Flame atomic absorption spectrometric determination of Cd(II), Ni(II), Co(II) and Cu(II) in tea and water samples after simultaneous preconentration of dithizone loaded on naphthalene

A simultaneous preconcentration procedure for the determination of Cd(II), Ni(II), Co(II) and Cu(II) by atomic absorption spectrometry is described. The method is based on solid phase extraction of the metal ions on dithizone loaded on naphthalene in a mini-column, elution with nitric acid and determination by flame atomic absorption spectrometry. The sorption conditions including NaOH concentration, sample volume and the amount of dithizone were optimized in order to attain the highest sensitivity. The calibration graph was linear in the range of 0.5–75.0 ng ml^?1 for Cd(II), 1.0–150.0 ng ml^?1 for Ni(II), 1.0–150.0 ng ml^?1 for Co(II) and 1.0–125.0 ng ml^?1 for Cu(II) in the initial solution. The limit of detection based on 3S_b was 0.13, 0.32, 0.33 and 0.43 ng ml^?1 for Cd(II), Ni(II), Co(II) and Cu(II), respectively. The relative standard deviations (R.S.D) for ten replicate measurements of 20 ng ml^?1of Cd(II), 100 ng ml^?1 of Ni(II), Co(II) and 75 ng ml^?1 of Cu(II) were 3.46, 2.43, 2.45 and 3.26%, respectively. The method was applied to the determination of Cd(II), Ni(II), Co(II) and Cu(II) in black tea, tap and river water samples.     

Simultaneous determination of iron and ruthenium by preconcentration on sulfopropyl sephadex cation exchanger

A new method for the simultaneous determination of iron and ruthenium at ultra-trace levels is proposed. The method is based on the formation of the iron and ruthenium complexes with 2,4,6-tri-(2-pyridil)-1,3,5-triazine (TPTZ) in the presence of hydroxylamine hydrochloride and buffer CH₂ClCOOH/CH₂ClCOONa (pH=3.0). The formation of the complexes and their retention on a cationic resin SP-Sephadex C25 were integrated in one step at 90 °C, with stirring for 90 min. Under these conditions a high preconcentration level was achieved for both analytes. The complexes retained on the solid phase were evaluated by second derivative spectrophotometry. The selected analytical wavelengths were 539.7 and 553.3 nm for the determination of ruthenium and iron, respectively, by using the zero crossing approach. The detection and quantification limits were 0.54 ng ml⁻¹ and 1.79 ng ml⁻¹ for ruthenium and 0.41 ng ml⁻¹ and 1.38 ng ml⁻¹ for iron. The proposed method was applied to the determination of both analytes in synthetic mixtures.     

Determination of moxifloxacin in tablets and human urine by square-wave adsorptive voltammetry

This work presents an electroanalytical methodology developed for square-wave voltammetry based in the electrochemical reduction in hanging mercury drop electrode (HMDE), which is simple, fast, reliable and sensitive for determination of moxifloxacin (MOXI) in tablets and spiked urine human samples. The support electrolyte that provided a more defined and intense peak current for MOXI determination was the phosphate buffer 0.04 mol l^{− 1} pH 8.0. In the best-optimized conditions the drug presented an only peak of reduction at − 1.38 V vs. Ag/AgCl, using an E_acc. of − 0.30 V. An LOD of 0.44 and 3.20 ng ml^{− 1} and an LOQ of 1.46 and 10.60 ng ml^{− 1} were found for the pure standard of moxifloxacin and in the presence of matrix, respectively. A good recovery was obtained for assay spiked urine samples and a good quantification of MOXI was achieved in a commercial formulation. The methodology proposed was more sensitive than the spectrofluorimetric and spectrophotometric method with precision and accuracy equivalent.     

Kinetic Determination of Mercury(II) at Trace Level from Its Catalytic Effect on a Ligand Substitution Process

