Thermodynamics of the solvent extraction of thorium and europium nitrates by neutral phosphorylated ligands

Solvent extraction of tetravalent thorium and trivalent europium ions from nitrate media into dichloromethane solution of triphenylphosphine oxide (TPPO) has been studied. The extractant was shown to be more efficient for europium than for thorium. A conventional log-log analysis reveals that the extraction of both metal nitrates takes place via the formation of the species with 1 : 2 metal to ligand ratio. Thermodynamic parameters i.e., ΔG°, ΔH° and ΔS° of the extraction process using 1,2-dichloroethane as diluent have been calculated based on the influence of the temperature on extraction equilibria in the range 293-313 K. While the extraction of europium is controlled by enthalpy changes, the extraction of thorium is an endothermic process and is driven by entropy changes. A comparison of these data with those obtained for the extraction of europium and thorium nitrates by two other related phosphorylated ligands, tri-n-octylphosphine oxide (TOPO) and diphenyl-N,N-dimethylcarbamoylmethylphosphine oxide (DФDMCMPO), indicates that DФDMCMPO coordinates presumably as a chelating ligand. This revised version was published online in July 2006 with corrections to the Cover Date.     

Selective spectrophotometric determination of thorium(IV) with 2-(5-Bromo-2-pyridylazo)-5-diethylaminophenol

A spectrophotometric study of the Th(IV) complex of a new reagent 2-(5-Bromo-2- pyridylazo)-5-diethylaminophenol (5-Br-PADAP) is presented. A reddish brown complex is formed at pH 4.86, and shows maximal absorbance at 580 nm with molar absorptivity of 1.66 × 10⁵ mol⁻¹ cm⁻¹ liter. Beer's law is obeyed over the range 0.0 to 15 μg of thorium. Rare earths ions like La³⁺, Ce³⁺, and Y³⁺ do not interfere because they form complexes with 5-Br-PADAP at higher pH's (>9.94) (1). A new method for determining trace amounts of thorium is proposed, which possesses the advantages of high sensitivity and selectivity.     

Extraction-separation of Eu(III) and Th(IV) ions from nitrate media into a room-temperature ionic liquid

Application of a room-temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄mim⁺][PF₆ ^?]), in the extraction of Eu(III) and Th(IV) ions from nitrate media using tri-n-octylphosphine oxide (TOPO) as extractant is investigated. The results are compared with those obtained in dichloromethane. It is shown that the europium ions are extracted via a solvation mechanism by formation of [Eu(TOPO) ₃ ³⁺ ](NO₃ ^?)₃ species in both [C₄mim⁺][PF₆ ^?] and dichloromethane. Nevertheless, application of the studied RTIL makes a significant improvement in the extraction efficiency of europium ions. A different attitude was observed for the extraction of thorium ions. In fact, although the analysis of the extraction data of these ions from sodium nitrate solutions confirms the formation of [Th(TOPO) ₃ ⁴⁺ ](NO₃ ^?)₄ species in dichloromethane, the extraction of these ions into the ionic liquid was not affected by the presence of TOPO. This latter outcome states the process takes place by a cation-exchange mechanism. It is found that the extraction of thorium ions diminishes in the presence of nitric acid. Interestingly, in contrast to the results observed in the extraction of thorium ions from sodium nitrate solutions, TOPO shows a co-operative effect on the extraction of these ions from nitric acid media. This allows considering the mechanism of the extraction of Th⁴⁺ ions from nitric acid media as a mixed ion exchange-solvation mechanisms by formation of [Th(TOPO)⁴⁺](NO₃ ^?)(PF₆ ^?)₃ species.     

