Adsorption of tert-butanol at the electrode from concentrated NaClO4 solutions

The parameters of the double layer for tert-butanol adsorption determined in the supporting electrolytes: 2 mol dm^?3, 3 mol dm^?3 and 4 mol dm^?3 NaClO₄, show an increase of tert-butanol adsorption on the mercury electrode together with the increase of NaClO₄ concentration. The adsorption of tert-butanol on the electrode takes place via the ?CH₃ group which is shown by the changes in the values of zero charge potentials, E _z. On the basis of the analysis of the changes of relative surface excess values, Γ′, and the parameters determining the maximum adsorption, the process of adsorption in the discussed systems can be recognized as a physical process. Besides, it can be said that a major drawback in the process of adsorption of the organic substance on the electrode is to remove water from the electrode surface.     

Free energies of aqueous mixtures of NaH2PO4 and NAClO4: Evidence for the species (H2PO4) 2 −2

The system NaH₂PO₄?NaClO₄ has been studied from 0.15 to 7.0 mole-kg^?1 at 25°C by the isopiestic method. The excess free energy of mixing is large and positive. The results confirm the formation of (H₂PO₄) ₂ ^?2 dimers with a stoichiometric association constantK _a=0.25±0.1 kg-mole^?1 at 25°C.     

Chromatofocusing of peptides on a sulfo-cation-exchange sorbent

Simple mobile phases containing no more than two active components were proposed for the formation of ascending pH gradients in a column filled with a sulfo-cation-exchange sorbent. The smoothest nearly linear pH gradients were obtained with the use of citric acid and Tris or NaH₂PO₄ and Tris as active components of the eluent and adjusting ionic strength (up to 0.1–0.3) in the starting solution or eluent; however, in the case of UV detection, the use of NaH₂PO₄ is preferable because of lower light absorption. Potentialities of the proposed approach in the chromatography of peptide mixtures on a sulfo-cation-exchange sorbent were demonstrated. Additions of acetonitrile to mobile phases improve the selectivity of the separation of peptides.     

Usefulness of chaotropic salt additive in RP‐HPLC of organic nonionized compounds

New synthesized 1,4‐disubstituted thiosemicarbazide derivatives were analyzed in the RP system, modified with the addition of salts; chaotropic (sodium hexafluorophosphate – Na PF₆), cosmotropic (sodium phosphate – NaH₂PO₄), and neutral (NaCl) on Zorbax XDB C18 column. The effect of the eluent composition on the analytes retention (k), system efficiency (N), peak symmetry (A_s), and LOD values were all examined and compared to unmodified organic‐aqueous mobile phase system. It was established that eluent modified with chaotropic salts addition was also the most advantageous according to other peak parameters such as the theoretical plates numbers and asymmetry factors. The lower LOD values were achieved in comparison to unmodified organic‐aqueous eluent system. Compatibility of lipophilicity parameters calculated by the use of computer software with experimental ones measured by RP‐HPLC was also the best for chaotropic modified mobile phase. To explain the observed phenomena, molecular modeling was performed for chosen representative compound in different environment representing examined mobile phase composition.     

A simple method for measuring excess adsorption isotherms of organic eluent components on reversed‐phase packing materials

A simple frontal analysis method has been developed for the reliable measurement of excess adsorption isotherms of an organic component on reversed‐phase adsorbents in a series of programmed concentration steps. In the present method, a peak, which is produced by refractive index change in column eluate, is detected at 589 nm; it represents the elution volume of the boundary. The method is applied to the measurement of the excess adsorption isotherms of organic eluent components from water on commercially available reversed‐phase stationary phases. The results are in good agreement with the previously reported isotherms. We also measure the excess adsorption isotherms of organic eluent components from solutions containing electrolytes. There are not any interference peaks on the elution traces. The method is thus reliably applicable to the evaluation of the excess adsorption of organic eluent components in practical systems.     

