A Pre-Concentration Procedure Using Cloud Point Extraction for the Determination of Manganese in Saline Effluents of a Petroleum Refinery by Flame Atomic Absorption Spectrometry

This paper describes the development of a cloud point extraction procedure for the determination of manganese in saline effluents by flame atomic absorption spectrometry (FAAS). The optimization step was performed using the Doehlert matrix involving the following variables: buffer concentration, pH and centrifugation time. The validation process was assessed as: parameters of the analytical curve, precision, effect of other ions in the proposed procedure, robustness test and accuracy. The proposed procedure allows the determination of manganese with a detection limit (3δ/S) of 0.60 μg L⁻¹, and a precision expressed as relative standard deviation (RSD) of 2.2 (n = 8) and 1.5% (n = 8) for a manganese concentration of 1 and 5 μg L⁻¹, respectively. The pre-concentration factor obtained was 84. The recovery achieved for the determination of manganese in the presence of several other metal ions demonstrated that this procedure could be satisfactorily applied to the analysis of environmental samples. The accuracy was confirmed by the analysis of CRM trace elements in water (NIST 1643d). This procedure was applied to the determination of manganese in saline effluents of a petroleum refinery. For three analyzed samples the manganese content varied between 44.9 and 67.9 μg L⁻¹.     

Application of multivariate techniques for optimization of direct method for determination of lead in naphtha and petroleum condensate by electrothermal atomic absorption spectrometry

A direct method is proposed for the determination of lead in naphtha and petroleum condensate by electrothermal atomic absorption spectrometry (ET AAS) using palladium as a permanent modifier. The procedure includes the dilution of 3 mL of sample (naphtha or petroleum condensate) to a final volume of 10 mL with xylene, and direct injection of 30 μL of this solution into the graphite furnace. The optimization of the instrumental conditions was performed using multivariate techniques. Firstly, a 2³ full factorial design was performed for preliminary evaluation of the factors: pyrolysis time, pyrolysis temperature and atomization temperature. This experiment showed that in the studied levels only the factors pyrolysis time and atomization temperature were significant. Then, a 3² full factorial design was performed for the determination of the critical conditions of these variables. The method allows the determination of lead using the standard calibration technique with a calibration curve from 2.6 to 30 μg L⁻¹ (correlation coefficient higher than 0.998). A limit of detection (3σ) of 0.8 μg L⁻¹ and a characteristic mass of 35 pg were obtained in the presence of palladium as modifier. The precision expressed as relative standard deviation (RSD) was 1.5 and 0.8% for lead concentrations of 3.0 and 30 μg L⁻¹ (n = 10). Recovery studies demonstrate that lead can be determined in naphtha and petroleum condensate using calibration with organic standard solutions. This method was applied for the determination of lead in three petroleum condensate and two naphtha samples. The concentrations found for the petroleum condensate was between 2.7 and 5.7 μg L⁻¹, while the naphtha samples did not contain any detectable lead.     

Determination of trace heavy metals in waters by flame atomic absorption spectrometry after preconcentration with 2,4-dinitrophenyldiazoaminoazobenzene on Amberlite XAD-2

A new column, solid-phase extraction (SPE), preconcentration method was developed for determination of Cd, Co, and Cu ions in natural water samples by flame atomic absorption spectrometry. The procedure is based on the retention of analytes in the form of 2,4-dinitrophenyldiazoaminoazobenzene (DNDAA) complex on a mini column of DNDAA-XAD-2 resin. The effects of pH, eluent type, eluent concentration, eluent volume, resin quantity, sample volume, sample flow rate, and matrix ions (Na, Ca, and Mg) were investigated on the recovery of the metals using model solutions. The detection limit for Cd, Co, and Cu was 0.062, 0.084, and 0.057 μg L⁻¹ and the quantification limit was 0.17, 0.24, and 0.12 μg L⁻¹ respectively. The method was validated by the analysis of a certified reference material with the results being in agreement with those quoted by manufactures. The developed method was applied to the determination of trace metal ions in tap water, river water samples with satisfactory results.     