Synthesis of poly(hydroxamic acid) ligand from polymer grafted corn‐cob cellulose for transition metals extraction

Poly(hydroxamic acid) ligand was synthesized using ester functionalities of cellulose‐graft‐poly(methyl acrylate) copolymer, and products are characterized by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, high‐resolution transmission electron microscopy, and X‐ray photoelectron spectroscopy analysis. The poly(hydroxamic acid) ligand was utilized for the sensing and removal of transition metal ions form aqueous solutions. The solution pH is found a key factor for the optical detection of metal ions, and the reflectance spectra of the [Cu‐ligand]ⁿ⁺ complex were observed to be the highest absorbance 99.5% at pH 6. With the increase of Cu²⁺ ion concentration, the reflectance spectra were increased, and a broad peak at 705 nm indicated that the charge transfer (π‐π transition) complex was formed. The adsorption capacity with copper was found to be superior, 320 mg g^?1, and adsorption capacities for other transition metal ions were also found to be good such as Fe³⁺, Mn²⁺, Co³⁺, Cr³⁺, Ni²⁺, and Zn²⁺ were 255, 260, 300, 280, 233, and 223 mg g^?1, respectively, at pH 6. The experimental data show that all metal ions fitted well with the pseudo‐second‐order rate equation. The sorption results of the transition metal ions onto ligand were well fitted with Langmuir isotherm model (R² > 0.98), which implies the homogenous and monolayer character of poly(hydroxamic acid) ligand surface. Eleven cycles sorption/desorption process were applied to verify the reusability of this adsorbent. The investigation of sorption and extraction efficiency in each cycle indicated that this new type of adsorbent can be recycled in many cycles with no significant loss in its original detection and removal capability. Copyright © 2016 John Wiley & Sons, Ltd.     

Metal‐Ion‐Mediated Tuning of Duplex DNA Binding by Bis(2‐(2‐pyridyl)‐1H‐benzimidazole)

Studies of double‐stranded‐DNA binding have been performed with three isomeric bis(2‐(n‐pyridyl)‐1H‐benzimidazole)s (n=2, 3, 4). Like the well‐known Hoechst 33258, which is a bisbenzimidazole compound, these three isomers bind to the minor groove of duplex DNA. DNA binding by the three isomers was investigated in the presence of the divalent metal ions Mg²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺. Ligand–DNA interactions were probed with fluorescence and circular dichroism spectroscopy. These studies revealed that the binding of the 2‐pyridyl derivative to DNA is dramatically reduced in the presence of Co²⁺, Ni²⁺, and Cu²⁺ ions and is abolished completely at a ligand/metal‐cation ratio of 1:1. Control experiments done with the isomeric 3‐ and 4‐pyridyl derivatives showed that their binding to DNA is unaffected by the aforementioned transition‐metal ions. The ability of 2‐(2‐pyridyl)benzimidazole to chelate metal ions and the conformational changes of the ligand associated with ion chelation probably led to such unusual binding results for the ortho isomer. The addition of ethylenediaminetetraacetic acid (EDTA) reversed the effects completely.     

Preparation,Structure, and Optical Properties of the 1D Chain Red Luminescent Europium Coordination Polymer: {[Eu2L6(DMF)­(H2O)]·2DMF·H2O}n (L = C9H6ClO2–)

The 1D chain red luminescent europium coordination polymer: {[Eu₂L₆(DMF)(H₂O)] · 2DMF · H₂O}_n ( I ) (L = 4‐chloro‐cinnamic acid anion, C₉H₆ClO₂^–, DMF = N, N‐dimethylformamide) was synthesized by the reaction of Eu(OH)₃ and 4‐chloro‐cinnamic acid ligand. The structure of the coordination polymer was determined by single‐crystal X‐ray diffraction analysis. It reveals that there exists two crystallographically nonequivalent europium atoms in each unit of this coordination polymer and Eu³⁺ ions are connected by two alternating bridging modes to form an endless polymer structure. The luminescent properties and energy transfer process in the complex are investigated at room temperature.     