Thermal decomposition of bisphenol A-based polyetherurethanes blown with pentane: Part II—Influence of the novel NaH2PO4/NaHSO4 flame retardant system

The thermal degradation process of ethoxylated bisphenol A (BPA) and oxyalkylenated 2,6-toluylenediamine-based polyurethane (PU) foams blown with pentane and flame retarded by novel NaH₂PO₄ and NaHSO₄ intumescent system (5:3, w/w) was studied by thermogravimetry coupled with mass spectrometry (TG–MS), thermogravimetry coupled with Fourier transform infrared spectroscopy (TG–FTIR), pyrolysis–gas chromatography coupled with mass spectrometry (Py/GC–MS) and diffuse reflectance Fourier transform spectroscopy (DRIFTS) methods. It has been found that NaH₂PO₄/NaHSO₄ system is active both at the initiation stage of PU decomposition as well as it catalyses cross-linking reactions that lead to enhanced char formation during degradation; both effects contribute to the overall flame retardation effect.     

Fast methods for screening of trichothecenes in fungal cultures using gas chromatography-tandem mass spectrometry

The excess adsorption isotherms of acetonitrile, methanol and tetrahydrofuran from water on reversed-phase packings were studied, using 10 different columns packed with C1-C6, C8, C10, C12, and C18 monomeric phases, bonded on the same type of silica. The interpretation of isotherms on the basis of the theory of excess adsorption shows significant accumulation of the organic eluent component on the adsorbent surface on the top of "collapsed" bonded layer. The accumulated amount was shown to be practically independent of the length of alkyl chains bonded to the silica surface. A model that describes analyte retention on a reversed-phase column from a binary mobile phase is developed. The retention mechanism involves a combination of analyte distribution between the eluent and organic adsorbed layer, followed by analyte adsorption on the surface of the bonded phase. A general retention equation for the model is derived and methods for independent measurements of the involved parameters are suggested. The theory was tested by direct measurement of analyte retention from the eluents of varied composition and comparison of the values obtained with those theoretically calculated values. Experimental and theoretically calculated values are in good agreement.     

Void volume determination and experimental probes in reversed phase chromatography

Summary In reversed-phase liquid chromatography with n-alkyl bonded silica, the dead volume (V₀) of the column is theoretically indeterminate owing to adsorption of organic modifier on n-alkyl chains and of water on silanol groups. With binary mobile phases, retention volumes of the mobile phase components and of their deuterated species are relaeed to the adsorption isotherms and V₀ by equations which can be solved with some assumptions on the adsorbed layer composition. Methanol-water and acetonitrile-water systems are studied. As the experimental excess isotherm shows a linear part in the concentration range 50–80% in organic modifier, the hypothesis of an adsorbed layer of constant composition in this range is possible. When increasing the water content of the mobile phase, adsorption of water occurs up to saturation of silanol groups. Then the assumption of a constant water content for a mobile phase having more than 50% of water is applied. With the hypothesis of a constant adsorbed content of organic modifier when the eluent has more than 80% of organic modifier, V₀ and the absolute isotherms are calculated over the entire range of mobile phase composition. Experimental retention behavior of the mobile phase components are totally explained by these V₀ determinations. The retention times of commonly used V₀ markers are compared with V₀ values. It is shown that, when buffering the eluent, no visible effect on the distribution equilibrium is observed, so that injection of concentrated potassium nitrate is a convenient method to measure V₀. With a few solutes with are UV detectable it is possible to measure V₀ whatever the mobile phase composition in methanol-water and acetonitrile-water systems.     

Mobile phases for the determination of polarizable anions on polystyrene/divinylbenzene anion-exchange resins

Anion-exchange resins have been prepared by chloromethylating 50%-crosslinked styrene-divinylbenzene copolymers (PS/DVB) followed by amination with trimethylamine. In addition to ion exchange, interactions with the anion-exchange matrix considerably contribute to the retention of polarizable anions on these sorbents. Additives in the eluent that can suppress adsorption sites of the stationary phase can decrease this effect. p-Hydroxybenzonitrile (0.15 mmol/L) in the eluent increases the NO ₃ ^? peak efficiency from 820 to 5100 theoretical plates per meter.     

