Determination of nickel in natural waters by FAAS after sorption on octadecyl silica membrane disks modified with a recently synthesized Schiff's base

A simple, highly sensitive, accurate and selective method for the determination of trace amounts of Ni²⁺ ions in water samples is proposed. The method is based on the separation and preconcentration of Ni²⁺ on an octadecyl-bonded silica (ODBS) membrane disk modified by a recently synthesized Schiff’s base N,N′-bis (3-methylsalicylidene) ortho phenylene diamine (MSOPD) at pH 7. The synthesis of this extractant ligand is also described. The retained nickel on the membrane was eluted with 2×5 ml 0.5 M HNO₃ and measured by flame atomic absorption spectrometry (FAAS) at 232.0 nm. The extraction efficiency and the influence of the type and least amount of eluent for the stripping of Ni²⁺ from the disks, pH, flow rates of sample solution and eluent, amount of MSOPD, effect of other ions, and breakthrough volume were evaluated. The maximum capacity of the membrane disks modified by 3 mg of MSOPD was found to be 146±4 μg Ni²⁺. The 3σ limit of detection of the method was 30 ng per 1000 ml and also an enrichment factor of 250 was obtained. The proposed method has been applied to the determination of nickel in several water samples with satisfactory results.     

Fabrication and characterization of hexahistidine-tagged protein functionalized multi-walled carbon nanotubes for selective solid-phase extraction of Cu and Ni

Hexahistidine-tagged protein functionalized multi-walled carbon nanotubes (MWCNTs/6His-tagged protein) were prepared and characterized by ultraviolet-visible spectrophotometry and atomic force microscopy. Both static and dynamical adsorption experiments showed that the MWCNTs/6His-tagged protein served as good sorbent for the solid-phase extraction of Cu²⁺ and Ni²⁺. Effective on-line sorption of Cu²⁺ and Ni²⁺ on the MWCNTs/6His-tagged protein packed microcolumn was achieved in a pH range of 3.0-4.5 and 4.5-6.0, respectively. The retained Cu²⁺ and Ni²⁺ were efficiently eluted with 0.2 mol L⁻¹ imidazole-HCl solution for on-line flame atomic absorption spectrometric determination. The MWCNTs/6His-tagged protein exhibited fairly fast kinetics for the sorption of Cu²⁺ and Ni²⁺, and offered up to 20,000 and 1800 times improvement in the tolerable concentrations of co-existing ions over the MWCNTs for solid-phase extraction of Cu²⁺ and Ni²⁺, respectively. On-line solid-phase extraction at a flow rate of 5.0 mL min⁻¹ for 60 s gave an enhancement factor of 29 for Cu²⁺ and 28 for Ni²⁺, a sample throughput of 45 h⁻¹, and a detection limit (3s) of 0.31 μg L⁻¹ for Cu²⁺ and 0.63 μg L⁻¹ for Ni²⁺. The precision for 11 replicate measurements was 2.4% for 10 μg L⁻¹ Cu²⁺, and 2.5% for 15 μg L⁻¹ Ni²⁺.     

Purification of monoclonal antibodies, IgG1, from cell culture supernatant by use of metal chelate convective interaction media monolithic columns

Monoclonal antibodies (MAbs) have diverse applications in diagnostics and therapeutics. The recent advancement in hybridoma technology for large‐scale production of MAbs in bioreactors demands rapid and efficient purification methods. Conventional affinity purification systems have drawbacks of low flow rates and denaturation of antibodies owing to harsh elution conditions. Here, we attempted purification of MAbs by use of a high‐throughput metal–chelate methacrylate monolithic system. Monolithic macroporous convective interaction media–iminodiacetate (CIM‐IDA) disks immobilized with four different metal ions (Cu²⁺, Ni²⁺, Zn²⁺ and Co²⁺) were used and evaluated for purification of anti‐human serum albumin IgG1 mouse MAbs from cell culture supernatant after precipitation with 50% ammonium sulfate. Elution with 10 mM imidazole in the equilibration buffer (25 mM MMA = MOPS (Morpholino propane sulfonic acid) + MES (Morpholino ethane sulfonic acid) + Acetate + 0.5 M NaCl, pH 7.4) resulted in a purification of 25.7 ± 2.9‐fold and 32.5 ± 2.6‐fold in experiments done using Zn²⁺ and Co²⁺ metal ions, respectively. The highest recovery of 85.4 ± 1.0% was obtained with a CIM‐IDA‐Zn(II) column. SDS–PAGE, ELISA and immuno‐blot showed that the antibodies recovered were pure, with high antigen‐binding efficiency. Thus, metal chelate CIM monoliths could be a potential alternative to conventional systems for fast and efficient purification of MAbs from the complex cell culture supernatant. Copyright © 2012 John Wiley & Sons, Ltd.     

