Slurry sampling for the determination of arsenic, cadmium, and lead in mainstream cigarette smoke condensate by graphite furnace–atomic absorption spectrometry and inductively coupled plasma–mass spectrometry

The slurry sampling technique has been applied for the determination of As, Cd, and Pb in mainstream cigarette smoke condensate (MS CSC) by graphite furnace-atomic absorption spectrometry (GF-AAS) and inductively coupled plasma-mass spectrometry (ICP-MS). The MS CSC of the 1R4F Reference Cigarette was collected by electrostatic precipitation and was subsequently prepared as two slurry samples with and without the dispersing agent Triton X-100. Comparison of results determined by ICP-MS analyses of the 1R4F MS CSC slurry samples with those from the conventional microwave digestion method revealed good agreement. The precision of Triton X-100 slurry sampling and of microwave-assisted digestion was better than 10% RSD, and both were superior to slurry sampling without use of Triton X-100. The accuracy of the analytical results for the Triton X-100 slurry sample was further verified by graphite furnace-atomic absorption spectrometry (GF-AAS). For GF-AAS, the method limits of detection are 1.6, 0.04, and 0.5 microg x L(-1) for As, Cd, and Pb, respectively. For ICP-MS, the method limits of detection are 0.06, 0.01, and 0.38 microg x L(-1) for As, Cd, and Pb, respectively. The MS CSC of the 1R4F Reference Cigarette was collected in accordance with the Federal Trade Commission (FTC) smoking regime (35 mL puff volume of 2-s puff duration at an interval of 60 s) and the concentrations of As, Cd and Pb were 6.0+/-0.5, 69.3+/-2.8, and 42.0+/-2.1 ng/cigarette, respectively.     

Scanning electron microscopy studies on surfaces from electrothermal atomic absorption spectrometry—III. The lanthanum modifier and the determination of phosphorus

Morphological studies on graphite surfaces by scanning electron microscopy are presented for platforms made from pyrolytic graphite, and for polycrystalline electrographite tubes with pyrolytic graphite coating in which phosphorus was determined without and with the addition of higher concentrations of lanthanum as the modifier. Lanthanum causes severe pitting and corrosion of the graphite surface already after relatively few determinations, and definite indication was found for the formation of intercalation compounds between lanthanum and graphite. No sign was found, however, for the formation of a dense coating of lanthanum carbide as proposed by several authors. The mechanism for the increase of phosphorus sensitivity is most probably the formation of a thermally stable compound involving lanthanum and phosphorus which leads to vaporization of phosphorus at high enough temperatures to obtain sufficient atomization and useful analytical signals. This is supported by the morphological changes of the graphite surface observed after application of higher lanthanum concentrations, and the resulting increased number of active carbon sites. Phosphorus alone also causes substantial corrosion of graphite, but with a completely different pattern. A very pronounced secondary coating of tube and platform wall is observed in the absence of lanthanum which is most probably supported by the formation and decomposition of compounds between phosphorus and graphite.     

Determination of chromium,manganese and vanadium in sediments and soils by modifier—free slurry sampling electrothermal atomic absorption spectrometry

Slurried sediment and soil samples of the certified reference materials with a highly elevated level of the metals of interest (Mn, Cr and V) were analysed by electrothermal atomic absorption spectrometry (ETAAS) with Zeeman effect background correction. The method of slurry preparation and time-temperature programmes were optimized and, finally, the use of chemical modifiers was not necessary. The effect of alternate spectral lines and gas mini-flows on characteristic masses of analytes was studied. The homogeneity of samples and the influence of short sample grinding were also discussed. The simple, aqueous standard based calibration graphs (except Mn at the concentration > 1000 mg kg⁻¹) were applied for the quantification of results. The results of determinations obtained by slurry sampling agreed well with the cetified values, and the relative standard deviations (RSDs) for the over-all analytical procedure repeatability (at slurries concentration level about 2 mg/2 ml) were less than 9.5%, except manganese (10.4%).     