Activity measurements in the ternary system NaBr+NaClO4+H2O at 25°C

The activity coefficients of sodium bromide in the ternary system NaBr+NaClO₄+H₂O were determined at 25°C and constant ionic strength of 0.1, 0.5, 1, 2, and 3 mol-kg^?1 from emf of the cell without, liquid junction $$ISE - Na|NaBr(m_A ), NaClO_4 (m_B ), AgCl_{(s)} 1 Ag$$ The experimental activity coefficients were comparatively analyzed by using the Harned, Scatchard, Pitzer and Lim-HOLL treatments. All these methods are adequate for the analysis of the experimental data. The results have been compared with those of Lanier for the system: NaCl+NaClO₄+H₂O. The Gibbs excess energy of mixing was obtained and qualitatively interpreted in terms of ionic interactions.     

Combined effects of mobile phase composition and temperature on the retention of homologous and polar test compounds on polydentate C8 column

Combined effects of temperature and mobile phase on the reversed phase chromatographic behavior of alkylbenzenes and simple substituted benzenes were investigated on a Blaze C₈ polydentate silica-based column, showing improved resistance against hydrolytic breakdown at temperatures higher than 60 °C, in comparison to silica-based stationary phases with single attachment sites. For better insight into the retention mechanism on polydentate columns, we determined the enthalpy and entropy of the transfer of the test compounds from the mobile to the stationary phase. The enthalpic contribution dominated the retention at 80% or lower concentrations of methanol in the mobile phase. Entropic effects are more significant in 90% methanol and in acetonitrile–water mobile phases. Anomalies in the effects of mobile phase on the enthalpy of retention of benzene, methylbenzene and polar benzene derivatives were observed, in comparison to regular change in enthalpy and entropy of adsorption with changing concentration of organic solvent and the alkyl length for higher alkylbenzenes. The temperature and the mobile phase effects on the retention are practically independent of each other and – to first approximation – can be described by a simple model equation, which can be used for optimization of separation conditions.     

Quantitative Separation of Volatile Fatty Acids by High-Pressure Liquid Chromatography

Abstract

Volatile fatty acids (acetic, propionic, butyric, isovaleric, and valeric) are separated isocratically on a reverse phase C₁₈ μBONDAPAK column in less than 20 min. The eluent was 0.01 M NaH₂PO₄ buffer, pH 3.5, containing 10% methanol. Separations were monitored by UV absorption at 210 nm. Peak height measurements gave quantitative linear responses from 0.25 μmole to 2.50 μmole of each acid.     

Kinetic study on reactive extraction for chiral separation of phenylsuccinic acid enantiomers

The kinetics of the extraction of phenylsuccinic acid (PSA) enantiomers by hydroxypropyl-β-cyclodextrin (HP-β-CD) in a modified Lewis cell was studied, in which HP-β-CD dissolved in 0.1 mol L^?1 NaH₂PO₄/H₃PO₄ buffer solution (pH = 2.5) was selected as the chiral extractant. PSA enantiomers were extracted from organic phase to aqueous phase in the extraction module. The theory of extraction accompanied by a chemical reaction has been used to obtain the intrinsic kinetics of this extraction module. The different parameters affecting the extraction rate such as agitation speed, interfacial area, initial concentration of PSA enantiomers in organic phase as well as HP-β-CD concentration in aqueous phase were separately studied. The experimental results demonstrate that the extraction reactions are fast. The reactions were found to be first order with respect to PSA and second order with respect to HP-β-CD with forward rate constants of 3.4 × 10^?2 m⁶ mol^?2 s^?1 for R-PSA and 9.96 × 10^?3 m⁶ mol^?2 s^?1 for S-PSA. These data will be useful in the design of extraction processes.     

