of fluorinated porous poly(spirobifluorene) via direct C?H arylation polycondensation is explored. Owing to the contorted structure and cross-linking nature, the obtained polymer FPSBF shows permanent porosities with Brunauer–Emmett–Teller specific surface area up to 700 m² g^?1 and exhibits a narrow pore size distribution with the dominant pore size at about 0.63 nm, which is more suitable for adsorption of small gas molecules. Based on the measured gas physisorption isotherms with pressure up to 1.13 bar, the obtained polymer shows good uptaking capacities for hydrogen (1.30 wt% at 1.0 bar and 77 K) and methane (4.80 wt% 1.0 bar and 273 K). Moreover, FPSBF has significant adsorption selectivity for CH₄ against N₂ and the estimated ideal adsorption selectivity ratio is up to 30/1 at 1.0 bar and 273 K, which makes the material possess potential application in gas separation.     

Simultaneous Determination of Two Synthetic Dyes Erytrosine and Sunset Yellow in a Pharmaceutical Syrup By First Derivative Visible Spectrophotometry

ABSTRACT.

A rapid first derivative spectrophotometric method for simultaneous determination of two synthetic dyes, erytrosine (E 127) and sunset yellow (E 110), in a mixture is proposed. The procedure does not require any separation step. The method was applied for determining the two compounds in a pharmaceutical syrup. Good linearity, accuracy, precision and selectivity were found, and the method is proposed for routine quality control purposes.     

Thallium(I) Selective Solid Membrane Electrode

Abstract

Heterogeneous membranes of 2.0 cm diameter were prepared from a 60:40 mixture of thallium(I) molybdoarsenate and Araldite, These membranes gave near Nernstian response to thallium(I) ions over the concentration range 10^?1 to 10^?3M but could be used for determination of thallium(I) down to 10^?5M. Slope of the log concentration-potential plot is improved in 10 and 25 percent acetone-water mixture. The response was independent of pH over the range 4.0 to 6.0, The response time of the electrode is few seconds and potentials generated are reproducible. The selectivity of the electrode over a large number of cations was studied. The values of selectivity coefficients are of the order 10^?2 for monovalent and 10^?3 for bivalent cations. Anions did not interfere. Potentiometric-titration of thallium nitrate with potassium chromate was also done using the membrane as an end point indicator electrode.     

Host-Guest Interaction in Ethylene and Ethane Separation on Zeolitic Imidazolate Frameworks as Revealed by Solid-State NMR Spectroscopy

The separation of ethane/ethylene mixture by using metal-organic frameworks (MOFs) as adsorbents is strongly associated with the pore size-sieving effect and the adsorbent-adsorbate interaction. Herein, solid-state NMR spectroscopy is utilized to explore the host-guest interaction and ethane/ethylene separation mechanism on zeolitic imidazolate frameworks (ZIFs). Preferential access to the ZIF-8 and ZIF-8-90 frameworks by ethane compared to ethylene is directly visualized from two-dimensional ¹H-¹H spin diffusion MAS NMR spectroscopy and further verified by computational density distributions. The ¹H MAS NMR spectroscopy provides an alternative for straightforwardly extracting the adsorption selectivity of ethane/ethylene mixture at 1.1∼9.6 bar in ZIFs, which is consistent with the IAST predictions.     

Synthesis and anion binding properties of 1,8-disulfonamidocarbazole dipyrromethane Schiff-base macrocycle & its amine analogue

A novel 1,8-disulfonamidocarbazole-dipyrromethane Schiff-base macrocycle (1) and its amine analogue (2) were designed and synthesised, and their anion binding properties were studied via UV–vis and ¹H NMR titration spectra. The obtained results showed that a small change in the macrocyclic structure (by reducing imines into the corresponding amines) produced a remarkable impact on its binding affinity and selectivity for anions. For example, macrocycle 1 displayed a 7.9:1 F^?/H₂PO₄^? selectivity; however, its amine analogue 2 showed a 78.5:1 F^?/H₂PO₄^? selectivity.     

