Kinetic spectrophotometric determination of traces of iron(II)

A simple method for the selective and sensitive kinetic spectrophotometric determination of iron (II) is described. The method is based on the oxidation reaction of reduced phenolphthalein by periodate in alkaline media. The change in absorbance was measured using the fixed time method. The effect of different variables on the reaction was investigated and optimum conditions were obtained. The calibration curve was linear in the range 50–3000 ng/mL, and a detection limit of 17 ng/mL was obtained. The relative standard deviation of ten replicate determinations of 200 ng/mL of Fe(II) was 1.2%. The determination of Fe(II) in the presence of a 50-fold amount of Fe(III) could be carried out. This article was submitted by the authors in English.     

Catalytic kinetic spectrophotometric determination of trace amounts of palladium with dahlia violet after separation and preconcentration on sulphydryl dextran gel

A sensitive and selective kinetic catalytic spectrophotometric method has been described for the determination of trace amounts of palladium(II). The method is based on the catalytic effects of palladium(II) on the reduction reactions of Dahlia Violet with sodium dihydrogen hypophosphite (NaH₂PO₂) in a sulfuric acid medium. Under optimal conditions, trace amounts of palladium(II) can be determined. A good linear range has been obtained in the concentration range of Pd(II) over 0.001–0.028 μg/mL with a detection limit of 5.9 × 10⁻¹⁰ g/mL. The method has been successfully applied to the determination of palladium(II) in ore and soil samples. The relative standard deviation was less than 5.0% (n = 11). The coexisting ions were eliminated by preconcentration and separation on sulphydryl dextran gel with satisfactory results. The text was submitted by the authors in English.     

Catalytic determination of ultra trace amounts of palladium by linear sweep voltammetry

A sensitive method is proposed for the determination of palladium, based on its catalytic effect on the reduction of malachite green by hypophosphite. The reaction rate is monitored by measuring the current of product of reaction at −0.79 V vs. Ag/AgCl reference electrode. The linear dynamic range is 30.0–300.0 ng/mL with a limit of detection of 10.0 ng/mL. The interference effects of many ions were studied. The method was used for the determination of Pd(II) in synthetic samples of dental alloys with satisfactory results.     

Kinetic spectrophotometric method for the determination of selenium(IV) by its catalytic effect on the reduction of spadns by sulphide in micellar media

A simple kinetic spectrophotometric method was developed for the determination of ultratrace amounts of Se(IV). The method is based on the reduction of spadns by sulphide in micellar media. The reaction was monitored spectrophotometrically by measuring the decrease in the absorbance of spadns at 515 nm with a fixed-time method. The decrease in the absorbance of spadns is proportional to the concentration of Se(IV) in the range 0.5–100 ng/mL with a fixed time of 2.5–7.0 min from the initiation of the reaction. The limit of detection is 0.3 ng/mL Se(IV). The relative standard deviation for the determination of 0.02 and 0.10 μg/mL Se(IV) was 2.10 and 1.95%, respectively. The method was applied to the determination of Se(IV) in water. The text was submitted by the authors in English.     

Extraction–thermal lens quantification of cobalt with Nitroso-R-Salt in two-phase aqueous systems with water-soluble polymer polyethylene glycol

A novel method is proposed for the extraction-thermal lens quantification of cobalt with Nitroso-R-Salt based on the distribution of the colored complex in a two-phase aqueous system on the basis of poly-ethylene glycol (PEG) and an ammonium sulfate solution followed by its thermal lens detection in the extract. The limit of detection is 0.3 μM (20 ng/mL); the lower limit of the analytical range is 0.7 μM (40 ng/mL); the relative standard deviation for the concentrations 1–50 μM makes 1–3% (n = 6, P = 0.95). In the determination of cobalt by spectrophotometry under the same conditions, the detection limit is 10 μM (0.6 μg/mL) and the lower limit of the analytical range is 40 μM (2.5 μg/mL). The precision of thermal lens measurements in PEG solutions is higher in comparison to that in aqueous ones because of the weaker interference of convection in aqueous solutions of PEG.     

