Electrothermal Atomic Absorption Spectrometry Determination Research Articles

Pt(IV)-ion imprinted ordered mesoporous organosilica for platinum preconcentration prior to electrothermal atomic absorption spectrometry determination in geological samples

Pt(IV) ion-imprinted thiocyanato-functionalized SBA-15 material (Pt(IV)S1) was proposed for preconcentration of Pt(IV) ions from digested geological samples before its electrothermal atomic absorption spectrometry (ETAAS) determination. The ion-imprinted material exhibited very good adsorption affinity towards Pt(IV) ions. Under the optimal pH (pH = 3) the maximum static adsorption capacity for Pt(IV) was equal to 175 mg g−1. The use of Pt(IV)S1 as an adsorbent allowed for the quantitative adsorption of Pt(IV) ions from solutions with concentrations up to 25 mg L−1. The creation of ion imprinted adsorption centres resulted in an increase of the adsorption rate and selectivity towards Pt(IV) compared to the similar non-ion imprinted material. The analytical procedure was based on the adsorption of Pt(IV) ions and dissolution of the Pt-loaded sorbent in a small volume of hydrofluoric acid before its dilution with 5% hydrochloric acid and introduction into an electrothermal atomizer. The enrichment factor of the proposed procedure was 38, while the limit of quantification was 0.079 mg kg−1.

Ultrasound-assisted dispersive micro-solid phase extraction of Pb(II) in water samples with in situ synthesis of magnetic Fe3O4-PbS nanocomposites followed by electrothermal atomic absorption spectrometry determination

Herein, an ultrasound-assisted dispersive magnetic micro-solid phase extraction (DM-μSPE) approach, along with electrothermal atomic absorption spectrometry (ETAAS) for the determination of lead at trace level in spring, well, river mineral and tap water samples was developed. The extraction step is based on the synthesis of PbS, following the sonochemical decomposition of L-cysteine used as sulphide precursor and its anchoring onto bare magnetite nanoparticles yielding the Fe3O4@PbS nanocomposite. Overall, DM-μSPE with in situ precipitation of PbS and retention onto magnetic sorbent requires a time as short as 6 min. After trapping Pb(II) as PbS, the magnetic nanocomposite was easily separated from the aqueous matrix by applying an external magnetic field and analyzed by ETAAS following slurry sampling. Different parameters involved in both the sorbent preparation/extraction and Pb quantification were optimized. Under optimal conditions, the method showed a detection limit of 0.02 μg L−1 Pb and a quantification limit of 0.07 μg L−1 Pb. The repeatability, expressed as relative standard deviation was 2% (for 0.6 μg L−1; n = 3). An experimental enrichment factor of 79 and an extraction efficiency of 99% were obtained. Finally, the method was applied for the determination of ultratrace levels of Pb(II) in spring, well, river mineral and tap water samples, showing quantitative recoveries in the range of 95–100%.

Separation and preconcentration of inorganic Se species in tap and natural waters using unfunctionalized nanosilica as sorption material in dispersive micro-solid phase extraction

A highly sensitive and selective method based on dispersive micro-solid phase extraction (D-μ-SPE) technique was developed for the determination of inorganic Se species. A very simple and fast preconcentration procedure involving the use of pure nanosilica for the extraction of Se(IV) complexed with ammonium pyrrolidine dithiocarbamate (APDC) was applied. Elution of the retained Se(IV) species from nanosilica was achieved with ethyl acetate followed by electrothermal atomic absorption spectrometry determination. For speciation analysis, Se(VI) was selectively quantified based on the difference between the concentrations of total inorganic Se and Se(IV) after a pre-reduction step. The interaction between the analyte and the extractant was characterized by FT-IR and an adsorption isotherm study. A 90% extraction efficiency was achieved after optimization of all factors concerning the extraction and elution steps, such as pH, ionic strength and type of chelating agent. Optimized conditions included pH = 2.0, 4.9 μmol L−1 APDC and the use of 1 mg nanosilica as adsorbent. A limit of detection of 1.4 ng L−1, a relative standard deviation of 4.8% and a 90-fold enhancement factor were obtained with 10 mL of sample. The developed method was finally applied to water samples from different origins and compositions, including rain, tap, underground, and sea.