Engineering properties of a camelid antibody affinity sorbent for Immunoglobulin G purification

An IgG-specific camelid antibody matrix (BAC, Naarden, The Netherlands), developed from an immune phage display library, was characterized regarding engineering properties including mass transfer characteristics. Uptake kinetics and equilibrium binding capacity were determined by a finite bath method. Adsorption kinetic parameters were also determined using a real time biosensor. Slightly different properties to conventional Staphylococcal protein A affinity media were shown; especially a 2–2.5 times lower maximal binding capacity with a value of 26 mg/ml polyclonal IgG was obtained. Mass transfer could be described by using a film and pore diffusion model (D_e = 5 × 10⁻⁸ cm²/s). Determined engineering parameters were used to predict breakthrough behaviour in column mode considering film and pore resistances. The dynamic binding capacity at 10% breakthrough did not change when residence time was at least 6 min.     

Rapid capillary zone electrophoresis method for the determination of metal cations in beverages

A rapid and reliable capillary zone electrophoresis method for the determination of inorganic cations was developed. The complete separation of K⁺, Ba²⁺, Ca²⁺, Na⁺, Mg²⁺, Mn²⁺, Ni²⁺, Cd²⁺, Li⁺ and Cu²⁺ can be achieved in 4 min with a simple electrolyte composed by 10 mM imidazole as the carrier buffer and background absorbance provider and acetic acid as the complexing agent (pH 3.60). Injection was performed hydrostatically by elevating the sample at 10 cm for 30 s. The running voltage was +25 kV at room temperature. Indirect UV-absorption detection was achieved at 185 nm. The detection limit was in the range between 0.06 mg/l (Mg²⁺) and 0.57 mg/l (K⁺) and the quantification limits ranged from 0.10 mg/l (Ni²⁺) to 0.80 mg/l (Cu²⁺). The calibration graphs were linear in the concentration range from the quantification limit till at least 1 g/l in K⁺, 10 mg/l in Ba²⁺, Ca²⁺, Mg²⁺, Mn²⁺, Ni²⁺ and Cd²⁺, 40 mg/l in Na⁺ and 12 mg/l in Li⁺ and Cu²⁺. The repeatability, intraday and interday analysis were ≤1.55% and ≤3.64% for migration time and ≤3.38% and ≤3.63% for peak area. The method developed has been applied to several beverage samples with only a simple dilution and filtration treatment of the sample. The proposed method is simple, fast, cheap and it is achieved with common products in either laboratory. For these reasons, it is a very useful method for routine analysis.     

Preparation and metal binding behavior of poly(4-vinylbenzyl 2-hydroxyethyl) sulfoxide and sulfone

In order to explore the reuse properties of oxidized chelating resin containing sulfur after adsorption, two kinds of novel chelating resins, poly[4-vinylbenzyl-(2-hydroxyethyl)] sulfoxide (PVBSO) and poly[4-vinylbenzyl-(2-hydroxyethyl)] sulfone (PVBSO₂), were synthesized using poly[4-vinylbenzyl-(2-hydroxyethyl)] sulfide (PVBS) as material. Their structures were confirmed by FTIR and XPS. The adsorption properties and mechanism for metal ions such as Au³⁺, Pt⁴⁺, Pd²⁺, Hg²⁺, Cu²⁺, Ni²⁺, Fe³⁺, Pb²⁺, Cd²⁺, and Zn²⁺ were investigated. Experimental results showed that PVBSO had good adsorption and selective properties for Au³⁺, Pd²⁺ and Cu²⁺ when the coexisting ion was Pt⁴⁺, Ni²⁺, Pb²⁺ or Cd²⁺. In the aqueous system containing Cu²⁺ and Pb²⁺ or Cu²⁺ and Cd²⁺, PVBSO₂ only adsorbed Cu²⁺. The selective coefficients of PVBSO and PVBSO₂ were α_Au/Pt = 4.8, α_Au/Pd = 11.8, α_Pd/Pt = 10.9, α_Cu/Ni = 2.5, α_Cu/Cd = 41.2, α_Cu/Pb = ∞, α_Cu/Ni = 3.0, α_Cu/Cd = ∞, α_Cu/Pb = ∞, respectively.     

