Preparation of a K+‐imprinted polymer for the selective recognition of K+ in food samples

An analytical method is reported for the preparation of K⁺‐imprinted nanoparticles using cryptand 222 as the complexing agent, methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the crosslinker and 2,2′‐azobisisobutyronitrile as the radical initiator. The prepared particles have a diameter of 200–250 nm. The maximum adsorption capacity of potassium ion‐imprinted polymer particles was 120 μmol/g. The optimum pH for quantitative extraction was 9.0. The nature of the eluent, eluent concentration, adsorption and desorption times, weight of the polymer material, aqueous phase, and desorption volumes were also studied. The relative selectivity coefficients of K⁺/Li⁺, K⁺/Na⁺, K⁺/Rb⁺ and K⁺/Cs⁺ were 48.10, 4.80, 29.70, and 43.4, respectively. The relative standard deviation and limit of detection of the method were obtained 1.61% and 4.62 ng/L, respectively. Finally, the method was applied for the determination of potassium ions from different samples using flame photometry.     

Ion chromatography with the indirect ultraviolet detection of alkali metal ions and ammonium using imidazolium ionic liquid as ultraviolet absorption reagent and eluent

Indirect ultraviolet detection was conducted in ultraviolet‐absorption‐agent‐added mobile phase to complete the detection of the absence of ultraviolet absorption functional group in analytes. Compared with precolumn derivatization or postcolumn derivatization, this method can be widely used, has the advantages of simple operation and good linear relationship. Chromatographic separation of Li⁺, Na⁺, K⁺, and NH₄⁺ was performed on a carboxylic acid base cation exchange column using imidazolium ionic liquid/acid/organic solvent as the mobile phase, in which imidazolium ionic liquids acted as ultraviolet absorption reagent and eluting agent. The retention behaviors of four kinds of cations are discussed, and the mechanism of separation and detection are described. The main factors influencing the separation and detection were the background ultraviolet absorption reagent and the concentration of hydrogen ion in the ion chromatography‐indirect ultraviolet detection. The successful separation and detection of Li⁺, Na⁺, K⁺, and NH₄⁺ within 13 min was achieved using the selected chromatographic conditions, and the detection limits (S/N = 3) were 0.02, 0.11, 0.30, and 0.06 mg/L, respectively. A new separation and analysis method of alkali metal ions and ammonium by ion chromatography with indirect ultraviolet detection method was developed, and the application range of ionic liquid was expanded.     

Ion-interaction chromatographic separation of metal cations in the presence of complexing agents

The mechanism of the separation of selected divalent metal cations (Zn²⁺, Ni²⁺, Co²⁺, Cd²⁺, Mn²⁺, Fe²⁺ and Pb²⁺) by ion-interaction chromatography (IIC) in the presence of complexing agents has been investigated; the dependence of the retention of the analyte on the concentration of the complexing ligand has been studied. Separations have been obtained on an octadecyl-bonded silica column, mobile phases containing an ion-interaction agent (octane sulfonate), eluting cations (Na⁺ ions) and a complexing ligand (oxalate anions).     

Functionalized SBA-15 mesoporous silica in ion chromatography of alkali,alkaline earths,ammonium and transition metal ions

The retention properties of a SBA-15 mesoporous silica functionalized with –(CH₂)₃COOH groups, synthesized by a co-condensation route, were investigated for the ion chromatography of different cationic species. A systematic study on the effect of different eluent compositions containing non-complexing (methanesulfonic acid) or complexing (oxalic or pyridine-2,6-dicarboxylic acids) eluents, in the presence of organic modifiers (CH₃CN, CH₃OH, CH₃NH₂) on the retention of cations (Li⁺, Na⁺, K⁺, Ca²⁺, Mg²⁺, Sr²⁺, Ba²⁺, NH₄⁺, Cu²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Co²⁺, Pb²⁺, Fe³⁺) chosen as model analytes and for their environmental importance, allowed us to elucidate the mechanisms (cation-exchange or complexation) involved in the retention on the SBA-15 phase. For the first time separations of cations on SBA-15 based stationary phases are investigated, providing the basis for further development of mesoporous silica chemistry for in-flow ion-exchange applications.     