Antimony speciation analysis by hydride trapping on hybrid nanoparticles packed in a needle trap device with electro-thermal atomic absorption spectrometry determination

Novel hybrid nanoparticles show faster antimony adsorption kinetics compared to single nanoparticles, becoming superior sorbents for analytical applications.

Selenium analysis by an integrated microwave digestion-needle trap device with hydride sorption on carbon nanotubes and electrothermal atomic absorption spectrometry determination

An integrated microwave assisted digestion (MW-AD) – needle trap device (NTD) for selenium determination in grape pomace samples is presented. The NTD was filled with oxidized multiwall carbon nanotubes (oxMWCNTS) where Se hydrides were preconcentrated. Determination was carried out by flow injection-electrothermal atomic absorption spectrometry (FI-ETAAS). The variables affecting the system were established by a multivariate design (Plackett Burman), indicating that the following variables significantly affect the system: sample amount, HNO3 digestion solution concentration, NaBH4 volume and elution volume. A Box-Behnken design was implemented to determine the optimized values of these variables. The system improved Se atomization in the graphite furnace, since only trapped hydrides reached the graphite furnace, and the pyrolysis stage was eliminated according to the aqueous matrix of the eluate. Under optimized conditions the system reached a limit of quantification of 0.11μgkg−1, a detection limit of 0.032μgkg−1, a relative standard deviation of 4% and a preconcentration factor (PF) of 100, reaching a throughput sample of 5samples per hour. Sample analysis show Se concentrations between 0.34±0.03μgkg−1 to 0.48±0.03μgkg−1 in grape pomace. This system provides minimal reagents and sample consumption, eliminates discontinuous stages between samples processing reaching a simpler and faster Se analysis.

Synthesis, characterization and theoretical investigation of magnetite nanoclay modified as a new nanocomposite for simultaneous preconcentration of lead and nickel prior to ETAAS determination

Magnetic natural montmorillonite clay nanoparticles modified by 3-[2-(2-aminoethylamino) ethylamino] propyl-trimethoxysilane (AAAPTS) were progress and used as a new adsorbent for contemporary extraction and precocentration of lead and nickel ions through magnetic solid-phase extraction (MSPE) process. Later adsorption, these ions were desorbed with nitric acid followed by electrothermal atomic absorption spectrometry determination. The processed Surface qualification of Co3O4@Clay with AAAPTS and the propagate nanoparticles were the study by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR) and vibrating sample magnetometer (VSM) were used to describe the adsorbent. The MSPE requirement was optimized. The detection limits of 3.3 and 0.5ngL−1 were obtained for lead and nickel, respectively. The linear range was 0.010–0.403ngmL−1 for lead and 0.004–0.062ngmL−1 for nickel. The relative standard variation of the process for eight replicate determination of 0.10 and 0.01ngmL−1 of Pb (II) and Ni (II) were ±2.0% and ±3.3%, respectively. The method was applied for the determination of purpose ions in various samples with great recoveries. Interaction of nanoparticles of Co3O4 with clay surfaces was studied by density functional theory calculations. Nanoparticles of Co3O4 are adsorbed favorably at the Co atoms on the clay surface.

Multiple response optimization of sequential speciation of chromium in water samples by in situ solvent formation dispersive liquid–liquid microextraction prior to electrothermal atomic absorption spectrometry determination