Synthesis and Chelating Properties of Polystyrene Supported Schiff Base (N,N′-disalicylidenepropylenetriamine) Resin Toward Some Divalent Metal Ions

A new polystyrene-supported Schiff base resin, N,N-bis(salicylidenepropylenetriamine)- aminomethyl polystyrene, has been synthesized through a reaction between the commercially available 4-chloromethyl polystyrene polymer and the Schiff base, N,N′-disalicylidenepropylenetriamine. The chelation behavior of this resin toward the divalent metal ions Cu^{2 +}, Ni^{2 +}, Zn^{2 +}, and Pb^{2 +} in aqueous solutions was investigated. Batch equilibration experiments were carried out as a function of contact time, pH, amount of metal-ion, polymer mass, and temperature. The amount of metal-ion uptake of the polymers was determined by using atomic absorption spectrometry (AAS). Results of the study revealed that the resin exhibited higher capacities and a more pronounced adsorption toward Cu^{2 +} and that the metal-ion uptake follows the order: Cu^{2 +} > Zn ^{2 +} > Ni^{2 +} > Pb²⁺. The adsorption and binding capacity of the resin toward the various metal ions investigated are discussed.     

A differential receptor for selective and quantitative multi-ion analysis for Co and Ni/Cu

The differential mode of complexation of chromogenic sensor 3 with Co²⁺ versus Ni²⁺ (or Cu²⁺) at pH 4.0 in water leads to new absorption bands at λ_max 620 nm in the case of Co²⁺, at λ_max 380 and 460 nm for Ni²⁺ and at λ_max 460 nm for Cu²⁺. These differential responses allow sensor 3 to be used for the selective and quantitative estimation of Co²⁺ and Ni²⁺ or Co²⁺ and Cu²⁺ from their mixtures.     

In-channel indirect amperometric detection of heavy metal ions for electrophoresis on a poly(dimethylsiloxane) microchip

In-channel indirect amperometric detection mode for microchip capillary electrophoresis with positive separation electric field is successfully applied to some heavy metal ions. The influences of separation voltage, detection potential, the concentration and pH value of running buffer on the response of the detector have been investigated. An optimized condition of 1200 V separation voltage, −0.1 V detection potential, 20 mM (pH 4.46) running buffer of 2-(N-morpholino)ethanesulfonic acid (MES) + l-histidine (l-His) was selected. The results clearly showed that Pb²⁺, Cd²⁺, and Cu²⁺ were efficiently separated within 80 s in a 3.7 cm long native separation PDMS/PDMS channel and successfully detected at a single carbon fibre electrode. The theoretical plate numbers of Pb²⁺, Cd²⁺, and Cu²⁺ were 1.2 × 10⁵, 2.5 × 10⁵, and 1.9 × 10⁵ m⁻¹, respectively. The detection limits for Pb²⁺, Cd²⁺, and Cu²⁺ were 1.3, 3.3 and 7.4 μM (S/N = 3).     

Vanillin-coumarin hybrid molecule as an efficient fluorescent probe for trace level determination of Hg(II) and its application in cell imaging

An efficient Hg²⁺ selective fluorescent probe (vanillin azo coumarin, VAC) was synthesized by blending vanillin with coumarin. VAC and its Hg²⁺ complex were well characterized by different spectroscopic techniques like ¹H NMR, QTOF-MS ES⁺, FTIR and elemental analysis as well. VAC could detect up to 1.25 μM Hg²⁺ in aqueous methanol solution through fluorescence enhancement. The method was linear up to 16 μM of Hg²⁺. Negative interferences from Cu²⁺, Ni²⁺, Fe³⁺, and Zn²⁺ were eliminated using EDTA as a masking agent. VAC showed a strong binding to Hg²⁺ ion as evident from its binding constant value (2.2 × 10⁵), estimated using Benesi-Hildebrand equation. Mercuration assisted restricted rotation of the vanillin moiety and inhibited photoinduced electron transfer from the O, N-donor sites to the coumarin unit are responsible for the enhancement of fluorescence upon mercuration of VAC. VAC was used for imaging the accumulation of Hg²⁺ ions in Candida albicans cells.     

