Thermal lens studies of the reaction of iron (II) with 1,10-phenanthroline at the nanogram level

The determination of iron(II) with 1,10-phenanthroline in aqueous solutions was carried out exemplarily by thermal lens spectrometry. The peculiarities of analytical reactions at the nanogram level of reactants can be studied using this method. Under the conditions of the competing reaction of ligand protonation, the overall stability constant for iron(II) chelate with 1,10-phenanthroline was determined at a level of n x 10(-7) mol L(-1), logbeta3 = 21.3+/-0.1. The rates of formation and dissociation of iron(II) tris-(1,10-phenanthrolinate) at a level of n x 10(-8) mol L(-1) were found to be (2.05+/-0.05) x 10(-2) min(-1) and (3.0+/-0.1) x 10(-3) min(-1), respectively. The conditions for the determination of iron(II) with 1,10-phenanthroline by thermal lensing were reconsidered, and ascorbic acid was shown to be the best reducing agent, which provided minimum and reproducible sample pretreatment. Changes in the conditions at the nanogram level improved both the selectivity and sensitivity of determination. The optimum measurement conditions for thermal lensing were determined not only by the absorption of the analyte and reagents, but also by the background absorption of the solvent. The limits of detection and quantification of iron(II) at 488.0 nm (excitation beam power 140 mW) are 1 x 10(-9) and 6 x 10(-9) mol L(-1), respectively; the reproducibility RSD for the range n x 10(-8)-n x 10(-6) mol L(-1) is 2-5%.     

Photometric determination of selenium with ferrocene

A sensitive spectrophotometric method for the determination of selenium has been developed. The method depends on a redox reaction between selenious acid in 8M hydrochloric acid and a chloroform solution of ferrocene. One mole of selenious acid produces 4 moles of ferricenium ions, which are then oxidized by bromine water. The resulting iron(III) is reduced to iron(II) and determined with 1,10-phenanthroline. The relative standard deviation for 20 mug of selenium was 1.1%. The apparent molar absorptivity of the final solution, referred to selenious acid, is 4.23 x 10(4) 1. mole(-1). cm(-1) at 512 nm. This method has been used to determine selenium in copper metal.     

Polarographic determination of trace amounts of thorium

A sensitive linear-sweep polarographic method for the determination of thorium is described. It is based on the thorium complex with Xylidyl Blue I (XBI) in a medium containing ethylenediamine, 1,10-phenanthroline, oxalic acid and ninhydrin, at pH 10.5-11.5. The complex has been proved to be Th(XBI)(2), with log beta' = 9.6. The method can be used to determine trace amounts of thorium over the range 3.5 x 10(-8)-3 x 10(-6)M. The detection limit is 1 x 10(-8)M. A solvent extraction procedure is necessary to eliminate interference from several cations. The method has been applied to determination of traces of thorium in minerals, with good results.     

Kinetic determination of traces of manganese in different materials by its catalytic effect on the methylene green-periodate reaction

The oxidation of Methylene Green by sodium periodate is a slow process. A kinetic method based on the catalytic effect of manganese(II) on this reaction in the presence of 1,10-phenanthroline as activator is described. The reaction is followed spectrophotometrically by measuring the decrease in the absorbance of the dye at 620 nm. Under the optimal experimental conditions [4 x 10(-5)M Methylene Green, 0.2M acetate buffer (pH 4), 2 x 10(-3)M 1,10-phenanthroline, 2.5 x 10(-3)M sodium periodate, 35 degrees ], manganese(II) between 0.2 and 30 ng ml is determined by the tangent method. The accuracy of the method and the influence of 44 foreign ions have been studied and an equation for the kinetics of the catalysed reaction is proposed. The procedure has been applied to the determination of manganese in water, milk and beer with excellent results.     

Investigation of the reaction of copper(I) with 2,9-dimethyl-1,10-phenanthroline at trace level by thermal lensing

The stability constants for copper(I) chelate with 2,9-dimethyl-1,10-phenanthroline are determined by thermal lensing, and the advantages over spectrophotometric determination of stability constants are shown. Changes in the photometric reaction when moving from the microgram to the nanogram level of reactants are discussed. The conditions for the thermal-lens determination of copper are optimized. The limit of detection of copper is 3x10(-8) mol dm(-3), and the linear calibration range 1x10(-7)-1x10(-5) mol dm(-3).     