Application of microwave-assisted dispersive liquid–liquid microextraction and graphite furnace atomic absorption spectrometry for ultra-trace determination of lead and cadmium in cereals and agricultural products

This study was designed to determine the ultra-trace amounts of lead (Pb) and cadmium (Cd) in various cereals (rice, wheat, barley, peas, beans, corn and lentil) obtained from the markets in Kermanshah city, West Iran. An efficient microextraction method was applied to separation and preconcentration of metal ions. This method is dispersive liquid–liquid microextraction based on solidification of floating organic drop, which overcomes the most important problems of other microextraction techniques. Some effective parameters on extraction were studied and, under optimised conditions, the enhancement factors were 122 and 115 for Cd and Pb, respectively. The calibration graphs were linear in the range of 0.1–50 µg kg^?1 with correlation coefficient more than 0.992. The detection limit was 0.05 µg kg^?1. The values of intra-day relative standard deviations and inter-day relative standard deviations were in the range of 4.7?5.3% and 6.0?6.8%, respectively. The Pb concentrations in rice and wheat samples were considerably higher than the allowable limits set by World Health Organization. The method was successfully applied to determination of the Pb and Cd in cereals, and application of the proposed method to the analysis of two certified reference materials produced results that were in good agreement with the certified values.     

Solidified floating organic drop microextraction–electrothermal atomic absorption spectrometry for ultra trace determination of antimony species in tea, basil and water samples

Solidified floating organic drop microextraction was applied as a separation/preconcentration step prior to the electrothermal atomic absorption spectrometric (ETAAS) determination of ultra trace of antimony species. The method was based on the formation of an extractable complex between Sb(III) and ammonium pyrrolidinedithiocarbamate at pH ~ 5, while Sb(V) was remained in the aqueous phase. The antimony extracted into 1-undecanol was determined by ETAAS. Total antimony was determined after the reduction of Sb(V) to Sb(III) with potassium iodide and ascorbic acid. The amount of Sb(V) was determined from the difference of concentration of total antimony and Sb(III). Under the optimum conditions an enhancement factor of 437.5 and a detection limit of 5.0 ng L^?1for the preconcentration of 25 mL of sample was achieved. The relative standard deviation at 300 ng L^?1 of antimony was found to be 3.5 % (n = 6). The proposed method was successfully applied to the determination of antimony in tea, basil and natural water samples.     

Supramolecular dispersive liquid–liquid microextraction-based solidification of floating organic drops combined with electrothermal atomic absorption spectrometry for determination of chromium species

A simple, sensitive and reliable method has been developed for separation and preconcentration of chromium (VI) from aqueous samples before determination by electrothermal atomic absorption spectrometry. The method is based on the extraction of the hydrophobic complex of chromium (VI) with ammonium pyrrolidine dithiocarbamate in the coacervates made up of decanoic acid reverse micelles in the water–tetrahydrofuran mixture. Parameters affecting the extraction efficiency of the analyte were studied and optimised. Under the optimum conditions, the linear range, enhancement factor, the limit of detection and limit of quantification were found to be 0.008–0.4 µg L^?1, 127, and 1.8 ng L^?1 and 6.0 ng L^?1, of Cr(VI), respectively. The relative standard deviation at the concentration level of 0.1 µg L^?1 Cr(VI) (n = 6) was 4.2%. Total chromium was determined after the oxidation of Cr(III) to Cr(VI) with permanganate in acidic medium. The method was successfully applied to the determination of chromium species in water and human serum samples.     

Evaluation of a generalized regression artificial neural network for extending cadmium’s working calibration range in graphite furnace atomic absorption spectrometry

A generalized regression artificial neural network (GRANN) was developed and evaluated for modeling cadmiums nonlinear calibration curve in order to extend its upper concentration limit from 4.0 g L^–1 up to 22.0 g L^–1. This type of neural network presents important advantages over the more popular backpropagation counterpart which are worth exploiting in analytical applications, namely, (1) a smaller number of variables have to be optimized, with the subsequent reduction in development hassle; and, (2) shorter development times, thanks to the fact that the adjustment of the weights (the artificial synapses) is a non-iterative, one-pass process. A backpropagation artificial neural network (BPANN), a second-order polynomial, and some less frequently employed polynomial and exponential functions (e.g., Gaussian, Lorentzian, and Boltzmann), were also evaluated for comparison purposes. The quality of the fit of the various models, assessed by calculating the root mean square of the percentage deviations, was as follows: GRANN > Boltzmann > second-order polynomial > BPANN > Gauss > Lorentz. The accuracy and precision of the models were further estimated through the determination of cadmium in the certified reference material Trace Metals in Drinking Water (High Purity Standards, Lot No. 490915), which has a cadmium certified concentration (12.00±0.06 g L^–1) that lies in the nonlinear regime of the calibration curve. Only the models generated by the GRANN and BPANN accurately predicted the concentrations of a series of solutions, prepared by serial dilution of the CRM, with cadmium concentrations below and above the maximum linear calibration limit (4.0 g L^–1). Extension of the working range by using the proposed methodology represents an attractive alternative from the analytical point of view, since it results in less specimen manipulation and consequently reduced contamination risks without compromising either the accuracy or the precision of the analyses. The implementation of artificial neural networks also helps to reduce the trial-and-error task of looking for the right mathematical model from among the many possibilities currently available in the various scientific and statistic software packages.     