Selective extraction and release using (EDTA-Ni)-layered double hydroxide coupled with catalytic oxidation of 3,3′,5,5′-tetramethylbenzidine for sensitive detection of copper ion

Copper is an important heavy metal in various biological processes. Many methods have been developed for detecting of copper ions (Cu²⁺) in aqueous samples. However, an easy, cheap, selective and sensitive method is still desired. In this study, a selective extraction-release-catalysis approach has been developed for sensitive detection of copper ion. Ethylenediaminetetraacetic acid (EDTA) chelated with nickel ion (Ni²⁺) were intercalated in a layered double hydroxide via a co-precipitation reaction. The product was subsequently applied as sorbent in dispersive solid-phase extraction for the enrichment of Cu²⁺ at pH 6. Since Cu²⁺ has a stronger complex formation constant with EDTA, Ni²⁺ exchanged with Cu²⁺ selectively. The resulting sorbent containing Cu²⁺ was transferred to catalyze the 3,3′,5,5′-tetramethylbenzidine oxidation reaction, since Cu²⁺ could be released by the sorbent effectively and has high catalytic ability for the reaction. Blue light emitted from the oxidation product was measured by ultraviolet–visible spectrophotometry for the determination of Cu²⁺. The extraction temperature, extraction time, and catalysis time were optimized. The results showed that this method provided a low limit of detection of 10 nM, a wide linear range (0.05–100 μM) and good linearity (r² = 0.9977). The optimized conditions were applied to environmental water samples. Using Cu²⁺ as an example, this work provided a new and interesting approach for the convenient and efficient detection of metal cations in aqueous samples.     

Photoactive chemosensors 4: a Cu protein cavity mimicking fluorescent chemosensor for selective Cu recognition

Fluorescent chemosensor 3 can sense Cu²⁺ ions (1-8 μM) even in the presence of elevated levels of Ni²⁺, Cd²⁺, Zn²⁺, Hg²⁺, Ag⁺ and Pb²⁺ (5000 μM). 3 can also analyze for Ag⁺ ions (50-500 μM) in the presence of Ni²⁺, Cd²⁺, Zn²⁺, Hg²⁺ and Pb²⁺ (5000 μM) but Cu²⁺ strongly interferes.     

Highly selective and sensitive paper-based colorimetric sensor using thiosulfate catalytic etching of silver nanoplates for trace determination of copper ions

A novel, highly selective and sensitive paper-based colorimetric sensor for trace determination of copper (Cu²⁺) ions was developed. The measurement is based on the catalytic etching of silver nanoplates (AgNPls) by thiosulfate (S₂O₃²⁻). Upon the addition of Cu²⁺ to the ammonium buffer at pH 11, the absorption peak intensity of AuNPls/S₂O₃²⁻ at 522 nm decreased and the pinkish violet AuNPls became clear in color as visible to the naked eye. This assay provides highly sensitive and selective detection of Cu²⁺ over other metal ions (K⁺, Cr³⁺, Cd²⁺, Zn²⁺, As³⁺, Mn²⁺, Co²⁺, Pb²⁺, Al³⁺, Ni²⁺, Fe³⁺, Mg²⁺, Hg²⁺ and Bi³⁺). A paper-based colorimetric sensor was then developed for the simple and rapid determination of Cu²⁺ using the catalytic etching of AgNPls. Under optimized conditions, the modified AgNPls coated at the test zone of the devices immediately changes in color in the presence of Cu²⁺. The limit of detection (LOD) was found to be 1.0 ng mL⁻¹ by visual detection. For semi-quantitative measurement with image processing, the method detected Cu²⁺ in the range of 0.5–200 ng mL⁻¹(R² = 0.9974) with an LOD of 0.3 ng mL⁻¹. The proposed method was successfully applied to detect Cu²⁺ in the wide range of real samples including water, food, and blood. The results were in good agreement according to a paired t-test with results from inductively coupled plasma-optical emission spectrometry (ICP-OES).     