A catalytic kinetic method (CKM) is presented for the determination of mercury(II) based on its catalytic effect on the rate of substitution of N-methylpyrazinium ion (Mpz⁺) onto hexacyanoferrate(II). The progress of the reaction was monitored spectrophotometrically at 655 nm by registering the increase in absorbance of the product [Fe(CN)₅(Mpz]²⁻ under the reaction conditions: 5 × 10⁻³ mol L⁻¹ [Fe(CN)₆]⁴⁻), 5 × 10⁻⁵ mol L⁻¹ [Mpz⁺], T = 25.0 ± 0.1°C, pH 5.00 ± 0.02 and ionic strength, I = 0.1 mol L⁻¹ (KNO₃). Quantitative rate data at specified experimental conditions showed a linear dependence of the absorbance after fixed time A _t on the concentration of mercury(II) catalyst in the range 20.06–702.1 ng mL⁻¹. The maximum relative standard deviations and percentage errors for the determination of mercury(II) in the range of 20.06–200.6 ng mL⁻¹ were calculated to be 1.7 and 2.7% respectively. The detection limit was found to be 7.2 ng mL⁻¹ of mercury(II). Accuracy (expressed in terms of recoveries) was in the range of 98–103%. Figures of merit and interference due to many cations and anions was investigated and discussed. The applicability of the method was demonstrated by determining the mercury(II) in different synthetic samples and confirming the results using atomic absorption spectrophotometry. The proposed method allowed determination of mercury(II) in the range 20.06–702.1 ng mL⁻¹ with very good selectivity and an output of 30 samples h⁻¹.__________From Zhurnal Analiticheskoi Khimii, Vol. 60, No. 6, 2005, pp. 654–661.Original English Text Copyright © 2005 by Surendra Prasad.This article was submitted by the author in English.     

Simultaneous determination of cobalt and chromium by ion chromatography with chemiluminescence detection and its application to glass analysis

A method is described for the simultaneous determination of very low levels of Co and Cr by high performance ion chromatography coupled with a chemiluminescence detection system. 0.1M K₂SO₄ solutions, adjusted to pH 3.0, were used as eluent to separate Co(II) and Cr(III) between them and from interferents. The detection system was the chemiluminescence of luminol/ H₂O₂ in alkaline medium catalyzed by such transition metals. Using a matrix solution analogous to soda-lime silica glass (dissolved in acids) calibration graphs were linear up to 0.5 ng ml^–1 for cobalt and up to 250 ng ml^–1 for chromium. The corresponding calculated detection limits (3 s) in such matrix were 0.05 ng ml^–1 and 15 ng ml^–1 for Co and Cr, respectively. The relative standard deviations were 1.4% at 0.5 ng ml^–1 Co level and 2.8% at the 200 ng ml^–1 Cr level. No interferences were observed from the more common metals, particularly those present in glass samples. The ion chromatography/ chemiluminescent method proposed has been successfully applied to the analysis of Co and Cr in glasses.     

Automated Method for the Selective Determination of Gold by On-Line Solvent Extraction and Reversed Micellar-Mediated Luminol Chemiluminescence Detection

A new method based on the direct coupling of on-line solvent extraction with chemiluminescence (CL) of luminol in reverse micelles is proposed for the determination of gold(III) in a reverse-flow injection system. In the on-line process, gold(III) is extracted from aqueous hydrochloric acid solution with tri-n-octylphosphine oxide in chloroform, followed by separation through a microporous Teflon membrane. A reversed micellar system of cetyltrimethylammonium chloride-water (buffered with sodium carbonate)-6:5 (v/v) chloroform-cyclohexane was used as a medium for the CL reaction. Linear calibration for gold was established over the concentration range 10-5000 ng ml⁻¹ and the detection limit was 1 ng ml⁻¹. Much higher tolerable levels of potential interfering metal ions were achieved for the present on-line procedure. The present method was applied to the analysis of industrial samples of silver-based alloy.     

Selective Extraction–Spectrophotometric Determination of Traces of Palladium in Catalysts

The simple, sensitive, and highly selective determination of palladium is based on the reaction between Pd(II) and 1,2-bis[methyl(2-aminocyclopentene carbodithioate)] ethane and extraction of the complex into dichloromethane. Beer's law is obeyed in the concentration range 0.19–10 μg ml⁻¹Pd. Relative standard deviations were 0.7–1.1%. The procedure has been successfully applied to the determination of palladium in different samples of catalysts.     

Fluorimetric determination of calcium by ion-pair extraction with cryptand 2.2.1 and eosin

A fluorimetric study on the extraction of calcium into 1,2-dichloroethane as an ion-pair, formed between the cryptand 2.2.1-calcium complex and the eosinate anion, is described. Optimum conditions for extraction are established and a new fluorimetric determination of ultratraces of calcium is proposed. A linear working range from 1.5 ng ml^–1 (detection limit) to 100 ng ml^–1 of calcium and a relative standard deviation of ± 2.9% at the 70 ng ml^–1 level are obtained. The equilibrium constants involved in the extraction process have been calculated and refined by the Letagrop-DISTR program. The proposed method has been tested for the direct determination of calcium in sugars.     

