GPC,CD and sedimentation analysis of poly-Lys and branched chain poly-Lys-poly-DL-Ala polypeptides

Three different poly-L-lysine (pLys) samples and a branched polypeptide poly-[L-Lys-(DL-Ala)_m] (poly-L-Lys-poly-DL-Ala, AK) were synthetized. Relative molar mass distribution, its average and the degree of polymerisation were determined by sedimentation analysis and gel permeation chromatography (GPC). The conformation of the polymers in solution was studied by circular dichroism (CD) spectroscopy at various pH values and ionic strengths. The data obtained by different methods were compared.A preliminary account of this work was read at the 4^th Conference on Colloid Chemistry, Eger, 1983.     

Separation and determination of sugars by reversed-phase high-performance liquid chromatography after pre-column microwave-assisted derivatization

In this study the possibility of derivatizing sugars using microwave irradiation was investigated. The amount of reagent, irradiation intensity, and derivatization time were optimized. In the derivatization of sugars with p-nitroaniline the reaction is complete within 5 min at 600 W when the p-nitroaniline-to-sugar and NaBH₃CN-to-sugar mole ratios were above 1.4 and 3.1, respectively. A Doehlert design was used to optimize the mobile phase for separation of p-nitroaniline-labeled sugars; and the best separation was obtained by use of 0.01 mol L⁻¹ acetate buffer at pH 4.40 containing 11.0% acetonitrile. Analysis using this method was highly sensitive and analysis time was short. Finally, a food sample was analyzed using the proposed method.     

Prediction of the chromatographic behaviour for a series of diuretic compounds

Summary The proportion of organic modifier and the pH of the acetonitrile-water mixtures used as mobile phases were optimized in order to separate a group of diuretic compounds covering a wide range of physyco-chemical properties. The Linear Solvation Energy Relationship (LSER) formalism based either on the multiparameter π^*, β and α scales or the single solvent polarity parameterE _T ^N , have been used to predict their chromatographic behaviour as a function of the percentage of acetonitrile in the eluent. Moreover, correlation established between retention and pH of the aqueous-organic mobile phases have been used to predict the chromatographic behaviour of the diuretic compounds studied as a function of the eluent pH. Linear correlation between a function of the eluent pH. Linear correlation between the chromatographic retention and theE _T ^N polarity parameter of mobile phases containing different percentages of organic modifier has been obtained Based on the knowledge of the acid-base dissociation constant the relation between retention and mobile phase pH has also been linearized. These relationship allowed an important reduction of the experimental retention data needed for developing a given separation and a great improvement in chromatographic optimization schemes.     

Identification of proteins,drying oils,waxes and resins in the works of art micro‐samples by chromatographic and mass spectrometric techniques

Simplified method for simultaneous identification of proteins, drying oils, waxes, and resins in the works‐of‐art samples was developed. Liquid chromatography with mass spectrometry and gas chromatography with mass spectrometry were used to identify natural materials most frequently encountered in historical paintings. Protein binders were extracted with ammonia and purified using miniaturized solid‐phase microextraction (Omix tips) to efficiently suppress matrix interferences. Zwitterionic stationary phase was used for separation of 16 underivatized amino acids analysis with hydrophilic interaction liquid chromatography that was subsequently quantified with liquid chromatography with mass spectrometry. Gas chromatography with mass spectrometry was used to analyze drying oils, waxes, and resins after one‐step saponification/transmethylation with (m‐trifluoromethylphenyl)trimethylammonium hydroxide (Meth‐Prep II). While the drawback of this reagent is low reactivity towards hydroxyl groups, sample pretreatment was much simpler as compared to the other methods. Fatty acids derivatization with the Meth‐Prep II reagent was compared with their silylation using N,O‐bis(trimethylsilyl) trifluoroacetamide/trimethylchlorosilane mixture. It was concluded that fatty acids analysis as their methyl esters instead of trimethylsilyl esters had a minor impact on the method sensitivity. The developed method was used to analyze samples from 16^th and 17^th century historical paintings.     

