On-line electrochemical preconcentration and flame atomic absorption spectrometric determination of manganese in urine samples

A sensitive and selective method was developed for the determination of traces of manganese in urine using on-line electrochemical preconcentration followed by flame atomic absorption spectrometry detection. A home made flow-through polypropylene cell (4.5 cm long × 0.8 cm diameter filled with glass marbles) with an effective inner volume of 0.5 ml containing a working and a counter electrode, both of glassy carbon and a Pt pseudo reference electrode was located in a flow injection manifold specially designed for the purpose of this work. The manganese was deposited from buffer solution of NH₃/NH₄Cl at pH 9.00 through an oxidizing process at a current of 400 mA during 7 min. A flow of HCl 0.1 mol l⁻¹ at 4 ml min⁻¹ through the cell, chemically dissolved the deposit. A small portion (15 μl) of the concentrate was introduced in a continuously flowing system by means of a timing device and was then carried to the detector for the manganese quantification. All electrochemical and spectroscopic variables as well as possible interferences in both systems were systematically studied. The relative standard deviations for ten consecutive measurements of manganese solutions of 2.0 and 20 μg l⁻¹ were of 2.3 and 1.5%, respectively, while for a sample processed five times was less then 5%. The accuracy of the developed procedure was evaluated by adding known amounts of manganese standard to urine samples and following the whole procedure. Recoveries within the range 97.2-102.8% were obtained. To further prove the accuracy, a Seronorm Trace Elements in Urine, Batch 403125 sample with a reported concentration of 13 μg Mn l⁻¹ was also analyzed. The experimental value obtained was of 12.7 ± 0.1 μg l⁻¹, which does not differ significantly from the reported amount (p < 0.05). A preconcentration factor of 40, a linear range between 0.015 and 60 μg l⁻¹ and a limit of detection of 15 ng l⁻¹ permitted the determination of manganese in real urine samples from non-exposed subjects in the range 0.5-2.8 μg l⁻¹.     

Preconcentration and determination of trace metals by flow injection micelle-mediated extraction using flame atomic absorption spectrometry

Micelle-mediated extraction/preconcentration is incorporated on-line into a flow injection system used to determine low levels of Cd(II), Co(II), Cu(II), Mn(II), Ni(II), Pb(II) and Zn(II) present in various samples. The analyte is complexed with HBDAP (N,N′-bis(2-hydroxy-5-bromo-benzyl)1,2-diaminopropane). Under optimal conditions, a solution of 30% (m/v) NaCl and a sample solution containing 2.5 mL of 1% (m/v) sodium dodecyl sulfate (SDS), 0.5 mL of 1.8 × 10⁻³ M HBDAP and 2.5 mL of pH 8.5 borate buffer solution in 25 mL were pumped through the cotton filled mini-column; onto which the surfactant-rich phase containing the complex is collected. A solution of 0.5 M HNO₃ in 50% acetone is used as the eluent. The limits of detection are (ng mL⁻¹) Cd = 0.39, Cu = 3.2, Co = 7.5, Mn = 3.0, Ni = 3.4, Pb = 17.9 and Zn = 0.89 if the sample is allowed to flow for 30 s, but improved for extended preconcentration periods. Analysis of liquid and solid reference materials showed good agreement with the certified values. Complex formation constants between HBDAP and these metal ions were also determined potentiometrically.     

Flow injection on-line ultrasound-assisted extraction of iron in meat samples coupled to a flame atomic absorption spectrometric system

Iron was extracted on-line from solid meat samples by a simple and rapid continuous ultrasound-assisted extraction system (CUES). The CUES is connected to a flow injection manifold, which allows the on-line flame atomic absorption spectrometric determination of iron. A Plakett–Burman design was used for the optimisation of the CUES. The method achieved a total sampling frequency of 11 samples per hour with a relative standard deviation for the complete procedure of 0.4%. The detection limit was 0.6 g g^–1 (dry mass) for a sample amount of 30 mg. Accurate results were obtained by measuring the certified reference materials BCR-186 (pig kidney) and BCR-184 (bovine muscle). The analytical procedure was applied to different real meat samples with satisfactory results.     