Application of Nb2O5–SiO2 in Pre-Concentration and Determination of Copper and Cadmium by Flow System with Flame Atomic Absorption Spectrometry

 The use of niobium (V) oxide, chemically adsorbed on silica gel surface (Nb₂O₅–SiO₂), as an adsorbent in a pre-concentration system for copper (II) and cadmium (II) determination was proposed. The procedure is based on the large ion-exchange capacity for the adsorption of copper (II) and cadmium (II) ions on the mini-column packed with Nb₂O₅–SiO₂, followed by elution with 2.0 mol L⁻¹ nitric acid and determination by flame atomic absorption spectrometry. Chemical and flow variables were optimized. The results demonstrated that the sample solutions containing copper (II) or cadmium (II) in a concentration range of 3.0 to 600.0 μg L⁻¹ and 3.1 to 100.0 μg L⁻¹ respectively, in a solution of pH 5.0 could be determined using a pre-concentration time of 2 min. The enrichment factor when using a sample volume of 10.2 mL and 2 min of pre-concentration was 17.5 and 20.3 for copper (II) and cadmium (II), respectively. The limit of detection for copper (II) and cadmium (II) was 0.5 μg L⁻¹ and 1.0 μg L⁻¹, respectively. The relative standard deviation (RSD) was lower than 1.4% for copper (II) and cadmium (II) when using a concentration of 25.0 μg L⁻¹ for both metals. The method was tolerant to other ions usually present in water samples. Good accuracy was obtained by the analysis of water reference material and environment samples. Correspondence: Universidade Federal de Santa Catarina, Departamento de Química, Florianópolis SC, Brazil. e-mail: carasek@qmc.ufsc.br Received July 16, 2002; accepted October 25, 2002     

Flow injection on-line hydrophobic sorbent extraction for flame atomic absorption spectrometric determination of cadmium in water samples

A flow injection system was developed for on-line sorbent extraction preconcentration and flame atomic absorption spectrometric determination of cadmium in natural water samples. The non-charged cadmium complex with diethyl-dithiophosphate (DDPA) was formed on-line in 0.1 mol L⁻¹ HNO₃ and retained on the hydrophobic poly-chlorotrifluoroethylene (PCTFE) sorbent material. The adsorbed complex was eluted with isobutyl methylketone (IBMK) and injected directly into the nebulizer via a flow compensation unit. All major chemical and flow parameters affecting the complex formation adsorption and elution as well as interference were studied and optimized. By processing 2.4 mL of sample, the enhancement factor was 39 and the sampling frequency was 50 h⁻¹. For 30 s preconcentration time the detection limit was 0.3 μg L⁻¹ and the relative standard deviation at 5.0 μg L⁻¹ Cd concentration level was 2.9%. The calibration curve was linear in the range 0.8–40.0 μg L⁻¹. The accuracy of the method was estimated by analyzing a certified reference material NIST-CRM 1643d (Trace elements in water). Good recoveries were obtained for spiked natural-water and waste-water samples. Correspondence: Aristidis N. Anthemidis, Laboratory of Analytical Chemistry, Department of Chemistry, Aristotle University, GR-Thessaloniki 54124, Greece     

Use of Benzoylthiourea Immobilized on Silica Gel for Separation and Preconcentration of Uranium(VI)

Benzoylthiourea immobilized on silica gel was prepared by two-step post-synthesis modification. The capacity of the chelating silica gel, which was characterized by FTIR, was 3.21 mmol · g⁻¹. The separation and enrichment of uranium(VI) from solutions was investigated. Effective extraction conditions were optimized in both batch and column methods prior to determination by spectrophotometry using arsenazo(III). The optimum pH range for quantitative adsorption is 4–7. Quantitative recovery of U(VI) was achieved by stripping with 0.1 mol · L⁻¹ HCl. The sorption capacity of modified silica gel was 0.85 mmol · g⁻¹ uranium(VI). Recovery of U(VI) was 99.1 ± 2.3% with a detection limit of 2 μg · L⁻¹. The preconcentration factor was 250, and the relative standard deviation was 1.53% for a 1 μg · L⁻¹ U(VI) solution. The method was used for the determination of uranium in synthetic samples and a soil sample.     