Electrolytic hydride generation atomic absorption spectrometry for the determination of antimony, arsenic, selenium, and tin – mechanistic aspects and figures of merit

This article deals with the electrocatalytic and electrochemical mechanisms of hydride formation and their dependence on hydrogen overvoltage. A three-electrode-arrangement was used to determine the hydrogen overvoltage of different cathode materials (Pt, Au, Ag, glassy carbon, Cd, Pb, amalgamated Ag). The applicability of these cathode materials was tested for hydride formation using As(III), As(V), Sb(III), Sb(V), Se(IV), and Sn(IV). Glassy carbon is the most suitable cathode material for hydride generation with As(III), Sb(III), Se(IV), and Sn(IV). Hg–Ag is well suited for the production of stibine and arsine. As(III), As(V), Sb(III), and Sb(V) were all converted into their hydrides with efficiencies > 90%. A detection limit in the range of 0.11–0.13 μg L^–1 for As and Sb (sample volume 200 μL) was obtained for cathode materials with a high hydrogen overvoltage. The precision of replicate measurements was better than 5% calculated as variation coefficient. The accuracy of the presented method was verified by analysis of certified reference materials and tissues of cancer patients. The recovery rates for As and Se were calculated to be 93–108%.     

Trace determination of cadmium in rice samples using solidified floating organic drop microextraction based on vesicular supramolecular solvent followed by flow-injection analysis–flame atomic absorption spectrometry

In this work, a solidified floating organic drop microextraction was developed based on a vesicular supramolecular solvent consisting of decanoic acid and quaternary ammonium. The method was used for preconcentration of trace amount of cadmium in different rice samples followed by flow-injection analysis–flame atomic absorption spectrometry. Several parameters affecting the extraction efficiency including pH, concentration of 1-(2-pyridylazo)-2-naphthol as the chelating agent, sample and extraction solvent volume, stirring rate, extraction time, salt effect, and interfering ions were investigated and optimized. Under the optimum conditions, a preconcentration factor of 84 was achieved. LOD and LOQ were found to be 0.09 and 0.31 µg L^?1, respectively. The calibration curve was linear within the range of 5.0–700 µg L^?1 (r²?>?0.9978). Intra- and inter-day precisions (RSD% n?=?3) were estimated 2.7 and 3.9% at the concentration of 20 µg L^?1, respectively. The accuracy of the method was successfully validated by analysis of an SRM-1643f standard reference material. Relative recoveries were achieved within the range of 93–107% elucidating suitability of the method for determination of cadmium in rice samples.     

Ultratrace determination of lead,cadmium and copper in environmental and biological samples by atomic absorption spectrometry after their separation and preconcentration using octadecyl silica membrane disks modified with a new n–s schiff base

Pb(II), Cd(II) and Cu(II) ions were separated and preconcentrated by solid-phase extraction on octadecyl-bonded silica membrane disks modified with a new S–N-containing Schiff base (bis-2-thiophenal propandiamine) (BTPD) followed by elution and atomic absorption spectrometric detection. The method was applied as a separation and detection method for lead(II), cadmium(II) and copper(II) in environmental and biological samples. Extraction efficiency and the influence of sample matrix, flow rate, pH, and type and minimum amount of stripping acid were investigated. The maximum capacity of the membrane disks modified by 4?mg of BTPD was found to be 668 ± 10, 480 ± 8 and 454 ± 7?µg of lead, cadmium and copper, respectively. The limit of detection of the proposed method is 0.25, 0.01 and 0.02?ng/mL for lead, cadmium and copper, respectively.     

