Simultaneous determination of trace uranium(VI) and zinc(II) by adsorptive cathodic stripping voltammetry with aluminon ligand

Uranium(VI) complexed with aluminon (3-[bis(3-carboxy-4-hydroxy-phenyl)methylene]-6-oxo-1,4-cyclohexadiene-1-carboxylic acid triammonium salt) was determined by adsorptive cathodic stripping voltammetry (ACSV) using a hanging mercury drop electrode. Trace uranium(VI) and zinc(II) can be simultaneously determined in a single scan in the presence of aluminon and urea. Optimal conditions were found to be: accumulation time; 180–200 s, accumulation potential; 50 mV versus Ag/AgCl, scan rate; 40 mV s⁻¹, supporting electrolyte; 0.1 M sodium acetate buffer at pH 6.5–7.0, and concentration of aluminon; 1×10⁻⁶ M. The linear range of uranium(VI) and zinc(II) were observed over the concentration range 2–33 and 30–120 ng ml⁻¹, respectively. The detection limit (S/N=3) are 0.2 ng ml⁻¹ (uranium) and 30 ng ml⁻¹ (zinc). A good reproducibility shows RSDs of 2.5–4.0% (n=10). The procedure offers high selectivity, with the presence of urea masking some metal ions.     

A sensitive flow-injection method for determination of trace amounts of nitrite

A new sensitive colour reaction for nitrite determination is presented. In acidic medium, nitrite was reacted with safranine to form a diazonium salt which caused the reddish-orange dye colour of the solution to change to blue. The carrier stream, into which the sample solution was injected, was doubly distilled water. The reagent solution stream, which contained safranine dye, hydrochloric acid and potassium chloride, was mixed with the carrier in a 3-m length of silicon tubing (bore 0.5 mm) maintained at 30°C in a thermostatic bath. The absorbance intensity was measured at 520 nm. The detection limit was 20 ng ml⁻¹ and the RSD% of 20 injections of 1 μg ml⁻¹ of nitrite was 0.65%. Analysis can be done at a rate of up to 30 h⁻¹. Under the optimum conditions in the concentration range of 30–4000 ng ml⁻¹ of nitrite ion, a linear calibration graph was obtained (r=0.9999). The method was applied successfully to the determination of nitrite in sausages.     

Spectrophotometric determination of nitrate and nitrite in soil and water samples with a diazotizable aromatic amine and coupling agent using column preconcentration on naphthalene supported with ion-pair of tetradecyldimethylbenzylammonium and iodide

Composite diazotization-coupling reagents containing sulfanilamide (SAM), sulfapyridine (SP) or sulfathiazole (ST) as the diazotizable aromatic amines and sodium 1-naphthol-4-sulfonate (NS) as the coupling agent using column preconcentration on naphthalene-tetradecyldimethylbenzylammonium(TDBA)-iodide adsorbent have been used for the spectrometric determination of trace nitrate and nitrite in soil and water samples. Nitrite ion reacts with SAM in the pH range 2.0–5.0, SP in the pH range 2.0–2.5 and ST in the pH range 2.0–3.3 in HCl medium to form water-soluble colourless diazonium cations. These cations were coupled with NS in the pH range 9.0–12.0 for the SAM system, 9.6–12.0 for the SP system and 8.5–12.0 for the ST system to be retained on naphthalene-TDBA-I material packed in a column. The solid mass is dissolved from the column with 5 ml of dimethylformamide and the absorbance is measured spectrometerically at 543 nm for SAM-NS, 533 nm for SP-NS and 535 nm for ST-NS. Nitrate is reduced to nitrite by a copper-coated cadmium reductor column and the nitrite is then treated with the diazotization-coupling reagent by column preconcentration. The absorbance due to the sum of nitrate and nitrite is measured and nitrate is determined by difference. The calibration graph was linear over the range 2–40 ng NO₂⁻-N ml⁻¹ and 1.5–30 ng NO₃⁻-N ml⁻¹ in aqueous samples for the SAM and ST systems and 2–48 ng NO₂⁻-N ml⁻¹ and 1.5–36 ng NO₃⁻-N ml⁻¹ in aqueous samples for the SP system, respectively. The sensitivity, accuracy and precision of the systems decreased in the order STSAMSP. The detection limits were 1.4 ng NO₂⁻-N ml⁻¹ and 1.1 ng NO₃⁻-N ml⁻¹ for SAM, 1.6 ng NO₂⁻-N ml⁻¹ and 1.2 ng NO₃⁻-N ml⁻¹ for SP, and 1.0 ng NO₂⁻-N ml⁻¹ and 0.75 ng NO₃⁻-N ml⁻¹ for ST, respectively. The preconcentration factors are 8, 5 and 6 for SAM-NS, SP-NS and ST-NS, respectively. Interferences from various foreign ions have been studied and the methods have been applied to the determination of ng ml⁻¹ levels of nitrite and nitrate in soil and water samples. The mean recovery was 95–102% for all three systems.     