The Synthesis of Novel Crown Ethers, Part VII [1]. Coumarin Derivatives of Benzocrowns and Cation Binding from Fluorescence Spectra

4-[3-(1-benzopyran-2-one)] derivativesof benzo[12]crown-4, benzo[15]crown-5 andbenzo-[18]crown-6 were synthesized from4-[3-(1-benzopyran-2-one)]-1,2-dihydroxy-benzenereacting with bis-ethyleneglycol dihalides orpentaethylene glycol ditosylate in alkali carbonate/DMF/water. The original products were identified byhigh resolution EI-mass spectra as well as IR,¹H-NMR and ¹³C-NMR spectroscopy. The 1 : 1binding constants of Mg²⁺, Li⁺, Na⁺ andK⁺ with the coumarin-benzocrowns were estimated usingfluorescence emission spectroscopy in acetonitrile.The complexing enhanced quenching fluorescence spectra(CEQFS) and complexing enhanced fluorescence spectra(CEFS) exhibited the ion binding powers due tocationic recognition rules of the macrocycles.     

Portable,lightweight, low power,ion chromatographic system with open tubular capillary columns

Basic operation principles of a lightweight, low power, low cost, portable ion chromatograph utilizing open tubular ion chromatography in capillary columns coated with multi-layer polymeric stationary phases are demonstrated. A minimalistic configuration of a portable IC instrument was developed that does not require any chromatographic eluent delivery system, nor sample injection device as it uses gravity-based eluent flow and hydrodynamic sample injection adopted from capillary electrophoresis. As a detection device, an inexpensive commercially available capacitance sensor is used that has been shown to be a suitable substitute for contactless conductivity detection in capillary separation systems. The built-in temperature sensor allows for baseline drift correction typically encountered in conductivity/capacitance measurements without thermostating device. The whole instrument does not require any power supply for its operation, except the detection and data acquisition part that is provided by a USB port of a Netbook computer. It is extremely lightweight, its total weight including the Netbook computer is less than 2.5 kg and it can be continuously operated for more than 8 h. Several parameters of the instrument, such as detection cell design, eluent delivery systems and data treatment were optimized as well as the composition of eluent for non-suppressed ion chromatographic analysis of common inorganic cations (Na⁺, NH₄⁺, K⁺, Cs⁺, Ca²⁺, Mg²⁺, transition metals). Low conductivity eluents based on weakly complexing organic acids such as tartaric, oxalic or pyridine-2,6-dicarboxylic acids were used with contactless capacitance detection for simultaneous separation of mono- and divalent cations. Separation of Na⁺ and NH₄⁺ cations was optimized by addition of 18-crown-6 to the eluent. The best separation of 6 metal cations commonly present in various environmental samples was accomplished in less than 30 min using a 1.75 mM pyridine-2,6-dicarboxylic acid and 3 mM 18-crown-6 eluent with excellent repeatability (below 2%) and detection limits in the low micromolar range. The analysis of field samples is demonstrated; the concentrations of common inorganic cations in river water, mineral water and snow samples were determined.     

Peak parking technique for the simultaneous determination of anions and cations

An ion chromatography method is described for the simultaneous determination of anions (Cl^–, NO₃^–, and SO₄^2–) and cations (Na⁺, NH₄⁺, K⁺, Mg²⁺, and Ca²⁺) using a single pump, a single eluent and a single detector. An anion-exchange column modified with chondroitin sulfate C facilitated the elution of the above three anions using 5 mM tartaric acid as the eluent in isocratic mode, whereas the same eluent facilitated the separation of the above five cations on a commercially-available cation-exchange column. The separation columns were connected in series via two six-port switching valves, so the required cation-exchange or anion-exchange separation could be carried out by selecting the appropriate positions for the switching valves. The separations were completed in 30 min.     

A Simple Method for Determination of Homologue Imidazolium Cations in Ionic Liquids Using IC with Direct Conductivity Detection

An investigation was carried out into the fast determination of five homologue imidazolium cations in ionic liquids by ion chromatography using a cation-exchange column and direct conductivity detection. Ethylenediamine, complex organic acid (citric acid, oxalic acid and tartaric acid) and organic modifiers (acetonitrile) were used as mobile phase. The influences of the eluent types, eluent concentration, eluent pH and column temperature on separation of the cations were discussed. Simultaneous separation and determination of the five homologue imidazolium cations in ionic liquids were achieved under an optimum condition. The optimized mobile phase was consisted of 0.25 mmol L^?1 ethylenediamine + 0.5 mmol L^?1 citric acid + 3% acetonitrile (v/v) (pH 4.1), set at a flow rate of 1.0 mL min^?1. The column temperature was 40 °C and detection limits were obtained in the range of 1.1–45.6 mg L^?1. The relative standard deviations of the chromatographic peak areas for the cations were <3.0% (n = 5). This method was successfully applied to separate imidazolium cations in ionic liquids produced by organic synthesis. The recoveries of spiked components were 92.5–101.9%.     