Adsorptive Separation of Acetylene from Light Hydrocarbons by Mesoporous Iron Trimesate MIL‐100(Fe)

A reducible metal–organic framework (MOF), iron(III) trimesate, denoted as MIL‐100(Fe), was investigated for the separation and purification of methane/ethane/ethylene/acetylene and an acetylene/CO₂ mixtures by using sorption isotherms, breakthrough experiments, ideal adsorbed solution theory (IAST) calculations, and IR spectroscopic analysis. The MIL‐100(Fe) showed high adsorption selectivity not only for acetylene and ethylene over methane and ethane, but also for acetylene over CO₂. The separation and purification of acetylene over ethylene was also possible for MIL‐100(Fe) activated at 423 K. According to the data obtained from operando IR spectroscopy, the unsaturated Fe^III sites and surface OH groups are mainly responsible for the successful separation of the acetylene/ethylene mixture, whereas the unsaturated Fe^II sites have a detrimental effect on both separation and purification. The potential of MIL‐100(Fe) for the separation of a mixture of C₂H₂/CO₂ was also examined by using the IAST calculations and transient breakthrough simulations. Comparing the IAST selectivity calculations of C₂H₂/CO₂ for four MOFs selected from the literature, the selectivity with MIL‐100(Fe) was higher than those of CuBTC, ZJU‐60a, and PCP‐33, but lower than that of HOF‐3.     

Analysis of Sub-Microgram Levels of Palladium (II) in Environmental Samples by Selective Extraction and Spectrophotometric Determination with N-p-Methoxyphenyl-2-Furylacrylohydroxamic Acid and 5-(Diethylamino)-2-(2-Pyridylazo) Phenol

Abstract

Nine new hydroxamic acids in conjunction with four pyridylazo reagents were explored for extractive separation and spectrophotometric determination of palladium in environmental samples. It was found that maximum sensitivity and selectivity was achieved by employing N-p-methoxyphenyl-2-furylacrylohydroxamic acid (MFHA) and 5-(diethylamino)-2-(2-pyridylazo) phenol (DEPAP). Palladium was first selectively extracted with MFHA in isoamyl alcohol at pH 2.7-3.5 and the extract was equilibrated with a mixture of 5 M HCl and 10^{? 3} M solution of DEPAP in ethanol. The resulting intensely green ternary complex was measured at 560 nm (σ 5.1 × 10⁴ l mole^?1 cm^?1). The extraction system is suitable for enrichment of palladium over 15 times without loss in recovery and enables determination of palladium at levels as low as 10^?4 ppm (0.1 ppb). The method tolerates the presence of a large number of diverse ions normally associated with palladium, including platinum metals, and was employed for the determination of palladium in standard catalysts, biological materials, and freshwaters.     

Metal cation control of electroosmotic flow magnitude in phospholipid‐coated capillaries

CZE has become widespread for the separation and analysis of biomolecules such as proteins and peptides, due to factors such as, the speed of the separations, low sample volume, and high resolution associated with the technique. However, the separation of biomolecules by CZE does present a significant challenge due to the electrostatic attraction and adsorption of cationic, or cation containing, biomolecules to the capillary surface. To that end numerous methods have been developed to passivate, or protect the surface, in order to prevent the adsorption of analytes. Yet, in the process of protecting the capillary surface, the potential for further modification of the EOF, a factor crucial to effective analyte resolution, is greatly diminished. In seeking to overcome this limitation we have explored the potential of incorporating a range of metal cations into a phospholipid bilayer capillary coating. It has previously been established that the inclusion of calcium into the separation buffer with a phospholipid coating will reverse the EOF in the capillary. Here, we present our investigation of a broader range of metal cations included in the separation buffer (Ca²⁺, Mg²⁺, Co²⁺, Ni²⁺, Sr²⁺, Ba²⁺, and Ce³⁺) revealing that the choice of metal cation can drastically influence the EOF, with observed values between ?3.80 × 10^?4 and ?5.74 × 10^?5 cm²/V·s.     

