The effect of solvent mixture composition on the extractive separation of technetium using a crown ether

Separation of⁹⁹Mo and^99mTc was studied using a crown ether diluted with benzene mixed with acetonitrile. The effect of concentration of the extracting agent as well as the pH of the aqueous solution on the distribution coefficient was investigated. Benzene mixed with acetonitrile in 13 ratio proved to be the best composition of the diluent. The extracted species has the general formula TcO₂.nH₂O.xCe.yC₆H₈O₆.zCH₃CN.     

Synergistic behaviour of crown ethers in the thenoyltrifluoroacetone extraction of technetium

The synergism of the crown ethers /CE/ dibenzene-18-crown-6 /DB18C6/ and 18-crown-6 /18C6/ has been investigated in the thenoyltrifluoroacetone /HTTA/ extraction of technetium from aqueous phase containing NaBH₄ into benzene at room temperature. The extracted synergistic species have the general formula TcO/OH/.TTA.CE. The order of synergism was found to be 18C6>DB18C6.     

Enantiomeric separation by capillary electrophoresis using a crown ether as chiral selector.

This paper reviews chiral separations of primary amines by capillary electrophoresis and crown ether as chiral selector. Two possible mechanisms of chiral recognition by host-guest complexation are discussed: (i) The substituents of the crown ether act as barriers for the guest compounds, and (ii) lateral electrostatic interactions between host and guest occur. Experimental conditions affecting the separation are discussed in detail. A literature overview of practical applications is presented as well. More than 80 different primary amines were analyzed, whereupon the majority could be resolved using a screening method. It is shown that a synergistic effect on the resolution of chiral amines is observed when the chiral crown ether and cyclodextrins are simultaneously used in the same buffer system. This approach opens interesting perspectives for further method optimization.     

Solvent extraction separation of rubidium with a crown ether for neutron activation analysis in rock samples

The extraction behavior of rubidium with a crown ether has been studied and methods for the separation and determination of rubidium have been developed. Rubidium was separated with tetraphenylborate from sample solution, and then quantitatively extracted into nitrobenzene by 18-crown-6 from 0.05 mol/l picric acid (pH 6) and back-extracted by 6 mol/l hydrochloric acid. Rubidium was determined by the neutron activation method in rock samples.     

Dehydrochlorination of polyvinylidene chloride (PVDC) in the presence of crown ether as a phase transfer agent

Films of polyvinylidene chloride (PVDC) were heterogeneously dehydrochlorinated by reacting them with KF-crown and KOH-crown complexes dissolved in benzene. Solutions were in contact with an excess of unhydrous salts. This three-phase reaction was very fast at 80°C and the removal of one chlorine atom per monomer unit was completed within 1 h. Further dehydrochlorination leads to triple-bond formation and to aromatization of the system due to the intramolecular 1,6 elimination. The former reaction is dominant when KOH-crown is used as the dehydrochlorinating agent and the latter is dominant in KF-crown/CaO systems. The apparent energy of activation of the initial dehydrochlorination process is estimated to be 6.7 kcal./mol.     

Trivalent molybdenum as volumetric reducing agent

Summary The purpose of the present investigation is to introduce trivalent molybdenum as a new analytical reducing agent, in hydrochloric as well as sulphuric acid media.The solution is prepared in 9N acid by electrolytic or mercuryreduction of the hexavalent form. It is preferentially stocked and used in high acid concentrations, whereby its stability in air is optimal, falling to half its titer after nearly two months. It has been tested with success as reductant for ceric, dichromate, ferric and vanadate. It has the advantage of being used in ordinary opened burettes. Titrations were followed potentiometrically in general, and alternately visually in decinormal media, whereby molybdenum blue appears at the end-point. The percentage error in fifteen discussed experiments never surpassed ±1%. Some oxidation titrations were also undertaken using iodate and bromate, with the same degree of accuracy, provided they were conducted in 6N acid. In weaker acid concentrations, equilibria were more slowly attained, with a more or less pronounced deviation, due to some oxidisability that necessitates controlled inert atmosphere.     