Determination of manganese in some medicinal plants and their infusions by a catalytic spectrophotometric method

The catalytic effect of manganese (II) on the oxidation of the azo dye 3-Methyl-6-(2-hydroxyethoxy)-2-[2-methoxy-4-N (N, N diethylamino) phenylazo] benzothiazolium methylsulphate, with potassium periodate in the presence of 1,10-phenanthroline in weakly acidic media was studied. The reaction was followed spectrophotometrically by measuring the decrease in the absorbance of the dye at 560 nm. Under the optimum conditions (4 x 10(-5) mol dm(-3) azo dye, 4 x 10(-4) mol dm(-3) potassium periodate, 1 x 10(-4) mol dm(-3) 1,10-phenanthroline, 0.1 mol dm(-3) buffer--pH 3.0, 70 degrees C, 8 min) manganese (II) in the range 0.1-5 ng cm(-3) could be determined by the fixed-time method with a detection limit of 0.035 ng cm(-3). The developed method is highly sensitive, selective, and simple. The method was applied successfully to the determination of total manganese in some medicinal plants and to analyse their infusions for trace amounts of total manganese and free manganese (II) ions without separation.     

Effects of auxiliary complex-forming agents on the rate of metallochromic indicator colour-change-III: mechanism of the colour change of tac in nickel-edta titrations

The rate of the ligand-substitution reaction of nickel(II)-TAC chelate (NiR(2)) with EDTA (Y) and 1,10-phenanthroline (X) has been determined spectrophotometrically in 20% v v dioxan over the pH range 5.7-6.3 at mu = 0.1 (KNO(3)) and 25 +/- 1 degrees . The substitution reaction with EDTA proceeds through the following two pathways: NiR(2) + H(+) right harpoon over left harpoon NiR(+) + HR, and NiR(2) + H(2)O right harpoon over left harpoon NiR(OH) + HR, The reaction of NiR(+) or NiR(OH) with EDTA is the rate-determining step, and k(1) = 2.1 x 10(3) l .mole(-1) .sec(-1) and k(2) = 7.9 x 10(6) l .mole(-1) .sec(-1).The substitution reaction with 1,10-phenanthroline proceeds as follows: NiR(+) + X right harpoon over left harpoon NiRX(+) At higher concentrations of 1,10-phenanthroline the release of TAC from NiR(2) by hydrogen ion is the rate-determining step, and k(3) = 2.4 x 10(5) l .mole(-1). sec(-1). At lower concentrations of 1,10-phenanthroline -d[NiR(2)]/dt is proportional both to [H(+)] and [X]. The value k(4) = 5.1 x 10(4) l. mole(-1). sec(-1) was calculated by the use of the steady-state approximation for [NiRX(+)]. The substitution with 1,10-phenanthroline proceeds much faster than that with EDTA. By the addition of a small amount of 1,10-phenanthroline, Ni can be titrated with EDTA at 50 degrees, with TAC as an indicator.     

The sensitive determination of nucleic acids using resonance light scattering quenching method

It is found that in hexamethylene tetramine (HMTA)-HCl buffer of pH 7.00, nucleic acids can quench the resonance light scattering (RLS) of europium (III) (Eu3+)-2-thenoyltrifluoroacetne (TTA)-1,10-phenanthroline (Phen) system. Based on this, a sensitive method for the determination of nucleic acids is proposed. The experiments indicate that under the optimum conditions, the quenched RLS intensity is in proportion to the concentration of nucleic acids in the range of 1.0x10(-10) to 2.0x10(-6) g ml-1 for fish sperm (fsDNA), 1.0x10(-11) to 1.0x10(-6) g ml-1 for yeast RNA (yRNA), 5.0x10(-11) to 5.0x10(-7) g ml-1 for calf thymus DNA (ctDNA). Their detection limits (S/N=3) are 0.03, 0.006 and 0.002 ng ml-1, respectively. Therefore, the proposed method is the most sensitive RLS method for the determination of nucleic acids so far. The interaction between nucleic acids and Eu3+-TTA-Phen is also discussed.     

