Use of Microspherical Sulfonated Hypercrosslinked Polystyrene in Ion Chromatography

The possibility of applying sulfonated cation exchangers on the basis of hypercrosslinked polystyrene (HCPS) of different ion-exchange capacity for the ion-chromatographic separation of alkali metal and ammonium cations was demonstrated. The effect of the nature and concentration of the eluent, the temperature of the chromatographic column, additions of an organic solvent to the eluent, and the ion-exchange capacity of the sorbent on the retention of cations was examined. An unusual selectivity of the sorbent for lithium and ammonium cations was found; the elution order can change for the Li⁺/Na⁺ and Rb⁺/NH⁺ ₄ pairs depending on the nature of the eluent, the temperature, additions of an organic solvent, and the structural characteristics of the sorbent. When dilute solutions of nitric acid are used as the eluent, the following elution order of cations was obtained: Na⁺ < Li⁺ < K⁺ < NH⁺ ₄ < Rb⁺ < Cs⁺ Mg²⁺ < Sr²⁺ < Ca²⁺ < Ba²⁺. Under the optimum conditions of separation (1 mM solution of sulfuric acid, 20°C) on sulfonated HCPS with an ion-exchange capacity of 0.07 mequiv/g, the separation of ammonium and alkali metal cations was achieved within 17 min.     

Zwitterionic ion chromatography with carboxybetaine surfactant-coated particle packed and monolithic type columns

Both particle packed (25 cm x 0.46 cm I.D. SUPELCOSIL 5 microm C18) and monolithic type (10 cm x 0.46 cm I.D. Merck Chromolith Performance C18) reversed-phase substrates were dynamically coated with a carboxybetaine type zwitterionic surfactant ((dodecyldimethyl-amino) acetic acid) and investigated as stationary phases for use in zwitterionic ion chromatography (ZIC). Investigations into eluent concentration and pH were carried out using KCl eluents containing 0.2 mM of the carboxybetaine surfactant to stabilise the column coatings. It was found that eluent concentration decreased anion retention whilst simultaneously increasing peak efficiencies, which may be due to the dissociation of intra- and inter-molecular salts of the carboxybetaine surfactant under higher ionic strength conditions. The Effect of eluent pH was an increase in anion retention with decreased eluent pH due to the increased protonation of the weak acid terminal group of the carboxybetaine, causing both a relative increase in the positive charge of the stationary phase and less repulsion of the anions by the dissociated weak acid group. The carboxybetaine-coated monolithic phase was applied to rapid anion separations using elevated flow rates and flow rate gradients.     

Generalization of the relativistic string model in the geometrical approach

We present a model of a one-dimensional extended relativistic object, whose motion is defined by the requirement that its time track in Minkowski space is a surface of the constant mean curvature H. The world surface of the relativistic string is a particular case of such surfaces, namely, a minimal surface with H=0. By differential-geometry methods the theory of the proposed object moving in three-dimensional space-time is reduced to one nonlinear equation – = Hsh. In the theory under consideration, there naturally arises the pair of Lax's operators needed to solve this nonlinear equation by the inverse scattering method.     

One Inequality for the Moduli of Continuity of Fractional Order Generated by Semigroups of Operators

Ukrainian Mathematical Journal - A new inequality for the moduli of continuity of fractional order generated by semigroups of operators is obtained. This inequality yields a generalization to the...     

Cycle detection algorithms and their applications

This paper considers several cycle detection algorithms. Proofs of their correctness are given, bounds for complexity are obtained, some number theory applications like the factorization of integers and the discrete log problem are examined.     

Capillary electrophoresis for the analysis of paralytic shellfish poisoning toxins in shellfish: Comparison of detection methods

Paralytic shellfish toxins (PSTs) are produced by marine and freshwater microalgae and accumulate in shellfish including mussels, oysters, and scallops, causing possible fatalities when inadvertently consumed. Monitoring of PST content of shellfish is therefore important for food safety, with currently approved methods based on HPLC, using pre‐ or postcolumn oxidation for fluorescence detection (HPLC‐FLD). CE is an attractive alternative for screening and detection of PSTs as it is compatible with miniaturization and could be implemented in portable instrumentation for on‐site monitoring. In this study, CE methods were developed for C⁴D, FLD, UV absorption detection, and MS—making this first report of C⁴D and FLD for PSTs detection. Because most oxidized toxins are neutral, MEKC was used in combination with FLD. The developed CZE‐UV and CZE‐C⁴D methods provide better resolution, selectivity, and separation efficiency compared to CZE‐MS and MEKC‐FLD. The sensitivity of the CZE‐C⁴D and MEKC‐FLD methods was superior to UV and MS, with LOD values ranging from 140 to 715 ng/mL for CZE‐C⁴D and 60.9 to 104 ng/mL for MEKC‐FLD. With the regulatory limit for shellfish samples of 800 ng/mL, the CZE‐C⁴D and MEKC‐FLD methods were evaluated for the screening and detection of PSTs in shellfish samples. While the CZE‐C⁴D method suffered from significant interferences from the shellfish matrix, MEKC‐FLD was successfully used for PST screening of a periodate‐oxidized mussel sample, with results confirmed by HPLC‐FLD. This confirms the potential of MEKC‐FLD for screening of PSTs in shellfish samples.     

Landau fragmentation and deformation effects in dipoSe response of sodium clusters

Recent experimental data on the dipole plasmon in axial sodium clusters Na _N ⁺ with 11 ≤ N ≤ 57 are analyzed within a self-consistent separable random-phase approximation (SRPA) based on the deformed Konh-Sham functional. Good agreement with the data is achieved. The calculations show that, while in light clusters plasmon properties (gross structure and width) are determined mainly by deformation splitting, in medium clusters with N τ 50 the Landau fragmentation becomes decisive. Moreover, in medium clusters shape isomers come to play with contributions to the plasmon comparable with the ground state one. As a result, commonly used methods of the experimental analysis of cluster deformation become useless and correct treatment of cluster shape requires microscopic calculations.