Solid phase extraction of zirconium as arsenazo(III) complex on agar and spectrophotometric determination

A new solid phase extraction method for the separation and determination of zirconium using agar as an adsorbent is described. The method is based on the adsorption of zirconium as arsenazo(III) complex on agar in a mini-column, elution with sulfuric acid-acetone mixture and determination by spectrophotometry. The effect of different parameters such as pH, concentration of the reagent, eluting reagent, and volume of the sample, amount of the adsorbent and interfering ions was investigated. The calibration graph was linear in the range of 5?C300 ng ml^?1 of zirconium under optimum conditions. The limit of detection based on 3S_b was 1.3 ng ml^?1 and the relative standard deviation (R.S.D) for ten replicate measurements of 15 and 200 ng ml^?1 of zirconium was 3.7 and 1.8%, respectively. The method was applied to the determination of zirconium in water and soil samples.     

Determination of selenomethionine by high performance liquid chromatography-direct hydride generation-atomic absorption spectrometry

A simple, reliable, trace determination of selenomethionine (Semet) based on a direct hydride generation atomic absorption spectrometric method was developed using sodium tetrahydroborate (0.3% in 0.2% NaOH) and hydrochloric acid (3 M). The method excluded any chemical pretreatment prior to hydride generation (HG). The optimized HG system was successfully coupled with the HPLC system. The detection limit (3σ of blank; n=5), reproducibility (R.S.D. of three successive analyses/day, performed on three different days), and repeatability (R.S.D. of three successive analyses) of the method were 1.08 ng ml⁻¹, 9.8% for 9.04 ng ml⁻¹ and 2.1–9.5% for 30.0–1.27 ng ml⁻¹ Semet as Se (standards prepared in Milli-Q water). Calibration graph was linear up to 30 ng ml⁻¹. This HPLC-HG-AAS method is very promising and successfully determined Semet (spiked) in human urine.     

Simultaneous determination of pharmaceutically active compounds in wastewater samples by solid phase extraction and high-performance liquid chromatography with diode array and fluorescence detectors

In the present work, an analytical method for the simultaneous determination of five anti-inflammatory drugs (acetaminophen, diclofenac, ibuprofen, ketoprofen and naproxen), an antiepileptic drug (carbamazepine) and a nervous stimulant (caffeine) is proposed for the routine analysis of these pharmaceuticals in wastewater influents and effluents from WWTPs. The method involves pre-concentration and clean-up by solid phase extraction (SPE) using Oasis HLB extraction cartridges. Final analysis of the selected pharmaceutical compounds was carried out by high-performance liquid chromatography (HPLC) with diode array detector (DAD). Confirmation of the presence of the fluorescence compounds (ibuprofen and naproxen) was performed by on-line fluorescence detection. Recoveries were ranged from 71 to 103% with relative standard deviation below 15.1%. Limits of quantification were in the range 6.2–319.8 and 3.0–160.0 ng ml⁻¹ for influent and effluent wastewater samples, respectively. The described method was applied to the determination of the drugs in wastewater samples from four treatment plants in Seville.     

Study and evaluation of a fluorimetric method for the determination of inorganic mercury in water

Summary A procedure for determining Hg(II) in water has been worked out. The cation reacts with bromine and fluorescein to form an ionic pair (ionic association) which is extracted with n-butyl acetate, and has an emission peak at 476 nm and an excitation peak at 452 nm. On optimum determination conditions, the detection limit was 0.4 ng ml^–1 and the linear range 1–20 ng ml^–1. The influence of different chemical species present in water samples was studied and the method was applied to determine Hg(II) in synthetic samples of water and in natural water with good recovery rates. In order to determine Hg(II) in samples of urban waste water, a simple pretreatment with HNO₃ is required. The method can be used to monitor Hg(II) contamination in water.     

Cloud point extraction and spectrophotometric determination of amaranth in food samples using nonionic surfactant Triton X-100 and tetrabutylammonium hydrogen sulfate

Cloud point extraction methodology was successfully employed for preconcentration of trace amounts of amaranth prior to its determination by spectrophotometry. The method was based on the extraction of amaranth as an ion pair with tetrabutylammonium ion from aqueous solution using Triton X-100 as non-ionic surfactant. The extracted surfactant rich phase was diluted with ethanol and its absorbance was measured at 518 nm by a spectophotometer. An optimum set of surfactant concentration, pH, equilibration temperature and time, tetrabutylammonium hydrogen sulfate and salt concentration were obtained. The calibration graph was linear in the range of 20–1600 ng ml^?1 of amaranth in the initial solution with r = 0.9993 (n = 12). Detection limit based on three times the standard deviation of the blank (3S_b) was 13.0 ng ml^?1 (n = 10), and the relative standard deviation (R.S.D) for 100 and 1000 ng ml^?1 of amaranth was 4.2 and 1.4% (n = 10), respectively. The proposed procedure was applied to the determination of amaranth in different food samples.     

