Analysis of DNA complexes with small solutes by CE with LIF detection

In this article, we describe the analysis of aptamers for Hg²⁺ ions through CE with LIF (CE‐LIF) detection using 2% poly(ethylene oxide) solutions containing OliGreen (fluorophore). In the presence of an EOF, DNA strands migrating against the EOF were detected at the cathode end. Four DNA strands – T₃₃, T₅C₂₈, T₅C₅T₂₃, and T₁₅C₅T₁₃ – could not be separated through CE‐LIF in the absence of Hg²⁺. At 0.3 mM Hg²⁺, however, all four were partially separated within 20 min, with SDs of the migration times all being less than 2.5%. From the CE, fluorescence, and ellipticity data, we concluded that the conformations of these four DNA strands all changed from random‐coil to folded structures as a result of T–Hg²⁺–T bonding. In addition, we found that this CE approach provided different electropherograms patterns for T₇, T₁₅, and T₃₃ in the absence and presence of Hg²⁺, indicating various interactions of the DNA strands with Hg²⁺. Using this simple, high‐resolution CE approach, we also demonstrated that adenosine triphosphate has a stronger interaction with the adenosine triphosphate aptamer than with either the platelet‐derived growth factor aptamer or T₃₃. This CE approach holds great potential for screening aptamers for small solutes, studying the catalytic activity of DNAzymes, and evaluating the biological functions of microRNA.     

Control of the Fluorescence of DNA‐templated Silver Nanoclusters by Adenosine Triphosphate and Mercury(II)

Several DNA templates with the sequence 5′‐T _n TAACCCCTAACCCCT ‐3′ (n = 0, 15, 30, and 45) were used to prepare DNA template–silver nanoclusters (DNA –Ag NCs ). The T _n sequence acts as a recognition element for Hg²⁺, while the rest of the sequence acts as a template for DNA –Ag NCs . At pH 3.0, the fluorescence intensity of DNA –Ag NCs is enhanced by ATP , and the enhanced fluorescence is quenched by Hg²⁺. The length of polyT shows a slight effect on the sensitivity for the detection of Hg²⁺ but almost no effect on the optical properties of DNA –Ag NCs . The fluorescence response of DNA –Ag NCs (T₁₅‐DNA –Ag NCs ) vs. Hg²⁺ concentration shows two linear ranges over 10–100 and 100–1000 nM , mainly because of the fluorescence quenching due to DNA conformational changes through T–Hg²⁺–T coordination and the formation of an amalgam with Ag NCs , respectively. The sensitivity of the T₁₅‐DNA –Ag NC probe was validated through the analysis of Hg²⁺ in spiked pond water. Based on the switch‐on and switch‐off fluorescence properties of T₁₅‐DNA –Ag NCs , an IMPLICATION logic gate was fabricated using the concentrations of ATP and Hg²⁺ as inputs and the fluorescence intensity at 585 nm as output.     

Fluorescence detection of mercury(II) and lead(II) ions using aptamer/reporter conjugates

We have developed a fluorescence technique for the detection of Hg²⁺ and Pb²⁺ ions using polythymine (T₃₃)/benzothiazolium-4-quinolinium dimer derivative (TOTO-3) and polyguanine (G₃₃)/terbium ions (Tb³⁺) conjugates, respectively. Hg²⁺ ions induce T₃₃ to form folded structures, leading to increased fluorescence of the T₃₃/TOTO-3 conjugates. Because Pb²⁺ ions compete with Tb³⁺ ions to form complexes with G₃₃, the extent of formation of the G₃₃-Tb³⁺ complexes decreases upon increasing the Pb²⁺ concentration, leading to decreased fluorescence at 545 nm when excited at 290 nm. To minimize interference from Hg²⁺ ions during the detection of Pb²⁺ ions, we conducted two-step fluorescence measurements; prior to addition of the G₃₃/Tb³⁺ probe, we recorded the fluorescence of a mixture of the T₃₃/TOTO-3 conjugates and Hg²⁺ ions. The fluorescence signal obtained was linear with respect to the Hg²⁺ concentration over the range 25.0-500 nM (R² = 0.99); for Pb²⁺ ions, it was linear over the range 3.0-50 nM (R² = 0.98). The limits of detection (at a signal-to-noise ratio of 3) for Hg²⁺ and Pb²⁺ ions were 10.0 and 1.0 nM, respectively. Relative to other techniques for the detection of Hg²⁺ and Pb²⁺ ions in soil and water samples, our present approach is simpler, faster, and more cost-effective.     