Stereoisomeric separation of pharmaceutical compounds using CE with a chiral crown ether

Optical pure (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid, a chiral crown ether, was successfully used as a chiral selector for the stereoisomeric separation of numerous real pharmaceutical compounds. Both practical and mechanistic aspects were described. Effects of chiral selector concentration under different pH values of BGE were discussed. Chiral recognition for the enantiomeric compounds with (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid was investigated through model compounds using CE and infrared spectroscopic techniques. Relations between the enantioselectivity of the chiral crown ether and the structural features of the studied compounds were also investigated. Unusual resolutions of compound-p and its enantiomer as well as compound-o and its 2b epimer were described. These compounds contained only tertiary amine, believed to be nonbinding with crown ethers in general. The possible mechanisms for the interaction between compound-o and the chiral crown ether were investigated using CE, electrospray MS (ESI-MS), and proton ((1)H) NMR spectroscopy. All experiments provided clear evidence that binding between compound-o and the chiral crown ether had occurred. ESI-MS spectra indicated that the complexes had a 1:1 stoichiometric ratio. The advantages and disadvantages of using chiral crown ether for stereoisomeric separations were compared with those using sulfated CDs.     

Extraction of technetium by crown ethers and cryptands

Extraction of technetium with dibenzo-18-crown-6 was studied from alkline media. Effects of crown cavity size, substitutions, organic solvents and type of base on the distribution coefficient were discussed. High separation factors of technetium from other elements in an irradiated uranium sample were attained.     

Substituted ethan phosphonic acid esters as reagents for the separation of molybdenum from rhenium by solvent extraction

New esters of the ethan phosphonic acids have been synthesized and their extraction properties studied with respect to Mo(VI), Re(VII), Fe(III),Au(III),Tl(III) and Sb(V). A possibility is shown for the analytical separation of molybdenum from rhenium (beta = 700). The state of these new extraction agents in carbon tetrachloride solution, and the mechanism of the extraction processes, have been investigated by means of infrared spectra.     

Comparison of the TEVA-Spec resin and liquid-liquid extraction methods for the separation of technetium in soil samples

When ICP-MS is used for⁹⁹Tc measurements, elements which interfere with⁹⁹Tc counting should be removed. In this study, a separation method using a novel chromatographic resin (TEVA·Spec^® resin) was compared with a liquid-liquid extraction (LLX) method for separation and concentration of⁹⁹Tc which was trapped in a solution after combustion of environmental soil samples. The results showed that Tc could be separated from Ru at high recoveries with both separation methods. Molybdenum, however, was not removed by LLX, while more than 99% of Mo in soil samples were removed by TEVA·Spec resin.     

Radiochemical separation of rhenium with crown ether for neutron activation analysis in rocks

The extraction behavior of perrhenate with crown ethers has been studied and methods for the separation and determination of rhenium have been developed. Perrhenate anion can be quantitatively extracted into nitrobenzene by benzo-15-crown-5 (B15C5) from 2M potassium hydroxide and back-extracted by sodium phosphate buffer solution. The molar ratio of B15C5 to KReO₄ in the extracted species is probably 21. Rhenium was satisfactorily determined by neutron activation method in rock samples.     

Selective solid-phase extraction of catecholamines by the chemically modified polymeric adsorbents with crown ether

A simple and selective one-step solid-phase extraction procedure using chemically modified polymer resin (Amberlite XAD-4) with crown ether was investigated for the measurement of urinary catecholamines. After loading the urine samples (adjusted to pH 4) on the synthesized adsorbent cartridge, the column was washed with methanol followed by water and then the adsorbed catecholamines were eluted by 1.0 mL of 6.0 M acetic acid. The effectiveness of sample clean-up method was demonstrated by reversed-phase ion-pair high-performance liquid chromatography with electrochemical detection. Under optimal condition, the recoveries of epinephrine, norepinephrine, and dopamine from spiked urine sample were >86% for all catecholamines. The detection limits (n=5) for epinephrine, norepinephrine, and dopamine were 37, 52, and 46 nmol/L, respectively.     

Extraction of strontium using an irradiated extraction agent of crown structure

The partition coefficient of strontium upon its extraction from the aqueous solutions of picric acid into chloroform containing DC-18-crown-6, B-15-crown-5 after their exposition to gamma radiation has been studied. A significant decrease of the partition coefficient in the studied range of doses 10–70 kGy was observed. This effect can be attributed to the radiolytic products of chloroform. The radiation destruction as well as dehydrogenation of crown ethers were not observed.     

Liquid chromatographic enantiomer separation of racemic amine using chiral crown ether stationary phase

Direct enantioseparation of racemic amine, amino-thiophene-2-yl-acetonitrile (TAN), on chiral crown ether stationary phase [Crownpak CR (+)] is described in this study. The elution behavior and the effect of acid additives on resolution of racemic amine, TAN, is intensely investigated. Moreover, the chiral recognition mechanism in this specific system is proposed based on computational methods with the density functional theory. Diastereomeric complexation of the ammonium ion of racemic amine inside the cavity of chiral crown ether appears essential for the chiral discrimination. The pH of the mobile phase containing acid additives also acts as an important factor for the chiral recognition.     