Analysis of the characteristic PSP profiles ofPyrodinium bahamense and several strains ofAlexandrium by HPLC based on ion-pair chromatographic separation, post-column oxidation, and fluorescence detection

Summary A sensitive HPLC method for determination of paralytic shellfish poisoning (PSP) based on ion-pair chromatographic separation of PSP toxins, post-column oxidation with periodic acid, and fluorescence detection has been used to determine toxin profiles ofPyrodinium bahamense and several strains ofAlexandrium. The HPLC chromatograms revealed clear differences betweenPyrodinium bahamense andAlexandrium strains. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996.     

A convenient synthesis of long-chain 4-substituted benzyloxycarbonyl alkanethiols for the formation of self assembled monolayers on metal substrates

New 4-substituted benzyl esters of 16-mercaptohexadecanoic acid were prepared by developing a practicable synthetic procedure and using readily available staring materials. The compounds synthesized have been characterized by NMR, MS, IR spectra and elemental analysis. The mercapto derivatives are precursors for the formation of self-assembled monolayers on metal substrates. Dedicated to Professor Dr. Manfred Hesse on the occasion of his 70 ^th birthday     

Determination of biogenic amines in fermented beverages and vinegars by pre-column derivatization withpara-nitrobenzyloxycarbonyl chloride (PNZ-Cl) and reversed-phase LC

Summary The reagentp-nitrobenzyloxycarbonyl chloride (PNZ-CI) was used for pre-column derivatization of biogenic amines (BAs) at ambient temperature followed by reversed-phase, liquid-chromatographic separation of the derivatives. Optimized derivatization of samples was achieved within 10 min in borate buffer by adding PNZ-Cl in acetonitrile (MeCN). Excess reagent was scavenged by subsequent addition of glycine in water. For LC a Superspher^? RP-18e column and gradient elution using a ternary gradient system containing sodium acetabe buffer (pH 6.1), sodium acetate buffer (pH 4.3) and MeCN, were used. The PNZ-derivatives were quantified by their UV-absorption at 265 nm. Detection limits of BAs were approximately 62–1000 μg L⁻¹ (injected amounts: 53–850 pg) at a signal-to-noise ratio of 3:1. The coefficients of determination were 0.9906–0.9992. Diaminohexane was used as internal standard. Recoveries of BAs ranged from 78–93% depending on the food matrix. This method was applied to the quantitative determination of 2-phenylethylamine, tryptamine, serotonin, putrescine, histamine, cadaverine, tyramine, spermidine, and spermine, in beer, wine, vinegars, and lactic fermented cabbage juice. Parts of the results were presented at the 35th Congress of the “Deutsche Gesellschaft für Ern?hrung”, Kiel, 19^th–20^th March 1998, and the “Regionaltagung der Lebensmittelchemiker”, Giessen, 9^th–10^th March 1998     

Evaluation of phenyldimethylethoxysilane treated high-performance thin-layer chromatographic plates. Application to analysis of flavonoids inScutellariae radix

Summary The retention and selectivity of flavonoids (baicalin, baicalein, wogonin, oroxylin A) inScutellariae radix have been studies by high-performance thin-layer chromatography on phenyldimethylethoxysilane-treated silica plates. The silica plates treated with phenyl groups were used for physical and chemical analysis. From elemental carbon analysis, the maximum number of bonded phenyl surface groups per gram was calculated to be 0.467×10²¹ (Oginal silica plate: Merck Art. 15109, Silica gel 100 F₂₅₄). With methanol-1/15 M phosphate buffer (pH 6.2) mixtures as mobile phase, baicalin, baicalein, wogonin, and oroxylin A inScutellariae radix were separated. It has been shown that phenyl-treated plates are more suitable for selective separation of baicalin, baicalein, wogonin, and oroxylin A than octadecyl-treated plates.     

