Aqueous Source Phase Research Articles

Synthesis and Mercurophilic Properties of Dithiocrown Ethers Having an Azulene Pendant

Dithiocrown ether derivatives (3) having an azulene pendant were synthesized by regioselective reaction of 8,8-dicyanoheptafulvene derivatives with malononitrile in the presence of sodium ethoxide to examine their extraction and transport of Hg(II) ion through a liquid membrane. The transport was driven by acidic conditions and was capable of moving metal cations 'up-hill'. Thus, it was possible to follow the transport of Hg(II) ion from the aqueous source phase to the organic layer and from the organic layer to the receiving phase. The carrier (3) displayed remarkable selectivity for Hg(II) ion.

Selective Transport of Silver(I) Ion Through Polymer Membranes Containing Thioether Donor Macrocycles as Carriers

The Preparation of polymer membrane and it′s selectivity to silver(I) ion from an aqueous solution containing seven metal cations, Co(II), Ni(II), Cu(II), Zn(II), Ag(I), Cd(II) and Pb(II), was studied. The source phase contained equimolar concentrations of the above mentioned cations with the source and receiving phases being buffered at pH 5.0 and 3.0 respectively. The effect of variation in the number of the macrocyclic sulfur atom donor set anssd the size of ring 9 and 16 member macrocycles on transport efficiency is presented. Silver(I) ion transport occurred (at 25°C) from the aqueous source phase across the polymer membrane (derived from cellulos triacetate) containing ligands 9‐membered, S3‐donor and16‐membered S4‐donor macrocycles as the ionophors in separate experiments into the aqueous receiving phase. Clear transport selectivity for silver(I) ion was observed using both thioether donor macrocycles. The efficiency of transport rate for silver(I) ion with using 9‐membered S3‐donor macrocycle as carrier was better than 16‐membered S4‐donor .

Effect of Solvent on Competitive Bulk Membrane Transport of Transition and Post Transition Metal Cations Using Decyl-18-crown-6

A series of competitive metal ion transport experiments have been performed. Each involved transport from an aqueous source phase across an organic membrane phase into an aqueous receiving phase. The source phase contained equimolar concentrations of cobalt(II), nickel(II), cupper(II), zinc(II), cadmium(II), silver(I) and lead(II) metal cations. The membrane phase incorporated ionophore, decyl-18-crown-6. The membrane solvents include: chloroform, dichloromethane, 1,2-dichloroethane, nitrobenzene and chloroform–nitrobenzene binary solvents. A good transport efficiency and selectivity of Pb2+ transport from aqueous solutions are observed in this investigation. The selectivity order for competitive bulk liquid membrane transport of the studied transition and post transition metal cations through chloroform is: Pb2+>Co2+>Ni2+>Ag+>Cd2+, but in the case of dichloromethane, 1,2-dichloroethane and nitrobenzene as liquid membranes, the selectivity sequences were found to be: Pb2+>Co2+>Cd2+>Cu2+>Ag+>Ni2+>Zn2+, Pb2+>Co2+>Ag+>Ni2+>Zn2+ and Pb2+>Co2+>Ni2+>Zn2+>Cd2+>Ag+, respectively. The transport rate of the metal cations in chloroform–nitrobenzene binary solvents is sensitive to the solvent composition. The transport processes were studied in absence and presence of the stearic acid and the results show that the sequence of selectivities and ion transport rates change in the presence of stearic acid.

Competitive bulk liquid membrane transport and solvent extraction of some transition and post-transition metal ions using acylthiourea ligands as ionophores

Competitive transport experiments involving metal ions from an aqueous source phase through a chloroform membrane into an aqueous receiving phase have been carried out using a series of acylthiourea ligands as the ionophore present in the organic phase. The source phase contained equimolar concentrations of cobalt(II), nickel(II), copper(II), zinc(II), silver(I), cadmium(II) and lead(II) with the source and receiving phases being buffered at a number of different pHs. Transport selectivity was observed for silver(I) in all but one case. Selectivity for silver(I) was also observed in a series of parallel solvent extraction experiments carried out under similar source and membrane phase conditions. An X-ray diffraction study of the silver(I) complex of the N,N-dibutyl-N′-benzoylthiourea from this series is reported. There are two crystallographically independent molecules in the asymmetric unit and each molecule consists of four silver(I) ligand complex units, hence giving rise to Z = 8. In each molecule, both chelate and monodentate co-ordination modes of complexation to silver(I) are evident. Hence, each silver is co-ordinated to a sulfur and oxygen atom from one ligand and to a shared (bridging) sulfur from another ligand. Each silver atom is thus co-ordinated to three donor atoms.