Simple flow-injection system for the simultaneous determination of nitrite and nitrate in water samples

A novel spectrophotometric reaction system was developed for the determination of nitrite as well as nitrate in water samples, and was applied to a flow-injection analysis (FIA). The spectrophotometric flow-injection system coupled with a copperised cadmium reductor column was proposed. The detection was based on the nitrosation reaction between nitrite ion and phloroglucinol (1,3,5-trihydroxybenzene), a commercially available phenolic compound. Sample injected into a carrier stream was split into two streams at the Y-shaped connector. One of the streams merged directly and reacted with the reagent stream: nitrite ion in the samples was detected. The other stream was passed through the copperised cadmium reductor column, where the reduction of nitrate to nitrite occurred, and the sample zone was then mixed with the reagent stream and passed through the detector: the sum of nitrate and nitrite was detected. The optimised conditions allow a linear calibration range of 0.03–0.30 μg NO₂⁻-N ml⁻¹ and 0.10–1.00 μg NO₃⁻-N ml⁻¹. The detection limits for nitrite and nitrate, defined as three times the standard deviation of measured blanks are 2.9 ng NO₂⁻-N ml⁻¹ and 2.3 ng NO₃⁻-N ml⁻¹, respectively. Up to 20 samples can be analyzed per hour with a relative standard deviation of less than 1.5%. The proposed method could be applied successfully to the simultaneous determination of nitrite and nitrate in water samples.     

Catalytic determination of cobalt at sub-nanogram levels using the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone with N-ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline by manual and flow-injection methods

A catalytic photometric method was developed for the determination of sub-nanogram levels of cobalt. The method is based on the catalytic effect of cobalt(II) on the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone with N-ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline (DAOS) to form a colored dye (λ_max=525 nm) in the presence of hydrogen peroxide. In this reaction system, 1,2-dihydroxybenzene-3,5-disulfonate (Tiron) acted as an effective activator for the catalysis of cobalt(II). Variation of reaction time between 5 and 10 min allows the determination range to be extended from 0.01 to 1.0 ng ml⁻¹. The reaction system can also be successfully adapted to flow-injection analysis (FIA). The dynamic range of the proposed flow-injection method was 0.01–1.0 ng ml⁻¹ and detection limit (signal/noise, S/N=3) was 5 pg ml⁻¹ at a sampling rate of 30 h⁻¹. Manual and flow-injection methods were applied to the direct determination of cobalt in pepperbush as a standard material.     

Spectrophotometric determination of nitrite based on its catalytic effect on the oxidation of carminic acid by bromate

A highly sensitive and selective method is described for the determination of trace amounts of nitrite based on its effect on the oxidation of carminic acid with bromate. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of carminic acid at 490 nm after 3 min of mixing the reagents. The optimum reaction conditions were 1.8×10⁻¹ mol l⁻¹ H₂SO₄, 3.8×10⁻³ mol l⁻¹ KBrO₃, and 1.2×10⁻⁴ mol l⁻¹ carminic acid at 30°C. By using the recommended procedure, the calibration graph was linear from 0.2 to 14 ng ml⁻¹ of nitrite; the detection limit was 0.04 ng ml⁻¹; the R.S.D. for six replicate determinations of 6 ng ml⁻¹ was 1.7%. The method is mostly free from interference, especially from large amounts of nitrate and ammonium ions. The proposed method was applied to the determination of nitrite in rain and river water.     