Photobehavior of (alpha-diimine)dimesitylplatinum(II) complexes

The photobehavior of complexes of the type Pt(diimine)(mes)2 is investigated (where diimine = 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), 3,4,7,8-tetramethyl-1,10-phenanthroline (tmp), 2,9-dimethyl-1,10-phenanthroline (2,9-dmp), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp), and 4,7-diphenyl-1,10-phenanthroline (dpp) and mes = the mesityl (2,4,6-trimethylphenyl) anion). For all compounds studied, solution RT emission is observed to be weak and excited-state lifetimes are found to be short (< or = 20 ns) regardless of solvent choice. Evidence is presented for energy-transfer quenching of Pt(dpp)(mes)2 luminescence in toluene by dissolved O2 (primarily producing singlet oxygen) with an observed quenching rate constant of kq > or = 1.3 x 10(9) M-1 s-1. Electron-transfer quenching is also observed in the presence of 3,5-dinitrobenzonitrile, yielding a quenching rate constant of kq > or = 1.6 x 10(9) M-1 s-1. The latter observation suggests that phase Pt(II) systems may have future value as excited-state reductants. All of the complexes display a much more intense and longer-lived luminescence in the solid state at room temperature. Several possible explanations for this dependence on phase are proposed, with the most probable mechanism involving radiationless deactivation in solution via rotation of the o-methyl groups of the mesityl ligands.     

Theoretical characterization of a typical hole/exciton-blocking material bathocuproine and its analogues

The structural, electronic, and carrier transport properties of bathocuproine (BCP), which is a typical hole/exciton-blocking material applied in organic light-emitting diodes (OLEDs), have been investigated based on density functional theory (DFT) and ab initio HF method. The detail characterizations of frontier electronic structure and lowest-energy optical transitions have been studied by means of time-dependent density functional theory (TD-DFT). Five BCP analogues, o-phenanthroline (1), 2,9-dimethyl-1,10-phenanthroline (2), 2,9-diphenyl-1,10-phenanthroline (3), 4,7-diphenyl-1,10-phenanthroline (4), and 2,9-bis(trifluoromethyl)-1,10-phenanthroline (5) have also been studied in order to select more suitable candidates of efficient hole-blocking materials. The calculated results showed that rigid planar structures, conjugate degrees, and substitute groups play crucial roles in the hole/exciton-blocking and electron-transport properties of these materials. The calculated geometries, ionization energies (IP), and energy gap between the singlet ground state and triplet excited state (E(T1)) were well in agreement with the experimental results. On the basis of the incoherent transport model, the calculated electron mobility of BCP is 1.79 x 10(-2) cm(2)/(V s), which is comparable to experimental results of 1.1 x 10(-3) cm(2)/(V s). The electron mobilities for compounds 1, 4, and 5 are 3.45 x 10(-2), 2.90 x 10(-2), and 1.40 x 10(-2) cm(2)/(V s), respectively. The calculated results indicated that compounds 1, 4, and 5 may be more effective hole/exciton-blocking materials than BCP.     

Flow injection electrogenerated chemiluminescence determination of vanadium and its application to environmental water sample

A selective flow injection electrogenerated chemiluminescence(CL) method for the determination of vanadium is described in this paper. It was based on the chemiluminescence reaction of luminol with vanadium(II), which was on-line electrogenerated from vanadate using a flow-through carbon electrolytic cell. Under the optimal conditions, the CL intensity was linear to the concentration of vanadium in the range of 5.0x10(-10)-1.0x10(-7) gml(-1) with a detection limit of 2x10(-10) gml(-1) vanadium. The relative standard deviation was 4% for 5.0x10(-8) gml(-1) vanadium in 11 repeated measurements. The method has been successfully applied to the determination of vanadium in environmental water samples.     

Kinetic spectrofluorimetric determination of silver, based on its catalytic effect on the oxidation of pyrocatechol-1-aldehyde 2-pyridylhydrazone by peroxodisulphate in the presence of 1,10-phenanthroline as activator

A kinetic fluorimetric method for the determination of silver is described, based on its catalytic effect on the oxidation of pyrocatechol-1-aldehyde 2-pyridylhydrazone by peroxodisulphate. In aqueous solution silver concentrations of 0.2-0.8 mug ml can be determined, and 10-80 ng ml in the presence of 1,10-phenanthroline as activator. The fluorescent species obtained (lambda(ex) 357 nm, lambda(em) 445 nm) results from oxidation of the reagent. The kinetic parameters and the interferences are reported, and the method is applied to the determination of silver in developed panchromatic plates.     