Silica spheres coated with C18‐modified gold nanoparticles for capillary LC and pressurized CEC separations

Nonporous monodispersed silica spheres of 1.3 μm were coated with gold nanoparticles (AuNPs) and subsequently coated with n‐octadecanethiol. By transmission electron microscopy analysis, the average diameter of the AuNPs on the silica spheres was determined to be 12 nm. The chromatographic and electrochromatographic properties of self‐assembled n‐octadecanethiol AuNP‐coated silica microspheres (C18‐AuNPs‐SiO₂) were investigated using a group of nonpolar PAHs. The stationary phase appears to display a characteristic reversed‐phase behavior. Higher separation efficiency and shorter separation times were obtained using pressurized CEC (pCEC) compared with capillary LC (CLC). A maximum column efficiency of about 2.5×10⁵ plates per meter and less than 18 min separation time for benzene were obtained in pCEC while only 66 507 plates per meter and an analysis time of nearly 100 min were observed in CLC mode. A chemical stability test of the C18‐AuNPs‐SiO₂ stationary phase under extremely high and low pH conditions demonstrated that it is stable at pH 12 and 1 for at least 60 h. The results confirm that C18‐AuNPs‐SiO₂ possesses a high rigidity to withstand high packing pressures and can be used as a good stationary phase for CLC and pCEC.     

Optimization of an anion-exchange high performance liquid chromatography-inductively coupled plasma-mass spectrometric method for the speciation analysis of oxyanion-forming metals and metalloids in leachates from cement-based materials

A method was developed for the speciation analysis of the oxyanions of As(III), As(V), Cr(VI), Mo(VI), Sb(III), Sb(V), Se(IV), Se(VI) and V(V) in leachates from cement-based materials, based on anion-exchange HPLC coupled with ICP-MS. The method was optimized in a two-step multivariate approach: the effect of sample pH and mobile phase composition on resolution, peak symmetry and analysis time was studied. Optimum conditions were then identified for the significant experimental factors by studying their interdependence. A mobile phase composition of 20 mM ammonium nitrate, 50 mM ammonium tartrate and pH 9.5 was found to be a compromise optimum for the separation of the target analytes using isocratic elution. The optimum condition provided separation of the analytes in less than 6 min, at a mobile phase flow rate of 1.0 mL/min. The signal intensities of the analytes were improved by adding 1% methanol to the mobile phase. The limit of detection of the method was in the range 0.2–2.2 μg/L for the various species. The effect of sample constituents was studied using spiked concrete leachates. The method was used to determine the target oxyanionic species in leachates generated from a concrete material in the pH range 3.5–12.4; CrO₄²⁻, MoO₄²⁻ and VO₄³⁻ were detected in most of the leachates.     

Chiral Separation of (R,R)-Tadalafil and Its Enantiomer in Bulk Drug Samples and Pharmaceutical Dosage Forms by Chiral RP-LC

A new simple isocratic chiral RP-LC method has been developed for the separation and quantification of the enantiomer of (R,R)-tadalafil in bulk drugs and dosage forms with an elution time of about 20 min. Chromatographic separation of (R,R)-tadalafil and its enantiomer was achieved on a bonded macro cyclic glycopeptide stationary phase. The method resolves the (R,R)-tadalafil and its enantiomer with a resolution (R _s) greater than 2.4 in the developed chiral RP-LC. The mobile phase used for the separation and quantification of (R,R)-tadalafil and its enantiomer involves a simple mixture of reverse phase solvents and the cost of analysis was drastically decreased. The test concentration is 0.4 mg mL⁻¹ in the mobile phase. This method is capable of detecting the enantiomer of (R,R)-tadalafil up to 0.0048 μg wrt test concentration 400 μg mL⁻¹ for a 20 μL injection volume. The drug was subjected to stress conditions of hydrolysis, oxidation, photolysis and thermal degradation. There was no interference of degradants with (R,R)-tadalafil and its enantiomer in the developed method. The developed chiral RP-LC method was validated with respect to linearity, accuracy, precision and robustness. The percentage recovery for the enantiomer of (R,R)-tadalafil in bulk drug samples and in dosage forms ranged from 97.0 to 102.5%. The test solution was found to be stable in the mobile phase for 48 h after preparation.     