Modified analcime loaded with zincon as a useful material for the separation and preconcentration of trace palladium and its determination by third-derivative spectrophotometry

This work assesses the potential of natural analcime zeolite as a sorbent for the preconcentration of palladium. Palladium is quantitatively retained on modified analcime zeolite loaded with zincon using the column method in the pH range from 2.5 to 3.5 at a flow rate of 1 mL/min. The palladium complex was removed from the column with 5.0 mL of dimethylsulfoxide (DMSO) and determined by third-derivative spectrophotometry. The detection limit is 0.03 μg/mL (signal-to-noise ratio = 3) in the final solution. Since it is possible to retain 0.15 μg of palladium from 600 mL of solution passing through the column, elution with 5.0 mL of DMSO gives a detection limit of 0.25 ng/mL for palladium in the initial aqueous solution. The calibration curve is linear over the range 0.1 to 5.0 μg/mL of palladium(II) in the final solution with a correlation coefficient of 0.9996. Seven replicated determinations of 5.0 μg of palladium in 5.0 mL dimethylsulfoxide gave a mean d ³ A/dλ³ (peak-to-peak signal between λ₂ = 625 and λ₁ = 654 nm) of 0.64 with a relative standard deviation of 1.2%. The sensitivity of the method (d ³ A/dλ³) is 0.5843 mL/μg of palladium(II) from the slope of the calibration curve. The interference of a large number of anions and cations has been studied and the optimized conditions developed were utilized for the determination of trace palladium in various synthetic and water samples. The text was submitted by the authors in English.     

Spectrophotometric determination of nickel in biological samples using 1-azobenzene-3-(3-hydroxyl-2-pyridyl)-triazene

A new sensitive and selective chromogenic reagent, 1-azobenzene-3-(3-hydroxyl-2-pyridyl)-triazene (ABHPT), was synthesized. It has been found that ABHPT reacts with nickel(II) in a borax buffer solution (pH 10.0) to form 2: 1 red complexes with the maximum absorption at 530 nm. The apparent molar absorptivity of the complex is 2.6 × 10⁵ L/(mol cm). Most metal ions can be tolerated in considerable amounts, whereby only zinc and mercury may interfere with the determination of nickel(II). Nevertheless, this can be easily eliminated by prior separation with sulfhydryl dextran gel. A new method for the spectrophotometric determination of trace nickel(II) was developed. Beer’s law is obeyed for 0–15 μg of nickel(II) in 25 mL of solution. The limit of quantification, limit of detection, and relative standard deviation are 0.74 ng/mL, 0.25 ng/mL, and 1.0%, respectively. The method has been applied to the determination of trace nickel(II) in biological samples with satisfactory results. The text was submitted by the authors in English.     

Determination of cobalt by catalytic-adsorptive differential pulse voltammetry in the presence of 2-aminocyclopentene-1-dithiocarboxylic acid and nitrite

A novel method for the determination of cobalt(II) by stripping voltammetry is described. It involves an adsorptive accumulation of the cobalt(II)-2-aminocyclopentene-1-dithiocarboxylic acid complex on a hanging mercury drop electrode, followed by a stripping voltammetric measurement of the catalytic reduction current of the complex at –1.4 V at pH = 9 (vs. Ag/AgCl). The effects of various experimental parameters on the catalytic current were investigated. An accumulation time of 60 s results in a low experimental limit of detection of 0.1 ng/mL of Co(II), and 0.50 to 40.0 ng/mL of cobalt can be determined. The relative standard deviation at 0.50 ng/mL is 2.8%. Possible interferences from co-existing ions were also investigated. Received: 17 August 1998 / Revised: 16 November 1998 / Accepted: 20 November 1998     

Determination of cobalt by catalytic-adsorptive differential pulse voltammetry in the presence of 2-aminocyclopentene-1-dithiocarboxylic acid and nitrite

