Spectrophotometric determination of copper(II) using oximidobenzotetronic acid

Summary Oximidobenzotetronic acid (OBTA) is proposed as a sensitive spectrophotometric reagent for the estimation of 0.5–3.0 ppm of copper(II) at 427 nm in 50% dioxan at p_H 5.3–7.5. For the estimation of 2 ppm Cu(II), 1.3 ppm Ni(II), 1.3 ppm Co(II), 3.2 ppm Fe(II), 10.3 ppm Fe(III), 9.7 ppm Ce(IV), 300 ppm acetate, 160 ppm oxalate, 95 ppm tartrate, 50 ppm citrate, as well as Zn(II), Cd(II), Hg(II)) Pb(II), Mn(II), As(III) as well as (V), Th(IV), Be(II), Ce(III), La(III), V(V) and Mo(VI), even when present in large quantities, do not interfere. The interference due to 25 ppm Bi(III), 20 ppm Sb(III), 20 ppm Sn(II), 25 ppm Sn(IV) and 30 ppm W(VI) can be removed by the addition of 95 ppm tartrate ions.

---

Zusammenfassung Oximidobenzotetronsäure wurde als empfindliches Reagens zur spektrophotometrischen Bestimmung von 0,5 bis 3,0 ppm Kupfer(II) bei 427 nm in 50%iger Dioxanlösung bei p_H 5,3 bis 7,5 vorgeschlagen. Die Anwesenheit von 1,3 ppm Ni(II), 1,3 ppm Co(II), 3,2 ppm Fe(II), 10,3 ppm Fe(III), 9,7 ppm Ce(IV), 300 ppm Acetat, 160 ppm Oxalat, 95 ppm Tartrat, 50 ppm Citrat sowie die Anwesenheit auch großer Mengen Zn(II), Cd(II), Hg(II), Pb(II), Mn(II), As(III) bzw. (V), Th(IV), Be(II), Ce(III), La(III), V(V) und Mo(VI) stören die Bestimmung von 2 ppm Cu(II) nicht. Der störende Einfluß von 25 ppm Bi(III), 20 ppm Sb(III), 20 ppm Sn(II), 25 ppm Sn(IV) und 30 ppm W(VI) kann durch Zusatz von 95 ppm Tartrat beseitigt werden.

     

Spectrophotometric determination of vitamin E (alpha-tocopherol) using copper(II)-neocuproine reagent

A coated graphite-epoxy ion-selective electrode for bismuth(III), based on the ion-pair between the [Bi(EDTA)](-) anion and tricaprylylmethylammonium cation (Aliquat 336S) incorporated onto a poly(vinylchloride) (PVC) matrix is constructed. A thin membrane film of this ion-pair, dibutylphthalate (DBPh) or ortho-nitrophenyloctylether (o-NPOE) in PVC was deposited directly onto a Perspex(R) tube which contained a graphite-epoxy conductor substrate attached to the end of a glass tube. The coating solution was prepared by dissolving 30% (w/w) of PVC in 10 ml of tetrahydrofuran following addition of 65% (w/w) DBPh or o-NPOE and 5% (w/w) of the ionic pair. The effect of pH, EDTA concentration and some cation and anion on the electrode response is investigated. The bismuth(III) ion-selective electrode shows a linear response in the bismuth(III) concentration range from 1.0 x 10(-8) to 1.0 x 10(-1) mol 1(-1) and 1.0 x 10(-7) to 1.0 x 10(-1) mol 1(-1) and a slope of 56.8 and 59.2 mV dec.(-1) for the polymeric membranes containing DBPh and o-NPOE, respectively. The lifetime of this electrode was superior to 1 year (over 1600 determinations for each polymeric membrane), with practical detection limits of 6.3 x 10(-9) and 4.4 x 10(-8) mol 1(-1) with these plasticizers. Application of this electrode with bismuth(III) determination in a stomach anti-acid sample is described.     

Spectrophotometric determination of copper(II) with 3-thianaphthenoyltrifluoroacetone

Summary Two visible spectrophotometric methods are described for the determination of Copper(II) with 3-thianaphthenoyltrifluoroacetone at a pH of 4.0. The effect due to pH, time, solvents, reagent concentration and diverse ions are reported. Beer's law is obeyed in both cases and the molar extinction coefficients at 410 and 430 nm are 9.3·10² and 2.9·10² respectively.

---

Zusammenfassung Zwei spektrophotometrische Verfahren zur Bestimmung von Kupfer(II) mit 3-Thianaphthenoyltrifluoraceton bei pH 4,0 wurden beschrieben. Der Einfluß von pH, Zeit, Lösungsmitteln, Reagenskonzentration und von diversen Fremdionen wurde ermittelt. Das Beersche Gesetz ist in beiden Fällen erfüllt. Der molare Extinktionskoeffizient beträgt bei 410 bzw. 430 nm 9,3·10² bzw. 2,9·10².