A sensitive and selective in situ solvent formation dispersive liquid–liquid microextraction (in situ DLLME) method followed by electrothermal atomic absorption spectrophotometry for sequential extraction and determination of trace level of chromium (Cr) species was developed. The preconcentration and extraction of Cr species were carried out using ammonium pyrrolidine dithiocarbamate as a chelating agent, and a water-immiscible ionic liquid based on in situ solvent formation as an extraction solvent. Various operating variables such as sample pH, the KPF6 amount and the ionic liquid volume on the extraction efficiency responses (EE%) of Cr(III) and Cr(VI) ions were investigated. Response surface methodology using central composite design was employed for modeling of the responses. Multi-response optimization with desirability function (DF) approach has been used to maximize EE% one Cr species in the presence of another species. After this step, DF was employed to optimize the variables to define the best extraction conditions for Cr speciation. Under the optimal extraction conditions, the calibration curves were linear in the concentration ranges of 20–200 ng L−1 for Cr(III) and 70–250 ng L−1 for Cr(VI) with the limit of detections of 3.7 ng L−1 for Cr(III) and 2.13 ng L−1 for Cr(VI). The relative standard deviations of five microextractions of 100 ng L−1 Cr(III) and Cr(VI) were 9.07 % and 2.39 %, respectively. Finally, the developed method was applied to the determination of Cr(III) and Cr(VI) ions in real water samples.

Dispersive liquid–liquid microextraction of trace amounts of molybdenum prior to electro-thermal atomic absorption spectrometry determination

In the present work, dispersive liquid–liquid microextraction method has been developed for preconcentration trace amount of molybdenum ion as a prior step to its determination by electro-thermal atomic absorption spectrometry. In the proposed approach, quin alizarin was used as a chelating agent and carbon tetrachloride and ethanol were selected as extraction and dispersive solvents, respectively. Some effective parameters on complex and extraction formation, such as the extraction and dispersive solvent type and volume, pH of sample solution, kind of chelating agent, centrifugation rate and time and salting out effect were studied and optimised. The calibration curve was linear in the range of 0.5–9.0 ng mL−1 with detection limit of 0.02 ng mL−1 (n = 8). The relative standard deviation was ±2.9% (n = 8, C = 4.0 ng mL−1) and the enrichment factor was 200. The proposed method was applied for determination of molybdenum in different water samples.

Suspended nanoparticles in surfactant media as a microextraction technique for simultaneous separation and preconcentration of cobalt, nickel and copper ions for electrothermal atomic absorption spectrometry determination

The aim of this study was to describe a new method of microextraction based on the suspension of alumina nanoparticles in the surfactant media for simultaneous separation and preconcentration of the ultra-traces of cobalt, nickel and copper ions. In this technique, the alumina nanoparticles were suspended in the non-ionic surfactant solution of Triton X-114. The analytes in the sample solution were adsorbed onto the nanoparticles. After the phase separation based on the cloud point of the mixture at 40°C, the nanoparticles settled down in the surfactant rich phase. Then 120μL of nitric acid (3.0molL−1) was added to the surfactant rich phase which caused desorption of the analytes. Finally, the liquid phase was separated by centrifugation from the nanoparticles and was used for the quantification of the analytes by the electrothermal atomic absorption spectrometry (ETAAS). The parameters affecting the extraction and detection processes were optimized. Under the optimized experimental conditions (i.e. pH∼8, Triton X-114, 0.05% (v/v); temperature 40°C), a sample volume of 25mL resulted in the enhancement factors of 198, 205 and 206 and detection limits (defined as 3Sb/m) of 2.5, 2.8 and 2.6ngL−1 for Co(II), Ni(II) and Cu(II) respectively. The sorbent showed high capacity for these metal ions (30–40mgg−1 sorbent). The method was successfully applied to the determination of the analytes in natural water samples.

Preconcentration of Trace Amounts of Pb(II) Ions without Any Chelating Agent by Using Magnetic Iron Oxide Nanoparticles prior to ETAAS Determination

This work investigates the potential of magnetic Fe3O4 nanoparticles as an adsorbent for separation and preconcentration of trace amounts of lead from water samples prior to electrothermal atomic absorption spectrometry (ETAAS) determination. No chemical modifier is required in graphite furnace. Pb(II) ion was adsorbed on magnetic Fe3O4 nanoparticles in the pH range of 5.5–6.5, and then magnetic nanoparticles (MNPs) were easily separated from the aqueous solution by applying an external magnetic field; so, no filtration or centrifugation was necessary. After extraction and collection of MNPs, the analyte ions were eluted using HNO3 1.0 mol L−1. Several factors that may affect the preconcentration and extraction process, such as pH, type, and volume of eluent, amount of MNPs, sample volume, salting out effect, and interference ions were studied and optimized. Under the best experimental conditions, linearity was maintained between 0.005–0.5 ng mL−1. Detection limits for lead were 0.8 ng L−1 based on 3Sb. The relative standard deviation of seven replicate measurements of 0.05 ng mL−1 of Pb(II) ions was 3.8%. Finally, the method was successfully applied to extraction and determination of lead ions in the water and standard samples.