Prussian Blue Modified Amperometric Hg2+ Ion Biosensor Based on Glucose Oxidase Inhibition

In this research a Hg²⁺ ion biosensor was developed by combining Prussian blue (PB) with glucose oxidase (GOx) – an enzyme that can be inhibited by Hg²⁺ ions. An application of PB in the design of Hg²⁺ ion biosensor enabled detecting changes in hydrogen peroxide reduction current at low operational potential of 0.2 vs Ag|AgCl,KCl_sat. The described Hg²⁺ ion biosensor exhibited wide linear range from 27 μM to 247 μM of Hg²⁺ and higher maximal detectable concentration of Hg²⁺ than other GOx inhibition-based biosensors, making it convenient for the analysis of samples with high concentration of Hg²⁺ ions.     

Spectral Luminescent Properties of Metal Chelates on the Basis of Aminomethylene Derivatives of 5-Pyrazolethione

The absorption and luminescence of bisbidentate complexes of aminomethylene derivatives of 5-pyrazolethione with Zn²⁺, Cd²⁺, Hg²⁺, and Pb²⁺ in dilute solutions in hydrocarbons and 95% ethanol are determined by the structure of the ligand in the complexes. In the Zn²⁺, Cd²⁺, and Hg²⁺ complexes, N···M coordination is realized, whereas in the Pb²⁺ complexes, S··· M. In the Zn-Cd-Hg series, a heavy-atom effect is revealed, which stimulates exclusively radiationless transitions involving the S ₁ and T states.     

Voltammetric determination of mercury (II) in aqueous media using glassy carbon electrodes modified with novel calix[4]arene

A novel calix[4]arene derivative containing benzothiazole group was coated on glassy carbon electrode (GCE) and then applied to the recognition of mercury ion. Cyclic and square wave voltammetric results showed that the modified electrode selectively recognizes Hg²⁺ ion in aqueous media. A new anodic stripping peak at −0.3 V (vs. Ag/Ag⁺) can be obtained by scanning the potential from −0.6 to 0.6 V, and the peak currents are proportional to the Hg²⁺ concentration. The modified electrode in a 0.1 M H₂SO₄+0.01 M NaCl solution shows linear voltammetric response in the range of 25-300 μg l⁻¹ and detection limit of 5 μg l⁻¹ (ca. 2.5×10⁻⁸ M). This modified GCE does not present any significant interference from alkali, alkaline and transition metal ions except for Pb²⁺, Ag⁺ and Cu²⁺ ions. Only 500, 50 and 100-fold molar excess of Pb²⁺, Ag⁺ and Cu²⁺ ions, respectively, can lead to voltammetric response comparable with that of Hg²⁺. The proposed method was successfully applied to determine mercury in natural water.     

Highly Sensitive Electrochemical Bioassay for Hg(II) Detection Based on Plasma-Polymerized Propargylamine and Three-Dimensional Reduced Graphene Oxide Nanocomposite

In this study, a nanocomposite consisting of three-dimensional reduced graphene oxide (3D-rGO) and plasma-polymerized propargylamine (3D-rGO@PpPG) was prepared and used as a highly sensitive and selective DNA sensor for detecting Hg²⁺. Given the high density of amino groups in the resultant 3D-rGO@PpPG nanocomposite, thymine-rich and Hg²⁺-targeted DNA was preferentially immobilized on the fabricated sensor surface via the strong electrostatic interaction between DNA strands and the amino-functionalized nanocomposites, followed by detecting Hg²⁺ through T–Hg²⁺–T coordination chemistry between DNA and Hg²⁺. The results of electrochemical measurements revealed that the anchored amount of DNA strands anchored on the 3D-rGO@PpPG nanofilm surface affects the determination of Hg²⁺ in aqueous solution. It showed high sensitivity and selectivity toward Hg²⁺ within concentrations ranging from 0.1 to 200 nM and displayed a low detection limit of 0.02 nM. The new strategy proposed also provides high selectivity of Hg²⁺ against other interfering metal ions, good stability, and repeatability. The excellent applicability of the developed sensor confirms the potential use of plasma-modified nanofilms for the detection of heavy metal ions in real environmental samples and water.     