     

A simple and selective flow-injection spectrophotometric determination of copper(II) by using acetylsalicylhydroxamic acid

A new simple, and rapid flow-injection spectrophotometric method is developed for the determination of trace amounts of Cu(II) by using a new chromogenic reagent acetylsalicylhydroxamic acid (AcSHA). The method is based on the formation of colored Cu(II)-(AcSHA)₂ complex. The optimum conditions for the chromogenic reaction of Cu(II) with AcSHA is studied and the colored (green) complex is selectively monitored at λ_max 700 nm. With the reagent carrier solvent (dimethylsulfoxide (DMSO) and acetate buffer, pH 4.2) flow-rate of 1 ml min⁻¹, a detection limit (2S) of 1 μg l⁻¹ Cu(II) was obtained at a sampling rate of 80 sample h⁻¹. The calibration graph was linear in the Cu(II) concentration range 5-120 μg l⁻¹. The relative standard deviation (n=10) was 0.64% for a sample containing 60 μg l⁻¹ Cu(II). The detailed study of various interferences confirmed the high selectivity of the developed method. The method was successfully applied to determine trace amounts of copper(II) in river and seawater samples. The accuracy of the method was demonstrated by the analysis of standard reference materials C12X3500 and C14XHS 50.     

Spectrophotometric determination of ascorbic acid using copper(II)-neocuproine reagent in beverages and pharmaceuticals

The proposed method for ascorbic acid (Vitamin C) (AA) determination is based on the oxidation of AA to dehydroascorbic acid with a Cu(II)-2,9-dimethyl-1,10-phenanthroline (neocuproine (Nc)) reagent in ammonium acetate-containing medium at pH 7, where the absorbance of the formed bis(Nc)-copper(I) chelate is measured at 450 nm. This chelate was formed immediately and the apparent molar absorptivity for AA was found to be 1.60 × 10⁴ dm³ mol⁻¹ cm⁻¹. Beer's law was obeyed between 8.0 × 10⁻⁶ and 8.0 × 10⁻⁵ M concentration range. The relative standard deviation for 90 μg AA was 3%. The Cu(II)-Nc reagent is a milder and therefore more selective oxidant than the conventional Fe(III)-1,10-phenanthroline (phen) reagent used for the same assay. This feature makes the proposed method superior for real samples such as fruit juices containing weak reductants such as citrate, oxalate and tartarate that otherwise produce positive errors in the Fe(III)-phen method when equilibrium is achieved. The developed method was applied to a number of commercial fruit juices, pharmaceutical preparations containing Vitamin C, and red wine. The meta-bisulfite content of wine was removed with an anion exchanger at pH 3 prior to analysis, and a difference extractive–spectrophotometric method of AA assay in wine was developed so as to suppress the interferences caused by wine anthocyanins and polyphenols. The findings of the developed method for fruit juices and pharmaceuticals were also statistically compared with those of HPLC so as to establish it as a reliable novel method.     

Spectrophotometric determination of cadmium(II) using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol

The complex of cadmium with the reagent 2-(-5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) has been studied. The composition, stability constant, and free energy change of formation of the complex have been determined. A sensitive spectrophotometric method for the determination of cadmium has been developed and applied for a range of concentration of 0.4–4.0 μg/ml cadmium using the complex Cd-5-Br-PADAP. The optimum conditions for maximum sensitivity of determination such as standing time, pH, wavelength, and order of addition have been determined. The effect of foreign ions on this method has been also studied.     

Spectrophotometric determination of nickel(II), palladium(II) and copper(II) in presence of each other and other ions with 1-(o-carboxyphenyl)-3-hydroxy-3-phenyltriazene

Summary 1-(o-Carboxyphenyl)-3-hydroxy-3-phenyltriazene was found to be an excellent spectrophotometric reagent for the determination of nickel(II), palladium(II) and copper(II). At pH 6.8–8.3, 2.4–3.5 and 2.2–3.8, nickel, palladium and copper form greenish yellow, yellowish orange and light green complexes with maximum absorption at 410, 410, 400 nm, respectively. The systems obey Beer's law with optimum ranges from 0.25 to 2.0 ppm for Ni(II), 0.5–4.0 for Pd(II) and 0.5–4.0 for Cu(II); the elements form 11 complexes with the instability constants 2.1×10^–5, 1.5×10^–5 and 2.0×10^–5, resepctively. Effects of other anions and cations on the colour systems have been studied and procedures for the determination of Ni(II), Pd(II) and Cu(II) in presence of each other are described.

---

Spektrophotometrische Bestimmung von Nickel(II), Palladium(II) und Kupfer(II) nebeneinander und in Gegenwart anderer Ionen mit Hilfe von 1-(o-Carboxyphenyl)-3-hydroxy-3-phenyltriazen

Zusammenfassung Ni, Pd und Cu bilden mit dem Reagens bei pH 6,8–8,3, 2,4–3,5 bzw. 2,2–3,8 grünlich-gelbe, gelblich-orange bzw. hellgrüne Komplexe mit Absorptionsmaxima bei 410, 410 bzw. 400 nm. Das Beersche Gesetz wird in den Bereichen 0,25–2,0, 0,5–4,0 bzw. 0,5–4,0 ppm befolgt. Die Elemente bilden 11-Komplexe mit den Instabilitätskonstanten 2,1 · 10^–5, 1,5 · 10^–5 bzw. 2,0 · 10^–5. Der Einfluß anderer Kationen und Anionen wurde untersucht und Arbeitsvorschriften werden angegeben.