A Coated Graphite Thorium‐Ion Selective Potentiometric Sensor Based on a Calix[4]arene Bearing Phosphoryl Groups

5,11,17,23‐Tetra‐tert‐butyl‐25,26,27,28‐tetrakis(diphenylphosphinoylmethoxy)calix[4]arene ( 1 )has been used for the preparation of a graphite coated thorium ion‐selective electrode (Th⁴⁺‐ISE). The plasticized PVC membrane containing 30% PVC, 58% ortho‐nitrophenyloctylether (NPOE), 4% sodium tetraphenylborate (NaTPB) and 8% ionophore was directly coated on a graphite rod. This sensor gave good Nernstian responses with a slope of 15.5 ± 0.1 mV/decade over a concentration range of 1 × 10^?5 ?1 × 10^?3 M of thorium ions with a limit of detection of 7.9 × 10^?6 M. The dynamic response time of the electrode to achieve a steady potential was found to be about 15 seconds. The potential of the prepared sensor was independent of the pH variation in the range 2.3–4.0. The selectivity relative to several mono‐, di‐ and tri‐valent metal ions, i.e. Li⁺, Na⁺, K⁺, Ag⁺, NH₄⁺, Sr²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, La³⁺, Sm³⁺, Dy³⁺, Er³⁺ and Y³⁺ was examined. This electrode can be used for 6 months without any considerable divergences in the potential response. The sensor was successfully used as an indicator electrode for the potentiometric titration of a thorium solution using a standard solution of EDTA.     

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

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

Crystal Structure and Luminescence of a Europium Nitrate Complex with Furancarboxylic Acid and 2,2′-Bipyridine

Abstract

A quaternary mixed ligand europium complex, [Eu(FA)₂NO₃bipy]₂, has been synthesized, where FA = α-furancarboxylic acid anion and bipy=2,2′-bipyridine. The europium complex crystallizes in the triclinic system, space group P1. Its structure was determined by X-ray diffraction methods. The two europium ions in the dimer are held together by four carboxylate groups of furancarboxylic acid and each europium ion is further bonded to one chelated bidentate nitrate and one 2,2′-bipyridine molecule. The coordination modes of the four carboxylate groups are divided into two types, bidentate bridging and tridentate bridging, making a coordination number of 9. Excitation and luminescence spectra observed at 77 K show that the europium ion site in the crystal has low symmetry and emission 5D ₁→⁷ F_J of the Eu³⁺ ion disappears after 20 μs.     

Chromium(III), manganese(II), iron(III), cobalt(II), nickel(II) and copper(II) complexes with a pentadentate, 15-membered new macrocyclic ligand

Complexes of Cr^III, Mn^II, Fe^III, Co^II, Ni^II and Cu^II containing a macrocyclic pentadentate nitrogen–sulphur donor ligand have been prepared via reaction of a pentadentate ligand (N₃S₂) with transition metal ions. The N₃S₂ ligand was prepared by [1 + 1] condensation of 2,6-diacetylpyridine with 1,2-di(o-aminophenylthio(ethane. The structures of the complexes have been elucidated by elemental analyses, molar conductance, magnetic susceptibility measurements, i.r., electronic and e.p.r. spectral studies. The complexes are of the high spin type and are six-coordinate.     

(Tetracycline)europium(III) Complex as Luminescent Probe for Hydrogen Peroxide Detection

Luminescence spectra of aqueous solutions containing a fixed concentration of tetracycline (TC) and increasing concentrations of Eu³⁺ were recorded both in the absence and presence of hydrogen peroxide (H₂O₂). In H₂O₂‐free solutions in which the Eu/TC molar ratio was varied from 1 : 1 to 8 : 1, the ⁵D₀→⁷F₀ transition consisted of only one peak at 580 nm. In the presence of H₂O₂, an extra peak appeared in the spectrum at 578 nm when the Eu/TC molar ratios were above 2.5. A detailed analysis of this spectral region revealed that at lower Eu/TC molar ratios (up to 2 : 1), the ⁵D₀→⁷F₀ transition experienced a slight blue shift. This indicates that at low Eu/TC molar ratios, the presence of H₂O₂ leads to two different environments of the trivalent europium ions, which most likely form bridged peroxide complexes with hydrogen peroxide (μ‐H₂O₂ ligand). Luminescence spectra measured in the presence of molybdate ions, which catalytically decompose H₂O₂, led to the disappearance of the extra europium(III) site that was formed in the presence of H₂O₂. The intensity of the hypersensitive ⁵D₀→⁷F₂ transition did not linearly depend on the H₂O₂/TC molar ratio. For H₂O₂/TC ratios up to 10, a sharp linear increase of the peak intensity was observed, but with further increase of the H₂O₂ concentration, the intensity remained nearly constant. For H₂O₂/TC ratios above 100, the intensity of this transition even started to decrease, which limits the use of the (tetracycline)europium(III) system to quantify hydrogen peroxide in solution.     