Synthesis and characterisation of a silicon oxide film solid-phase extraction system for lead traces determination: an all the way green analytical method

In this work, an all the way green analytical procedure based on a silicon oxide film-solid phase extraction system is proposed for lead traces determination. From the synthesis of a solid phase extraction (SPE) system and throughout the metal preconcentration and determination only aqueous media were employed. Characterisation of the film was carried out by Scanning Electron Microscopy and Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy. Preconcentration conditions, prior to Pb(II) Electrothermal Atomic Absorption Spectrometry (ETAAS) determination, such as adsorption and desorption time, pH and temperature, were optimised. Langmuir, Freundlich and Dubinin-Radushkevich isotherm models were analysed along with the evaluation of adsorption energy and standard free energy (ΔG 0). The greatest adsorption was obtained with incubation at pH 7 and 37°C. By using a small volume of 0.5 mol L−1 HNO3 (0.5 mL) lead was desorbed from the silicon oxide film after 2 h incubation, generating low amount of waste. The films showed better adjustment for the Langmuir model (R2 = 0.989). The detection limit (3.29σ) for Pb(II) was 0.228 µg L−1. The developed procedure is 10-fold more sensitive in comparison to direct ETAAS determination. Recovery values from soft tap-water and soft well-water were above 95%. When hard water was analysed, Pb(II) adsorption was found to be interfered by Mg2+ and Ca2+. After five preconcentration cycles relative recovery was found not to decay below 90%, indicating that the silicon oxide film could be used for multiple lead determinations.

Correction of structured molecular background by means of high-resolution continuum source electrothermal atomic absorption spectrometry—Determination of antimony in sediment reference materials using direct solid sampling

A simple, fast and accurate procedure is proposed for the determination of antimony in certified sediment reference materials using direct solid sampling high-resolution continuum source electrothermal atomic absorption spectrometry and iridium as a permanent modifier. The less sensitive resonance line at 231.147 nm has been used in order to allow the introduction of larger sample mass. Six certified reference materials, one river, one estuarine and four marine sediments have been analyzed. The use of iridium as a permanent modifier caused an increase of 30% in sensitivity and stabilized antimony in the sediment to a pyrolysis temperature of 1100 °C. Significant background absorption with pronounced rotational fine structure was observed at the optimum atomization temperature of 2100 °C, which coincided with the analyte atomic absorption in time. This background was found to be due to the electron excitation spectra of mostly the SiO and in part the PO molecules, and could be eliminated by applying a least-squares background correction algorithm. A characteristic mass of 28 pg Sb was obtained, and the limit of detection (3 σ, n = 10) was 0.02 μg g −1, calculated for 0.2 mg of sample. The results obtained for six certified reference materials with concentrations between 0.40 and 11.6 ± 2.6 μg g −1 Sb were in agreement with the certified values according to a Student's t-test for a 95% confidence level, using aqueous standards for calibration. The precision, expressed as relative standard deviation, ranged between 7% and 17% ( n = 5).

Cloud point extraction for cobalt preconcentration with on-line phase separation in a knotted reactor followed by ETAAS determination in drinking waters

A novel method for cobalt preconcentration by cloud point extraction with on-line phase separation in a PTFE knotted reactor and further determination by electrothermal atomic absorption spectrometry (ETAAS) is proposed. The cloud point system was formed in the presence of non-ionic micelles of polyethyleneglycolmono- p-nonylphenylether (PONPE 7.5) and it was retained on the inner walls of a knotted reactor (KR). The surfactant rich-phase was removed from the knotted reactor with 75 μL of methanol acidified with 0.8 mol L −1 nitric acid, directly into the dosing hole of the L’Vov graphite tube. An enrichment factor of 15 was obtained with a preconcentration time of 60 s, with respect to the direct determination of cobalt by ETAAS in aqueous solutions. The value of the detection limit for the preconcentration of 5 mL of sample solution was 10 ng L −1. The precision, expressed as the relative standard deviation (R.S.D.), for 10 replicate determinations at 0.5 μg L −1 Co level was 4.5%. Verification of the accuracy was carried out by analysis of a standard reference material (NIST SRM 1640e “Trace elements in natural water”). The method was successfully applied to the determination of cobalt in drinking water samples.