Tandem dispersive liquid–liquid microextraction coupled with micro-sampling flame atomic absorption spectrometry for rapid determination of lead(II) and cadmium(II) ions in environmental water samples

ABSTRACT

Tandem dispersive liquid liquid microextraction coupled with micro - sampling flame atomic absorption spectrometry for rapid determination of lead2 and cadmium2 ions in environmental water samples. A simple method termed as tandem dispersive liquid–liquid microextraction coupled with micro-sampling flame atomic absorption spectrometry is used for determination of the lead(II) and cadmium(II) ions in different environmental water samples. According to the proposed method, the target analytes are extracted from an aqueous sample solution (10 mL) into a micro-volume of an organic solvent, and then they are selectively back-extracted into an aqueous acceptor solution (150 μL) to increase the compatibility of the extractant phase with a final analyser system and provide a suitable enrichment factor. The developed method is very fast, implemented in just about 7 min, and provides a high sample clean-up. The factors influencing the extraction efficiency including the type and volume of the organic solvent, pH and volume of the acceptor solution, and number of extractions are thoroughly examined and optimised. Under the optimal experimental conditions, the developed method provides a good linearity (in the range of 0.4–300 ng mL^?1 (R² ≥ 0.994)), and low limits of detection (in the range of 0.07–0.31 ng mL^?1). Finally, the method is successfully applied for the direct determination of the understudied analytes in the river, dam, and well water samples.     

Preconcentration of Pb2+ by iron oxide/amino-functionalized silica core–shell magnetic nanoparticles as a novel solid-phase extraction adsorbent and its determination by flame atomic absorption spectrometry

The use of iron oxide/amino-functionalized silica core–shell magnetic nanoparticles for preconcentration of Pb²⁺ followed by its consecutive atomic absorption spectrometry determination is described. Effects of various operating variables, namely, solution pH, initial Pb²⁺ concentration, contact time, adsorbent dosage, sample volume, concentration and volume of desorbing solution, and co-existing ions on solid-phase extraction (SPE) of Pb²⁺ were studied by batch equilibrium technique. The experimental adsorption data were well fitted to the Langmuir isotherm model. The Langmuir adsorption capacity and equilibrium time were found to be 100 mg g^?1 and 20 min, respectively. The adsorption data were also fitted to kinetic pseudo-first-order and pseudo-second-order models. Kinetic studies showed that the adsorption followed pseudo-second-order model. Under the optimal SPE conditions, the enrichment factor, detection limit and relative standard deviation for determination of Pb²⁺ were found to be 211, 1 μg L^?1, and 3.7 % for 50 μg L^?1, respectively. The proposed method was successfully applied to the determination of lead in a real sample with satisfactory results.     

Highly selective micro-sequential injection lab-on-valve (μSI-LOV) method for the determination of ultra-trace concentrations of nickel in saline matrices using detection by electrothermal atomic absorption spectrometry

A highly selective procedure is proposed for the determination of ultra-trace level concentrations of nickel in saline aqueous matrices exploiting a micro-sequential injection Lab-On-Valve (μSI-LOV) sample pretreatment protocol comprising bead injection separation/pre-concentration and detection by electrothermal atomic absorption spectrometry (ETAAS). Based on the dimethylglyoxime (DMG) reaction used for nickel analysis, the sample, as contained in a pH 9.0 buffer, is, after on-line merging with the chelating reagent, transported to a reaction coil attached to one of the external ports of the LOV to assure sufficient reaction time for the formation of Ni(DMG)₂ chelate. The non-ionic coordination compound is then collected in a renewable micro-column packed with a reversed-phase copolymeric sorbent [namely, poly(divinylbenzene-co-N-vinylpyrrolidone)] containing a balanced ratio of hydrophilic and lipophilic monomers. Following elution by a 50-μL methanol plug in an air-segmented modality, the nickel is finally quantified by ETAAS. Under the optimized conditions and for a sample volume of 1.8 mL, a retention efficiency of 70 % and an enrichment factor of 25 were obtained. The proposed methodology showed a high tolerance to the commonly encountered alkaline earth matrix elements in environmental waters, that is, calcium and magnesium, and was successfully applied for the determination of nickel in an NIST standard reference material (NIST 1640-Trace elements in natural water), household tap water of high hardness and local seawater. Satisfying recoveries were achieved for all spiked environmental water samples with maximum deviations of 6 %. The experimental results for the standard reference material were not statistically different to the certified value at a significance level of 0.05.     