A stoichiometric imprinted chelating resin for selective recognition of copper(II) ions in aqueous media

This work reports the preparation of a new copper(II) ion-imprinted polymer (IIP) material, using 5,6;14,15-dibenzo-1,4-dioxa-8,12-diazacyclopentadecane-5,14-diene (DBDA15C4) and 2-vinylpyridine (VP) as a non-vinylated chelating agent and a functional vinyl monomer, respectively. The Cu²⁺ ion can form stable complexes with DBDA15C4 and VP. The stoichiometries of Cu²⁺-DBDA15C4 and ternary Cu²⁺-DBDA15C4-VP complexes were elucidated using conductometric and spectrophotometric methods, and found to be Cu²⁺(DBDA15C4), Cu²⁺(DBDA15C4)₂ and Cu²⁺(DBDA15C4)(VP)₂. The results obtained from solution studies were also supported by ab initio theoretical calculations. The resulting ternary complex Cu²⁺(DBDA15C4)(VP)₂ was copolymerized with ethyleneglycoldimethacrylate, as a cross-linking monomer, via bulk polymerization method. The imprinted copper ion was removed from the polymeric matrix by 0.1 M HNO₃. The Cu²⁺-imprinted polymer particles were characterized by IR spectroscopy and elemental analysis. Optimum pH range for rebinding of Cu²⁺ on the IIP and equilibrium binding time were 7.0-7.5 and 45 min, respectively. Sorbent capacity and enrichment factor for Cu²⁺ were obtained as 75.3 ± 1.9 μmol g⁻¹ and 100, respectively. In selectivity study, it was found that imprinting results in increased affinity of the material toward Cu²⁺ ion over other competitor metal ions with the same charge and close ionic radius. The prepared IIPs were repeatedly used and regenerated for five times without a significant decrease in polymer binding affinities.     

On-line preconcentration and simultaneous determination of heavy metal ions by inductively coupled plasma-atomic emission spectrometry

A flow injection analysis system for on-line preconcentration and simultaneous determination of Bi³⁺, Cd²⁺, Co²⁺, Cu²⁺, Fe³⁺, Ni²⁺, Pb²⁺ and Zn²⁺ in aqueous samples by inductively coupled plasma (ICP)-atomic emission spectrometry with a charge coupled detector is described. The preconcentration of analytes is accomplished by retention of their chelates with sodium diethyldithiocarbamate in aqueous solution on a solid phase containing octadecyl silica in a minicolumn. Methanol, as eluent, is introduced into the conventional nebulizer of the ICP instrument. The effects of different parameters, including preconcentration flow rate (equal to sample flow rate (SR)), eluent flow rate (ER), weight of solid phase (W) and eluent loop volume (EV), were optimized by the super-modified simplex method. The optimum conditions were evaluated to be SR 7.2 ml min⁻¹, ER 3.5 ml min⁻¹, W of 100 mg and EV of 0.8 ml. An enrichment factor of 312.5 for each analyte was obtained. The detection limits of the proposed method for Bi³⁺, Cd²⁺, Co²⁺, Cu²⁺, Fe³⁺, Ni²⁺, Pb²⁺ and Zn²⁺ were evaluated as 1.3, 1.0, 0.8, 0.3, 14.7, 0.5, 5.5 and 0.1 ng l⁻¹, respectively. The effect of several metal ions on percent recovery was also studied. The method was applied to the recovery of these heavy metals from real matrices and to the simultaneous determination of these cations in different water samples.     

Ultrasensitive Cu sensing by near-infrared-emitting CdSeTe alloyed quantum dots

The near-infrared (NIR)-emitting CdSeTe alloyed quantum dots (AQdots) that capped with l-cysteine were applied for ultrasensitive Cu²⁺ sensing. The sensing approach was based on the fluorescence of the AQdots selectively quenched in the presence of Cu²⁺. Experimental results showed a low interference response towards other metal ions. The possible quenching mechanism was discussed on the basis of the binding between l-cysteine and the metal ions. In addition, biomolecules have low effect on the fluorescence due to the minimized interferences in NIR region. The response of the NIR optical sensor was linearly proportional to the concentration of Cu²⁺ ranging from 2 × 10⁻⁸ to 2 × 10⁻⁶ mol L⁻¹. Furthermore, it has been successfully applied to the detection of Cu²⁺ in vegetable samples.     

Interactions between an amphipathic di‐histidine peptide and a metal affinity chromatographic resin derived from a bis(tacn)butane chelating ligand