Multibubble sonoluminescence of europium(III) chloride in heavy water

A weak glow in the region of the Eu³⁺ photoluminescence spectrum was detected against the background of the continuum of the solvent emission during multibubble sonolysis of air- or argon-saturated EuCl₃ solutions (0.1 mol L⁻¹) in heavy water. No characteristic sonoluminescence of the europium ion in aqueous solutions was observed earlier. Possible reasons for the low yield of Eu³⁺ sonoluminescence compared with other lanthanide ions (Ln³⁺) are discussed and the influence of europium on the spectrum of the solvent continuum related, in particular, to quenching of the electron-excited sonolysis products H₂O* (D₂O*) and Eu³⁺* in electron transfer reactions. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1793–1796, September, 2008.     

Synthesis,structure, and solvent-extraction properties of tridentate oxime ligands and their cobalt(II), nickel(II), copper(II), zinc(II) complexes

Synthesis of four different types of ligands Ar[COC(NOH)R] _n (Ar = biphenyl, n = 1, HL¹; Ar = biphenyl, n = 2, H₂L²; Ar = diphenylmethane, n = 1, HL³; Ar = diphenylmethane, n = 2, H₂L⁴; R = furfurylamine in all ligands) and their dinuclear Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ complexes is reported herein. These compounds were characterized by elemental analysis, ICP-OES, FT-IR spectra, and magnetic susceptibility measurements. The ligands were further characterized by ¹H NMR. The results suggest that dinuclear complexes of HL¹ and HL³ have a metal to ligand mole ratio of 2: 2 and dinuclear complexes H₂L² and H₂L⁴ have a metal to ligand mole ratio of 2: 1. Square pyramidal or octahedral structures are proposed for complexes of oxime ligands. Furthermore, extraction abilities of the four ligands were also evaluated in chloroform using selected transition metal picrates such as Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Pb²⁺. The ligands show strong binding ability towards Hg²⁺ and Cu²⁺ ions.     

Solvent extraction of thorium from nitric acid solutions using di-N-butyl sulfoxide (DBSO) in xylene

The extraction of thorium(IV) from nitric acid solutions by di-n-butyl sulfoxide (DBSO) in xylene has been investigated as a function of acid, extractant and the metal concentration. The effect of contact time and diverse ions on the extraction has been examined. Phosphate, fluoride, oxalate and perchlorate reduce the extraction to some extent. The extraction of other metal ions, especially impurities associated with thorium in ores, has been measured under optimised conditions selected for thorium extraction. Na(I), K(I), Ca(II), Sr(II), Mn(II), Fe(II), Ni(II), Zn(II), Pb(II), Al(III), Ti(IV) and Hf(IV) are not extracted. Among the stripping solutions employed for back-extraction, deionized water is found to be the best and more than 99% thorium can be back-extracted in three stages. The extracted species is supposed to be Th(NO₃)₄·2DBSO. The extraction is found to be almost independent of the thorium concentration in the range between 4.3·10^–4–4.3·10^–2M and inversely dependent upon the temperature. The values of thermodynamic functions H, G and S for extraction equilibrium have been evaluated to be –19.6±2.9 kJ·mole^–1, –18.1±2.0 kJ·mole^–1 and –5.0±2.9 J·mole^–1·K^–1, respectively.     

