Determination of arsenic in petroleum refinery streams by electrothermal atomic absorption spectrometry after multivariate optimization based on Doehlert design

This paper reports the development of a methodology for the determination of arsenic in petroleum refinery aqueous streams containing large amounts of unknown volatile organic compounds, employing electrothermal atomic absorption spectrometry with polarized Zeeman-effect background correction. In order to make the procedure applicable, the influence of chemical modification and the drying step was examined. Also, pyrolysis and atomization temperatures and the amount of nitric acid added to the sample were optimized using a multivariate approach based on Doehlert matrix. Obtained results indicate that, in this kind of sample, arsenic must be determined by standard addition procedure with a careful control of the drying step temperature and ramp pattern. In order to evaluate the accuracy of the procedure, a test was performed in six spiked samples of petroleum refinery aqueous streams and the relative errors verified in the analysis of such samples (added As between 12.5 and 190 μg l⁻¹) ranged from −7.2 to +16.7%. The detection limit and the relative standard deviation were also calculated and the values are 68 pg and 7.5% (at 12.5 μg l⁻¹ level), respectively.     

Preconcentration and determination of ultra trace amounts of arsenic(III) and arsenic(V) in tap water and total arsenic in biological samples by cloud point extraction and electrothermal atomic absorption spectrometry

A new approach for developing a cloud point extraction-electrothermal atomic absorption spectrometry has been described and used for determination of arsenic. The method is based on phase separation phenomenon of non-ionic surfactants in aqueous solutions. After reaction of As(V) with molybdate towards a yellow heteropoly acid complex in sulfuric acid medium and increasing the temperature to 55 °C, analytes are quantitatively extracted to the non-ionic surfactant-rich phase (Triton X-114) after centrifugation.To decrease the viscosity of the extract and to allow its pipetting by the autosampler, 100 μl methanol was added to the surfactant-rich phase. An amount of 20 μl of this solution plus 10 μl of 0.1% m/v Pd(NO₃)₂ were injected into the graphite tube and the analyte determined by electrothermal atomic absorption spectrometry.Total inorganic arsenic(III, V) was extracted similarly after oxidation of As(III) to As(V) with KMnO₄. As(III) was calculated by difference. After optimization of the extraction condition and the instrumental parameters, a detection limit (3σ_B) of 0.01 μg l⁻¹ with enrichment factor of 52.5 was achieved for only 10 ml of sample. The analytical curve was linear in the concentration range of 0.02-0.35 μg l⁻¹. Relative standard deviations were lower than 5%. The method was successfully applied to the determination of As(III) and As(V) in tap water and total arsenic in biological samples (hair and nail).     

Use of 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide immobilized on silica gel for automated preconcentration and selective determination of antimony(III) by flow-injection electrothermal atomic absorption spectrometry

Selective sorption of Sb(III) on a microcolumn packed with 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide immobilized on silica gel (DPTH-gel) has been used for determination of Sb(III). A flow-injection system comprising a microcolumn connected to the tip of the autosampler was used for preconcentration. The sorbed antimony was eluted with nitric acid directly into the graphite furnace and determined by AAS. The detection limit for antimony under the optimum conditions was 0.3 ng mL^–1. This procedure was used for determination of antimony in natural water, soil, vegetation, and a certified sample of a city waste incineration ash (BCR 176).     

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.     

Automated determination of tin and nickel in brass by on-line anodic electrodissolution and electrothermal atomic absorption spectrometry

The application of an on-line metallic alloy dissolution system using anodic electrodissolution in a flow injection system for the determination of tin and nickel in copper alloys is described. After the electrolyzed material was collected in the autosampler cup, determination was carried out using electrothermal atomic absorption spectrometry (ETAAS). Using specific software developed in Turbo Pascal 7.0, it is possible to control electrolysis time, intensity of the applied current, and triggering of the three-way solenoid valves that push the fluids. Through manipulation of these variables, it is possible to adjust the analytical signal to within the working range of the spectrometer. Calibration of the spectrometer was accomplished by processing reference material. For tin, relative standard deviations for a series of measurements (n=5) performed on the same point and on different points of the sample was smaller than 2 and 4%, respectively; for nickel, 2 and 5%, respectively. The results for tin and nickel were in good agreement with those obtained through application of the classical methodology, as well as with data obtained by optical emission spectrometry. The detection limit for tin was 0.001% (w/w), whereas for nickel it was 0.003% (w/w). The analytical throughput is 30 samples h⁻¹.     