A novel method for the determination of cobalt(II) by stripping voltammetry is described. It involves an adsorptive accumulation of the cobalt(II)-2-aminocyclopentene-1-dithiocarboxylic acid complex on a hanging mercury drop electrode, followed by a stripping voltammetric measurement of the catalytic reduction current of the complex at –1.4 V at pH = 9 (vs. Ag/AgCl). The effects of various experimental parameters on the catalytic current were investigated. An accumulation time of 60 s results in a low experimental limit of detection of 0.1 ng/mL of Co(II), and 0.50 to 40.0 ng/mL of cobalt can be determined. The relative standard deviation at 0.50 ng/mL is 2.8%. Possible interferences from co-existing ions were also investigated. Received: 17 August 1998 / Revised: 16 November 1998 / Accepted: 20 November 1998     

Determination of lead traces in water and liqueurs by derivative atom trapping flame atomic absorption spectrometry

 A new method for the direct determination of lead traces using derivative atom trapping flame atomic absorption spectrometry (DAT-FAAS) with an improved water-cooled stainless steel trapping equipment in an air-acetylene flame was investigated. The optimum conditions concerning the sensitivity were studied. For a 1 min collection, the characteristic concentration (given as derivative absorbance of 0.0044) and the detection limit (3s) were 1.4 ng/mL and 0.27 ng/mL, respectively. This is 361 and 74-fold better than those of the conventional flame atomic absorption spectrometry (FAAS) and comparable to those of graphite furnace atomic absorption spectrometry (GFAAS). The detection limit and sensitivity of DAT-FAAS for a 3 min collection time were 2 and 3 orders of magnitude higher than those of conventional FAAS. The present method was applied to the determination of lead in water and liqueur samples with a recovery range of 94–108% and a relative standard deviation of 3.5–5.6%. Received: 10 January 1996/Revised: 9 December 1996/Accepted: 20 December 1996     

Simultaneous spectrophotometric determination of trace amounts of cobalt, nickel, and copper using the partial least-squares method after the preconcentration of their 2-aminocyclopentene-1-dithiocarboxylate complexes on microcrystalline naphthalene

A spectrophotometric method for the determination of trace amounts of cobalt(II), nickel(II), and copper(II) after the adsorption of their 2-aminocyclopentene-1-dithiocarboxylate complexes on microcrystalline naphthalene has been developed. These complexes are adsorbed on microcrystalline naphthalene at pH 4.5 by shaking for 5 min. The formed solid mass is separated by filtration, and dissolved in dimethylformamide. The absorption spectra were processed using the partial least-squares multivarate calibration method for the analysis of a ternary mixture of Co(II), Ni(II), and Cu(II). The detection limits for Co(II), Ni(II), and Cu(II) were 3.3, 10.0, and 0.8 ng/mL, respectively. The total relative standard error for applying the method to 20 synthetic samples in the concentration ranges of 20–400 ng/mL Co(II), 60–400 ng/mL Ni(II), and 4–400 ng/mL Cu(II) was 1.53%. The proposed method was also successfully applied to the determination of Co(II), Ni(II), and Cu(II) in alloys. The text was submitted by the authors in English.     

Determination of vitamin B12 in pharmaceutical preparations by a highly sensitive fluorimetric method

A fluorimetric method for the determination of vitamin B₁₂ has been developed. The fluorescence emission was measured at λ_ex/λ_em275/305 nm in phosphate buffer solution (pH 7.0), and the experimental variables and possible interference were studied. The linear calibration range was 1.000 ng/mL to 100.0 ng/mL with a correlation coefficient of 0.9994 and a detection limit of 0.1 ng/mL. The method is rapid, simple and highly sensitive. It was used to determine vitamin B₁₂ in pharmaceutical preparations. The recovery was 96%–98% and the relative standard deviation was in the range of 1.8%–2.7%. The results agreed with those obtained by spectrophotometry. Received: 17 July 2000 / Revised: 4 September 2000 / Accepted: 7 September 2000     