Electrothermal atomic absorption spectrometry determination of aluminium in parenteral nutrition and its components

Aluminium concentration in samples of total parenteral nutrition solutions and samples of their individual components were analysed to know the exposure to this element. The median aluminium content obtained for the total parenteral nutrition solutions was 105.7 μg/L; for their individual components, 10% calcium gluconat and 1 M monopotasic phosphate were the most contaminated, as well as the 1 M sodium bicarbonate. The great variability found in the aluminium content of solutions suggests that contamination occurs during the manufacturing process.

The oxidation of Cr(III) to Cr(VI) in the environment by atmospheric oxygen during the bush fires

The presence of Cr(VI) in soils and plants of remote unpolluted areas can be explained by partial oxidation of Cr(III) with atmospheric oxygen during seasonable bush fires, which are rather frequent event in South Africa. Experiments with thermal treatment of a veld grass, Hyperthelia dissoluta, in muffle furnace at high temperature, followed by electrothermal atomic absorption spectrometry (ETAAS) determination of chromium, show a remarkable increase in Cr(VI) concentration from initial 2.5 to 23.2% after the treatment of grass ash at 500 °C and to 58.1% at 900 °C. Before ETAAS determination, the two chromium species of interest were separated by the treatment of samples with 0.1 M Na 2CO 3. Thermodynamic calculations confirm the possibility of Cr(III) to Cr(VI) oxidation with atmospheric oxygen at high temperature in alkaline media, which is typical for vegetation ash. Analysis of field samples show that percent of Cr(VI), in respect to the total amount of chromium increased from initial 2.5% in grass to 9.3% in ash of grass. Without oxidation the percent of Cr(VI) in grass and ash of grass should be a constant value. After the fire Cr(VI) concentration in top soil (0–3 cm) increased from 0.3 ± 0.05 to 1.8 ± 0.5 μg g −1 and the total Cr from 26 ± 9 to 69 ± 14 μg g −1. The reason for the appearance of additional amount of Cr on top soil can be explained by condensation of chromium species from flame and shouldering ash on a soil surface. The results of studies demonstrate that Cr(VI) is formed by Cr(III) oxidation with atmospheric oxygen at high temperature during bush fires.

Comparative Studies on Chemical Modification by Diethyldithiocarbamate for ETV-ICP-OES and ETAAS Determination of Chromium and Nickel

The chemical modification of diethyldithiocarbamate (DDTC) in electrothermal vaporization inductively coupled plasma optical emission spectrometry (ETV-ICP-OES) and in electrothermal atomic absorption spectrometry (ETAAS) was comparatively investigated. The experimental results indicated that the formation of Cr- and Ni-DDTC chelates enhanced significantly the emission signals of Cr and Ni in ETV-ICP-OES, but decreased the absorption signal of Cr and Ni in ETAAS. The different role of DDTC in ETV-ICP-OES and ETAAS was attributed to the different functions of the graphite furnace in the two techniques. The graphite furnace was used as both a vaporizer and an atom-vessel for analytes in ETAAS, but only used as a vaporizer for the sample in ETV-ICP-OES. Thermal gravimetric analysis of Cr- and Ni-DDTC chelates and UV-Vis analysis of the sample vapor collected in CHCl3 after vaporization of their chelates from the graphite furnace indicated that the analytes were vaporized and transported into ICP as their chelates. In addition, the vaporization mechanism of Cr and Ni was also briefly discussed.