Graphene-based solid-phase extraction combined with flame atomic absorption spectrometry for a sensitive determination of trace amounts of lead in environmental water and vegetable samples

Graphene, a novel class of carbon nanostructures, has great promise for use as sorbent materials because of its ultrahigh specific surface area. A new method using a column packed with graphene as sorbent was developed for the preconcentration of trace amounts of lead (Pb) using dithizone as chelating reagent prior to its determination by flame atomic absorption spectrometry. Some effective parameters on the extraction and complex formation were selected and optimized. Under optimum conditions, the calibration graph was linear in the concentration range of 10.0–600.0 μg L⁻¹ with a detection limit of 0.61 μg L⁻¹. The relative standard deviation for ten replicate measurements of 20.0 and 400.0 μg L⁻¹ of Pb were 3.56 and 3.25%, respectively. Comparative studies showed that graphene is superior to other adsorbents including C18 silica, graphitic carbon, and single- and multi-walled carbon nanotubes for the extraction of Pb. The proposed method was successfully applied in the analysis of environmental water and vegetable samples. Good spiked recoveries over the range of 95.3–100.4% were obtained. This work not only proposes a useful method for sample preconcentration, but also reveals the great potential of graphene as an excellent sorbent material in analytical processes.     

Coprecipitation of lead and cadmium using copper(II) mercaptobenzothiazole prior to flame atomic absorption spectrometric determination

A coprecipitation method using a combination of 2-mercaptobenzothiazole (MBT) as a chelating reagent and copper as the coprecipitate carrier is described for the determination of trace lead and cadmium by flame atomic absorption spectrometry. The coprecipitation conditions, such as the effect of pH, the amount of carrier element and reagent, standing time, sample volume and matrix effects were examined in detail. It was found that lead and cadmium are coprecipitated quantitatively (≥95%) with Cu(II)-MBT at pH 9 and that the relative standard deviations (n = 7) were ≤1.6%. When using the enrichment factors of 150-fold for lead and cadmium, the detection limits (3s/b) obtained are 1.08 for lead and 0.04 μg L⁻¹ for cadmium. The method was validated with spiked sea water, stream water, well water, and vegetable samples.     

Cadmium determination in biological samples by direct solid sampling flame atomic absorption spectrometry

A direct solid sampling flame atomic absorption spectrometric procedure for trace determination of cadmium in biological samples has been developed. Test samples (0.05–2.00 mg) were ground and weighed into small polyethylene vials, which were connected to the device for solid sample introduction into a conventional air/acetylene flame. Test samples were carried as a dry aerosol to a quartz cell, placed between the burner and the optical path, which had a perpendicular entrance and a slit in the upper part. The atomic vapor generated in the flame produced a transient signal that was totally integrated within 1 s. The effect of operating conditions and the extent of grinding on the analytical signal were evaluated. Background signals were always low and a characteristic mass of 0.29 ng Cd was obtained. Calibration was performed using different masses of solid certified reference materials. Results obtained for certified and in-house reference materials were typically within the 95% confidence interval of the certified and/or reference value, and the precision, expressed as relative standard deviation, was between 3.8 and 6.7%. The proposed system is simple and it might be adapted to conventional atomic absorption spectrometers allowing the determination of Cd in more than 80 test samples per hour, excluding weighing.     

Multiwalled carbon nanotubes microcolumn preconcentration and determination of gold in geological and water samples by flame atomic absorption spectrometry

The potential of multiwalled carbon nanotubes (MWNTs) as solid-phase extraction adsorbent for the separation and preconcentration of gold has been investigated. Gold could be adsorbed quantitatively on MWNTs in the pH range of 1–6, and then eluted completely with 2 mL of 3% thiourea in 1 mol L^− 1 HCl solution at a flow rate of 0.5 mL min^− 1. A new method using a microcolumn packed with MWNTs as sorbent has been developed for the preconcentration of trace amount of Au prior to its determination by flame atomic absorption spectrometry. Parameters influencing the preconcentration of Au, such as pH of the sample, sample flow rate and volume, elution solution and interfering ions, have been examined and optimized. Under the optimum experimental conditions, the detection limit of this method for Au was 0.15 µg L^− 1 with an enrichment factor of 75, and the relative standard deviation (R.S.D) was 3.1% at the 100 µg L^− 1 Au level. The method has been applied for the determination of trace amount of Au in geological and water samples with satisfactory results.     