Silver(i) complexation of linked 2,2′-dipyridylamine derivatives. Synthetic, solvent extraction, membrane transport and X-ray structural studies

Synthesis of the 2,2'-dipyridylamine derivatives di-2-pyridylaminomethylbenzene 1, 1,2-bis(di-2-pyridylaminomethyl)benzene 2, 1,3-bis(di-2-pyridylaminomethyl)benzene 3, 2,6-bis(di-2-pyridylaminomethyl)pyridine 4, 1,4-bis(di-2-pyridylaminomethyl)benzene 5, and 1,3,5-tris(di-2-pyridylaminomethyl)benzene 6 are reported together with the single-crystal X-ray structures of 2, 3, and 5. Reaction of individual salts of the type AgX (where X = NO(3)(-), PF(6)(-), ClO(4)(-), or BF(4)(-)) with the above ligands has led to the isolation of thirteen Ag(I) complexes, nine of which have also been characterised by X-ray diffraction. In part, the inherent flexibility of the respective ligands has resulted in the adoption of a range of coordination arrangements. A series of liquid-liquid (H(2)O/CHCl(3)) extraction experiments of Ag(I) with varying concentrations of 1-6 in the organic phase have been undertaken, with the counter ion in the aqueous phase being respectively picrate, perchlorate and nitrate. In general, extraction efficiencies for a given ionophore followed the Hofmeister order of picrate > perchlorate > nitrate; in each case the tris-dpa derivative 6 acting as the most efficient extractant of the six systems investigated. Competitive seven-metal bulk membrane transport experiments (H(2)O/CHCl(3)/H(2)O) employing the above ligands as the ionophore in the organic phase and equimolar concentrations of Co(II), Ni(II), Zn(II), Cu(II), Cd(II), Pb(II) and Ag(I) in the aqueous source phase were also undertaken, with transport occurring against a pH gradient. Under the conditions employed 1 and 5 yielded negligible transport of any of the metals present in the source phase while sole transport selectivity for Ag(I) was observed for 2-4 and 6.

Selective Transport of Copper(II) Ion across a Polymer Membrane Incorporating a Difunctional Schiff-base Ionophore

The selective polymer membrane transport of Cu(II) from an aqueous solution containing seven metal cations, Co(II), Ni(II), Cu(II), Zn(II), Ag(II), Cd(II) and Pb(II), was studied .The source phase contained equimolar concentrations of the above-mentioned cations, with the source and receiving phases being buffered at pH 4.9 and 3.0, respectively. Cu(II) ion transport occurred (J=2.82 × 10−7 mol/h at 25 °C) from the aqueous source phase across the polymer membrane (derived from cellulose triacetate) containing ligand (I) as the ionophore, into the aqueous receiving phase. Clear transport selectivity for Cu(II) was observed.

Metal-Ion Recognition—Selective Bulk Membrane Transport of Silver(I) Using Thioether Donor Macrocycles as Ionophores, and X-Ray Structure of the Silver Complex of an S4-Donor Ring

Competitive metal-ion transport experiments, each involving transport from an aqueous source phase containing equimolar concentrations of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(i), and lead(II) across a chloroform membrane phase to an aqueous receiving phase have been carried out. The membrane phase incorporated an ionophore chosen from a series of thioether-containing macrocycles. For those systems that displayed transport behaviour, sole selectivity for silver(I) was observed under the conditions employed. The effect of variation in the macrocyclic sulfur atom donor set and the presence of hydrophilic ring substituents on transport efficiency is presented. An X-ray structure of the 1 : 1 silver(I) nitrate complex of a 16-membered, S4-donor macrocycle shows the presence of four crystallographically independent macrocycles displaying conformational isomerism. Each silver(I) has an approximate tetrahedral geometry, being bound to three sulfur atoms from three different macrocycles and to one nitrato ligand to yield a three-dimensional network.

Carrier-facilitated bulk liquid membrane transport of iron(III)-siderophore complexes utilizing first coordination sphere recognition.