Online preconcentration system for determining ultratrace amounts of Cd in vegetal samples using thermospray flame furnace atomic absorption spectrometry

A system has been developed for online preconcentration and determination of Cd using thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS). It is based on the solid-phase extraction of Cd in an Amberlite XAD-2 minicolumn loaded with 2-(2-thiazolylazo)-5-dimethylaminophenol (TAM), and the metal ion is eluted with 1 mol L⁻¹ hydrochloridric acid, followed by its determination. The online system allows determining Cd with a detection limit of 8.0 ng L⁻¹ and a quantification limit of 25.0 ng L⁻¹. The precision (repeatability), calculated as the relative standard deviation (% RSD) in sample solutions containing 0.5 and 3.0 μg L⁻¹ of Cd, was 6.1 and 4.5%, respectively. The preconcentration factor obtained was 24. The system’s accuracy was confirmed by analyzing the following certified reference materials (CRMs): Rice flour NIES 10b, Apple leaves NIST 1515 and Orchard leaves NBS 1571. This procedure was applied to the determination of Cd in cabbage and powdered guarana samples.     

Ion-Chromatographic Determination of Low Concentrations of Nitrate in Solutions of High Salinity

The determination of low concentrations of inorganic anions in water samples of high salinity is one of the most difficult tasks in analytical chemistry. There is, however, an increasing demand for the exact and reliable determination of nutrients even at very low concentration levels in environmental samples of complex composition. We therefore present the development, quality control and application of an easy and rugged method that makes possible the determination of trace amounts of nitrate in solutions with high concentrations of chloride (>30 000 mg L⁻¹) and a hundred-fold excess of bromide ions, based on ion chromatography with UV detection at λ = 210 nm. While chloride ions show no absorbance at this wavelength, a bromide concentration >1500 μg L⁻¹ severely interferes with nitrate determination at the trace level. On the contrary, at nitrate concentrations of >500 μg L⁻¹, this bromide interference becomes negligible. Consequently, to overcome the impact of bromide on the trace level determination of nitrate, all samples are spiked with a definite volume of a nitrate standard solution to obtain an overall nitrate concentration of >500 μg L⁻¹ which allows the exact and reliable determination of nitrate concentrations down to 25 μg L⁻¹. We will report the successful application of the method to samples of high salinity.     

A Novel Simplified Column-Switching Technique for the Determination of Traces of Bromate in High Concentration Matrices

The column-switching technique has been widely used to determine trace level ions in the presence of high concentration matrix. A novel simplified column-switching method is proposed where bromate (as a model compound) was determined using this technique. The switching time window was confirmed by the retention time of determined ions. This technique can completely carry out the same function as the other column-switching technique do, but only one extra ten-way injection valve coupled to ion chromatograph was used. By using column-switching technique, it is possible to determine 0.2 μg L⁻¹ bromate in the presence of 100 mg L⁻¹ chloride by direct injection of 2000 μL without any pretreatment and the relative standard deviation (RSD) of the peak height for the eleven successive injections of 0.2 μg L⁻¹ bromate solution is 23.1%. The detection limit for bromate is 0.09 μg L⁻¹, which showed the method was very sensitive. The technique has been applied to the determination of bromate in drinking water, and the spike recovery is in the range of 96–104%.     

Ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate as a solvent for extraction of lead in environmental water samples with detection by graphite furnace atomic absorption spectrometry

A novel method is described for the preconcentration of ultratrace amounts of lead in water. Dithizone is employed as a chelator forming a neutral lead-dithizone complex to extract lead ions from aqueous solution into the ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate. Under optimal conditions, the extraction efficiency in one step and back-extraction efficiency with 5 mL of 0.1 mol L⁻¹ nitric acid were 99.9 and 99.8% for 20 μg of lead in 1 L of water solution, respectively. Preconcentration coupled with graphite furnace atomic absorption spectrometry was developed for the determination of lead in environmental water samples. The calibration graph was linear with a correlation coefficient of 0.998 at levels near the detection limits up to at least 0.1 μg L⁻¹. The detection limit, calculated as three times the standard error of the estimated calibration graph, is 1.0 ng of lead per liter of water sample. The determination of lead was free from interference from almost all cations and anions, and from humic acid in water from plant rot. Lead recoveries between 97.8 and 100.8% for spiked samples prove the accuracy of the method.     

Application of Continuous-Flow Liquid Phase Microextraction to the Analysis of Phenolic Compounds in Wastewater Samples

A novel method for the determination of phenolic compounds (phenol, o-cresol, m-cresol, 2,4-dimethylphenol, 2,3-dimethylphenol and 3,4-dimethylphenol) in water samples was developed by combined continuous-flow liquid-phase microextraction (CFME) with gas chromatography-flame ionization detection (GC-FID). The effects of extraction solvent type and volume, flow rate of sample solution, extraction time, salt concentration and pH on the extraction performance were investigated and optimized. The calibration curves and analyses of real samples were obtained under the following conditions: 3.0 μL n-Amyl acetate, 1.5 mL min⁻¹ flowing rate, 15 min extracting time and pH 1.5. The developed protocol was found to yield a linear calibration curve in the concentration ranged from 10 to 10000 μg L⁻¹ for the target analytes, and the limits of detection ranged from 2.32 to 2.95 μg L⁻¹. Good repeatabilities of extraction were obtained, with relative standard deviation (R.S.D.) values below 6.89%. The results demonstrated that the CFME followed with GC-FID is a simple and reliable technique for the determination of phenolic compounds in water samples.     

Study of Solid Phase Extraction Prior to Spectrophotometric Determination of Platinum with N-(3,5-Dimethylphenyl)-N′-(4-Aminobenzenesulfonate)-Thiourea

A highly sensitive, selective and rapid method for the determination of platinum based on the rapid reaction of platinum(IV) with N-(3,5-dimethylphenyl)-N′-(4-aminobenzenesulfonate)-thiourea (DMMPT) and the solid phase extraction of the Pt(IV)-DMMPT complex with C₁₈ membrane disks was developed. In the presence of pH = 3.8 buffer solution and cetyl trimethylammonium bromide (CTMAB) medium, DMMPT reacts with platinum to form a violet complex of a molar ratio of 1:3 (platinum to DMMPT). This complex was enriched by solid phase extraction with C₁₈ membrane disks, and an enrichment factor of 200 was obtained. The molar absorptivity of the complex is 9.51 × 10⁴ L · mol⁻¹ · cm⁻¹ at 755 nm, and Beer’s law is obeyed in the range of 0.01–3.0 μg mL⁻¹ in the measured solution. The relative standard deviation for eleven replicate samples of 0.01 μg mL⁻¹ level is 1.79%. The detection limit reaches 0.02 μg L⁻¹ in the original samples. This method was applied to the determination of platinum in water and soil samples. The relative standard deviations are 2.9–3.4%. The recoveries are 94–105%. The values of determination obtained agree with those of the ICP-MS method. The results are satisfactory.     

Selective extraction and preconcentration of cerium(IV) in water samples by cloud point extraction and determination by inductively coupled plasma optical emission spectrometry

Cloud point extraction (CPE) was used for the selective extraction and separation of cerium(IV) from aqueous solutions. The method is based on the formation of cerium(IV)-n-p-tolylbenzohydroxamic acid (n-TBHA) complex that is extracted into the micellar phase (Triton X-114) at a temperature above the cloud point temperature (CPT). After phase separation, the surfactant rich phase was diluted up to 1.0 mL and determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). Under the optimum extraction conditions and instrument parameters, by preconcentration of only 10.0 mL of sample in the presence of 0.09% Triton X-114, an enhancement factor of 13.8 was obtained. The analytical curve was linear in the range of 1.5–1200 μg L⁻¹ and the detection limit was 0.4 μg L⁻¹. The method was applied to the determination of Ce(IV) in water samples with satisfactory results.     