Determination of vitamin B<Subscript>12</Subscript> using a chemiluminescence flow system

A method to determine vitamin B₁₂ by measuring the chemiluminescence (CL) intensities using a flow injection (FI) system has been proposed. It is based on the catalytic effect of cobalt(II) in vitamin B₁₂ on the CL reaction between luminol and hydrogen peroxide in a basic medium. The increment of the CL intensity is proportional to the concentration of vitamin B₁₂ in the range 8.68–86.9 ng/mL (r ² = 0.9984) with a detection limit (3σ) of 0.89 ng/mL. The CL response is obtained in 10 s at a flow rate of 3.0 mL/min with a relative standard deviation (RSD) of less than 2.5% (n = 6). The method has been successfully applied to the determination of vitamin B₁₂ in pharmaceutical injections. The text was submitted by the authors in English.     

Kinetic-spectrophotometric determination of Sb(V) based on its reaction with iodide in the presence of methylene blue

A rapid, simple, and sensitive kinetic method is developed for the determination of trace amounts of Sb(V). The method is based on the reaction of Sb(V) with iodide in acidic media in the presence of methylene blue. The reaction was monitored spectrophotometrically by measuring the decrease in the absorbance at 664 nm by a fixed-time technique of 60 s. The method allowed the determination of Sb(V) at concentrations between 0.01 and 2.2 μg/mL. The limit of detection was 0.006 μg/mL and the relative standard deviation for ten replicate measurements of 0.5 μg/mL Sb(V) was 1.2%. The method was applied to the determination of Sb(V) in tap water and spring water with satisfactory results. The text was submitted by the authors in English.     

Sensitive reaction rate method for the determination of low levels of formaldehyde with photometric detection

A simple and rapid method is proposed for the determination of ultra trace amounts of formaldehyde. It is based on the catalytic effect of formaldehyde on the oxidation of Brilliant cresyl blue by bromate. The reaction is monitored photometrically by measuring the decrease in absorbance of the dye. Formaldehyde in the range of 0.005–2.300 μg/mL can be determined with a limit of detection of 0.003 μg/mL. The relative standard deviation for ten replicate measurements of 1.5 μg/mL formaldehyde is 0.1%. The method was used for the determination of formaldehyde in real samples with satisfactory results. Received: 26 May 1998 / Revised: 30 September 1998 / Accepted: 3 October 1998     

Flame atomic absorption spectrometric determination of trace amounts of palladium,gold and nickel after cloud point extraction

In this article, a sensitive cloud point extraction procedure for the preconcentration of trace amounts of palladium, gold and nickel prior to their determination by flame atomic absorption spectrometry has been developed. The cloud point extraction method is based on the complexation of Pd(II), Au(II), and Ni(II) ions with 1-(2-pyridylazo)-2-naphthol and entrapping in non-ionic surfactant Triton X-114. The main factors affecting cloud point extraction efficiency, such as pH of sample solution, concentration of 1-(2-pyridylazo)-2-naphthol and Triton X-114, equilibration temperature and time, were investigated in detail. Under the optimized conditions, calibration curves were constructed for the determination of palladium, gold and nickel according to the general procedure. Linearity was maintained from 0.01 to 1.0 μg/mL for palladium, 10.0 μg/mL to 1.5 μg/mL for gold, and 10.0 μg/mL to 0.5 μg/mL for nickel. Detection limits based on three times the standard deviation of the blank divided by the slope of analytical curve (3Sb/m) for Pd(II), Au(III), and Ni(11) ions were 3.4, 3.9, and 2.4 μg/mL, respectively. Seven replicate determination of a mixture of 0.5 μg/mL palladium and gold and 0.2 μg/mL nickel gave a mean absorbance of 0.174, 0.150, and 0.201 with relative standard deviation ±1.5, ±1.3, and ±1.8%, respectively. The high efficiency of cloud point extraction to carry out the determination of analytes in complex matrices was demonstrated. The proposed method has been applied for determination of trace amount of palladium, gold and nickel in certified reference material and water samples with satisfactory results.     