The extraction and determination of molybdenum as the thiocyanate complex

A method is presented for the determination of molybdenum by extraction of its thiocyanate complex with methyl isobutyl ketone. The method is accurate to ±4% or 3 μg of molybdenum, whichever is greater. The only elements which cause interference are rhenium (serious), platinum, palladium, rhodium, selenium and tellurium. The method has been applied to a number of standard samples with excellent results.     

Precipitation separation of strontium and calcium from acidic solutions using crown ether and tungstosilicic acid

Strontium forms a compound of composition (SrL)₂A·nH₂O with low solubility (5.0·10^–6 mol Sr·dm^–3) in the presence of 18-crown-6 (L) and tungstosilicic acid (H₄A) in acid media, as has been found by radiometric precipitation titration. Formation of the compound with limited solubility was used for separation of strontium and calcium from 1 mol·dm^–3 HCl. It is possible to separate strontium in the range from trace to 6 mmol·dm^–3 in the presence of calcium with its concentration up to 0.2 mol ·dm^–3 and the recovery determined was 95% of Sr and 5% Ca or 90% of Sr and 4% Ca, respectively. The ratio of Sr/Ca depends on the stability constants ratio of metal-L (⊃_SR/⊃_ca) in the case of gradual addition of L. Potassium up to the concentration of 0.05 mol·dm^–3 does not influence recovery of strontium.     

The separation of titanium from vanadium and molybdenum by cupferron solvent extraction

The isolation of small amounts of titanium from vanadium and molybdenum before the spectrophotometric determination of titanium as the “pertitanate” complex has been achieved by a. solvent extraction procedure using cupferron and chloroform at pH 6 in the presence of EDTA.     

Spectrophotometric determination of sodium by ion-pair extraction with crown ether complexes and monoanionic dyes

A highly selective photometric procedure for the determination of sodium in blood serum is proposed, based on the ion-pair extraction of a sodium—cryptand complex. A comparative study of cryptands with various cavity sizes, different pairing anions and extraction solvents is described. The use of cryptand 211, picrate and toluene, as ligand, pairing anion and extraction solvent, respectively, allows sodium to be determined at the μg ml^?1 level. A 350-fold amount of potassium (by weight) does not interfere, nor do other alkali metals. Possible interferences by multivalent cations are masked by EDTA.     

Chiral separation of gemifloxacin in sodium-containing media using chiral crown ether as a chiral selector by capillary and microchip electrophoresis

Chiral crown ether, (+)-(18-crown-6)-tetracarboxylic acid (18C6H(4)), is an effective chiral selector for resolving enantiomeric primary amines owing to the difference in affinities between 18C6H(4) and each of the amine enantiomers. In addition to the destacking effect of sodium ion in the sample solution, the strong affinity of sodium ion to the polyether ring of crown ether is unfavorable to chiral capillary electrophoresis using 18C6H(4) as a chiral selector. In this report, the chiral separation of gemifloxacin dissolved in a saline sample matrix using 18C6H(4) was investigated. Adding a chelating agent, ethylenediaminetetraacetic acid (EDTA), to the run buffer greatly improved the separation efficiencies and peak shapes. The successful chiral separation of gemifloxacin in a urinary solution was demonstrated for both capillary and microchip electrophoresis.     

Homogeneous liquid-liquid extraction method for the selective separation and preconcentration of ultra trace molybdenum

A new simple and efficient homogeneous liquid-liquid extraction method for the selective separation and preconcentration of molybdenyl ions was developed. α-Benzoin oxime (ABO) was investigated as a complexing ligand, and perfluorooctanoate ion (PFOA⁻) was applied as a phase-separator agent under strongly acidic conditions. Under the optimal conditions ([ABO] = 2.1 × 10⁻³ M, [PFOA⁻] = 1.8 × 10⁻² M, [HNO₃] = 1.7 M, [acetone] = 11.8% (v/v)), 10 μg of molybdenum in 5 ml aqueous phase could be extracted quantitatively into 40 μl of the sedimented phase. The maximum concentration factor was 125-fold. Thiocyanate was applied as a chromogenic reagent for the direct spectrophotometric determination of molybdenum in the sedimented phase. The reproducibility of the proposed method is at the most 2.4%.The influence of the type and concentration of acid solution, the concentration of ABO, the type and volume of the water-miscible organic solvent, the concentration of PFOA⁻, and the effect of different diverse ions on the extraction and determination of molybdenum(VI) were investigated. The proposed method was applied to the extraction and determination of molybdenum(VI) in natural water, Spinach, and Lucerne samples. A satisfactory agreement exists between the results obtained by the proposed method and those reported by GF-AAS.