An ion-exchange method for speciation of antimony by flow injection electrothermal atomic absorption spectrometry

In this work, a simple preconcentration system, achieved by replacing the sample tip of the autosampler arm by a micro-column packed with Amberlite IRA-910 or silica gel chelating resin functionalised with 1,5-bis(di-2-pyridyl)methylene tbiocarbohydrazide (DPTH-gel), is developed for the determination of Sb(V) and total antimony, respectively. Different factors including pH of sample solution, ionic strength, concentration and volume of eluent, sample flow rate, sample loading time and matrix effects for preconcentration were investigated. The method has been applied to the determination of antimony species in different samples.     

Determination of antimony(III) and total antimony by single-drop microextraction combined with electrothermal atomic absorption spectrometry

A simple and sensitive method for using electrothermal atomic absorption spectrometry (ET AAS) with Rh as permanent modifier determination of Sb(III) and total Sb after separation and preconcentration by N-benzoyl-N-phenylhydroxylamine (BPHA)-chloroform single drop has been developed. Parameters, such as pyrolysis and atomization temperature, solvent type, pH, BPHA concentration, extraction time, drop size, stirring rate and sample volume were investigated. Under the optimized experimental conditions, the detection limits (3σ) were 8.0 ng L⁻¹ for Sb(III) and 9.2 ng L⁻¹ for total Sb, respectively. The relative standard deviations (R.S.Ds.) were 6.6% for Sb(III) and 7.1% for total Sb (c = 0.2 ng mL⁻¹, n = 7), respectively. The enrichment factor was 96. The developed method has been applied successfully to the determination of Sb(III) and total Sb in natural water samples.     

Direct determination of arsenic and antimony in naphtha by electrothermal atomic absorption spectrometry with microemulsion sample introduction and iridium permanent modifier

This paper reports the determination of arsenic and antimony in naphtha by employing electrothermal atomic absorption spectrometry (ETAAS) as the analytical technique. In order to promote the direct determination of the analytes in the very volatile naphtha, the formation of a microemulsion with different surfactants (Triton X-100 and Brij-35) and different chemical modification strategies were tested. The results indicated that Triton X-100 is the best emulsification agent for naphtha in both As and Sb determination when it is employed at a concentration of 1% w/v in the microemulsion. Under these conditions, the microemulsion was stabile for at least 2 h. By using Brij-35 it was possible to achieve good stability only in the first 15 min. Among all chemical modification approaches investigated (Ir permanent modifier, W-Ir permanent modifier, and Pd modifier), the Ir permanent modifier provided better sensitivity for both analytes and allowed a higher pyrolysis temperature, which decreased the background signals at lower levels. Under the best conditions established in this work, an RSD of 4.6% (20 g L^–1) and a detection limit of 2.7 g L^–1 were observed for arsenic. For antimony, an RSD of 4.0% (20 g L^–1) and a detection limit of 2.5 g L^–1 were obtained. The accuracy of the procedure was assessed by analyzing spiked samples of naphtha from different origins.     

Non-chromatographic determination of ultratraces of V(V) and V(IV) based on a double column solid phase extraction flow injection system coupled to electrothermal atomic absorption spectrometry

In this work, a non-chromatographic procedure for the on-line determination of ultratraces of V(V) and V(IV) is presented. The method involves a solid phase extraction-flow injection system coupled to electrothermal atomic absorption spectrometry (SPE-FI-ETAAS). The system holds two microcolumns (MC) set in parallel and filled with lab-made mesoporous silica functionalized with 3-aminopropyltriethoxy silane (APS) and mesoporous silica MCM-41, respectively. The pre-concentration of V(V) is performed by sorption onto the first MC (C1) filled with APS at pH 3, whilst that of V(IV) is performed by sorption onto the second column (C2) filled with mesoporous silica MCM-41 at pH 5. Aqueous samples containing both analytes are loaded and, after pre-concentration (pre-concentration factor PCF = 10, sorption flow rate = 1 mL min⁻¹, sorption time = 10 min), they are eluted in separate vessels with hydroxylammonium chloride (HC) 0.1 mol L⁻¹ in HCl 0.5 mol L⁻¹ (elution volume = 1 mL, elution flow rate = 0.5 mL min⁻¹). Afterwards, both analytes are determined through ETAAS with graphite furnace. Under optimized conditions, the main analytical figures of merit for V(V) and V(IV) are, respectively: detection limits (3 s): 0.5 and 0.6 μg L⁻¹, linear range: 2-100 μg L⁻¹ (both analytes), sensitivity: 0.015 and 0.013 μg⁻¹ L and sample throughput: 6 h⁻¹ (both analytes). Recoveries of both species were assayed in different water samples. Validation was performed through certified reference materials for ultratraces of total vanadium in river water.     