Light energy conversion with pheophytina monolayer at the SnO2 optically transparent electrode

The photoelectrochemical, absorption and fluorescence properties of pheophytin a mono- and multilayers, deposited on optically transparent tin oxide electrodes and quartz slides were investigated. Spectra of photocurrents coincided with the absorption spectra of photosynthetic pigment in monolayers at the SnO₂/solution interfaces. The anodic and cathodic photocurrents were measured at various electrode potentials. Effects of pH, electrode potentials, and concentration of redox reagents on the conversion of solar energy in monolayers on optically transparent electrodes are discussed. The absorption and fluorescence spectral characteristics, and fluorescence lifetime measurements of pheophytina in monolayers and thin films are also discussed in view of the aggregation properties of the photosynthetic pigment. The thermodynamics of adsorption of large amphiphilic compounds at the interface between two immiscible liquids is considered. The adsorption behavior of pheophytin a dissolved in different solvents is investigated. The thermodynamic parameters of pheophytin a adsorption at octane/water and benzene/water interfaces were determined.Presented at the Symposium, 76^th CSC Congress, Sherbrooke, Quebec, May 30–June 3, 1993, honoring Professor Donald Patterson on the occasion of his 65^th birthday.     

Determination of 8-hydroxyquinoline sulfate in tuberculin solutions by planar and high performance liquid chromatography

Summary TLC and HPLC methods for the determination of the preservative, 8-hydroxyquinoline sulfate in PPD-T tuberculin solution were developed. The planar chromatography method involved separation of 8-hydroxyquinoline sulfate on a TLC plate using a butyl-acetate: formic acid: 2-propanol mobile phase, detection and quantitation by densitometric scanning. The HPLC method was on a LiChrosorb RP-18 column with acetonitrile-water (65:35 v/v) mobile phase, adjusted to pH 3.05 by phosphoric acid. Linearity, reproducibility and accuracy were found to be satisfactory. Under selected conditions, the limit of detection (LOD) of both methods was similar-about 25 ng. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

Analysis of organic pollutants in water at trace levels using fully automated solid-phase extraction coupled to high-performance liquid chromatography

Summary A method has been developed for the determination of trace levels of 32 pesticides, 19 explosives and 16 polycyclic aromatic hydrocarbons (PAH) in water in three individual steps. Solid-phase enrichment (SPE) is coupled to high-performance liquid chromatography (HPLC) with a fully automated system. The organic pollutants are enriched on reusable cartridges packed with adsorbent materials: pesticides and explosives on a mixed bed of divinylbenzene-ethylvinylbenzene copolymers (LiChrolut EN^?) and perfluorinated polyethylene (PolyF^?), and polycyclic aromatic hydrocarbons on C₁₈-modified silica (Zorbax^? ODS1). Thermally assisted desorption (TAD) has been shown to increase the recovery of analytes significantly. As all enriched analytes are transferred to the detector, only fifty millilitres of sample is needed for each single on-line analysis, compared with at least a litre for conventional methods. The separation of the enriched organic analytes is performed on specialized HPLC columns based on reversed-phase materials. The limits of detection of the system employed were found to be below 100 ng L⁻¹. Use of fluorescence detection for the polycyclic aromatic hydrocarbons resulted in limits of detection in the upper pg L⁻¹ range. Thek values, number of theoretical plates, the recovery rates and the limits of detection of this method for fast screening of organic pollutants from three fifty-millilitre aqueous samples are described. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

类球形正交LiMnO2的制备、微结构和电化学性能

以共沉淀法得到的类球形MnCO₃为前驱物，制备了类球形正交LiMnO₂(So-LiMnO₂)，采用XRD、SEM和N₂吸附技术对样品进行表征；与非球形正交LiMnO₂(No-LiMnO₂)进行了对比研究。结果表明：o-LiMnO₂的堆垛层错度、结晶状况、颗粒形貌和大小与前驱物的微结构密切相关；在80次电化学循环测试过程中，So-LiMnO₂经15次循环可达最大的放电容量152 mAh·g^-1，其容量衰减平均每次循环0.58 mAh·g^-1；而No-LiMnO₂要经过38次循环才能达到最大放电容量128 mAh·g^-1，容量衰减平均每次循环高达1.24 mAh·g^-1。TEM和EDS分析证明：由一次粒子团聚的类球形So-LiMnO₂能有效地抑制电解液对材料的腐蚀、减少Mn的溶解，从而提高了电化学循环能力。     