Two Rhodamine-based Turn on Chemosensors with High Sensitivity,Selectivity, and Naked-Eye Detection for Hg2+

Two novel rhodamine-based fluorescence enhanced molecular probes (RA₁ and RA₂) were synthesized, which were both designed as comparative fluoroionophore and chromophore for the optical detection of Hg²⁺. The recognizing behaviors were investigated both experimentally and computationally. They exhibited high selectivity and sensitivity for Hg²⁺ over other commonly coexistent metal ions in CH₃CN/H₂O (1:1, V/V) solution. Test shows that hydroxy benzene of rich electron was beneficial to the chelate of Hg²⁺ with sensors. The detection limit was measured to be at least 0.14 μmol/L. After addition of Hg²⁺, the color changed from colourless to pink, which was easily detected by the naked eye in both solution and hydrogel sensor.     

A High Efficient Electrocatalytic Activity of Metal-organic Frameworks ZnO/Ag/ZIF-8 Nanocomposite for Electrochemical Detection of Toxic Heavy Metal Ions

A novel electrochemical sensor on ZIF-8 nanocomposites (Ag/ZnO/ZIF-8) was developed to analyze the mercury ions (Hg²⁺). The ZIF-8 materials are one of the 3-dimensional porous metal-organic frameworks with highly accessible pores and great surface area. The ZIF-8 nanocomposites were prepared through simple sol-gel methods and their physio-chemical properties were characterized via different analytical analyses. As a result of cyclic voltammetry, Ag/ZnO/ZIF-8 exhibited a better electrocatalytic behavior towards the detection of mercury ions (Hg²⁺). Furthermore, the composite modified electrode was then inspected as a sensor for DPV detection of mercury ions. The nanocomposite sensor performed a wide linear range from 0.5 μM to 140 μM with a low detection limit of 40 nM, and high sensitivity of 56.06 μA μM⁻¹ cm⁻². Moreover, the ZIF-8 composite sensor showed a higher selectivity toward the detection of mercury ions (Hg²⁺). The real-time applications of the ZIF-8 composites sensor were inspected in various samples with good sensitivity.     

Polythymine Oligonucleotide‐Modified Gold Electrode for Voltammetric Determination of Mercury(II) in Aqueous Solution

Polythymine oligonucleotide (PTO)‐modified gold electrode (PTO/Au) was developed for selective and sensitive Hg²⁺ detection in aqueous solutions. This modified electrode was prepared by self‐assembly of thiolated polythymine oligonucleotide (5′‐SH‐T₁₅‐3′) on the gold electrode via Au? S bonds, and then the surface was passivated with 1‐mercaptohexanol solution. The proposed electrode utilizes the specific binding interactions between Hg²⁺ and thymine to selectively capture Hg²⁺, thereby reducing the interference from coexistent ions. After exchanging the medium, electrochemical reduction at ?0.2 V for 60 s, voltammetric determination was performed by differential pulse voltammetry using 10 mM HEPES; pH 7.2, 1 M NaClO₄ as supporting electrolyte. This electrode showed increasing voltammetric response in the range of 0.21 nM Hg²⁺, with a relative standard deviation of 5.32% and a practical detection limit of 60 pM. Compared with the conventional stripping approach, the modified electrode exhibits good sensitivity and selectivity, and is expected to be a new type of green electrode.     

Catalytic gold nanoparticles for fluorescent detection of mercury(II) and lead(II) ions

In this study, we developed a fluorescence assay for the highly sensitive and selective detection of Hg²⁺ and Pb²⁺ ions using a gold nanoparticle (Au NP)-based probe. The Hg–Au and Pb–Au alloys that formed on the Au NP surfaces allowed the Au NPs to exhibit peroxidase-mimicking catalytic activity in the H₂O₂-mediated oxidation of Amplex UltraRed (AUR). The fluorescence of the AUR oxidation product increased upon increasing the concentration of either Hg²⁺ or Pb²⁺ ions. By controlling the pH values of 5 mM tris–acetate buffers at 7.0 and 9.0, this H₂O₂–AUR–Au NP probe detected Hg²⁺ and Pb²⁺ ions, respectively, both with limits of detection (signal-to-noise ratio: 3) of 4.0 nM. The fluorescence intensity of the AUR oxidation product was proportional to the concentrations of Hg²⁺ and Pb²⁺ ions over ranges 0.05–1 μM (R² = 0.993) and 0.05–5 μM (R² = 0.996), respectively. The H₂O₂–AUR–Au NP probe was highly selective for Hg²⁺ (>100-fold) and Pb²⁺ (>300-fold) ions in the presence of other tested metal ions. We validated the practicality of this simple, selective, and sensitive H₂O₂–AUR–Au NP probe through determination of the concentrations of Hg²⁺ and Pb²⁺ ions in a lake water sample and of Pb²⁺ ions in a blood sample. To the best of our knowledge, this system is the first example of Au NPs being used as enzyme-mimics for the fluorescence detection of Hg²⁺ and Pb²⁺ ions.     