Biosorption of heavy metals on Aspergillus fumigatus immobilized Diaion HP-2MG resin for their atomic absorption spectrometric determinations

A solid phase extraction procedure based on biosorption of copper(II), lead(II), zinc(II), iron(III), nickel(II) and cobalt(II) ions on Aspergillus fumigatus immobilized Diaion HP-2MG has been investigated. The analytical conditions including amounts of A. fumigatus, eluent type, flow rates of sample and eluent solutions were examined. Good recoveries were obtained to the spiked natural waters. The influences of the concomitant ions on the retentions of the analytes were also examined. The detection limits (3sigma, N = 11) were 0.30 μg l⁻¹ for copper, 0.32 μg l⁻¹ for iron, 0.41 μg l⁻¹ for zinc, 0.52 μg l⁻¹ for lead, 0.59 μg l⁻¹ for nickel and 0.72 μg l⁻¹ for cobalt. The relative standard deviations of the procedure were below 7%. The validation of the presented procedure is performed by the analysis of three standard reference materials (NRCC-SLRS 4 Riverine Water, SRM 1515 Apple leaves and GBW 07605 Tea). The procedure was successfully applied for the determination of analyte ions in natural waters microwave digested samples including street dust, tomato paste, black tea, etc.     

Arsenic speciation in natural water samples by coprecipitation-hydride generation atomic absorption spectrometry combination

A speciation procedure for As(III) and As(V) ions in environmental samples has been presented. As(V) was quantitatively recovered on aluminum hydroxide precipitate. After oxidation of As(III) by using dilute KMnO₄, the developed coprecipitation was applied to determination of total arsenic. Arsenic(III) was calculated as the difference between the total arsenic content and As(V) content. The determination of arsenic levels was performed by hydride generation atomic absorption spectrometry (HG-AAS). The analytical conditions for the quantitative recoveries of As(V) including pH, amount of aluminum as carrier element and sample volume, etc. on the presented coprecipitation system were investigated. The effects of some alkaline, earth alkaline, metal ions and also some anions were also examined. Preconcentration factor was calculated as 25. The detection limits (LOD) based on three times sigma of the blank (N: 21) for As(V) was 0.012 μg L⁻¹. The satisfactory results for the analysis of arsenic in NIST SRM 2711 Montana soil and LGC 6010 Hard drinking water certified reference materials for the validation of the method was obtained. The presented procedure was successfully applied to real samples including natural waters for arsenic speciation.     

Coprecipitation with metal hydroxides for the determination of beryllium in seawater by graphite furnace atomic absorption spectrometry

Coprecipitation first with magnesium hydroxide, next with tin(IV) hydroxide is developed for the determination of traces of beryllium in sea-water. To a 200-ml sample is added a sodium hydroxide solution to form magnesium hydroxide at pH 11.5, on which beryllium is quantitatively coprecipitated. The precipitate is separated by centrifugation and dissolved in 2 ml of 12 mol/l hydrochloric acid. The resulting solution (ca. 10 ml) is mixed with 2 mg of tin (IV) carrier and the pH is adjusted to 5.0 to collect the beryllium on tin (IV) hydroxide, leaving magnesium ions in the solution. The tin (IV) hydroxide is centrifuged, dissolved in 0.1 ml of 5 mol/l hydrobromic acid, and then diluted to 1 ml with water. Magnesium is so added as to be 500 g/ml for increasing the sensitivity about four times, and the beryllium in the solution is determined by graphite furnace atomic absorption spectrometry. The experiments with synthetic seawater samples showed that pg — g amounts of beryllium can be coprecipitated on the metal hydroxides and beryllium at the low ng/1 level can be determined with reasonable precision (RSD < 10%). The detection limit of the proposed method is 0.5 ng/l of beryllium in seawater.     