Phase separation in aqueous solutions of polyethylaminophosphazene hydrochloride during heating

It is shown that aqueous solutions of polyethylaminophosphazene hydrochloride undergo phase separation during heating. This phenomenon is studied in detail at pH 3.5 (0.1 M citrate buffer) in relation to the composition of the system with the use of nephelometry and high-sensitivity DSC. The cloud points and the enthalpy of phase separation of the system are determined, and its phase diagram is constructed. The system features a lower critical solution temperature: w _2,cr = 7.3 × 10⁻⁴ and T _cr = 34.3°C. The enthalpy of phase separation is 12.8 ± 0.6 J/g of the polymer, regardless of the system composition. A new approach to the analysis of DSC data on the phase separation of aqueous solutions of polymers during heating is advanced on the basis of calorimetric parameters coupled with the data on the composition of coexisting phases. Through this approach, the main contribution to the heat effect of phase separation of the system under study is related to a change in the energy state of a polyethylaminophosphazene hydrochloride molecule as a result of its dehydration.     

Arsenic sorption and redox transformation on iron‐impregnated ordered mesoporous carbon

Ordered mesoporous carbon has been actively investigated for its potential applications as catalyst supports, electrochemical materials and gas separation media. In this study, we tested an iron‐modified ordered mesoporous carbon (FeOMC) for its ability to adsorb arsenic from the aqueous phase. The FeOMC synthesis involved the preparation of an ordered silica template SBA‐15, in situ polymerization of acrylic acid in the template, carbonization and template removal to obtain the ordered mesoporous carbon, and iron impregnation. Batch experiments showed that the pH level of the solution had a major impact on arsenic sorption. Further, we found that the presence of anions (i.e. PO₄^3? and SiO₃^2?) could significantly decrease the sorption of both arsenate and arsenite. Arsenite oxidation to arsenate was observed in alkaline solutions, with or without anions being present. The oxidation of arsenite was attributed to both direct and catalytic reactions with the surface functional groups on the ordered mesoporous carbon. Adsorption of arsenic on FeOMC could be well explained by the surface complexation model. Copyright © 2007 John Wiley & Sons, Ltd.     

A study of the behaviour of some new column materials in the chromatographic analysis of Cinchona alkaloids

Summary A major problem in the HPLC analysis of alkaloids is the poor peak shape and consequently low resolution, due to the interactions of the basic alkaloids with the residual acidic silanol groups of most reversed phase materials. The performance of new packing materials specially designed for the separation of basic compounds has been studied using mobile phases without the special additives commonly applied in the analysis of alkaloids. Strongly basic Cinchona alkaloids were used as test compounds. Retention characteristics and selectivities of each material were studied, after mobile phase optimisation for the column. The influence of the major factors (nature and content of the organic modifier, pH value, salt concentration) affecting resolution was studied. The mobile phases were chosen so that they could be used in thermospray LC-MS. The addition of salts to the mobile phase improves separation but in general the modification of the mobile phase gave little change in selectivity. The performance of silica-based C₁₈ material proved superior to the polymer materials tested.     

Optimization of the composition and pH of the mobile phase used for separation and determination of a series of quinolone antibacterials regulated by the European Union

Summary To ensure the safety of human food the European Union (EU) has set tolerance levels for quinolone compounds in animal products, so screening and confirmatory analytical methods are required for monitoring of these drugs. In this work, the proportion of organic modifier and the pH of acetonitrile-water mixtures used as mobile phases were optimized for separation of a group of quinolones. Linear solvation energy relationship (LSER) formalism based on the single solvent polarity parameterE _T ^N was used to predict the chromatographic behaviour of the compounds as a function of the amount of acetonitrile in the mobile phase. Correlation between retention and the pH of aqueous-organic mobile phases has also been used to optimize mobile-phase pH. The optimized mobile phase was a linear gradient starting from 18∶82 (v/v) acetonitrileacetate + formate buffer, pH 2.5. Quality data were determined and were satisfactory. The method detection limit was approximately 10 ng mL⁻¹ for most of the quinolones studied. The proposed mobile phase is compatible with mass spectrometric detection of the substances.