Laser-induced fluorescence with an OPO system. Part II: direct determination of lead content in seawater by electrothermal atomization–laser-excited atomic fluorescence (ETA–LEAF)

Fluorescence was induced by coupling a laser with an optical parametric oscillator (OPO) to develop an analytical method for the direct determination of lead content, at ultra-trace level, in seawater by electrothermal atomization-laser-excited atomic fluorescence (ETA-LEAF). The optimization of atomization conditions, laser pulse energy, and mainly temporal parameters allowed us to reach a 3 fg detection limit (0.3 ng L(-1)) despite the low repetition rate of the device. The expected error on predicted concentrations of lead, at trace levels, in seawater was below 15%.     

Validation,using a chemometric approach,of gas chromatography–inductively coupled plasma–atomic emission spectrometry (GC–ICP–AES) for organotin determination

The coupling between gas chromatography (GC) and inductively coupled plasma-atomic emission spectrometry (ICP-AES) has been optimised using experimental designs. Four factors were considered in order to assist the crucial part of the coupling which is the analytes passing through the transfer line. The methodological approach based on the planning of fractional designs is described and justified according to an optimal experimentation. Then, the GC-ICP-AES-based method has been validated by means of statistical tests performed on calibration curves and evaluation of accuracy, precision and limits of detection (LOD), according to ISO standards and IUPAC recommendations. The absolute LOD are found to be quite similar to those obtained using flame photometer. Relative LOD ranged between 20 and 80 ng (Sn) L(-1) after liquid-liquid extraction of the analytes. When solid phase micro-extraction (SPME) is used, LOD are sub 10 ng (Sn) L(-1). The repeatability is 3-10%, according to the extraction used. Analyses of reference sediment, fresh and waste waters confirm the suitability and capabilities of GC-ICP-AES for organotin determination in the environment. The statistical approach has been demonstrated to be a powerful methodological tool, enhancing the experimental part by providing reliable analytical results.     

Simultaneous determination of zinc,copper, lead,and cadmium in fuel ethanol by anodic stripping voltammetry using a glassy carbon–mercury-film electrode

A new, versatile, and simple method for quantitative analysis of zinc, copper, lead, and cadmium in fuel ethanol by anodic stripping voltammetry is described. These metals can be quantified by direct dissolution of fuel ethanol in water and subsequent voltammetric measurement after the accumulation step. A maximum limit of 20% (v/v) ethanol in water solution was obtained for voltammetric measurements without loss of sensitivity for metal species. Chemical and operational optimum conditions were analyzed in this study; the values obtained were pH 2.9, a 4.7-m thickness mercury film, a 1,000-rpm rotation frequency of the working electrode, and a 600-s pre-concentration time. Voltammetric measurements were obtained using linear scan (LSV), differential pulse (DPV), and square wave (SWV) modes and detection limits were in the range 10^–9–10^–8 mol L^–1 for these metal species. The proposed method was compared with a traditional analytical technique, flame atomic absorption spectrometry (FAAS), for quantification of these metal species in commercial fuel ethanol samples.     

Dispersive liquid–liquid microextraction combined with flow injection inductively coupled plasma mass spectrometry for simultaneous determination of cadmium, lead and bismuth in water samples

Dispersive liquid–liquid microextraction (DLLME) was combined with flow injection inductively coupled plasma mass spectrometry for simultaneous determination of cadmium, lead and bismuth in water samples. The metal elements were complexed with sodium diethyldithiocarbamate, and then the complexes were extracted into carbon tetrachloride by using DLLME. Under the optimized conditions, the enrichment factors for Cd, Pb and Bi are 460, 900 and 645 in 5 mL of a spiked water sample, respectively. The calibration graphs for the three metals are linear in the range of concentrations from <10 ng L^?1 to 1,000 ng L^?1. The detection limits are 0.5 ng L^?1, 1.6 ng L^?1 and 4.7 ng L^?1, respectively. The relative standard deviations for ten replicate measurements of 50 ng L^?1 cadmium, lead and bismuth are 2.6%, 6.7%, and 4.9%, respectively, and the relative recoveries in various water samples at a spiking level of 50 ng L^?1 range from 83.6% to 107.0%.