Effect of 18-Crown-6 on the Separation Selectivity of Organic Compounds by Reversed-Phase High-Performance Liquid Chromatography

The effect of the addition of 18-crown-6 to the water–methanol and water–acetonitrile mobile phase on the selectivity of the separation of different derivatives of phenol, aniline, and benzoic acid by reversed-phase high-performance liquid chromatography was studied. It was demonstrated that the retention of compounds with the protonated primary amino group is increased in the presence of 18-crown-6 in the eluent, which can be explained by complexation between analyte compounds and macrocycles. For compounds containing the hydroxyl group (phenol and its derivatives), the addition of 18-crown-6 to the mobile phase leads to some decrease in retention. It was demonstrated that the selectivity of 18-crown-6 can change depending on the nature of the positional isomer (ortho, meta, orpara) of the analyte and the nature of the solvent increasing or decreasing the complexing ability of the sorbate with the macrocycle. The effect of the concentration of crown ether on the retention of compounds with the protonated amino group was revealed, and the complexation mechanism was suggested.     

Eluent-Induced Separation of Inorganic Cations in Capillary Liquid Chromatography with Contactless Conductivity Detector

A non-suppressed contactless conductivity detector has been used as a capillary detector in a capillary ion chromatograph, combining a reversed-phase C30 column permanently modified with ionic surfactant. The C30 column (100 × 0.32 mm. id) was modified with sodium dodecyl sulfate (SDS) for the separation of inorganic cations. Monovalent cations could be separated by the proposed system, in which methanesulfonic acid (MSA) and SDS were employed as the mobile phase component, but divalent cations could not be eluted under this condition. As for the case of SDS used as the eluent, an H⁺-cation-exchange column was placed before the sample injector to convert the Na⁺ from the eluent into H⁺, and when the mixture of MSA and dodecyl sulfuric acid was used as the eluent, the retention of cations was improved and baseline separation of the cations was achieved within 23 min. The effect of the eluent composition on the retention behavior of inorganic cations was investigated. The repeatability of retention time and peak height varied from 0.39 to 0.58 and 2.21 to 3.25 % as relative standard deviation, respectively.

     

Eluent-Induced Separation of Inorganic Cations in Capillary Liquid Chromatography with Contactless Conductivity Detector

A non-suppressed contactless conductivity detector has been used as a capillary detector in a capillary ion chromatograph, combining a reversed-phase C30 column permanently modified with ionic surfactant. The C30 column (100 × 0.32 mm. id) was modified with sodium dodecyl sulfate (SDS) for the separation of inorganic cations. Monovalent cations could be separated by the proposed system, in which methanesulfonic acid (MSA) and SDS were employed as the mobile phase component, but divalent cations could not be eluted under this condition. As for the case of SDS used as the eluent, an H⁺-cation-exchange column was placed before the sample injector to convert the Na⁺ from the eluent into H⁺, and when the mixture of MSA and dodecyl sulfuric acid was used as the eluent, the retention of cations was improved and baseline separation of the cations was achieved within 23 min. The effect of the eluent composition on the retention behavior of inorganic cations was investigated. The repeatability of retention time and peak height varied from 0.39 to 0.58 and 2.21 to 3.25 % as relative standard deviation, respectively.     

Separation and quantitative determination of dioxouranium(VI) and thorium(IV) ions in the presence of different metallic ions by TLC using iso-propyldithiophosphoric acid as complexing agent

The separation of uranium and thorium from matrices containing various metal ions, was studied. The mobile phase contains isopropyldithiophosphoric acid (i-PrDTP), as a complexing agent, in order to differentiate the studied species by modifying their retention. The paper reports the successful separation and the quantitative determination of uranium and thorium in the presence of Ni²⁺, Co²⁺ and Ag⁺ in the concentration range 2.5–2.5 μg/μl for uranium and 2.5–30 μg/μl for thorium.     