Flow injection determination of nitrite by fluorescence quenching

A simple, sensitive and selective fluorimetric method for the determination of nitrite ion in waters using a merging zones flow injection system is described. The fluorimetric determination is based on the measurement of the quenching effect produced by nitrite on proflavine (3,6-diaminoacridine) fluorescence (λ_ex/λ_em=290/519 nm).

The optimum experimental conditions were investigated by merging 0.5 ml of the sample and 0.5 ml of a solution of 5 mg l⁻¹ of proflavine (in 0.1 M HCl) in a flow injection system, on-line connected to a flow-cell placed in the conventional sample compartment of a spectrofluorimeter. The selected carrier solution and final flow rate were 0.1 M HCl and 0.5 ml min⁻¹, respectively. A reaction coil of 2 ml was used. As a result of the simplicity of this system, a sample throughput of about 50 samples h⁻¹ can be achieved with the proposed methodology.

The detection limit was 1.1 ng ml⁻¹ (3σ criterion) of nitrite. The repeatability for five sample injections containing 100 ng ml⁻¹ of nitrite was ±0.3% and the observed linear range extended up to 400 ng ml⁻¹. Also, the effect of interferences from various metals and anions commonly present in waters was also studied.

The method was successfully applied to the determination of low levels of nitrite in different water samples (river, fountain, tap and commercial drinking waters).     

Catalytic method for the determination of traces of tungsten by linear scan voltammetry

A novel, sensitive and selective catalytic method for the determination of tungsten is described, based on the W(VI-catalysed redox reaction between methyl red and Ti(III) in a hydrochloric acid medium; methyl red exhibits a sensitive oscillopolarographic wave at −0.68 V vs. SCE in NaOH solution. A calibration graph from 3.2 to 72 ng ml⁻¹ W (detection limit 1.1 ng ml⁻¹) is obtained by the fixed-reaction time procedure. The influence of 29 foreign ions on the catalytic determination of W was examined; none interfered at < 100-fold excess. The method is used to determine W in steel and ore samples, with satisfactory results.     

Extraction and spectrophotometric determination of cobalt(II) with isonitroso-5-methyl-2-hexanone

A simple and selective method is proposed for the extraction of cobalt(II) for its spectrophotometric determination using (HIMH) as an extractant. Cobalt(II) forms a yellow coloured complex with HIMH which can be extracted into chloroform. The calibration curve is rectilinear in the concentration range 0.1–5.0 μg ml⁻¹ of cobalt(II). The extracted species shows an absorption maximum at 400 nm with molar absorptivity of 1.135×10⁴ l mol⁻¹ cm⁻¹. The method has been applied for the determination of cobalt in synthetic mixtures, pharmaceutical, biological and high speed steel samples.     

Catalytic flow injection determination of vanadium by oxidation of N-(3-sulfopropyl)-3,3',5,5'-tetramethylbenzidine using bromate

A catalytic flow-injection (FI) method was developed for the determination of 10⁻⁹ mol l⁻¹ levels of vanadium(IV, V). The method is based on the catalytic effect of vanadium(V) on oxidation of N-(3-sulfopropyl)-3,3′,5,5′-tetramethylbenzidine (TMBZ·PS) using bromate as oxidant to form a yellow dye (λ_max=460 nm). The use of 5-sulfosalicylic acid (SSA) as an activator enhanced the sensitivity of the method. The calibration graphs with a working range 0.05–8.0 ng ml⁻¹ were obtained for vanadium(V). Vanadium(IV) was also determined, being oxidized by bromate. The detection limit (signal/noise, S/N=3) was 0.01 ng ml⁻¹ (ca. 2×10⁻¹⁰ mol l⁻¹) vanadium. The relative standard deviations (R.S.D.) for 15 determinations of 0.5 ng ml⁻¹ vanadium, and for ten determinations of 0.1 and 1.0 ng ml⁻¹ vanadium were 0.41, 2.6 and 0.25%, respectively, with a sampling rate of 15 samples h⁻¹. The proposed method was successfully applied to the determination of vanadium in natural waters.     