Catalytic adsorptive stripping voltammetry versus electrothermal atomic absorption spectrometry in the determination of trace cobalt and chromium in human urine

Two methods of the determination of cobalt and chromium in human urine of non-occupationally exposed populations—highly sensitive catalytic adsorptive stripping voltammetry (CAdSV) and electrothermal atomic absorption spectrometry (ET-AAS)—are evaluated and compared. The CAdSV methods are based on adsorptive accumulation of a cobalt–nioxime (1,2-cyclohexanedione dioxime) or a chromium–DTPA (diethylenetriammine- N, N, N′, N″, N″-pentaacetic acid) complexes on a hanging mercury drop electrode, followed by a stripping voltammetric measurement of the catalytic reduction current of the adsorbed complex in the presence of sodium nitrite in case of cobalt or in the presence of sodium nitrate in case of chromium determination. In the CAdSV procedure UV-photolysis was used for the sample pre-treatment; the ET-AAS determination did not require any separate preliminary decomposition of the analyte urine samples. The accuracy of the procedures was checked by the analysis of commercially available quality control urine samples. The detection limits (3 σ) were 0.13 μg l −1 for Co and 0.18 μg l −1 for Cr in ET-AAS determination and 0.007 μg l −1 for Co and 0.002 μg l −1 for Cr in CAdSV measurements. Precision (R.S.D.) was less than 5% for both methods. The study has shown that the CAdSV is a more reliable and sensitive technique for the determination of very low cobalt and chromium contents in urine, the detection of which is not possible when using the AAS technique.

Flow-injection sample preconcentration for ion-pair chromatography of trace metals in waters

Selected trace transition metal ions have been determined in an FIA/HPLC hyphenated system using on-line preconcentration on cellulose functionalised sorbent Cellex P. For HPLC separation ion-pair chromatography was employed with spectrophotometric detection at 510 nm using post-column derivatisation with PAR. Favourable kinetic conditions of sorption and elution as well as optimisation of hyphenated system allowed to obtain detection limits at sub-μg L −1 level at 25 min preconcentration time. The developed method was employed for determination of Co(II), Ni(II), Cd(II) and Mn(II) in river water with reasonable agreement of obtained results with electrothermal AAS determination.

Microwave sample-digestion procedure for determination of arsenic in moss samples using electrothermal atomic absorption spectrometry and inductively coupled plasma mass spectrometry.

Arsenic in moss samples was determined by electrothermal atomic absorption spectrometry (ETAAS) after microwave-assisted sample digestion. Two different sample masses (500 mg and 1000 mg) and three different microwave ovens were used in the digestion. There was a slight difference in the digestion efficiency, as determined by the residual carbon concentrations of 500 mg digested samples, between the microwave ovens. The arsenic results obtained for moss reference samples were, in most cases, satisfactory. However, phosphorus was found to have a reducing influence on the arsenic peak area in the ETAAS determination. According to the results, it was not possible to reduce the phosphorus interference by increasing the amount of Mg(NO(3))(2) in the Pd-Mg chemical modifier. The arsenic results obtained by ETAAS were compared to those obtained by inductively coupled plasma mass spectrometry (ICP-MS).

Development of an on-line solvent extraction system for electrothermal atomic absorption spectrometry utilizing a new gravitational phase separator. Determination of cadmium in natural waters and urine samples

A novel flow injection (FI) on-line solvent extraction preconcentration/separation system coupled to electrothermal atomic absorption spectrometry (ETAAS), which can tolerate high aqueous to organic flow rate ratios, was developed. The organic extract was effectively separated from a large volume of aqueous phase in a newly designed gravitational phase separator. The performance of the system was illustrated for ultra-trace cadmium determination using ammonium diethyldithiophosphate (DDPA) as chelating agent and isobutyl methyl ketone (IBMK) as extractant. The ETAAS determination and solvent extraction are successfully synchronized through a parallel-operated sequence. The obtained enrichment factor was 24.6 with a sampling frequency of 30 h−1. The detection limit was 2.8 ng l−1 and the precision (RSD at 0.2 µg l−1 Cd) was 3.2%. The proposed method was evaluated by analyzing certified reference materials and applied to the analysis of natural waters and urine samples.