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1.
The theory of pH-stat chelatometric titrations recently developed [Anal. Chim. Acta 456 (2002) 313] is experimentally substantiated here. The titrations of four representative doubly charged cations having different behaviour (copper, zinc, calcium, magnesium) are taken as examples. Copper is titratable between pH 3 and 5, zinc between 3 and 6, calcium between 6 and 10, and magnesium between 7 and 10. The shapes of the titration plots agree well with the theory, accounting for simultaneous equilibria involving proton exchange. The technique yields accurate and precise results, which compare favourably with those of other instrumental techniques, in particular photometric titrations. 相似文献
2.
M. M. Antonijević R. P. Mihajlović B. V. Vukanović 《Journal of Solid State Electrochemistry》2001,5(1):29-35
The results obtained in potentiometric titrations of copper(II), mercury(II) and iron(III) with standard EDTA solutions are
presented. The titration of copper(II) at pH values in the range from 8.11 to 10.99 (ammonia buffer) and the titration of
mercury(II) and iron(III) at pH values from 3.59 to 5.65 (acetate buffer) were performed. The titration end-point (TEP) was
detected with an indicator electrode made from natural crystalline pyrite as an electrochemical sensor. The results obtained
in potentiometric titration with the pyrite electrode were compared with those obtained using a platinum electrode (Fe3+), a Cu ion selective electrode (Cu2+) and a Hg electrode (Hg2+). Accurate and reproducible results with good agreement were obtained, but higher potential changes at the TEP were obtained
using the pyrite electrode. In the course of the titration the potential was established within less than 1 min, whereas at
the TEP it was within about 2–3 min. The potential changes at the TEP were in the range from 60 to 200 mV per 0.1 ml EDTA,
according to the stability constant of the complex formed. The highest potential changes, ranging from 160 to 200 mV, were
obtained in the titration of iron(III) at pH 3.59. Reverse titration was also performed and accurate and reproducible results
were obtained. Moreover, titration of halogenide and thiocyanate with standard mercury(II) solutions, as well as cyanide with
silver(I) solution, were performed and accurate and reproducible results were again obtained.
Received: 20 February 1998 / Accepted: 19 November 1999 相似文献
3.
《Journal of Coordination Chemistry》2012,65(3-4):321-331
Abstract 1-Hexadecyl-1,4,8,11-tetraazacyclotetradecane (hexadecyl cyclam) and 1-(3,7,11,15-tetramethyl) hexadecyl-1,4,8,11-tetraazacyclotetradecane (tetramethylhexadecyl cyclam) have been synthesized and their deprotonation and ligand-metal formation constants, K, determined for Cu(II), Zn(II) and Pb(II). The coupling of a long hydrocarbon chain to a ring nitrogen decreased the general ability of the cyclam ring to complex with metal ions. The greatest effect appeared to be for Cu(II) decreasing from a pK of 27 for cyclam to about 17. The titrations were fitted by HYPERQUAD and the concentrations of the intermediate complexes obtained as a function of pH. Metal-ligand complexes LMH2 4+, LMH2+ and LM2+ can coexist through a wide pH range. We have also calculated a composite metal-binding constant, K′, to reflect more accurately the overall ability of these ligands to bind a metal at any particular pH. K′, which is 14.6 for (hexadecyl cyclam)-Cu(II), is constructed from the concentrations of all the metal-chelated species at pH = 7. Generally, K′ is much lower than K. 相似文献
4.
5.
Carlo Maccà 《Analytica chimica acta》2002,456(2):313-323
Chelatometric titrations can be effectively monitored by means of the pH-stat technique. During the addition of the primary titrant (the chelating agent), the pH of the titrated solution is kept at a pre-selected value by adding a strong base as the auxiliary titrant. The equivalence point is characterised by a sudden change in the ratio between the added volumes of auxiliary and primary titrant solutions, i.e. in the slope of the linearly segmented titration plot representing the volume of the base against the volume of the chelating agent. The slope of the linear segments depends on the reactions involving proton exchange, which accompany the primary complexation reaction. The dependence of the shape of the plots on the imposed pH for typical titrations (magnesium(II) and copper(II)) is examined and the conditions for the feasibility of pH-stat chelatometric titrations are discussed. 相似文献
6.