Determination of column selectivity toward polycyclic aromatic hydrocarbons

An empirical test is described for the evaluation of column selectivity in reversed-phase liquid chromatography. Using a test mixture of three polycyclic aromatic hydrocarbons (PAH), overall column selectivity toward PAH was assessed for over 20 different commercial C₁₈ columns. Retention behavior was correlated to phase type (i.e., monomeric and polymeric surface modification chemistry) for custom synthesized phases. A classification scheme is proposed in which commercial C₁₈ columns are grouped into three classes based on retention behavior: monomeric-like, polymeric-like, and intermediate phase selectivity toward PAH. Correlation of retention behavior of the test mixture with the separation of PAH mixtures and with more general column properties (e.g., phase thickness) is discussed.     

Chromatographic separation of prebiotic oligosaccharides. Case study: separation of galacto-oligosaccharides on a cation exchanger

Chromatographic separation of prebiotic oligosaccharides, galacto-oligosaccharides from a typical post-reaction mixture containing unreacted substrate lactose and by-products glucose and galactose was investigated. A commercial cation-exchange resin Dowex 50WX4 was chosen as a prospective preparative-scale adsorbent and separation performance of its four ionic forms, H⁺, Na⁺, K⁺ and Ca²⁺, was tested. Since adsorption equilibrium isotherms were linear within the entire investigated range of concentrations, they were determined by pulse experiments for all saccharides present in a typical post reaction mixture including tri- and tetragalacto-oligosaccharides. From the four counter ions listed above, hydrogen offered the best selectivity and column performance. The selected H⁺-form of the cation exchanger was further investigated by means of frontal analysis where high ionic strength and elevated viscosity appear and can play a substantial role. Breakthrough curves were measured for monosaccharides, lactose, glucose–lactose mixture and a multicomponent commercial mixture of galacto-oligosaccharides, Vivinal^® GOS. The breakthrough curves were successfully described by the dispersive plug flow model with linear driving force approximation.     

Thin-Layer Chromatographic Separation of Copper and Mercury Chelates

Abstract

Thin-layer chromatographic separation of metal ions has become immensely popular in analytical chemistry in view of its speed, selectivity and applicability at tracer level. Quinoline-2-aldehyde thiosemicarbazone^1,2 was found to form yellow coloured chelates with metal ions such as copper, nickel, zinc, mercury, iron and lead at pH 7.5 and extract into chloroform. This, however reduces the sensitivity of the reagent as a chromogenic agent but the chromatographic run of the chelates on a thin layer of silica gel coated on glass plate increases the specificity and selectivity of the reagent. In this article we propose a method for separation of copper and mercury chelates from binary mixtures containing chelates of zinc, lead, iron and nickel. The method is applicable for analysis of synthetic mixtures and standard samples.     

Molecularly imprinted polymers prepared in aqueous solution selective for [Sar,Ala]angiotensin II

Conventional molecular imprinting technology allows the synthesis in organic solvents of molecularly imprinted polymers (MIPs) selective toward relatively low molecular weight compounds. However, synthesis in aqueous media of chemically and mechanically stable MIPs that can recognize biomolecules such as peptides and proteins still is a great challenge. In this article, we report the successful synthesis of peptide-selective MIPs in aqueous solution. HPLC evaluation of these polymers with a water-based mobile phase showed their selectivity for the peptide, [Sar¹,Ala⁸]angiotensin II (SA), that had been used as the template, but not for its parent peptide angiotensin II (AII). The binding capacity and selectivity of our MIPs depended on the ratio of template to functional monomer in the polymerization mixture, as well as on the ionic strength and pH of the chromatographic mobile phase. These MIPs can be used for chromatographic detection of the octapeptide [Sar¹,Ala⁸]angiotensin II in aqueous solution, with a detection limit of 8 pmol and a response that is linear (r²>0.99) over the concentration range 0.4-20 μM.