Adsorptive stripping voltammetric determination of antimony

A new method is described for the determination of antimony based on the cathodic adsorptive stripping of Sb(III) complexed with 2′,3,4′,5,7-pentahydroxyflavone(morin) at a static mercury drop electrode (SMDE). The reduction current of the adsorbed antimony complex was measured by 1.5th-order derivative linear-sweep adsorption voltammetry. The peak potential is at −0.51 V (vs. SCE). The effects of various parameters on the response are discussed. The optimized analytical conditions were found to be: supporting electrolyte, chloroacetic acid (0.04 mol/l, pH 2.3); concentration of morin, 5×10⁻⁶ mol/l; accumulation potential, −0.25 V (vs. SCE); scan rate, 100 mV/s. The limit of detection and the linear range were 7×10⁻¹⁰ mol/l and 1.0×10⁻⁹3.0×10⁻⁷ mol/l Sb(III) for a 2-min accumulation time, respectively. This method has been applied to the determination of Sb(III) in steel and brass samples and satisfactory results were obtained. The adsorptive voltammetric characteristics and composition of the Sb(III)–morin complex were studied.     

Ion chromatographic determination of traces of some oxoanions with direct spectrophotometric detection

Investigation of the use of a single analytical procedure using the non-suppressed ion chromatographic method with direct spectrophotometric detection capable of determining eight oxoanions simultaneously is presented in this paper. Potassium phosphate was found to be the most suitable eluent for UV absorbance detection at 205 nm. Oxoanions AsO³⁻₃, SeO²⁻₃, AsO³⁻₄, VO⁻₃, SeO²⁻₄, WO²⁻₄, MoO²⁻₄ and CrO²⁻₄ were detected at ng ml⁻¹ levels with well separated peaks at retention time < 25 min. The working range is in the range ng ml⁻¹ to 50 μg ml⁻¹. The method is sufficiently sensitive to determine As (V), V(V), Mo(VI) and Cr(VI) anions (and NO⁻₃) directly in a river water sample. The accuracy of these results was established by comparison with conventional atomic absorption methods.     

A new chelating sorbent for metal ion extraction under high saline conditions

A new chelating polymeric sorbent was developed by functionalizing Amberlite XAD-16 with 1,3-dimethyl-3-aminopropan-1-ol via a simple condensation mechanism. The newly developed chelating matrix offered a high resin capacity and faster sorption kinetics for the metal ions such as Mn(II), Pb(II), Ni(II), Co(II), Cu(II), Cd(II) and Zn(II). Various physio-chemical parameters like pH-effect, kinetics, eluant volume and flow rate, sample breakthrough volume, matrix interference effect on the metal ion sorption have been studied. The optimum pH range for the sorption of the above mentioned metal ions were 6.0–7.5, 6.0–7.0, 8.0–8.5, 7.0–7.5, 6.5–7.5, 7.5–8.5 and 6.5–7.0, respectively. The resin capacities for Mn(II), Pb(II), Ni(II), Co(II), Cu(II), Cd(II) and Zn(II) were found to be 0.62, 0.23, 0.55, 0.27, 0.46, 0.21 and 0.25 mmol g⁻¹ of the resin, respectively. The lower limit of detection was 10 ng ml⁻¹ for Cd(II), 40 ng ml⁻¹ for Mn(II) and Zn(II), 32 ng ml⁻¹ for Ni(II), 25 ng ml⁻¹ for Cu(II) and Co(II) and 20 ng ml⁻¹ for Pb(II). A high preconcentration value of 300 in the case of Mn(II), Co(II), Ni(II), Cu(II),Cd(II) and a value of 500 and 250 for Pb(II) and Zn(II), respectively, were achieved. A recovery of >98% was obtained for all the metal ions with 4 M HCl as eluting agent except in the case of Cu(II) where in 6 M HCl was necessary. The chelating polymer showed low sorption behavior to alkali and alkaline earth metals and also to various inorganic anionic species present in saline matrix. The method was applied for metal ion determination from water samples like seawater, well water and tap water and also from green leafy vegetable, from certified multivitamin tablets and steel samples.     