Speciation of silicon and phosphorous using liquid chromatography coupled with sector field high resolution ICP-MS

Sector-field high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) has been used, at R=3000, to resolve spectral interferences caused by N₂⁺ and CO⁺ on ²⁸Si⁺, and NOH⁺ and NO⁺ on ³¹P⁺, thereby facilitating the speciation of these elements. Polydimethylsiloxanes (PDMS), ranging from 162 g mol⁻¹ to 16 500 g mol⁻¹, and their silanol breakdown products, have been separated by size exclusion and reverse phase chromatography, respectively, and detected using HR-ICP-MS. Detection limits (as Si) of between 12–30 ng ml⁻¹ and 0.1–4 ng ml⁻¹ were obtained for the PDMS and silanol compounds, respectively. Quantitative and reproducible methods have been developed for the analysis of four common organophosphorous pesticides in blood plasma, and inorganic phosphates in food, with detection limits of between 0.9–2 ng ml⁻¹ and 1–39 ng ml^−1, respectively.     

Determination of some selected polycyclic aromatic hydrocarbons in environmental samples by high-performance liquid chromatography with fluorescence detection

Summary Analytical methods for the determination in environmental samples, of some selected Polycyclic Aromatic Hydrocarbons (PAH's), which are included on the EPA Priority Pollutant list, have been developed and evaluated. The methodology involves the extraction of PAH's from water samples by solvent extraction with dichloromethane. Solid samples were ultrasonically extracted with acetone/hexane and the extract was cleaned up on a silica gel/alumina column. The concentrated and cleaned up extracts were analysed by HPLC on a polymeric C₁₈ column using a gradient of acetonitrile/water as the mobile phase and fluorescence detection. Typical detection limits lie in the range of 1–30 ng ml^–1 of the analytes, but after sample pretreatment detection limits of 10–300 ng l^–1 were obtained. The extraction, clean-up and HPLC methodology was applied to the determination of selected PAH's in coal washings samples and the method was validated by the quantification of PAH's in a natural contaminated and a spiked sediment.     

Selective Determination of Nickel in Biological Samples by High Performance Liquid Chromatography

A highly selective method for the determination of trace amounts of nickel(II) by high performance liquid chromatography was developed. 2-[(2-Hydroxyphenyl)azo]-4,5-diphenylimidazole (HAI) was used for pre-column derivatization of nickel(II) in reversed-phase chromatographic separation followed by spectrophotometric detection. In the presence of nickel(II), iron(III), cobalt(II), copper(II), cadmium(II), zinc(II), manganese(II), aluminum(III) and vanadium(V), only nickel(II) chelate with HAI gave a resolved peak in chromatograms with a C8-bonded reversed phase column and a 45% (w/w) acetonitrile-water mobile phase containing 1.0 × 10⁻⁴ mol kg⁻¹ ethylenediaminetetraacetic acid and 5.0 × 10⁻³ mol kg⁻¹ sodium acetate (pH 7.5). The nickel(II) chelate was detected spectrophotometrically at 585 nm. When 100 µL of a test solution was injected, the calibration graph was linear up to 240 pg for nickel(II), and the detection limit defined as three times the standard deviation of the reagent blank was 0.8 pg at 0.001 absorbance unit full scale. The proposed method was applied to the analysis of rice, tea leaves and mussels.     

Voltammetric determination of methyl parathion, ortho, meta and para nitrophenol with a carbon paste electrode modified with C18

Summary The determination of methyl-parathion (MPT), ortho (ONP), meta (MNP) and para nitrophenol (PNP) has been studied by differential pulse voltammetry with a carbon-paste electrode modified with 50% (w/w) of C₁₈. A study of the influence of the pH in the preconcentration cell and the measurement cell was carried out for an electrode with 50% modifier and an accumulation time of 5 min. The voltammograms were recorded with a sweep rate of 40 mV s^–1 and a pulse amplitude of 50 mV. With the optimum conditions of pH for both of the steps, various other variables were studied. The variables for each compound were optimized and the possibility of application to the determination of a mixture of the four compounds was investigated. The determination limits found for all the compounds are: 2 ng ml^–1 for ONP, 5 ng ml^–1 for MNP, 4.3 ng ml^–1 for PNP and 7.9 ng ml^–1 for MPT. The method was applied to samples of a small lake which gathers rain water and water filtered from land on which cereals are grown.     