Extractive spectrophotometry of the molybdenum (III) 1,10-phenanthroline thiocyanate and 2,2'-bipyridyl thiocyanate complexes

New extraction spectrophotometric methods for the determination of small amounts of molybdenum have been developed, using thiocyanate and 1,10-phenanthroline or 2,2'-bipyridyl as reagents in the presence of chlorostannous acid. Extracts of the ternary complexes of tervalent molybdenum in 1,2-dichloroethane obey Beer's law in the range 1-10 mug/ml at 525 nm. A 10-fold excess of iron and vanadium and 100-fold excess of tungsten, phosphorus and silicate do not interfere.     

Use of N-benzyl-2-naphthohydroxamic acid as a highly selective reagent for solvent extraction and spectrophotometric determination of vanadium(V)

N-Benzyl-2-naphthohydroxamic acid extracts vanadium(V) selectively and quantitatively into chloroform from 2-8.5M hydrochloric acid in the presence of Mo(VI), Zr(IV) and Ce(IV). The extraction takes place quickly and gives a stable reddish-violet extract which shows an absorption maximum at 505 nm with molar absorptivity of (5.34 +/- 0.05) x 10(3) 1.mole(-1).cm(-1). The optimum range for the determination is 2.2-7.4 ppm of vanadium(V) in the final solution. The method has been used for the determination of vanadium in steels.     

Sensing of trace copper ion by a solid phase extraction-spectrophotometry using a poly(vinyl chloride) membrane containing bathocuproine

A new sensitive and selective spectrophotometric method for the determination of trace copper using a poly(vinyl chloride) membrane containing 4,7-diphenyl-2,9-dimethyl-1,10-phenanthroline (bathocuproine) and o-nitrophenyl-octylether as the solid phase extraction medium. Copper(I) in an aqueous sample solution is trapped on the membrane with an anion species, picrate ion, to form copper(I)-bathocuproine-picrate complexes, and the copper complexes,i.e. copper(I), were concentrated in the membrane. The absorbance of the orange membrane was measured at 480 nm using a spectrophotometer, and the concentration of the copper was then calculated using a calibration graph, which expressed the relationship between the copper(I) concentration and the membrane absorbance after coloring for 10 min. The detectable concentration of copper in a sample solution was in the range of 1.5 x 10(-7)-4.3 x 10(-5)M. The reproducibility of the absorbances of membranes was 0.193 +/- 9.44 x 10(-3) with a 4.9% relative standard deviation on five repeated measurements for the sample containing 1.2 x 10(-5)M of copper(II) under the same experimental conditions.     

Ion-exchange separation and spectrophotometric determination of vanadium in environmental samples

A selective and sensitive method for the extraction and spectrophotometric determination of vanadium(V) in microgram quantities is described. The molar absorptivity of the yellow vanadium(V)-caffeic acid-Aliquat 336 extract is 1.3 x 10(4) 1.mole(-1).cm(-1) at 370nm. The method is compared with the atomic-absorption spectrometric method and applied to the trace determination of vanadium in steel, alloys, a rock and environmental samples.     

New colorimetric methods for the determination of trazodone HCl,famotidine, and diltiazem HCl in their pharmaceutical dosage forms

Two sensitive and simple spectrophotometric methods are developed for the determination of trazodone HCl, famotidine, and diltiazem HCl in pure and pharmaceutical preparations. The methods are based on the oxidation of the cited drugs with iron(III) in acidic medium. The liberated iron(II) reacts with 1,10-phenanthroline (method A) and the ferroin complex is colorimetrically measured at 510 nm against reagent blank. Method B is based on the reaction of the liberated Fe(II) with 2,2-bipyridyl to form a stable colored complex with lambda(max )at 520 nm. Optimization of the experimental conditions was described. Beer's law was obeyed in the concentration range of 1-5, 2-12, and 12-32 microg mL(-1) for trazodone, famotidine, and diltiazem with method A, and 1-10 and 8-16 microg mL(-1) for trazodone and famotidine with method B. The apparent molar absorptivity for method A is 1.06x10(5), 2.9x10(4), 1.2x10(4) and for method B is 9.4x10(4 )and 1.6x10(4), respectively. The suggested procedures could be used for the determination of trazodone, famotidine, and diltiazem, both in pure and dosage forms without interference from common excipients.     