Carrier-facilitated bulk liquid membrane (BLM) transport from an aqueous source phase through a chloroform membrane phase to an aqueous receiving phase was studied for various hydrophilic synthetic and naturally occurring Fe(III)-siderophore complexes using first coordination sphere recognition. Iron transport systems were designed such that two cis coordination sites on a hydrophilic Fe(III) complex are occupied by labile aquo ligands, while the other four coordination sites are blocked by strong tetradentate ligands (siderophores). The labile aquo coordination sites can be "recognized" by a liquid membrane-bound hydrophobic bidentate ligand, which carries the hydrophilic Fe(III)-siderophore complex across the hydrophobic membrane to an aqueous receiving phase. The system is further designed for uphill transport of Fe(III) against a concentration gradient, driven by anti-port H(+) transport. Three tetradentate siderophore and siderophore mimic ligands were investigated: rhodotorulic acid (H(2)L(RA)), alcaligin (H(2)L(AG)), and N,N'-dihydroxy-N,N'-dimethyldecanediamide (H(2)L(8)). Flux values for the transport of Fe(L(x))(OH(2))(2)(+) (x = RA, AG, 8) facilitated by the hydrophobic lauroyl hydroxamic acid (HLHA) membrane carrier were the highest when x = 8, which is attributed to substrate lipophilicity. Ferrioxamine B (FeHDFB(+)) was also selectively transported through a BLM by HLHA. The process involves partial dechelation of ferrioxamine B to produce the tetradentate form of the complex (Fe(H(2)DFB)(OH(2))(2)(2+)), followed by ternary complex formation with HLHA (Fe(H(2)DFB)(LHA)(+)) and transport across the membrane into the receiving phase. Uphill transport of ferrioxamine B was confirmed by increased flux as [H(+)](source phase) < [H(+)](receiving phase). The membrane flux of ferrioxamine B occurs near neutral pH, as evidence that ternary complex formation and ligand exchange are viable processes at the membrane/receptor surface of microbial cells.

Metal ion recognition. Interaction of a series of successively N-benzylated derivatives of 1,4,8,11-tetraazacyclotetradecane (cyclam) with selected transition and post-transition metal ions

The interaction of a series of N-benzylated cyclam ligand derivatives incorporating from one to four N-benzyl groups with cobalt(II), zinc(II), cadmium(II), lead(II) and silver(I) nitrates is reported; the results are compared with those obtained in a prior study involving the formation of the corresponding complexes of nickel(II) and copper(II) with this ligand series. The isolation of a selection of 1 ∶ 1 (metal ∶ ligand) complexes has been carried out and X-ray diffraction structures of five such products have been determined. In each complex the metal ion is coordinated to the N4-donor set of the cyclam ring with the latter adopting either a trans-I or a trans-V configuration; monodentate or bidentate nitrato ligands complete the respective coordination spheres. Coordination numbers range from five in a zinc(II) complex, through six in two cadmium(II) complexes, to eight in two lead(II) complexes. Competitive bulk membrane transport experiments (water/chloroform/water) have been carried out in which each of the five benzylated ligands were in turn employed as the ionophore in the chloroform phase. The respective aqueous source phases (buffered at pH 4.9) contained an equimolar mixture of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I) and lead(II) nitrates. The aqueous receiving phase was buffered at pH 3.0. Under these conditions, high selectivity for copper(II) was observed for each of the ionophores incorporating one or two N-benzyl groups whereas no transport for any of the seven metals present in the source phase was observed for the tribenzylated derivative. In marked contrast to the above behaviour, the tetra-N-benzyl derivative yielded sole transport selectivity for silver(I) under similar conditions. 1H NMR and 13C NMR titration experiments in CD3CN–CDCl3 confirmed the 1 ∶ 1 stoichiometry of the silver(I) tetra-N-benzylcyclam complex in this solvent mixture.

Carrier-facilitated bulk liquid membrane transport of iron(iii) hydroxamate complexes utilizing a labile recognition agent and amine recognition in the second coordination sphere