Temperature-controlled ionic liquid-liquid-phase microextraction for the pre-concentration of lead from environmental samples prior to flame atomic absorption spectrometry

Hydrophobic ionic liquid could be dispersed into infinite droplets under driving of high temperature, and then they can aggregate as big droplets at low temperature. Based on this phenomenon a new liquid-phase microextraction for the pre-concentration of lead was developed. In this experiment, lead was transferred into its complex using dithizone as chelating agent, and then entered into the infinite ionic liquid drops at high temperature. After cooled with ice-water bath and centrifuged, lead complex was enriched in the ionic liquid droplets. Important parameters affected the extraction efficiency had been investigated including the pH of working solution, amount of chelating agent, volume of ionic liquid, extraction time, centrifugation time, and temperature, etc. The results showed that the usually coexisting ions containing in water samples had no obvious negative effect on the recovery of lead. The experimental results indicated that the proposed method had a good linearity (R = 0.9951) from 10 ng mL⁻¹ to 200 ng mL⁻¹. The precision was 4.4% (RSD, n = 6) and the detection limit was 9.5 ng mL⁻¹. This novel method was validated by determination of lead in four real environmental samples for the applicability and the results showed that the proposed method was excellent for the future use and the recoveries were in the range of 94.8-104.1%.     

A novel fiber-packed column for on-line preconcentration and speciation analysis of chromium in drinking water with flame atomic absorption spectrometry

A novel on-line preconcentration and determination system based on a fiber-packed column was developed for speciation analysis of Cr in drinking water samples prior to its determination by flame atomic absorption spectrometry (FAAS). All variables involved in the development of the preconcentration method including, pH, eluent type, sample and eluent flow rates, interfering effects, etc., were studied in order to achieve the best analytical performance. A preconcentration factor of 32 was obtained for Cr(VI) and Cr(III). The levels of Cr(III) species were calculated by difference of total Cr and Cr(VI) levels. Total Cr was determined after oxidation of Cr(III) to Cr(VI) with hydrogen peroxide. The calibration graph was linear with a correlation coefficient of 0.999 at levels near the detection limit and up to at least 50 μg L⁻¹. The relative standard deviation (R.S.D.) was 4.3% (C = 5 μg L⁻¹ Cr(VI), n = 10, sample volume = 25 mL). The limit of detection (LOD) for both Cr(III) and Cr(VI) species was 0.3 μg L⁻¹. Verification of the accuracy was carried out by the analysis of a standard reference material (NIST SRM 1643e “Trace elements in natural water”). The method was successfully applied to the determination of Cr(III) and Cr(VI) species in drinking water samples.     

Evaluation of different permanent modifiers for the determination of arsenic in environmental samples by electrothermal atomic absorption spectrometry

Single noble metal permanent modifiers such as, Rh, Ir, and Ru, as well as mixed tungsten plus noble metal (W-Rh, W-Ru, W-Ir) permanent modifiers thermally deposited on the integrated platform of transversally heated graphite atomizer were employed for the determination of arsenic in sludges, soils, sediments, coals, ashes and waters by electrothermal atomic absorption spectrometry. Microwave digests of solid samples and water samples were employed for obtaining the analytical characteristics of the methods with different permanent modifiers. The performance of the modifiers for arsenic determination in the real samples depended strongly on the type of permanent modifier chosen. The single noble metal (Rh, Ir and Ru) permanent modifiers were suitable for the analyte determinations in simpler matrices such as waters (recoveries of certified values 95-105%), but the analyte recoveries of certified values in sludges, soils, sediments, coals, and ashes were always lower than 90%. On the other hand, for the determination of arsenic, using W-Rh, W-Ru, and W-Ir permanent modifiers presented recoveries of certified values within 95-105% for all the samples. Long-term stability curves obtained for the determination of arsenic in environmental samples with different permanent modifiers (Rh, Ir, Ru, W-Rh, W-Ir, W-Ru) showed that the improvement in the tube lifetime depends on the tungsten deposit onto the platform. The tungsten plus noble metal permanent modifier presents a tube lifetime of at least 35% longer when compared with single permanent modifier. The results for the determination of As employing different permanent modifiers in the samples were in agreement with the certified reference materials, since no statistical differences were found after applying the paired t-test at the 95% confidence level.     