Solvent extraction of cobalt(II), zinc(II) and europium(III) with 4-thiobenzoyl-2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-one (SBMPP)

Solvent extraction of⁶⁵zinc,⁶⁰cobalt and^152+154europium from aqueous buffers into benzene containing 4-thiobenzoyl-2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-one (SBMPP) has been investigated in detail (μ=0.1, T=26±1°C). The species extracted and the values of log K_ex, where K_ex refers to the extraction equilibrium, are ZnL₂ (−2.68) CoL₂(−3.08) and EuL₃(−7.08), where L is the anion of the ligand. The sulfur analog appears to be more effective than the parent ligand 4-benzoyl-2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-one in the extraction of zinc(II) and cobalt(II), whereas the reverse is true with europium(III).     

Ultrasensitive mercury(II) ion detection by europium(III)-doped cadmium sulfide composite nanoparticles

With the biomolecule glutathione (GSH) as a capping ligand, Eu³⁺-doped cadmium sulfide composite nanoparticles were successfully synthesized through a straightforward one-pot process. An efficient fluorescence energy transfer system with CdS nanoparticles as energy donor and Eu³⁺ ions as energy accepter was developed. As a result of specific interaction, the fluorescence intensity of Eu³⁺-doped CdS nanoparticles is obviously reduced in the presence of Hg²⁺. Moreover, the long fluorescent lifetime and large Stoke's shift of europium complex permit sensitive fluorescence detection. Under the optimal conditions, the fluorescence intensity of Eu³⁺ at 614 nm decreased linearly with the concentration of Hg²⁺ ranging from 10 nmol L⁻¹ to 1500 nmol L⁻¹, the limit of detection for Hg²⁺ was 0.25 nmol L⁻¹. In addition to high stability and reproducibility, the composite nanoparticles show a unique selectivity towards Hg²⁺ ion with respect to common coexisting cations. Moreover, the developed method was applied to the detection of trace Hg²⁺ in aqueous solutions. The probable mechanism of reaction between Eu³⁺-doped CdS composite nanoparticles and Hg²⁺ was also discussed.     

Cation Complexation by a Lower Rim Calix(4)arene Derivative: Structural,Electrochemical and Thermodynamic Studies

The synthesis and characterization (¹H and ¹³C NMR) of a partially substituted lower rim p-tert-butylcalix(4)arene, namely, 5,11,17,23-tetra-4-tert-butyl-25,27-bis(diethylphosphate amino)ethoxy-26,28-dihydroxycalix[4]arene (1), are reported. The solution thermodynamics of the ligand in a variety of solvents at 298.15?K was investigated through solubility (hence standard Gibbs energy of solution) measurements while the calorimetric technique was used to derive the standard solution enthalpy. These data were used to calculate the standard entropy of solution. An enthalpy–entropy compensation effect is shown and, as a result, slight variations are observed in the transfer Gibbs energies of this ligand from the reference to other solvents. ¹H NMR, conductance and calorimetric measurements were carried out to establish the degree of interaction of the ligand with univalent (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺ and Ag⁺) and bivalent (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Pb²⁺, Cd²⁺, Hg²⁺, Cu²⁺, Zn²⁺) cations in acetonitrile, methanol, N,N-dimethylformamide and propylene carbonate. No complexation was found between this ligand and univalent cations in these solvents. As far as the bivalent cations are concerned, interaction between 1 and these cations was found only in acetonitrile. The versatile behaviour of this ligand with bivalent cations in this solvent is reflected by the formation of complexes of different stoichiometry. Thus the interaction of 1 with alkaline-earth (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺) and Pb²⁺ metal cations leads to the formation of 1:2 (cation:ligand) complexes. However, for other bivalent metal cations (Cu²⁺, Zn²⁺, Cd²⁺ and Hg²⁺) the complex stoichiometry was found to be 1:1. The results are discussed in terms of the key role played by acetonitrile in processes involving calix[4]arene derivatives.     