Carrier-facilitated bulk liquid membrane transport from an aqueous source phase through a chloroform membrane phase to an aqueous receiving phase was studied for various Fe(III) hydroxamate complexes (siderophore mimics) using second coordination sphere recognition. Iron transport systems were designed using a strategy whereby a tetradentate siderophore mimic sequesters iron(III), leaving two labile aquated coordination sites for ternary complex formation. This aquated complex reacts with a bi-functional host/guest molecule capable of acting as a host for the iron complex via ternary complex formation, while simultaneously serving as a guest for a membrane-bound host (carrier). The bi-functional molecules utilized contain a hydroxamate host for Fe(III) binding and a protonated primary amine that can be “recognized” by a liquid membrane-bound hydrophobic ionophore, which carries the hydrophilic Fe(III)-complex across the hydrophobic membrane to an aqueous receiving phase. Four protonated amine hydroxamic acids were investigated as bi-functional host/guest molecules: β-alanine hydroxamic acid (H2Lala)+, L-glutamic acid γ-monohydroxamic acid (H3Lglu)+, glycine hydroxamic acid (H2Lgly)+, and L-lysine hydroxamic acid (H3Llys)2+. These four bidentate ligands were each coordinated to Fe(III) along with the tetradentate N,N′-dihydroxy-N,N′-dimethyldecanediamide (H2L8) to form ternary complexes [Fe(L8)(HxLy)z; x = 1 or 2; y = ala, glu, gly, or lys; z = 0, +1, or +2] that were transported through a chloroform bulk liquid membrane by the lipophilic host carrier cis-dicyclohexano-18-crown-6 (DC18C6). No carrier-dependent flux was observed for Fe(L8)(HLglu), probably due to intramolecular H-bonding. Flux values for the transport of Fe(L8)(HxLy)z (x = 1 or 2; y = ala, gly, or lys; z = +1 or +2) facilitated by the membrane carrier (DC18C6) were highest when y = gly and lowest when y = ala. Equilibrium constants pertaining to two-phase distribution or ion pairing, second coordination sphere host–guest formation, and overall extraction were determined and used to rationalize variations in flux values.

Competitive bulk membrane transport and solvent extraction of transition and post transition metal ions using mixed-donor acyclic ligands as ionophores

Competitive transport experiments involving metal ion transport from an aqueous source phase across a chloroform membrane phase into an aqueous receiving phase have been carried out using a series of open-chain mixed-donor ligands as the ionophore in the organic phase. The source phase contained equimolar concentrations of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I) and lead(II), with the source and receiving phases being buffered at pH 4.9 and 3.0, respectively. Clear transport selectivity for silver(I) was observed in all cases. This was also observed in a series of parallel solvent extraction experiments carried out under similar source and membrane phase conditions. Stability constant data confirm that all these ligands show significant affinity for silver(I) in methanol. An X-ray diffraction study of the silver(I) complex of a tripodal NS3-donor ligand from the present series is reported. This complex occurs as two crystallographically independent molecules with both forms having a 1 ∶ 1 silver ∶ ligand ratio. The metal coordination geometry of the first form is distorted tetrahedral, with three coordination sites occupied by the three sulfur atoms of the ligand and the fourth site filled by an oxygen atom of the nitrate anion. The silver ion in the second form is five-coordinate being bound to the ligand's apical nitrogen as well as to its three sulfur donors. The remaining position is again occupied by a nitrate oxygen, with the metal coordination geometry in this case best described as distorted trigonal bipyramidal.

A selective uphill transport of copper through bulk liquid membrane using Janus Green as an anion carrier

Abstract A bulk liquid membrane consisted of 1.8×10−4 M Janus Green in chloroform that placed between an aqueous source phase containing 0.5 M sodium thiocyanate at pH 7 and an aqueous receiving phase with 0.1 5 M histidine at pH 7 results in an uphill transport of copper from the source phase to the receiving phase. The amount of copper transport through the liquid membrane after 180 min was 97.0±1.7%. The presence of other metals such as Cd2+, Zn2+, Hg2+, Mg2+, Ag1+, Ni2+, Pb2+, Fe3+, K1+, Co2+ doesn't change the efficiency of copper transport.

Metal ion recognition. The interaction of cobalt(ii), nickel(ii), copper(ii), zinc(ii), cadmium(ii), silver(i) and lead(ii) with N-benzylated macrocycles incorporating O2N2-, O3N2- and O2N3-donor sets