Combination of dispersive liquid-liquid microextraction with flame atomic absorption spectrometry using microsample introduction for determination of lead in water samples

The dispersive liquid-liquid microextraction (DLLME) was combined with the flame atomic absorption spectrometry (FAAS) for determination of lead in the water samples. Diethyldithiophosphoric acid (DDTP), carbon tetrachloride and methanol were used as chelating agent, extraction solvent and disperser solvent, respectively. A new FAAS sample introduction system was employed for the microvolume nebulization of the non-flammable chlorinated organic extracts. Injection of 20 μL volumes of the organic extract into an air-acetylene flame provided very sensitive spike-like and reproducible signals.Some effective parameters on the microextraction and the complex formation were selected and optimized. These parameters include extraction and disperser solvent type as well as their volume, extraction time, salt effect, pH and amount of the chelating agent. Under the optimized conditions, the enrichment factor of 450 was obtained from a sample volume of 25.0 mL. The enhancement factor, calculated as the ratio of the slopes of the calibration graphs with and without preconcentration, which was about 1000. The calibration graph was linear in the range of 1-70 μg L⁻¹ with a detection limit of 0.5 μg L⁻¹. The relative standard deviation (R.S.D.) for seven replicate measurements of 5.0 and 50 μg L⁻¹ of lead were 3.8 and 2.0%, respectively. The relative recoveries of lead in tap, well, river and seawater samples at the spiking level of 20 μg L⁻¹ ranged from 93.8 to 106.2%. The characteristics of the proposed method were compared with those of the liquid-liquid extraction (LLE), cloud point extraction (CPE), on-line and off-line solid-phase extraction (SPE) as well as co-precipitation, based on bibliographic data. Operation simplicity, rapidity, low cost, high enrichment factor, good repeatability, and low consumption of the extraction solvent at a microliter level are the main advantages of the proposed method.     

Determination of gold by nanometer titanium dioxide immobilized on silica gel packed microcolumn and flame atomic absorption spectrometry in geological and water samples

A new method has been developed for the determination of gold based on separation and preconcentration with a microcolumn packed with nanometer TiO₂ immobilized on silica gel (immobilized nanometer TiO₂) prior to its determination by flame atomic absorption spectrometry. The optimum experimental parameters for preconcentration of gold, such as pH of the sample, sample flow rate and volume, eluent and interfering ions, have been investigated. Gold could be quantitatively retained by immobilized nanometer TiO₂ in the pH range of 8-10, then eluted completely with 0.1 mol L⁻¹ HNO₃. The detection limit of this method for Au was 0.21 ng mL⁻¹ with an enrichment factor of 50, and the relative standard deviation (R.S.D.) was 1.8% at the 100 ng mL⁻¹ Au level. The method has been applied for the determination of trace amounts of Au in geological and water samples with satisfactory results.     

Preconcentration of trace metals with 2-(methylthio)aniline-functionalized XAD-2 and their determination by flame atomic absorption spectrometry

2-(Methylthio)aniline-modified Amberlite XAD-2 has been synthesized by coupling it through a NNNH group. The resulting chelating resin, characterized by elemental analysis, thermogravimetric analysis and infrared spectra, was used to preconcentrate Cd, Hg, Ni, Co, Cu and Zn ions. Several parameters, such as the distribution coefficient and sorption capacity of the chelating resin, pH and flow rates of uptake and stripping, and volume of sample and eluent, were evaluated. The effect of electrolytes and cations on the preconcentration was also investigated. The recoveries were >96%. The procedure was validated by standard addition and analysis of a standard river sediment material (GBW 08301, China). The developed method was utilized for preconcentration and determination of Cd, Hg, Ni, Co, Cu and Zn in tap water and river water samples by flame atomic absorption spectrometry with satisfactory results. The 3σ detection limit and 10σ quantification limit for Cd, Hg, Ni, Co, Cu and Zn were found to be 0.022, 0.028, 0.033, 0.045, 0.041, 0.064 μg l⁻¹ and 0.041, 0.043, 0.052, 0.064, 0.058, 0.083 μg l⁻¹, respectively.     