The amounts of adsorption of Cu2+, Ni2+, and Zn2+ from single, binary, and tertiary nitrate solutions onto glutaraldehyde cross-linked chitosan beads were measured. The beads had an average particle size and pore volume of 2 mm and 0.06 cm3/g, respectively, and had a BET surface area of 60 m2/g. All experiments were performed at 298 K as a function of initial pH (2.0–5.0), total metal concentration (0.77–17.0 mol/m3), and molar concentration ratio (0.25–4) in the aqueous phase. It was shown that the amount of metal adsorption generally increased with increasing solution pH. Competitive adsorption was significant in binary and tertiary systems when Cu2+ was present. The selectivity factor reached maximum in an equilibrium pH range of 5.1–5.3 and 4.5–4.9 for the Cu-Ni and Cu-Zn binary systems, respectively. This adsorbent provided a possibility for selective separation of Cu2+ from such multi-component solutions. 相似文献
7.
《Journal of Coordination Chemistry》2012,65(20):2149-2163
L-DOPA is an important neurotransmitter that is found in the brain and as a hormone in the circulatory system. We report in this article the similarities and differences in behaviour of this important neurotransmitter as a chelating agent among some divalent and trivalent metal ions using potentiometric titration in aqueous solutions at 25.0?±?1.0°C. The careful and detailed potentiometric titrations of L-DOPA with Al3+, Cr3+, Fe3+, Cu2+, and Zn2+ are discussed and compared. UV-Vis-spectroscopy is utilized for both the free L-DOPA and for the Fe3+/L-DOPA system. The characteristic peak due to the π?→?π* transition of the free L-DOPA at ~280?nm (ε280?nm?=?1927?±?65?M?1?cm?1 between pH values of 2.0 to 3.0) disappeared when the iron solution was added to the L-DOPA sample in the same pH range. For the Fe3+/L-DOPA system we have observed a new peak at 470?nm with ε470?=?800?±?50?M?1?cm?1. These comparison studies of the similarities and differences among these di- and tri-valent metal ions shed light on these systems in aqueous solutions. The appropriate metal simulation and speciation diagrams were constructed using the model that fit the titration data points. 相似文献
8.
Two new indole derivatives have been synthesized by a one-pot procedure and their potential as fluorescence probes for metal ions was investigated. The sensor capability of 1 and 2 toward cations such as Ag+, Cu2+, Zn2+, Cd2+, Pb2+, and Hg2− was studied in dichloromethane solution by absorption, fluorescence emission, and 1H NMR titrations. Both probes showed selectivity for Ag+ and Hg2+ ions. The results suggest that these compounds may serve as promising models for future design of novel and more potent sensors. 相似文献
9.
Complex matrices and rather high acidity in environmental samples are often the impelling challenges for the used running buffers of capillary electrophoresis. Twelve binary acid-base buffers were evaluated for separation of Cr(VI)/Cr(III), Co2+ and Zn2+ in a sample containing various salts by capillary electrophoresis with contactless conductivity detector. The malic acid (MA) systems including MA-His (histidine), MA-Arg (arginine) and MA-Tris (tris(hydroxymethyl)aminomethane) were selected as the candidates with powerful separation efficiency and good response sensitivity. In the MA-Tris buffer, optimization were further carried out in terms of the pH value and the concentration of MA, and the optimal conditions were obtained as 6 mM MA-Tris and 2 mM 18-crown-6 at pH 3.5. Furthermore, a real application was demonstrated by analyzing the plating rinse water (pH 0.8), in which the Ca2+, Na+, Cr(VI)/Cr(III), Co2+ and Zn2+ were all detected by adjusting at pH 3.5 with 5% (v/v) diluent ammonia. Both the cations, e.g., K+, Ca2+, Na+, Mg2+, and the common high concentration anions in the sample, e.g., Cl−, SO42− and NO3− did not cause any disturbance to the concerned analytes. 相似文献
10.
A new ratiometric fluorescent sensor ( 1 ) for Cu2+ based on 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) with di(2‐picolyl)amine (DPA) as ion recognition subunit has been synthesized and investigated in this work. The binding abilities of 1 towards different metal ions such as alkali and alkaline earth metal ions (Na+, K+, Mg2+, Ca2+) and other metal ions ( Ba2+, Zn2+, Cd2+, Fe2+, Fe3+, Pb2+, Ni2+, Co2+, Hg2+, Ag+) have been examined by UV‐vis and fluorescence spectroscopies. 1 displays high selectivity for Cu2+ among all test metal ions and a ~10‐fold fluorescence enhancement in I582/I558 upon excitation at visible excitation wavelength. The binding mode of 1 and Cu2+ is a 1:1 stoichiometry determined via studies of Job plot, the nonlinear fitting of the fluorometric titration and ESI mass. 相似文献
11.