The interaction of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I) and lead(II) with a series of mixed-donor, N-benzylated macrocyclic ligands incorporating O2N2-, O3N2- and O2N3-donor sets has been investigated. The log K values for the respective 1 ∶ 1 complexes in 95% methanol (I = 0.1 mol dm−3; Et4NClO4, 25 °C) have been determined potentiometrically and the results compared with the values obtained previously for the parent (non-benzylated) macrocyclic systems. Examples of N-benzylation of individual parent macrocycles leading to enhanced discrimination for silver(I) are presented. In the case of a dibenzylated O3N2-ring and a tribenzylated O2N3-ring, both 17-membered, high selectivity for this ion was observed relative to the other metal ions investigated. Competitive mixed-metal transport experiments across a bulk chloroform membrane have been performed using the benzylated derivatives as ionophores. For each experiment the source contained equimolar concentrations of the above metal ions and transport was performed against a pH gradient; the aqueous source and receiving phases were buffered at pH 4.9 and 3.0, respectively. In parallel to the log K results, transport selectivity for silver(I) was exhibited by the di- and tri-benzylated ligands mentioned above. The remaining ligands proved to be poor ionophores, showing no significant metal ion transport under the conditions employed. In a further study, high silver ion (transport) selectivity was maintained when the above tribenzylated ligand was incorporated as the ionophore in a polymer inclusion membrane system. Single metal and mixed (seven-metal) solvent extraction experiments employing similar aqueous source and chloroform phases to those used in the bulk membrane transport runs have also been performed for the tribenzylated ligand derivative; significant selectivity for silver was again maintained in these solvent extraction experiments. An X-ray study of [AgL]ClO4 (where L is the above-mentioned dibenzylated derivative) confirms that all donor atoms of the macrocycle coordinate to the silver ion; the latter is five-coordinate with the complex cation exhibiting a highly distorted trigonal bipyramidal geometry.

Metal ion recognition. Selective interaction of silver(i) with tri-linked N2S2-donor macrocycles and their single-ring analogues

The interaction of four tri-linked N2S2-donor macrocyclic ligands and their single ring analogues with silver(I) has been investigated. The 3 ∶ 1 (metal ∶ ligand) stoichiometries of the silver(I) complexes of the tri-linked species in dimethyl sulfoxide-d6/CDCl3 were confirmed by means of NMR titrations involving the incremental addition of silver(I) nitrate to the respective ligands in the above solvent mixture and following the corresponding induced shifts in the 1H NMR spectrum. Solid 3 ∶ 1 (metal ∶ ligand) complexes were isolated for each of the parent (unsubstituted) tri-linked ligands. Competitive solvent extraction experiments (water/chloroform) and related bulk membrane transport (water/chloroform/water) experiments have been performed in which each of the four tri-linked ligands as well as their single ring analogues were employed as the extractant/ionophore in the chloroform phase. In both sets of experiments the respective aqueous source phases (buffered at pH 4.9) contained an equimolar mixture of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I) and lead(II) nitrates. For membrane transport the aqueous receiving phase was buffered at pH 3. Under the conditions employed, both the solvent extraction and the bulk membrane transport experiments resulted in high extraction/transport selectivity for silver(I) relative to the other six metal ions present.

Calix[4]resorcinarene and alkylaminomethylated calix[4]resorcinarene-mediated transport of some metal complexes through chloroform bulky liquid membrane

Spectrophotometry and pH measurements were used to study the non-substituted and ortho-substituted calix[4]resorcinarene-mediated transport of Cu(II) and Co(III) complexes with diamine and amino acids from an aqueous source phase to an aqueous receiving phase through a bulky chloroformic membrane. The non-substituted derivative was found to extract complex cations as the anionic ionophore, exchanging protons for the complex across the phase boundary. That is why the reextraction is not effective without acidifying of the receiving phase. The ortho-substituted calix[4]resorcinarenes extract complexes in the form of ionic pairs, which in turn promote their reextraction into receiving phase.

Separation of Co(II) and Ni(II) ions by supported and hybrid liquid membranes

Abstract In this work a competitive transport of an equimolar mixture of cobalt(II) and nickel(II) across supported and hybrid liquid membranes is presented. In both types of membranes di-2-ethylhexylphosphoric acid (D2EHPA) as well as commercial extractants, i.e. Cyanex® 272, 301, and 302 were used as ion carriers. In experiments with the supported liquid membranes, the support applied for the liquid membrane was microporous, hydrophobic polypropylene Celgard® 2500. This film was soaked in 0.1 M organic solution of an ionic carrier in kerosene. The hybrid liquid membranes were made by composition of the cation-exchange membranes (CEM) with bulk liquid membrane in the system: CEM–organic phase–CEM. The source aqueous phase was composed of an equimolar mixture of Co(II) and Ni(II) ions in sulfuric acid aqueous solutions. As receiving phase, sulfuric acid solutions of higher concentration than the source phase were utilized. The influence of several factors on cation transport selectivity and effectiveness has been explored. These factors include the effect of (a) acidity of the source and receiving phases, (b) initial concentration of metal ions in the source phase and (c) concentration of ion carrier in membranes. It is shown that supported and hybrid liquid membranes, containing phosphoorganic acids allow to separate a Co(II)/Ni(II) equimolar mixture. The separation of Co(II)/Ni(II) was found to be governed by the ionic carrier used as well as the acidity of the aqueous source phase. In the hybrid liquid membrane processes lower metal ion fluxes than in supported liquid membranes processes were observed. On the other hand, higher separation coefficients for Co(II)/Ni(II) were found for hybrid than for supported liquid membrane processes.