A rapid and selective LC method for simultaneous determination of cyclosporin a and its major metabolite (AM1) in human serum at room temperature

A simple and highly selective isocratic reverse-phase high performance liquid chromatography (RP-LC) method at room temperature is developed in order to determination of Cyclosporine A (CyA) and its major metabolite (AM1) in serum samples of kidney transplanted patients. The method uses a phenyl column stationary phase, acetonitrile–water–methanol 47:50:3 as mobile phase and 215 nm detector wavelength, at room temperature. The solid phase extraction procedure using cyano disposable extraction column was carried out to separtate the CyA and AM1 with recovery 99±6 and 98±10, respectively. A linear correlation was found at the range of 40–1000 ng ml⁻¹ for CyA and 25–500 ng ml⁻¹ for AM1. The average intra and inter-day variations were 5.03 and 7.89% for CyA, 5.92 and 8.12% for AM1, respectively. The detection limit of 20 ng ml⁻¹ was found for CyA and 12.5 ng ml⁻¹ for AM1. Also, the clinical application of the method using serum concentration against time profile from kidney transplantated patients is reported.     

Spectrophotometric method for determination of vanadium and its application to industrial, environmental, biological and soil samples

The very sensitive, fairly selective direct spectrophotometric method for the determination of trace amount of vanadium (V) with 1,5-diphenylcarbohydrazide (1,5-diphenylcarbazide) has been developed. 1,5-diphenylcarbohydrazide (DPCH) reacts in slightly acidic (0.0001–0.001 M H₂SO₄ or pH 4.0–5.5) 50% acetonic media with vanadium (V) to give a red–violet chelate which has an absorption maximum at 531 nm. The average molar absorption coefficient and Sandell’s sensitivity were found to be 4.23×10⁴ l mol⁻¹ cm⁻¹ and 10 ng cm⁻² of V^v, respectively. Linear calibration graph were obtained for 0.1–30 μg ml⁻¹ of V^v: the stoichiometric composition of the chelate is 1:3 (V: DPCH). The reaction is instantaneous and absorbance remain stable for 48 h. The interference from over 50 cations, anions and complexing agents has been studied at 1 μg ml⁻¹ of V^v. The method was successfully used in the determination of vanadium in several standard reference materials (alloys and steels), environmental waters (potable and polluted), biological samples (human blood and urine), soil samples, solution containing both vanadium (V) and vanadium (IV) and complex synthetic mixtures. The method has high precision and accuracy (s=±0.01 for 0.5 μg ml⁻¹).     

Extraction and spectrophotometric determination of trace amount of Pd(II) with 2,2'-dithiodianiline

A method for the extraction-spectrophotometric determination of palladium with 2,2′-dithiodianilline (DTDA) is described. DTDA–Pd(II) complex is extracted from an aqueous solution with pH 3 into isobutyl methyl ketone (IBMK) layer. The absorbance is measured at 397 nm and the molar absorptivity found to be 1.47×10⁶ l mol⁻¹ cm⁻¹. The complex system conforms to Beer's law over the range 0.3–220 ng ml⁻¹ palladium (II). The effect of pH (1–6), NaClO₄ concentration, DTDA concentration and shaking time were studied. The ratio of the metal ion to ligand molecules in the complex and its stability constant were found to be 1:1 and 1.45×10⁶, respectively. The tolerance limit for many cations and anions have been determined. Finally the method has been applied successfully to the determination of palladium in synthetic mixtures, alloy and catalyst samples.     