A PVC membrane electrode based on bis(2-nitrophenyl)disulfide carrier exhibits a very good response for Zn2+ in a wide concentration range (from 2.9×10−7 to 3.2×10−2 mol l−1) with a slope of 29.9±0.4 mV per decade of Zn2+ concentration. The response time of the sensor is about 10 s and the membrane can be used for more than 3 months without any observed divergence in potentials. The proposed sensor exhibits very good selectivity for Zn2+ over many cations and can be used in a wide pH range (2-9). This assembly served also as an indicator electrode in potentiometric titrations involving zinc ions and direct potentiometric determination of zinc ions in real and synthetic samples. 相似文献
12.
A new method for electrochemical titrations is proposed, based on the redox transformation of the test species by means of a controlled-potential pulsed current, followed by measurement of the potential in the intervals between the current pulses: the end-point is found by means of Sörensen's linearization technique. Investigations on various metal ions (Ag+, Cu2+, Cd2+, Pb2+) have shown that the accuracy and sensitivity, which depend on the nature of the species titrated, are comparable with those of other titration techniques. The method permits analytical separations and determinations of metal ions in mixtures. No particularly elaborate instrumentation is required and the apparatus described is simple to use, reliable and inexpensive. 相似文献
13.
A number of terminal N-alkylated linear tetraaza and pentaaza ligands were prepared. Their ligand protonation constants and some transition and post-transition metal (Ni2+, Cu2+, Zn2+, and Cd2+) complex stability constants were determined by potentiometric titration methods. In general, methylation and ethylation at the terminal nitrogen atoms caused the corresponding ligand nitrogen basicity to increase; however, the corresponding metal complex stabilities were decreased compared to the non-alkylated structural analogs, presumably due to a steric effect. 相似文献
14.
A new perylene diimide (PDI) ligand (1) functionalized with a dipicolylethylenediamine (DPEN) moiety was synthesized and first
used as a colorimetric and fluorometric dual-channel sensor to specifically detect the presence of Cu2+ over a wide range of other cations. The solution of 1 (10 μmol/L) upon addition of Cu2+ displayed distinguishing pink color compared with other cations including K+, Ni2+, Ca2+, Mn2+, Na+, Sr2+, Zn2+, Co2+, Cd2+, Mg2+, Cr3+, Ag+, and Ba2+, indicating the sensitivity and selectivity of 1 to Cu2+. Thus, the advantage of this assay is that naked-eye detection of Cu2+ becomes possible. Moreover, among these metal ions investigated, only Cu2+ quenched more than half fluorescent intensity of 1. The ESI-TOF spectrum of a mixture of 1 and CuCl2 in combination of the fluorescence titration spectra of 1 (10 μmol/L) upon addition of various amounts of Cu2+ revealed the formation of a 2:1 metal-ligand complex through the metal coordination interaction.
Supported by the National Natural Science Foundation of China (Grant Nos. 20872101 & 20772086) 相似文献
15.
Xin Yu Deng Wei Tao Xu Ming Liu Mei Xiang Yang Qian Jiang Zhu 《Supramolecular chemistry》2013,25(9):616-624
ABSTRACTMetal cations in aqueous solutions at different pHs (1.5, 4.5 and7.2) can be detected using the known inclusion complex H33258@Q8 as a fluorescent probe. Indeed, the fluorescence intensity of H33258 increases rapidly upon increasing the amount of Q[8] up to a Q[8]:H33258 ratio of 2:1, even at pH 1.5. The experimental results reveal that the probe not only exhibited selective recognition of metal cations at different pH but also showed different recognition for metal cations at different pHs. At pH 7.2, the probe responded to quite a variety metal cations, including one of the third main group elements, Al3+, four transition metal cations, Hg2+, Fe3+, Fe2+, and Cr3+ and three lanthanide cations Eu3+, Tm3+ and Yb3+; At pH 4.5, the probe responded to only two transition metal cations, Hg2+ and Fe3+. Unexpectedly, the probe lost its recognition properties at pH 1.5. 相似文献
16.
Acid—base potentiometric titrations of haematite (α-Fe2O3) suspensions in mixtures of the non-specifically adsorbing electrolyte KNO3 and the nitrates of the specifically adsorbing ions Ca2+, Cd2+ and Pb2+ show that the cross-over point of the titration curves, plotted as σ0(pH), can be interpreted as the point of zero charge (pzc) only if there is no specific adsorption or if the amount of specifically adsorbed cations is so small that all of it is quantitatively adsorbed. This finding implies that the usual procedure for obtaining the pzc from cross-over points of titration curves must be reconsidered in the case of specific adsorption. In reality an Esin—Markov coefficient is measured, the relation of which to the surface charge requires further thermodynamic analysis. 相似文献
17.