HPLC Method for Determination of Rosiglitazone in Plasma

A fast and sensitive high performance liquid chromatography method for quantitative determination of rosiglitazone in human plasma has been developed. The extraction from plasma was performed using solid-phase extraction (SPE) on C4 silica (100 mg) disposable extraction cartridges (DEC). The separation of rosiglitazone and two metabolites was achieved on a Phenomenex® Synergi 4 µm MAX-RP (150 × 4.6 mm) column, protected by a guard column. The mobile phase was 0.01 M ammonium acetate, pH 7.0 - acetonitrile (65:35, v/v). (3S)-3-OH-quinidine was used as internal standard. The analytes were detected using fluorescence detection. The method was validated. The limit of quantitation was 1 ng mL⁻¹ and the detection limit was 0.25 ng mL⁻¹ for rosiglitazone in human plasma. The recovery was 90% for rosiglitazone. Linearity was observed over a range of 1-1000 ng mL⁻¹ (r²=0.9959). The intra- and inter-day precision (C.V.) did not exceed 8.7 %. Applicability of the method was demonstrated by a clinical pharmacokinetic study. A healthy volunteer received in two separate phases 4 mg and 8 mg rosiglitazone maleate as a single oral dose. Plasma concentrations were measured for 24 h in both phases.     

Ionic liquid-based ultrasound-assisted dispersive liquid–liquid microextraction combined with electrothermal atomic absorption spectrometry for a sensitive determination of cadmium in water samples

A new method was developed for the determination of cadmium in water samples using ionic liquid-based ultrasound-assisted dispersive liquid–liquid microextraction (IL-based USA-DLLME) followed by electrothermal atomic absorption spectrometry (ETAAS). The IL-based USA-DLLME procedure is free of volatile organic solvents, and there is no need for a dispersive solvent, in contrast to conventional DLLME. The ionic liquid, 1-hexyl-3-methylimidazolium hexafluorophosphate (HMIMPF₆), was quickly disrupted by an ultrasonic probe for 1 min and dispersed in water samples like a cloud. At this stage, a hydrophobic cadmium–DDTC complex was formed and extracted into the fine droplets of HMIMPF₆. After centrifugation, the concentration of the enriched cadmium in the sedimented phase was determined by ETAAS. Some effective parameters of the complex formation and microextraction, such as the concentration of the chelating agent, the pH, the volume of the extraction solvent, the extraction time, and the salt effect, have been optimized. Under optimal conditions, a high extraction efficiency and selectivity were reached for the extraction of 1.0 ng of cadmium in 10.0 mL of water solution employing 73 µL of HMIMPF₆ as the extraction solvent. The enrichment factor of the method is 67. The detection limit was 7.4 ng L^− 1, and the characteristic mass (m₀, 0.0044 absorbance) of the proposed method was 0.02 pg for cadmium (Cd). The relative standard deviation (RSD) for 11 replicates of 50 ng L^− 1 Cd was 3.3%. The method was applied to the analysis of tap, well, river, and lake water samples and the Environmental Water Reference Material GSBZ 50009-88 (200921). The recoveries of spiked samples were in the range of 87.2–106%.     

Voltammetric study of the interaction of lomefloxacin (LMF)–Mg(II) complex with DNA and its analytical application

The voltammetric behavior of the LMF-Mg(II) complex with DNA at a mercury electrode is reported for the first time. In NH₃–NH₄Cl buffer (pH=9.10), the adsorption phenomena of the LMF–Mg(II) complex were observed by linear sweep voltammetry. The mechanism of the electrode reaction was found to be a reduction of LMF in the complex, and the composition of the LMF–Mg(II) complex is 2:1. In the presence of calf thymus DNA (ctDNA), the peak current of LMF–Mg(II) complex decreased considerably, and a new well-defined adsorptive reduction peak appeared at −1.63 V (vs. SCE). The electrochemical kinetic parameters and the binding number of LMF–Mg(II) with ctDNA were also obtained. Moreover, the new peak currents of LMF–Mg(II)–DNA system increased linearly correlated to the concentration of DNA in the 4.00×10⁻⁷–2.60×10⁻⁶ g ml⁻¹ range when the concentrations of LMF–Mg(II) complex was fixed at 5.00×10⁻⁶ mol l⁻¹, with the detection limits of 2.33×10⁻⁷ g ml⁻¹. An electrostatic interaction was suggested by electrochemical method.