Macrocyclic ligand design. Interaction of selected transition and post-transition metal ions with a new N2O2-donor macrocycle incorporating a pyridylmethyl pendant arm

A pyridylmethyl derivative of a 14-membered, N2O2-donor macrocycle (L) and its complexes with cobalt(II), copper(II), zinc(II), silver(I), cadmium(II) and lead(II) have been prepared. Thermodynamic stabilities of the 1∶1 (metal∶ligand) complexes in 95% methanol (I = 0.1 mol dm−3, NEt4ClO4; 25 °C) and crystal structures of the 1∶1 complexes of copper(II), silver(I) and lead(II) with L were determined. The structure of the copper complex shows the presence of a cation of type [CuL(NO3)]+; it has a distorted octahedral geometry in which one co-ordination site is occupied by a unidentate nitrate ligand. In contrast, the cationic silver complex is of type [AgL]+ with the two pyridine ring nitrogen atoms of L dominating the co-ordination environment, which may be regarded as essentially two-co-ordinate. On the other hand, the lead complex, [PbL(NO3)(ClO4)], is eight-co-ordinate and incorporates bidentate nitrate and unidentate perchlorate ligands. A competitive mixed-metal transport experiment across a bulk chloroform membrane incorporating L as ionophore was performed. The aqueous source phase contained equimolar concentrations of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I), and lead(II) as their nitrate salts. Under the influence of a back proton gradient, silver and copper were preferentially transported to the aqueous receiving phase.

Metal-ion recognition. Competitive bulk membrane transport of transition and post transition metal ions using oxygen–nitrogen donor macrocycles as ionophores

A series of competitive metal ion transport experiments have been performed. Each involved transport from an aqueous source phase across a chloroform membrane phase into an aqueous receiving phase. The source phase contained equimolar concentrations of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I) and lead(II) while the membrane phase incorporated an ionophore chosen from a series of single-ring and double-ring macrocyclic ligands (incorporating mixed oxygen–nitrogen donor sets) together with hexadecanoic acid. The transport process was ‘driven’ by a back flux of protons, maintained by buffering the source and receiving phases at pH 4.9 and 3.0, respectively. Transport selectivity for copper(II) was observed in all cases. The results confirm that consideration of the mass balance of the metal ions present across all three transport phases is important for a fuller understanding of the nature of the discrimination process for the present systems.

Solvent Microextraction with Simultaneous Back-Extraction for Sample Cleanup and Preconcentration: Preconcentration into a Single Microdrop

A preconcentration technique which employs a microliter-size liquid membrane has been developed in order to obtain a large enrichment factor (EF) in a short time. The 30-μL n-octane liquid membrane, confined inside a small Teflon ring, is layered over 1.60 mL of aqueous source phase (sample), which is buffered at pH 13. The receiving phase is either a 1.00- or a 0.50-μL aqueous drop buffered at pH 2.1, that is suspended in the 30-μL membrane phase directly from the tip of a microsyringe needle. When the sample solution is stirred, basic analytes are extracted into the organic membrane phase and back-extracted simultaneously into the microdrop because they are neutral at high pH and protonated at low pH. After extracting for a prescribed time, the microdrop is taken back into the syringe needle and injected directly into an HPLC for quantification. In 15 min, the EFs in the 1.00-μL receiving drop are about 500 for methamphetamine, mephentermine, and methoxyphenamine, and about 160 for 2-phenylethylamine. E...

Transport of Cu(II) with hydroxamic acid through a liquid membrane

N-Hydroxy- N-naphthylbenzamides ( 3) were synthesized for examining their ability to extract and transport Cu(II) through a liquid membrane. The transport was proton-driven and was capable of moving metal ions `up-hill'. Thus, it was possible to follow the transfer of Cu(II) from the aqueous source phase to the organic layer and from the organic layer to the receiving phase. The N-hydroxy- N-(2-naphthyl)benzamide ( 3b) carrier displayed much more remarkable selectivity for Cu(II) compared with N-hydroxy- N-(1-naphthyl)benzamide ( 3a). This difference in selectivity was explained in terms of the stability of the Cu(II) complex in chloroform.