Solid Phase Extraction and Spectrophotometric Determination of Silver with 2-(2-Quinolylazo)-5-diethylaminoaniline as Chromogenic Reagent

 A new chromogenic reagent, 2-(2-quinolylazo)-5-diethylaminoaniline(QADEAA), was synthesized. A highly sensitive, selective and rapid method for the determination of silver was developed. It is based on the rapid reaction of silver (I) with QADEAA and the solid phase extraction of colored chelate using reversed-phase separation cartridge. At pH 6.5 in the presence of sodium dodecyl sulfonate (SDS), QADEAA reacts with silver to form a violet chelate in a molar ratio of 1:2 (silver to QADEAA). This chelate was enriched by solid phase extraction. The retained chelate can be eluted from the cartridge with ethanol. In ethanol medium, the molar absorptivity of the chelate is 1.36×10⁵ L·mol⁻¹·cm⁻¹ at 590 nm. Beer’s law is obeyed in the range 0.01–0.6 μg L⁻¹. The relative standard deviation for eleven replicate samples of 0.01 μg L⁻¹ level is 1.9%. The detection limit reaches the 0.02 μg L⁻¹ level. This method shows satisfactory results when used for the determination of silver in water. Correspondence: Department of Chemistry, Yuxi Teacher’s College, Yuxi, 653100, P.R. China. e-mail: hugiufena@163.com Received 19 August 2002; accepted 20 October 2002     

Rapid, sensitive and selective spectrophotometric determination of phosphate as an ion associate of 12-molybdophosphate with Astra Phloxine

A highly sensitive and selective reaction of 12-molybdophosphate with the polymethine dye Astra Phloxine has been used for the spectrophotometric determination of phosphate. If the concentration of phosphate is less than 1 μmol L⁻¹, supersaturated solutions of ion associate (IA) are stable without the use of a surfactant. Under these conditions, a new band appears in the absorption spectrum at 574 nm. The color of the IA develops immediately after mixing of reagents and remains constant over several hours. The molar absorptivity of the IA is 1.54 × 10⁵ L mol⁻¹ cm⁻¹. The calibration graph is linear between 0.02 and 0.8 μmol L⁻¹ of phosphate. The limit of detection is 7 nmol L⁻¹. Phosphate was determined in pure chemicals and water samples, including Dead Sea water.     

Fluorometric determination of DNA using nano-SiO2 particles as an effective dispersant and stabilizer for acridine orange

A sensitive fluorometric method for the determination of ctDNA (calf thymus DNA) is presented. It has good selectivity and sensitivity and uses nano-SiO₂ particles as an effective dispersant and stabilizer for acridine orange (AO). Compared to resonance light scattering (RLS) and the conventional method that uses organic dyes as fluorescence probe, the new method is more tolerant towards coexisting foreign substances and also more stable. With 20 mg nano-SiO₂ particles, 10 μmol L⁻¹ AO, at pH 8.01 and an ionic strength of 0.02 mol L⁻¹, the interaction of AO with nano-SiO₂ and ctDNA results in fluorescent signal enhancement. The extent of enhancement was in good proportion to the concentration of ctDNA at excitation/emission wavelengths of 490/523 nm, respectively. The calibration curve was linear over 0.66–55.60 μg mL⁻¹. The determination limit (3σ) was 15 μg mL⁻¹. The method was applied to the determination of ctDNA in synthetic samples with satisfactory results.     