Substoichiometric Extraction of Mercury by Diethyldithiocarbamic Acid

The substoichiometric extraction of Hg²⁺ using diethyldithiocarbamic acid and ²⁰³Hg tracer was studied. Chloroform was employed to remove the complexes from the aqueous media which were 0.5M H₂SO₄ or 1 M HClO₄ and 0 to 5 M NaCL. - Systems containing Cl^? allowed extraction of Hg²⁺ for all DDC/Hg molar ratios, the extracted complexes being HgCl(DDC) and Hg(DDC)₂. Their exchange constant was determined. - In the absence of Cl^?, no extraction could be effected in either system if the DDC/Hg molar ratio was < 1; the H₂SO₄ system remained clear, whereas a precipitate of HgClO₄(DDC) formed in the HClO₄ system. For molar ratios > 1, the extraction of Hg²⁺ increased linearly with the addition of DDC, the extracted complex being Hg(DDC)₂.     

Structural characterization of alachlor complexes with transition metal ions by electrospray ionization tandem mass spectrometry

Electrospray ionization mass (ESI-MS) spectrometry was used to investigate the nature of metal complexes of alachlor and their dissociations on activation. Ions of the first row transition metal series were employed to react with alachlor and the products were subjected to collision-induced dissociation (CID) for further structural characterization. The formation of diverse complex ions including doubly charged metal/alachlor complexes; [3L + M]²⁺ and [4L + M]²⁺ (L: alachlor and M: transition metal ions) were observed depending on the experimental conditions including the tube lens offset voltage (TLOV) and relative concentrations of alachlor and transition metal ions. It is clear that complexation with transition metal ions alters the reactive site of alachlor, promoting the loss of chlorine over the loss of CH₃OH that is the major reaction pathway in uncomplexed system. Direct elimination of chlorine from alachlor molecule was confirmed by the use of MnBr₂ instead of MnCl₂. These evidences clearly illustrate the catalytic activities of the metal ions through insertion mechanism. The function of transition metal ions in complexation was emphasized comparing the fragmentation patterns with those of protonated molecule. A change in the oxidation state of copper from + 2 to + 1 during the dissociation of metal complex was observed in company with elimination of radicals which is specific for the copper complex ions.     

Syntheses,Structures, and Bioactivities Evaluation of some Transition Metal Complexes with 4,4'-Diacetylcurcumin

Stoichiometric reactions of 4,4'-diacetylcurcumin ( HL ) with series of transition metal ions, namely Fe³⁺, Co²⁺, Ni²⁺ and Zn²⁺, in methanol result in the corresponding homoleptic metal complexes. All the obtained complexes were characterized by elemental analysis, high resolution mass spectrometry, IR spectroscopy, magnetic moment and single-crystal X-ray diffraction. Structural analyses are unprecedentedly performed for the Fe^III, Co^II, and Ni^II complexes and reveal octahedral mononuclear complexes with the compositions [Fe(L)₃] and [M(L)₂(MeOH)₂] (M = Co²⁺, Ni²⁺, Zn²⁺) for trivalent and divalent metal ions, respectively. In all complexes, the deprotonated ligands serve as monoanionic and bidentate ligands with (O,O)-chelating β-diketonate moieties. The free ligand HL exhibits considerable antiproliferative effects for the human MCF-7 breast and HepG2 liver cancer cells with IC₅₀ values of 20.91 ± 2.16 μg · mL^–1 and 12.85 ± 1.85 μg · mL^–1, respectively. The Co^II and Zn^II complexes with IC₅₀ values in the range of 14.53–20.80 μg · mL^–1 for MCF-7 breast and 8.48–10.68 μg · mL^–1 for HepG2 liver cancer cells show stronger antiproliferative effects than HL, the Fe^III and Ni^II complexes cause weaker reductions of the growth of the two tested cancer cell lines.     