Separation and speciation of selenium in food and water samples by the combination of magnesium hydroxide coprecipitation-graphite furnace atomic absorption spectrometric determination

A simple and economic separation and speciation procedure for selenium in food and water samples have been presented prior to its graphite furnace atomic absorption spectrometry (GFAAS). Magnesium hydroxide coprecipitation system for selenium(IV) was applied to the separation and speciation of selenium ions. The influences of the various analytical parameters for the quantitative recoveries of selenium ions like pH, amounts of magnesium ions as carrier elements, etc. on were examined. The effects of the alkaline and earth alkaline metals, some transition metals and some anions on the recoveries of selenium(IV) were also investigated. The recoveries of analytes were found greater than 95%. No appreciable matrix effects were observed. The detection limit, defined as three times the blank standard deviation (3σ), was 0.030 μg l⁻¹. The preconcentration factor for the presented system was 25. The proposed method was applied to the speciation of selenium(IV), selenium(VI) and determination of total selenium in natural waters and microwave digested various food samples with satisfactory results. The procedure was validated with certified reference materials. The relative errors and relative standard deviations were below 6% and 10%, respectively.     

Supramolecular microextraction of cobalt from water samples before its microsampling flame atomic absorption spectrometric detection

The supramolecular solvent system consists of tetrahydrofuran (THF) and 1-decanol, that was used as an extraction solvent for a microextraction procedure for the preconcentration and separation of Co(II). The proposed supramolecular-based procedure was combined with microsampling flame atomic absorption spectrometry for the determination of cobalt at trace levels in water samples. N-Benzoyl-N,N-diisobutylthiourea was used to chelate Co(II) in an aqueous solution. Quantitative extraction efficiency was obtained at pH 6.5. The effects of analytical parameters including pH, amount of ligand, type, ratio and volume of supramolecular solvent, sample volume and interfering ions were investigated for optimisation of the procedure. The proposed supramolecular solvent-based microextraction procedure (Ss-ME) exhibits a limit of detection (LOD) of 1.29 µg L^?1 and a limit of quantification (LOQ) of 3.88 µg L^?1. The procedure was validated by addition/recovery tests and by applying TMDA 64.2 and TMDA 53.3 water certified reference materials. The microextraction method was successfully applied for the preconcentration and determination of cobalt in water samples.     

Determination of some trace metals in water and sediment samples by flame atomic absorption spectrometry after coprecipitation with cerium (IV) hydroxide

A cerium(IV) hydroxide coprecipitation method was developed for the determination of some trace elements (Cu, Co, Pb, Cd, Ni) in aqueous solutions, water and sediment samples by flame atomic absorption spectrometry (AAS). Several parameters governing the efficiency of the coprecipitation method were evaluated including pH of sample solution, amount of carrier element, volume of sample solution and the effect of possible matrix ions The procedure was validated by the analysis of GBW 07309 standard reference material sediment and by use of a method based on a solid phase extraction.     

Determination of cadmium by flame atomic absorption spectrometry after preconcentration on naphthalene-methyltrioctylammonium chloride adsorbent as tetraiodocadmate (II) ions

A sensitive and simple solid-phase preconcentration procedure for enrichment of cadmium prior to analysis by flame atomic absorption spectrometry (FAAS) is described. The method is based on the adsorption of cadmium as CdI₄²⁻ on naphthalene-methyltrioctylammonium chloride adsorbent, elution by nitric acid and subsequent determination by FAAS. The effect of pH, iodide concentration, sample flow rate, volume of the sample and diverse ions on the recovery of the analyte was investigated and optimum conditions were established. A preconcentration factor of 40 was achieved using the optimum conditions. The calibration graph was linear in the range 1-100 ng ml⁻¹ cadmium in the initial solution. The detection limit based on the 3S_b criterion was 0.6 ng ml⁻¹ and the relative standard deviations (RSD) were 3.9 and 1.05% for 5 and 40 ng ml⁻¹, respectively (n=8). The method was successfully applied to the determination of cadmium added to river, tap and Persian Gulf water samples.