Determination of copper in sulfide minerals by Zeeman electrothermal atomic absorption spectrometry

A method for the determination of copper in some sulfide minerals (lorandite, realgar, orpiment, marcasite, stibnite, galenite and sphalerite) by Zeeman electrothermal atomic absorption spectrometry is presented. After the dissolution of samples, copper was extracted with sodium diethyldithiocarbamate into different organic solvents (carbon tetrachloride, chloroform and methylisobutyl ketone) at pH 11.0–12.0. The procedure was verified by standard addition. The standard deviation (SD) for 0.5 ng Cu is 0.01 ng, the relative standard deviation ranges from 3.5 to 5.5% and the detection limit of the method, calculated as 3 SD of the blank, was found to be 0.05 μg · g^–1. Received: 26 May 1997 / Revised: 10 September 1997 / Accepted: 16 September 1997     

Chemiluminescence flow system for the determination of Fe(II) and Fe(III) in water

A novel chemiluminescence (CL) flow system has been developed for the sequential determination of Fe(II) and Fe(III) in water. Fe(II) was detected by its catalytic effect on the CL reaction between luminol immobilized on an anion exchange resin column and dissolved oxygen; Fe(III) was determined by difference measurement after on-line conversion to Fe(II) in a reducing mini-column packed with Cu plated Zn granules. For both ions, the calibration graph was linear in the range 1 × 10^–9 to 1 × 10^–6 g/mL, and the detection limit was 4 × 10^–10 g/mL. A complete analysis could be performed in 1.5 min with a relative standard deviation of less than 5%. The system could be reused for over 200 times and has been applied successfully to the determination of Fe(II) and Fe(III) in natural water samples. Received: 13 March 1997 / Revised: 3 June 1997 / Accepted: 6 June 1997     

Determination of guaiphenesin and sodium benzoate in Liqufruta garlic cough medicine by high performance liquid chromatography

A new and simple isocratic high-performance liquid chromatographic method with ultraviolet detection is described for simultaneous determination of active guaiphenesin and preservative sodium benzoate in Liqufruta garlic cough medicine formulation. The chromatographic separation was achieved using a Zorbax CN; 150 mm × 4.6 mm and 5 μm particle size column employing acetonitrile and water (20: 80, v/v) containing 0.1% formic acid (pH 3.5 ± 0.05) as the mobile phase. The method was validated with respect to linearity, range, precision, accuracy, specificity, limit of detection and limit of quantitation. The both analytes were detected by UV-Vis detector at 245 nm. The method was linear over the concentration range of 0.2–0.8 mg/mL and 0.02–0.06 mg/mL for guaiphenesin and sodium benzoate, respectively. The limit of detection was found to be 0.14 μg/mL for GP and 0.06 μg/mL for SB and the quantification limit was 0.54 μg/mL for GP and 0.22 for SB. Accuracy, evaluated as recovery, was in the range of 97.8–100.0%. Intra-day precision and intermediate precision showed relative standard deviation <1% in each case.     

Rapid determination of subnanogram urapidil using flow injection enhancement chemiluminescence

A sensitive flow-injection (FI) chemiluminescence (CL) for the determination of urapidil is described in this paper. It is based on the enhancement effect of urapidil on the CL reaction between luminol and hydrogen peroxide. The increment of CL intensity is proportional to the concentration of urapidil in the range 0.1−10 ng/mL (R ²=0.9986), with a detection limit (3σ) of 0.03 ng/mL. The whole process, at a flow rate of 2.0 mL/min, including sampling and washing, could be completed in 0.5 min, and the relative standard deviation (RSD) at the concentration of 0.1, 1.0, and 10.0 ng/mL was less than 3.0% (n = 5). The proposed method has been successfully applied for the determination of urapidil in pharmaceutical preparation, human urine, and serum. The text was submitted by the authors in English.