Detection of Hg2+ with NBD-based colorimetric chemosensor: Practical application to water samples and test strips

A new nitrobenzoxadiazole (NBD)-based chemosensor N′-(7-nitrobenzo[c][1,2,5]oxadiazol-4-yl)thiophene-2-carbohydrazide ( NTCH) was synthesized for detecting Hg²⁺. NTCH could sense Hg²⁺ through a color change method from pale yellow to pink. Binding ratio of NTCH and Hg²⁺ was determined to be 1:1 with the analysis of electrospray ionization mass spectrometry and Job plot. Detection limit turned out to be 0.69 μM. In addition, NTCH could be successfully utilized for detecting Hg²⁺ in real water samples and visible color test strips. The probing mechanism of NTCH to Hg²⁺ was explained with ¹H nuclear magnetic resonance (NMR) titration, Job plot, electrospray ionization mass spectrometry (ESI-MS), and theoretical calculations.     

Molecular Assembly Directed by Metal–Aromatic Interactions: Control of the Aggregation and Photophysical Properties of Zn–Salen Complexes by Aromatic Mercuration

There is widespread interest in non‐covalent bonding and weak interactions, such as electrostatic interactions, hydrogen bonding, solvophobic/hydrophobic interactions, metal–metal interactions, and π–π stacking, to tune the molecular assembly of planar π‐conjugated organic and inorganic molecules. Inspired by the roles of metal–aromatic interaction in biological systems, such as in ion channels and metalloproteins, herein, we report the first example of the use of Hg²⁺–aromatic interactions to selectively control the assembly and disassembly of zinc–salen complexes in aqueous media; moreover, this process exhibited significant “turn on” fluorescent properties. UV/Vis and fluorescence spectroscopic analysis of the titration of Hg²⁺ ions versus complex ZnL¹ revealed that the higher binding affinity of Hg²⁺ ions (compared to 13 other metal ions) was ascribed to specific interactions between the Hg²⁺ ions and the phenyl rings of ZnL¹ ; this result was also confirmed by ¹H NMR spectroscopy and HRMS (ESI). Further evidence for this type of interaction was obtained from the reaction of small‐molecule analogue L¹ with Hg²⁺ ions, which demonstrates the proximity of the N‐alkyl group to the aromatic protons during Hg²⁺‐ion binding, which led to the consequential H/D exchange reaction with D₂O. DFT modeling of such interactions between the Hg²⁺ ions and the phenyl rings afforded calculated distances between the C and Hg atoms (2.29 Å) that were indicative of C? Hg bond‐formation, under the direction of the N atom of the morpholine ring. The unusual coordination of Hg²⁺ ions to the phenyl ring of the metallosalen complexes not only strengthened the binding ability but also increased the steric effect to promote the disassembly of ZnL¹ in aqueous media.     

Detection of Metal Ions (Cu2+, Hg2+) and Cocaine by Using Ligation DNAzyme Machinery

The Cu²⁺‐dependent ligation DNAzyme is implemented as a biocatalyst for the colorimetric or chemiluminescence detection of Cu²⁺ ions, Hg²⁺ ions, or cocaine. These sensing platforms are based on the structural tailoring of the sequence of the Cu²⁺‐dependent ligation DNAzyme for specific analytes. The tethering of a subunit of the hemin/G‐quadruplex DNAzyme to the ligation DNAzyme sequence, and the incorporation of an imidazole‐functionalized nucleic‐acid sequence, which acts as a co‐substrate for the ligation DNAzyme that is tethered to the complementary hemin/G‐quadruplex subunit. In the presence of different analytes, Cu²⁺ ions, Hg²⁺ ions, or cocaine, the pretailored Cu²⁺‐dependent ligation DNAzyme sequence stimulates the respective ligation process by combining the imidazole‐functionalized co‐substrate with the ligation DNAzyme sequence. These reactions lead to the self‐assembly of stable hemin/G‐quadruplex DNAzyme nanostructures that enable the colorimetric analysis of the substrate through the DNAzyme‐catalyzed oxidation of 2,2′‐azinobis(3‐ethylbenzothiazoline‐6‐sulfonic acid), ABTS^2?, by H₂O₂ into the colored product ABTS^.?, or the chemiluminescence detection of the substrate through the DNAzyme‐catalyzed oxidation of luminol by H₂O₂. The detection limits for the sensing of Cu²⁺ ions, Hg²⁺ ions, and cocaine correspond to 1 nM , 10 nM and 2.5 μM , respectively. These different sensing platforms also reveal impressive selectivities.     