Determination of trace amounts of cadmium and copper by atomic absorption spectrometry after simultaneous extraction and preconcentration using a new water-soluble polyacrylic acid/alumina sorbent

An analytical method using alumina modified with water-soluble polyacrylic acid polymer for the simultaneous separation and preconcentration of trace Cu and Cd in a column system, and their determination by flame atomic absorption spectrometry was developed. The conditions for coating Al₂O₃ with polyacrylic acid were optimized, then the column was packed with 50 mg of this sorbent. Cd and Cu solution was passed through a glass column at pH 4.5, and elution was carried out with 5 mL of 0.05 M HCl at a flow rate of 1 mL min⁻¹. A sorption capacity of 10 mg Cu and 12 mg Cd was obtained for 1 g sorbent. The detection limit was calculated as 4.5 μg L⁻¹ for Cu and 1.54 μg L⁻¹ for Cd in the final solution. Enrichment factors of 300 for Cd and 400 for Cu were obtained.     

Flow injection fluorimetric determination of L-dopa and dopamine based on a photochemical inhibition process

An automatic procedure has been developed for the determination of L-dopa and dopamine. It is based on the strong inhibition of the photochemical reaction between thionine blue and ethylenediamine-tetraacetic acid by these catecholamines. The proposed flow-injection method allows for the fluorimetric determination of L-dopa in the range of 1.9–98 μg mL⁻¹ and that of dopamine in the range of 1.9–75 μg mL⁻¹ with a sampling frequency of 35 samples h⁻¹. The method was applied successfully to the determination of dopamine in pharmaceutical preparations.     

Determination of rhodium in water samples using cloud point extraction (CPE) coupled with flame atomic absorption spectrometry (FAAS)

Cloud point extraction was applied as a method for preconcentration of rhodium after formation of a complex with 2-propylpiperidine-1-carbodithioate (2-PPC), and later determined by flame atomic absorption spectrometry using TritonX-114 as surfactant. Rhodium was complexed with 2-PPC in an aqueous phase and kept for 15 min in a thermostatted bath at 40 °C. Separation of the two phases was accomplished by centrifugation for 15 min at 4000 rpm. The chemical variables affecting the cloud point extraction were optimized and successfully applied to rhodium determination in various water samples. Under optimized conditions, the preconcentration system (100 mL sample) permitted an enhancement factor of 50. The detection limits obtained under optimal conditions was 0.052 ng mL⁻¹. The extraction efficiency was investigated at different rhodium concentrations (7.0–42.0 μg mL⁻¹), and good recoveries (96.42–99.14%) were obtained using this method. It has been applied to the determination of rhodium in water and was compared with reported methods in terms of Student’s ‘t’-test and variance ratio ‘f’-test.     

Cloud Point Preconcentration and Flame Atomic Absorption Spectrometric Determination of Cobalt and Nickel in Water Samples

 Cloud point methodology was successfully used to preconcentrate trace amounts of Co and Ni as a prior step to their determination by flame atomic absorption spectrometry. 1-Nitroso-2-naphthol and polyethylene glycol-p-nonylphenylether (PONPE 7.5) are used as hydrophobic ligand and nonionic surfactant, respectively. Optimization was performed of the variables effecting complexation and phase separation. Additionally, the influence of viscosity on the analytical signal was investigated. Under the experimental conditions used, preconcentration of only 10 mL of sample in the presence of 0.075% (v/v) PONPE 7.5 permitted the detection of 1.09 μg L⁻¹ of Ni and 1.22 μg L⁻¹ of Co with enhancement factors of 29 and 27 for Ni and Co, respectively. The relative standard deviations (n=5) at concentrations of 80 and 50 μg L⁻¹ for Co and Ni were 2.53 and 2.89%, respectively. Good recoveries in the range of 96–105% were obtained for spiked samples. The effect of different interferent species was studied. The proposed method was applied to the determination of Ni and Co in different water samples. Correspondence: Department of Analytical Chemistry, Faculty of Chemistry, Tabriz University, Tabriz, Iran. e-mail: manzoori@tabrizu.ac.ir Received September 1, 2002; accepted November 8, 2002