High selective determination iron(II) by its enhancement effect on the fluorescence of pyrene-tetramethylpiperidinyl (TEMPO) as a spin fluorescence probe

A novel fluorescence method determination for iron(II) with a high selectivity and sensitivity has been proposed, based on the enhancement of fluorescence signals resulting from specific redox reaction between synthesized spin fluorescence probe pyrene-tetramethylpiperidinyl (TEMPO) and iron(II). Under the experimental conditions, fluorescent probe displayed a rapid and linear response for iron(II) over the concentration range from 2.4 x 10(-7) to 3.6 x 10(-6) mol/L. The limit of detection was 4.0 x 10(-8) mol/L. The relative standard deviation of six replicate measurements was 1.90% for 3.0 x 10(-7) mol/L iron(II). Because of the specific redox reaction between developed spin fluorescence probe and iron(II), there are few interference by other ions, especially in the presence of relative high concentration iron(III). The method has been successfully applied for iron(II) determinations in two different kinds of real samples. Results determined by the proposed method agree favorably with those determined UV-vis spectrometry method with 1,10-phenanthroline.     

Flow injection analysis for oxidation state speciation of vanadium(IV) and vanadium(V) in natural water.

A sensitive and simultaneous spectrophotometric flow injection method for the determination of vanadium(IV) and vanadium(V) is proposed. The method is based on the effect of ligands such as 2,4,6-tris(2-pyridyl)-1,3,5-triazine (TPTZ) and diphosphate on the conditional redox potential of iron(III)/iron(II) system. A four-channel flow system is assembled. In this flow system, diluted hydrochloric acid (1.0 x 10(-2) mol dm(-3)) as a carrier for standard/sample, acetate buffer (pH 5.5) as a carrier for diphosphate solution, an equimolar mixed solution of iron(III) and iron(II) and a TPTZ solution are delivered, so that the baseline absorbance can be established by forming a constant amount of iron(II)-TPTZ complex (lambda(max) = 593 nm). Vanadium(IV) and/or vanadium(V) (400 microL) and diphosphate (200 microL) solutions are simultaneously introduced into the flow system; in this system the diphosphate solution passes through a delay coil. The potential of the iron(III)/iron(II) system increases in the presence of TPTZ, and therefore vanadium(IV) is easily oxidized by iron(III) to vanadium(V) to produce an iron(II)-TPTZ complex (a positive peak for vanadium(IV) appears). On the other hand, the potential of the redox system decreases in the presence of diphosphate, so that vanadium(V) can be easily reduced by iron(II) to vanadium(IV). In this case, the amount of iron(II) decreases according to the amount of vanadium(V). As a result, the produced iron(II)-TPTZ complex decreases (a negative peak for vanadium(V) appears). In this manner, two peaks for vanadium(IV) and vanadium(V) can be alternately obtained. The limits of detection (S/N = 3) are 1.98 x 10(-7) and 2.97 x 10(-7) mol dm(-3) for vanadium(IV) and vanadium(V), respectively. The method is applied to the simultaneous determination of vanadium(IV) and vanadium(V) in commercial bottled mineral water samples.     

Potentiometric redox determination of gold(III) and its application to alloys

The simple potentiometric method proposed for the indirect determination of 1–10 mg of gold(III) is based on reduction to the metal with excess of cobalt(II) in the presence of 1,10-phenanthroline or 2,2'-bipyridine at pH 3 and 50°C, and titration of the unused cobalt(II) complex with iron(III) chloride solution. Many metal ions can be tolerated; Ag(I) and Pd(II) are eliminated by precipitation with sodium chloride and 1,10-phenanthroline or 2,2'-bipyridine, respectively, but Hg(II), Fe(III) and Pt(IV) interfere. The method is applied to the determination of gold in alloys.