     

Simultaneous spectrophotometric determination of copper(II) and zinc(II) based on their kinetic separation in flow-injection systems

Flow-injection methods are developed for the spectrophotometric analysis of binary copper(II) and zinc(II) mixtures. They are based on measurements of a differential kinetic signal caused by ligand-exchange reactions that occur in the flow between the complexes of these metals with the same chromogenic reagent (4-(2-pyridylazo)-resorcinol or zincon) and aminopolycarboxylic acids. Two different approaches are used for the kinetic separation (or masking) of these metals followed by the on-line processing of the recorded signal by regression analysis. One of them is monitoring an indicator reaction in the stopped-flow mode, and the other is recording the separated peaks in the flow-injection system with two reaction zones reaching the detector over certain periods. The optimum detection conditions were found (c _min = 0.03 μg/mL), which allow the detection of the studied metal ions in mixtures in a ratio of no more than 1: 5 with a relative error of no more than 5%, good precision (RSD < 10%, n = 6, P = 0.95), and high throughput (90 h^?1). The developed procedures were tested in the analysis of model mixtures and pharmaceutical preparations.     

Spectrophotometric flow-injection analysis of mercury(II) in pharmaceuticals with p-nitrobenzoxosulfamate

A new, simple and rapid spectrophotometric FI method for the accurate and precise determination of Hg(II) in pharmaceutical preparations has been developed. The method is based on the measuring the decrease of absorbance intensity of p-nitrobenzoxosulfamate (NBS) due to the complexation with Hg(II). The absorption peak of the NBS, which is decreased linearly by addition of Hg(II), occurs at 430 nm in 2×10⁻⁴ mol l⁻¹ HNO₃ as a carrier solution. Optimization of chemical and FI variables has been made. A micro column consisting of several packing materials applied instead of reaction coil was also investigated. A background level of Fe(III) maintained in reagent carrier solution with NBS was found useful for sensitivity and selectivity. Under the optimized conditions, the sampling rate was over 100 h⁻¹, the calibration curve obtained were linear over the range 1-10 μg ml⁻¹, the detection limit was lower than 0.2 μg ml⁻¹ for a 20 μl injection volume, and the precision [S_r=1% at 2 μg ml⁻¹ Hg(II) (n=10)] was found quite satisfactory. Application of the method to the analysis of Hg(II) in pharmaceutical preparations resulted a good agreement between the expected and found values.     

Spectrophotometric determination of traces of selenium(IV) in various environmental samples using the flow-injection technique (FIT)

A simple, sensitive, and rapid flow-injection spectrophotometric method was developed for the determination of trace amounts of selenium(IV). The method is based on the oxidation reaction of 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) by selenium(IV) followed by the coupling reaction with chromotropic acid (4.5-dihydroxy naphthalene-2.7-disulphonic acid) in a basic medium (phosphate buffer, pH 10.5) to give a pink derivative with λ_max 530 nm that is stable for more than 7 days at 35°C. The reaction and flow conditions of the full experimental design were optimized. A detection limit (2s) of 0.25 μg/L Se(IV) was obtained at a sampling rate of 10 samples per hour. Beer’s law is obeyed for a Se(IV) concentration range of 0.05–0.5 μg/mL at the wavelength of maximum absorption. The detailed study of various interference ions indicates that the method is highly selective. The method was successfully applied to the determination of traces of selenium(IV) in various water samples. The results obtained were in good agreement with those obtained by the reported methods at the 95% confidence level. The text was submitted by the authors in English.     

Sequential flow-injection spectrophotometric determination of iron(II) and iron(III) by copper(II)-catalyzed reaction with Tiron

A flow injection method for the sequential determination of iron(II) and iron(III) was developed. It is based on the differential reaction kinetics of iron(II) and iron(III) with Tiron in a double-injection FI system. The proposed method employs the accelerating action of copper(II) for the oxidation of iron(II) in the presence of Tiron. A linear calibration graph is obtained for iron (II) and iron(III) in the concentration range 1.8 × 10^–5– 1.8 × 10^–4 mol/L; the throughput of samples is 30 injections/h.     

Spectrophotometric determination of uranium(VI) with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol in a flow-injection system

The direct determination of uranium(VI) by a flow-injection procedure is based on spectrophotometric measurement with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol in the present of fluoride. The interfering effects of many commonly occuring elements were studied. The calibration curve was linear over the range 0.5–20 mg 1^?1 uranium(VI). The relative standard deviation obtained on a leach liquor containing 10 mg 1^?1 uranium(VI) was 1.9%. The procedure is rapid and convenient, and up to 40 samples can be analysed per hour.