Osmotic and activity coefficients of {yNaH2PO4+(1−y)Na2SO4}(aq) at the temperature 298.15 K

The osmotic coefficients of the mixed electrolyte solution {yNaH₂PO₄+(1−y)Na₂SO₄}(aq) have been measured by the isopiestic method, at the temperature T=298.15 K. The activity coefficients of NaH₂PO₄ and Na₂SO₄ were calculated by Scatchard's neutral-electrolyte method and by Pitzer and Kim's treatment for mixed-electrolyte solutions. The Scatchard interaction parameters are used for calculation of the excess Gibbs energy as a function of ionic strength and ionic-strength fraction of NaH₂PO₄. Also, the Zdanovskii's rule of linearity is tested.     

Zur hochspannungselektrophoretischen Trennung anorganischer Ionen unter besonderer Berücksichtigung der Platinmetalle. VI

Zusammenfassung Die hochspannungselektrophoretische Wanderung der Halogenokomplexe der Platinmetalle und verschiedener Metallionen in anorganischen Salzlösungen (NaCl, NaBr, NaJ, NaHSO₄, Na₂SO₄, NaH₂PO₄, NaNO₃, NaBO₂ u. a.) wurde untersucht und im Fall des NaCl die Abhängigkeit der Wanderungsgeschwindigkeitw und der Fleckengröße w von der Elektrolytkonzentration und der Konzentration der Auftragslösung gemessen. U. a. wurde festgestellt, daß die Wanderungsgeschwindigkeiten und Fleckengrößen der Halogenokomplexe und Metallionen von der Art des als Elektrolyt verwendeten Salzes teilweise merklich abhängig sind. So lassen sich in einer 0,1-m NaJ-Lösung die Chlorokomplexe des Os, Ir und Pt gut trennen, wobei für die Wanderungsgeschwindigkeiten die Abstufung gilt: Os > Pt > Ir. Mögliche Ursachen der Abhängigkeiten (Komplexbildungen u. a.) werden diskutiert. Auch wird die Anwendbarkeit verschiedener Salzlösungen für Trennungen an Hand von Beispielen (Pt, Pd, Re, Au; Se, Te, Hg, Os u. a.) gezeigt.

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The high-voltage electrophoretic separation of inorganic ions with special attention to the platinum metals. VI

Summary The high voltage electrophoretic migration of the halogenocomplexes of the platinum metals and various metal ions in inorganic salt solutions (NaCl, NaBr, NaI, NaHSO₄, NaH₂PO₄, NaNO₃, NaBO₂ etc.) was studied and the dependence of the migration velocityw and the spot size w on the electrolyte concentration of the added solution was measured. Among other things it was established that the migration speeds and the spot-sizes of the halogeno complexes and the metal ions are dependent in part and markedly on the kind of salt used as electrolyte. Thus, for instance, the chloro-complexes of Os, Ir and Pt are well separable in a 0.1 molar solution of NaI, whereby the gradation holds Os > Pt > Ir. Possible reasons for the dependencies (complex formations etc.) are discussed. Likewise the applicability of various salt solutions for separations on the basis of examples are shown (Pt, Pd, Re, Au, Te, Hg, Os, and others).

     

Ion‐exchange vs reversed‐phase chromatography for separation and determination of basic psychotropic drugs

Ion exchange chromatography, an alternative to reversed‐phase (RP) chromatography, is described in this paper. We aimed to obtain optimal conditions for the separation of basic drugs because silica‐based RP stationary phases show silanol effect and make the analysis of basic analytes hardly possible. The retention, separation selectivity, symmetry of peaks and system efficiency were examined in different eluent systems containing different types of buffers at acidic pH and with the addition of organic modifiers: methanol and acetonitrile. The obtained results reveal a large influence of the salt cation used for buffer preparation and the type of organic modifier on the retention behavior of the analytes. These results were also compared with those obtained on an XBridge C₁₈ column. The obtained results demonstrated that SCX stationary phases can be successfully used as alternatives to C₁₈ stationary phases in the separation of basic compounds. The most selective and efficient chromatographic systems were applied for the quantification of some psychotropic drugs in fortified human serum samples. Copyright © 2015 John Wiley & Sons, Ltd.     