Spectrofluorimetric determination of levofloxacin in tablets, human urine and serum

A spectrofluorimetric method to determine levofloxacin is proposed and applied to determine the substance in tablets and spiked human urine and serum. The fluorimetric method allow the determination of 20–3000 ng ml⁻¹ of levofloxacin in aqueous solution containing acetic acid–sodium acetate buffer (pH 4) with λ_exc=292 and λ_em=494 nm, respectively. Micelle enhanced fluorescence improves the sensibility and allows levofloxacin direct measurement in spiked Human serum (5 μg ml⁻¹) and urine (420 μg ml⁻¹), in 8 mM sodium dodecyl sulphate solutions at pH 5.     

High sensitive determination of trace amount of cobalt by catalytic adsorptive stripping voltammetry

A very sensitive and selective catalytic adsorptive cathodic stripping procedure for trace measurements of cobalt is presented. The method is based on adsorptive accumulation of cobalt-CCA (calcon carboxylic acid) complex onto a hanging mercury drop electrode followed by reduction of the adsorbed species by voltammetric scan using differential pulse modulation. The reduction current is enhanced catalytically by nitrite. The effect of various parameters such as pH, concentration of CCA, concentration of nitrite, accumulation potential and accumulation time on the selectivity and sensitivity were studied. The optimum condition for the analysis of cobalt, include pH 5.2 (Acetate buffer), 2.1 μM clacon carboxylic acid, 0.032 M sodium nitrite and an accumulation potential of 0.05 V (versus Ag/AgCl). Under these optimum conditions and for an accumulation time of 60 s, the measured peak current at −0.480 V is proportional to the concentration of cobalt over the entire concentration range tested 0.003–2.0 ng ml⁻¹ with a detection limit of 1 pg ml⁻¹ for an accumulation time of 60 s and 2.0–10.0 ng ml⁻¹ for an accumulation time of 40 s. The relative standard deviations for ten replicate measurement of 0.5 ng ml⁻¹ of cobalt were 3.1%. The main advantage of this new system is the microtrace Co(II) determination by ASV. The method was applied to determination of cobalt in a water sample and some analytical grade salts with satisfactory results. Published in Elektrokhimiya in Russian, 2009, Vol. 45, No. 2, pp. 221–228. The article is published in the original.     

Determination of trace amounts of beryllium using derivative spectrophotometry in non-ionic micellar medium

A rapid and sensitive method for the trace level determination of beryllium based on the formation of a 1:2 complex (λ_max 560 nm) with 1,4-dihydroxy-9,10-anthracenedione in an aqueous medium containing Triton X-100 is reported. Beer’s law is followed in the range 3.60–360 ng ml⁻¹ of Be(II). The molar absorptivity and Sandell’s sensitivity are 1.68×10⁴ l mol⁻¹cm⁻¹ and 0.54 ng cm⁻², respectively; detection limit is 0.23 ng ml⁻¹ of Be(II). Analysis of synthetic mixtures of composition similar to that of alloys and spiked samples of distilled water, gave results that are in agreement with their beryllium content.     

Two different strategies for the fluorimetric determination of piroxicam in serum

Two different spectrofluorimetric methods for the determination of piroxicam (PX) in serum are presented and discussed. One of them is based on the use of three-way fluorescence data and multivariate calibration performed with parallel factor analysis (PARAFAC) and self-weighted alternating trilinear decomposition (SWATLD). This methodology exploits the so-called second-order advantage of the three-way data, allowing to obtain the concentration of the studied analyte in the presence of any number of uncalibrated (serum) components. The method was developed following two different procedures: internal standard addition and external calibration with standard solutions, which were compared and discussed. The second approach investigated is based on the combination of solid-phase extraction (SPE) and room temperature fluorimetry. Both methods here presented yield satisfactory results. The concentration range in which PX could be determined in serum was 1–10 μg ml⁻¹. The limits of quantification for the experimental solutions using the chemometric approach were 0.09 μg ml⁻¹ for the standard addition mode and 0.12 μg ml⁻¹ using external calibration (both for PARAFAC and SWATLD algorithms). In the solid-surface fluorimetric method, the calibration graph was linear up to 0.22 μg ml⁻¹ and the limit of quantification was 0.02 μg ml⁻¹.