Application of Artificial Neural Network and Multiple Linear Regression Retention Models for Optimization of Separation in Ion Chromatography by Using Several Criteria Functions

This work focuses on problems regarding empirical retention modelling and optimization of separation in ion chromatography. Influences of eluent flow rate and concentration of eluent competing ion (OH^–) on separation of seven inorganic anions (fluoride, chloride, nitrite, sulphate, bromide, nitrate, and phosphate) were investigated. Artificial neural networks and multiple linear regression retention models in combination with several criteria functions were used and compared in global optimization process. It can be seen that general recommendations for optimization of separation in ion chromatography is application of chromatography exponential function criterion in combination with artificial neural networks retention model.     

Determination of Imidazolium Ionic Liquid Cations by Ion-Pair Chromatography Using a Monolithic Column and Direct Conductivity Detection

Determination of four imidazolium ionic liquid cations by ion-pair chromatography was carried out using direct conductivity detection. Chromatographic separations were performed on a silica-based monolithic column with 1-heptanesulfonic acid sodium + acetonitrile + citric acid as eluent. Carbon number rule and influence of acetonitrile on the retention of imidazolium cations were discussed. Detection limits (S/N = 3) for the cations were 2.1–55.9 mg L^?1. Relative standard deviations (RSD, n = 5) for peak areas were less than 3.0%. The method has been successfully applied to the determination of two ionic liquids synthesized by organic chemistry lab.     

Studies on the mechanism of coagulation

Summary In previous work it was found that at certain concentrations of anionic surface agents the particles of positive silver iodide sols became coated with a double adsorbed layer of the surface active agent; under these conditions stable sols were formed the properties of which were found to be dependent on the nature of the head group of the surface active agent. Utilising this fact stable sols have been prepared of silver iodide particles coated with sodium tetradecyl sulphate and their stability and electrophoretic behaviour examined in the presence of a number of cations of different valency. The cations used were, Th⁺⁺⁺⁺, La⁺⁺⁺, Ba⁺⁺, Ca⁺⁺, Mg⁺⁺, Zn⁺⁺, UO₂ ⁺⁺, Mn⁺⁺, Cd⁺⁺, Na⁺, K⁺ and Li⁺. The curves of stability as a function of ionic strength and particle radius revealed marked specificity of the cations; this was attributed to cation binding with the sulphate groups of the second layer of adsorbed surface active agent. The results obtained appear to be in general agreement with those predicted in the theoretical treatment given in part 4.

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Zusammenfassung In einer der vorausgehenden Arbeiten wurde gefunden, da? bei gewissen Konzentrationen von anionischen oberfl?chenaktiven Agenzien die Teilchen von positiven Silberjodidsolen mit einer doppelten adsorbierten Schicht des Agens überzogen werden; unter diesen Bedingungen werden stabile Sole gebildet, deren Eigenschaften abh?ngig von der Kopfgruppe des Agens sind. Indem man diese Tatsache anwendet, kann man Partikel aus Silberjodid, überzogen mit Natriumtetradecylsulfat, herstellen und ihre Stabilit?t und ihr elektrophoretisches Verhalten in Gegenwart einer Reihe von Kationen von verschiedener Valenz prüfen. Verwendet wurden die Kationen Th⁺⁺⁺⁺, La⁺⁺⁺, Ba⁺⁺, Ca⁺⁺, Mg⁺⁺, Zn⁺⁺, UO₂ ⁺⁺, Mn⁺⁺, Cd⁺⁺, Na⁺, K⁺ und Li⁺. Die Stabilit?tskurven als Funktion der Ionenst?rke und des Partikelradius zeigen deutliche Spezifit?t in Abh?ngigkeit von den Kationen. Dies wird der Bindung der Kationen mit den Sulfatgruppen der zweiten Schicht des adsorbierten Agens zugeschrieben. Die Ergebnisse scheinen in allgemeiner übereinstimmung mit den Voraussagen der theoretischen überlegung, dargestellt in Teil IV, zu stehen.

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One of us (A. W.) wishes to thank the British Council for a Scholarship and the University of Cambridge for the award of theOliver Gatty Studentship.     