Cr(VI)在Mg-Al型类水滑石上的吸附-脱附性研究I. 吸附性

研究了Cr(VI)在带结构正电荷的Mg-Al型类水滑石(HTlc)上的吸附性能, 考察了pH、无机电解质添加剂NaCl, NaNO₃, Na₂SO₄和Na₃PO₄及有机添加剂EDTA和柠檬酸等因素的影响, 并结合红外光谱和XRD实验结果探讨了吸附机理. 研究表明, Mg-Al型HTlc对Cr(VI)有很强的吸附能力, 其吸附动力学和吸附等温线分别符合准二级速率方程和Langmuir方程, 饱和吸附量达105 mg/g, 有望成为一种优良的含Cr(VI)污水处理剂和Cr(VI)污染土壤修复剂. 初始pH增大, 吸附量降低. 无机电解质和有机添加剂均能明显抑制Cr(VI)在HTlc上的吸附, 其抑制吸附作用的强弱顺序分别为Na₃PO₄≥Na₂SO₄≥NaCl>>NaNO₃和柠檬酸＞EDTA. Cr(VI)在HTlc上的吸附可分为层间的离子交换吸附和外表面的吸附, 其中外表面的吸附层在微观上又可分为因化学键合作用而形成的内络合层和因静电作用而形成的外络合层.     

Retention parameters of aromatic hydrocarbons with mono-substituted polar groups in binary RP-HPLC systems

Summary Capacity factor (k′) values of aromatic hydrocarbons with mono-substituted polar-groups are correlated for reversed-phase systems involving stationary phases with C₁₈ or C₄ ligands chemically bonded to silica and a binary aqueous eluent containing modifiers: methanol, acetonitrile, tetrahydrofuran, isopropanol, dioxane or dimethoxyethane. The relative retention variations of the solutes are interpreted with special consideration of their interactions with non-polar stationary phases and the molecular structure of the modifiers and solutes. Rules for retention and selectivity optimisation in RP-HPLC systems are given.     

Development and validation of a hydrophilic interaction liquid chromatographic method for determination of aromatic amines in environmental water

A simple, precise, and accurate hydrophilic interaction liquid chromatographic (HILIC) method has been developed for the determination of five aromatic amines in environmental water samples. Chromatography was carried out on a bare silica column, using a mixture of acetonitrile and a buffer of NaH₂PO₄–H₃PO₄ (pH 1.5, containing 10 mM NaH₂PO₄) (85:15, v/v) as a mobile phase at a flow rate of 1 mL min⁻¹. Aromatic amines were detected by UV absorbance at 254 nm. The linear range of amines was good (r² > 0.998) and limit of detection (LOD) within 0.02–0.2 mg L⁻¹ (S/N = 3). The retention mechanism for the analytes under the optimum conditions was determined to be a combination of adsorption, partition and ionic interactions. The proposed method was applied to the environmental water samples. Aromatic amines were isolated from aqueous samples using solid-phase extraction (SPE) with Oasis HLB cartridges. Recoveries of greater than 75% with precision (RSD) less than 12% were obtained at amine concentrations of 5–50 μg L⁻¹ from 100 mL river water and influents from a wastewater treatment plant (WWTP). The present HILIC technique proved to be a viable method for the analysis of aromatic amines in the environmental water samples.     

Relationship between retention and molecular structure of pyrimidine bases

Summary The influence of the type and position of CH₃, NH₂ and OH groups in the pyrimidine ring, the eluent composition and the surface chemistry of the stationary phase on the retention of pyrimidine bases in reversed-phase liquid chromatography was investigated. On the basis of the hypothesis about the additivity of the adsorption energy the contribution of various structural groups on retention has been established.