1,3-Di(2-pyridylmethoxy)-p-tert-butyldihomooxacalix[4]arene-crown-6 (2) was synthesized for the first time. 2 was isolated in a cone conformation in solution at room temperature, as established by NMR spectroscopy (1H, 13C and NOESY). Complete assignment of both proton and carbon NMR spectra was achieved by a combination of COSY, HSQC and HMBC experiments. The binding properties of ligand 2 towards alkali, alkaline earth, transition and heavy metal cations have been assessed by phase transfer and proton NMR titration experiments. The results are compared to those obtained with other dihomooxacalix[4]arene-crowns-6 and closely-related calix[4]arene-crown derivatives. 2 shows a preference for the soft heavy metal cations (except for Cd2+), with a very strong affinity for Ag+. Some transition metal cations are also well extracted. 2 forms 1:1 complexes with K+, Ca2+ and Ag+, and 1H NMR titrations indicate that they should be encapsulated into the cavity defined by the crown ether unit and by the two pyridyl pendant arms. A 1:2 (ML2) complex is formed with Zn2+ and two species, probably 1:1 and 1:2 complexes, are obtained with Pb2+. 相似文献
18.
《Journal of Coordination Chemistry》2012,65(2):284-295
Potentiometric titration was used to determine the potentiometric diagrams of complexes of adenine with Al3+, Cr3+, and Fe3+. IR and Raman spectra of solids show that the interaction of adenine with Cr3+ is not as strong as the other metals. Fe3+ binds to adenine at low and medium pH values at an Fe3+–adenine ratio of 6, while Al3+ binds to adenine at all pH values at an Al3+–adenine ratio of 8. The IR band associated with N-9–H is split into two components at high and low wavenumbers; IR band splitting has been observed for groups with a large dipole moment such as carbonyl and phosphate. To the best of our knowledge, this is the first time to see the splitting of IR bands involving a nitrogen. We also obtained potentiometric titration plots for adenine with Al3+, Cr3+, and Fe3+, independently, in various molar ratios which showed an interaction with adenine, consistent with the IR and Raman findings. Metal–adenine-hydroxo complexes were formed. 相似文献
19.
Cihan Topcu Gamze Lacin Vedat Yilmaz Fatih Coldur Bulent Caglar Osman Cubuk 《Analytical letters》2018,51(12):1890-1910
A novel copper(II)-selective electrode based on graphite oxide/imprinted polymer composite was developed for the electrochemical monitoring of copper(II) (Cu2+) ions. The electrode exhibited highly selective potentiometric response to Cu2+ with respect to common alkaline, alkaline earth and heavy metal cations. The composite composition studies indicated that the most suitable composite composition performing the most promising potentiometric properties was 20.0% ionophore (Cu2+-ion imprinted polymer), 10.0% paraffin oil, 5.0% multiwalled carbon nanotubes, and 65.0% graphite oxide. The fabricated electrode exhibited a linear response to Cu2+ over the concentration range of 1.0?×?10??6–1.0?×?10??1?M (correlation coefficient of 0.9998) with a sensitivity of 26.1?±?0.9?mV decade??1. The detection limit of the fabricated electrode was determined to be 4.0?×?10??7?M. The electrode worked well in the pH range of 4.0–8.0. The electrode had stable, reversible and fast potentiometric response (3?s). In addition, the electrode had a lifetime of more than 1 year. The analytical applications of the proposed electrode were performed using as an indicator electrode for the potentiometric titration of Cu2+ with ethylene diamine tetraacetic acid solution and for the determination of Cu2+ of spiked river, dam, and tap water samples. The obtained results for potentiometric titration and water samples were satisfactory. 相似文献
20.
A PVC membrane electrode for Ni2+ ions based on a recently synthesized mercapto compound, as an ionophore was prepared. The electrode exhibits a Nernstian slope of 28-30 mV per concentration decade at wide concentration range of (1.0×10−2-1.0×10−7 M). It has a fast response time of <15 s and can be used for at least 4 weeks. The potentiometric response is independent of the pH of the test solution in the pH range 5-8.5. The proposed electrode revealed good selectivities over a wide variety of other cations including alkali, alkaline earth, transition and heavy metal ions. It was successfully applied to the direct determination and potentiometric titration of nickel ion with EDTA. 相似文献