Preparation and evaluation of a novel chiral stationary phase based on covalently bonded chitosan for ligand-exchange chromatography

A novel chiral stationary phase based on chitosan covalently bonded onto silica gels has been prepared and used for the separation of various alpha-amino acid enantiomers as well as alpha-hydroxycarboxylic acid enantiomers by chiral ligand-exchange chromatography with copper(II) as a complexing ion. The methanol content and copper(II) ion concentration in the eluent affected retentivity and enantioselectivity. Furthermore, a plausible chiral recognition mechanism for resolution of alpha-amino acids was proposed.     

Retention of some glucosinolates in anion exchange chromatography. Part I: Qualitative study on a silica-trialkylammonium exchanger

Summary The retention and separation of glucosinolates, as organic anions, were studied on a silica-based strong anion exchanger under isocratic elution conditions. All glucosinolates carry the same functional ionic group (-OSO ₃ ^– ), however they do not have the same retention in anion exchange chromatography. The plots of capacity factors of organic anions versus the reciprocal of eluent ion concentration show good linearity. From the slope and y-intercept data the major retention mechanisms are interpreted as ion exchange and reversed-phase interactions. The effects of nature and concentration of the eluent ion and the influence of organic modifier addition to the aqueous buffered mobile phase are also investigated. Direct and indirect UV detection were used.Our results open the way for the development of new systems for intact glucosinolate analysis which are easier to use than the present ion-pairing chromatographic method.     

Influence of co-ions in the eluent on the separation factor of lithium isotopes

The influence of co-ions in the eluent on the separation factor () of lithium isotope separation has been studied by ion exchange chromatography. A strongly acid cation exchange resin (Dowex 50W-X8) was used for the separation of lithium isotopes. The co-ions used in eluent were H⁺, K⁺, Ba²⁺, Cu²⁺, Al³⁺ and Cr³⁺ as their chlorides. From the experiments, it was found that⁶Li was enriched in the resin phase and⁷Li in solution phase. At the same distribution coefficient (K_d=30), the separation factor increased linearly with the charge of co-ion (=1.0022 to 1.0039).     

Influence of reversed- and normal-phase liquid chromatographic eluents in the fragmentation of selected chlorinated herbicides in thermospray liquid chromatography-mass spectrometry

The effect of two completely different mobile phase compositions, reversed-phase acetonitrile-water + ammonium acetate and normal-phase cyclohexane, were compared in filament-on thermospray liquid chromatography-mass spectrometry (LC-MS) for the determination of selected chlorinated herbicides such as chloroatrazines and chlorinated phenoxyacetic acids. By using acetonitrile-water + 0.05 M ammonium acetate mixtures in positive ion mode thermospray LC-MS, the chloroatrazine herbicides showed the acetonitrile adduct ion [M + (CH₃CN)H]⁺ as the base peak, whereas the chlorinated phenoxyacetic acids showed no signal. In contrast, when cyclohexane, which is reported for the first time as an eluent in the thermospray technique, was used as the mobile phase the chlorinated phenoxyacetic acid herbicides exhibited [M – H]⁺, [M – Cl]⁺ and M⁺˙ as the main ions. Negative ion mode thermospray LC-MS showed [M – H]^? as the base peak for the chloroatrazines in the different mobile phases, whereas the chlorinated phenoxyacetic acids exhibited [M + H]^?, [M + Cl]^? or [M – HCl]^? as the base peaks in cyclohexane and [M + acetate]^? in acetonitrile-water-ammonium acetate.     

Evaluation of behaviour of linear monoamines CH3-(CH2)n−1-NH2 (n=1-6) in ion chromatography

This paper reports the results on a study of ion chromatography (IC) behaviour on strong cationic exchange column of CH₃-(CH₂)_n−1-NH₂ (n=1-6) type linear monoamines. The eluents were mixtures of HCl-NaCl, HNO₃-NaNO₃, HClO₄-NaClO₄, H₂SO₄-Na₂SO₄, HClO₄-NaClO₄-CH₃CN. Amines were revealed with an amperometric detector. The influence of different counter-ions on retention factors, k′, is discussed. Relationships between k′ and pE (E=sum of Na⁺ and H⁺ concentrations), and length of alkylic chain, and sensitivity coefficient S, are reported and discussed. The addition of acetonitrile (ACN) in the eluent was also taken into account. Suitable considerations are derived from these data. An example of monoamines separation is given.