Spectroscopic Characterization of <Emphasis Type="Italic">N,N-bis</Emphasis>(2-{[(2,2-Dimethyl-1,3-Dioxolan-4-yl)Methyl]Amino}Ethyl) N′,N′-Dihydroxyethanediimidamide and Its Complexes

A new dioxime ligand, N,N-bis(2-{[(2,2-dimethyl-1,3-dioxolan-4-yl)methyl]amino} ethyl)N′,N′-dihydroxyethanediimidamide (H₂L), and its mononuclear complexes with Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ and Cd²⁺ are synthesized. H₂L forms transition metal complexes [Co(LH)₂(H₂O)₂] and [M(LH)₂] (M = Ni²⁺, Cu²⁺) with a metal : ligand ratio of 1 : 2. Complexes [M(H₂L)(Cl)₂] (Zn²⁺, Cd²⁺) have a metal : ligand ratio of 1 : 1. The mononuclear Co²⁺, Ni²⁺, and Cu²⁺ complexes indicate that the metal ions coordinate ligand through its two N atoms, as the most of dioximes. In the Co²⁺ complex, two water molecules and in the Zn²⁺ and Cd²⁺ complexes two chloride ions are also coordinated to the metal ion. The structures of these compounds are identified by elemental analyses, IR, ¹H and ¹³C NMR, electronic spectra, magnetic susceptibility measurements, conductivity, and thermogravimetric analysis.__________From Koordinatsionnaya Khimiya, Vol. 31, No. 7, 2005, pp. 540–544.Original English Text Copyright © 2005 by Canpolat, Kaya.The text was submitted by the authors in English.     

Synthesis,structures, and property studies on Zn(II), Ni(II), and Cu(II) complexes with a Schiff base ligand containing thiocarbamide group

A Schiff base ligand containing thiocarbamide group of 4-phenyl-1-(4-methoxyl-1-phenylethylidene)thiosemicarbazide (HL) and its three mononuclear metal complexes of ZnL₂ (1), NiL₂ (2), and CuL₂ (3) have been synthesized. Elemental analysis, IR, and X-ray single crystal diffraction characterizations for the ligand and the three complexes have been carried out. In the three complexes, the central metallic ions of Zn²⁺, Ni²⁺, and Cu²⁺ coordinate with two deprotonated ligands of L⁻, respectively. In 1, Zn²⁺ ion adopts a distorted tetrahedral geometry, while in 2 and 3, both the Ni²⁺ and Cu²⁺ ions possess distorted square planar configurations. For the four compounds, UV–Vis spectra have been measured and DFT calculations at B3LYP/LANL2DZ level of theory prove that the electronic spectra of HL and 1 are corresponding with electronic transitions of n → π* and π → π* in the ligand itself and the electronic spectra of 2 and 3 are attributed to intraligand electronic transitions as well as d–d electronic transitions. Electrochemical investigations reveal that the different metal–ligand interactions have changed the peak shapes and peak locations, which are corresponding with the DFT-B3LYP/LANL2DZ calculational results. Fluorescence spectra measurements indicate that the ligand emits purple fluorescence and the complex 1 emits stronger blue fluorescence, while the complexes 2 and 3 quench fluorescence. The thermal analyses result show that the three complexes undergo two similar decomposition processes because of their similar geometric configurations.     

A Prussian blue-based reactive electrode (reactrode) for the determination of thallium ions

A reactive electrode (reactrode) made of Prussian blue (PB), graphite and paraffin can be used for a selective determination of thallium ions down to a concentration of 2 · 10^–8 mol 1^–1. The working principle of the reactrode is that thallium ions can be pumped into Prussian blue during alternating oxidation-reduction cycles. After a preconcentration of thallium ions in PB, the voltammetric determination follows as usually in anodic stripping voltammetry, i.e. the thallium ions are reduced to thallium metal which is subsequently oxidized to give the anodic stripping signal. The peculiarity of the Prussian blue-thallium system is that the thallium ions are situated in the holes of the PB matrix. When reduced to metallic thallium, they are substituted by potassium ions. Cd²⁺, Fe³⁺, Zn²⁺, Cu²⁺ and Ni²⁺ do not interfere up to a hundredfold excess, NH₄⁺ does not interfere up to a thousandfold – and Bi³⁺ up to tenfold excess. The interference by Pb²⁺ can be suppressed with EDTA.