15-Hydroxybenzomonothia-15-crown-5 with the sulfur atom linked with the benzene ring and the derived sulfoxide: synthesis,structure, and complexation with the metal cations

Novel 15-hydroxybenzomonothia-15-crown-5 containing the sulfur atom linked with the benzene ring and its S-oxide were synthesized. The stability constants for the complexes of the obtained benzocrown ethers and a reference 15-hydroxybenzo-15-crown-5 with Na, Ca, Ag^I, Cd, Hg^II, and Pb^II perchlorates were determined by ¹H NMR titration. In MeCN-d₃, the benzothiacrown ether demonstrates a high selectivity towards the thio- and oxothiophilic Hg²⁺ (logK ₁ = 7.1) and Pb²⁺ ions (logK ₁ = 7.4). In MeCN-d₃-D₂O mixtures, the stabilities of the most of complexes decrease sharply due to competitive hydration of the metal cations except for the “soft” Ag⁺ and Hg²⁺ ions having low affinity for the “hard” oxygen atoms and, on the contrary, very high affinity for the “soft” S^II atoms. This results in the change in selectivity of complexation: at the water content in solution of 20%, the benzothiacrown ether binds preferably the Hg²⁺ (logK ₁ = 5.0) and Ag⁺ ions (logK ₁ = 2.7). In MeCN-d₃, the benzothiacrown-derived sulfoxide is a weak and non-selective complexing agent towards all the metal cations under study; the reference 15-hydroxybenzo-15-crown-5 forms more stable complexes with the oxophilic sodium, calcium, and lead(ii) cations. The conformational features of the benzocrown ethers and their metal complexes established by NMR spectroscopy and X-ray diffraction are discussed. The found characteristics of the complexing ability of benzomonothia-15-crown-5 where the sulfur atom is in conjugation with the benzene ring reveal that the macrocyclic ligands with such a structure are promising as high-selective and efficient complexing agents for the “soft” mercury(ii) and silver(i) cations in acetonitrile-water mixtures.     

Effect of selenium on the Hg,Zn, Fe and Co content of yeast cells

The yeast cells, Saccharomyces cerevisiae, were exposed to Hg²⁺ ions (10^–4M) and SeO₂ (2·10^–4–10^–2M) or Se- methionine (2·10^–4M). Instrumental neutron activation analysis (INAA) was used to analyze changes in the Hg, Zn, Fe and Co levels in these cells. When the yeast was incubated in a medium containing 10^–3M and 10^–2M SeO₂, the Hg content of the yeast markedly increased. It was also found that the uptake of Se and Hg influenced the levels of Zn, Fe and Co found in the cells. While the presence of Se-methionine (Se-Met), SeO₂ or Hg²⁺ ions caused increases in the intracellular Zn levels, the combined presence of Hg²⁺ and SeO₂ and their assumed interaction, reduced the efficiency of Se for increasing the Zn content of yeast.     

Extraction studies of metal complexes with some macrocyclic tetraaza ligands and xanthene dyes : Spectrophotometric determination of Cadmium(II) with Tetramethyltetraazacyclotetradecane and Erythrosin A

The liquid-liquid extraction of ion-pair complexes of zinc(II), copper(II) and cadmium(II) is described. The macrocyclic ligands 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (4Me-cyclam-14) and rac-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (Tet b) are used with xanthene dyes as the counter ions. The apparent extraction constants (D′_c) are reported. The sequences of extraction efficiency of both ligands are related to the structure of the complexes. The apparent molar absorptivity of the Cd(4Me-cyclam-14)—erythrosin A ion-associate is 1.1 × 10⁵ l mol^? cm^?1. The calibration graph is linear over the range 0—10^?5 M, which allows even 0.05 μg ml^?1 cadmium to be determined in a 0.5 M sodium hydroxide medium. No interference was observed from Ni²⁺, Pb²⁺, Zn²⁺, Mg²⁺, Sn⁴⁺, Ga³⁺, Al³⁺ and Fe³⁺. Interferences were Cu²⁺, Hg²⁺, Ag⁺ and large anions.