The interactive behavior of an amphipathic peptide with the Cu²⁺, Ni²⁺, and Zn²⁺ complexes of 1,4‐bis(triazacyclonon‐1‐yl)butane), bis(tacn)^but, immobilized onto Sepharose CL‐4B, has been investigated. The effects of incubation time, as well as the incubation buffer pH and ionic strength, have been examined. The binding data have been interrogated using Langmuir, Langmuir‐Freundlich, bi‐Langmuir, and Temkin isothermal models and Scatchard plots. These results confirm that this amphipathic peptide binds with relatively high capacities to the immobilized Cu²⁺‐ and Ni²⁺‐1,4‐bis(triazacyclonon‐1‐yl)butane)‐Sepharose CL‐4B sorbents via at least two discrete sites. However, the corresponding immobilized Zn²⁺‐sorbent had low binding capacity. Moreover, the magnitude of the binding capacities of these sorbents was dependent on the pH and ionic strength of the incubation buffer. These results are relevant to the isolation of E. coli expressed recombinant proteins that incorporate this and related amphipathic peptide tags, containing two or more histidine residues, located at the N‐ or C‐terminus of the recombinant protein, and the co‐purification of low abundance host cell proteins of diverse structure, by immobilized metal ion affinity chromatographic methods.     

Mechanism of Charge Transfer Initiation by the Dimethyl Phenyl Phosphine/Fe(III) Catalyst System

The dimethyl phenyl phosphine (DMPP) initiated polymerization of methyl methacrylate (MMA) in dimethylsulfoxide was studied. Polymerization of MMA in this system required the presence of transition metal ions like Fe³⁺ or Cu²⁺. Kinetic studies showed that the propagation was free radical in nature. An interaction between DMPP and MMA was detected spectrophotometrically. A proposed mechanism involves a transition metal ion-activated dipole interaction between the carbonyl oxygen and the phosphorus atom with the ultimate formation of a methyl methacrylate type of free radical.     

Extraction and preconcentration capacity of bifunctionalized diamine-thiol polysiloxane immobilized ligand system towards some divalent cations

Porous solid bi-organofunctionalized diamine-thiol polysiloxane immobilized ligand system of the general formula P-(CH₂)₃- X, (where P represents [Si-O]_n siloxane network and X represents a mixture of diamine; -NH(CH)₂NH₂ and thiol; -SH functional groups) has been prepared by hydrolytic polycondensation of TEOS with a mixture of 3-mercaptopropyltrimethoxysilane and 3- (2-aminoethylimino)propyltrimethoxysilane agents. The ligand system was evaluated for extraction and preconcentartion of a series of divalent metal ions from aqueous solutions including: Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺. Both batch and dynamic methods were used to examine maximum sorption capacity. The maximum binding capacity followed the sequence; Cu²⁺ > Pb²⁺ > Cd²⁺ > Ni²⁺ > Zn²⁺ > Co²⁺ at pH 5.5. Measurement of variation of sorption of metal ions with temperature yielded negative values of ΔG° and positive values of ΔS° and ΔH° indicating a spontaneous and endothermic process of binding metal ions to the ligand system.     

1-Aminoanthracene-9,10-dione based chromogenic molecular sensors: effect of nature and number of nitrogen atoms on metal ion sensing behavior

To examine the consequences of nature and number of nitrogen atoms on metal ion sensing properties, four new molecular receptors based on 1-aminoanthracene-9,10-dione as chromogenic moiety and different types of nitrogen atoms viz. arylamine, alkylamine, and pyridyl nitrogen as appendages have been synthesized. These receptors in CH₃OH/H₂O (1:1) (v/v) at pH 7.0, on addition of heavy metal ions show selective and/or semi-selective interactions. These binding interactions are visible to naked eye due to remarkable color change and are associated with λ_max shift by 85-125 nm. Molecular receptor 2, with two sp² hybridized nitrogen atoms and one arylamine nitrogen, selectively binds with Cu²⁺ but 2-Cu²⁺ complex is stable only between pH 7.0 and 8.75. However, the conversion of imine nitrogen to alkylamine in molecular receptor 6, increases the binding ability toward Cu²⁺ along with significant binding affinities toward Ni²⁺ and Co²⁺. Receptor 6 shows the stability of its complexes in the order Cu²⁺>Ni²⁺>Co²⁺ in a broader pH range 6-12. Dipicolylamine based receptor 8, possessing two pyridyl nitrogen atoms, one tertiaryamine and one arylamine nitrogen atoms as ligating sites, also binds semiselectively in the order Cu²⁺>Co²⁺>Ni²⁺. Receptor 10, possessing anilide group in the place of arylamine in receptor 8, on addition of Cu²⁺, Ni²⁺ or Co²⁺ shows bathochromic shift of λ_max associated with color change from yellow to russet (brown) and on addition of Zn²⁺ shows hypsochromic shift of its λ_max associated with disappearance of yellow color. Additionally, all the four chemosensors show ratiometric response toward all these metal ions and thus increase the usability and the dynamic range of estimation.