Determination of Cd by electrothermal atomic absorption spectrometry after electrodeposition on a graphite probe modified with palladium

Traces of Cd were determined by electrothermal atomic absorption spectrometry after electrochemical preconcentration on a commercial graphite ridge probe modified with Pd. The Pd electrochemically deposited on the probe surface served not only as the modifier but it also protected the graphite surface. Cd was electrodeposited at a controlled potential − 1.2 V (vs. saturated calomel electrode) using the Pd-modified graphite probe as a working electrode. The sensitivity of Cd determination remained unchanged for 300 electrodeposition and atomization cycles. The detection limit (3σ_blank) was improved with increasing time of electrolysis and was 1.2 ng l^− 1 for a 10 min electrolysis time in the presence of 0.1 mol l^− 1 NaNO₃. The procedure was applied for the determination of Cd in (1 + 1) diluted seawater and in (1 + 1) diluted urine samples using the standard addition method.     

微型氢化物发生-原子吸收光谱法测定纺织品中的痕量砷和锑

采用三毛细管微型在线氢化发生技术和装置, 建立了氢化物发生-电热石英管原子吸收法测定纺织品中痕量As、 Sb的分析方法. 研究了共存离子对As、 Sb检测的干扰及消除方法. 结果表明: 该方法除Co、 Sn对As和Ni对Sb有干扰外, 其它干扰元素允许量都较大. 采用酒石酸和KI混合掩蔽剂可抑制Co、 Sn对As和Ni对 Sb的干扰. As和Sb的检出限分别为0.7和0.4 ng/L, 已用于测定纺织品中痕量As和Sb的分析.     

Total arsenic content of nine species of Antarctic macro algae as determined by electrothermal atomic absorption spectrometry

Total arsenic in nine species Antarctic macro algae has been measured, by electrothermal atomic absorption spectrometry using a Pd/Mg(NO₃)₂ matrix modifier, to determine their capacity to accumulate the element. Macro algae were collected in February during the 2000 austral summer season at Jubany Station (Argentinean scientific station) around Potter Cove, King George Island. An optimized two-step microwave (MW) program was used to digest the samples. Dried samples were treated with HNO₃, H₂O₂, and HF, left overnight, then subjected to the first MW cycle. After cooling HNO₃ and HClO₄ were added and samples were subjected to the second MW cycle of digestion treatment. The effect of power and time on As recovery was examined. The analytical features of the method were: detection limit, 0.24 g g^–1 (dry mass); precision (RSD), 4.2–5.7%; recovery 91–105%. A wide range of As-retention capacity (41.0–447 g g^–1 dry mass) was observed among the different species. The highest levels of As were found in Phaeurus antarcticus (447 g g^–1 dry mass). This organism satisfies several prerequisites to be considered for consideration as a biomonitor in future studies.     

Determination of trace impurities in titanium dioxide by direct solid sampling electrothermal atomic absorption spectrometry

A true direct solid sampling electrothermal atomic absorption spectrometry method with Zeeman-effect background correction (Analytik Jena ZEEnit 60 AAS) was developed for the determination of As, Cd, Hg, Pb, Sb and Zn in powdered titanium dioxide of pharmaceutical, food and cosmetics grade. The interaction of the titanium matrix and graphite surface of the sample carrier boat in a transversely heated graphite tube atomizer was investigated. Conversion of titanium dioxide to interfering TiO₂–TiC-liquid phase, running out the sampling boat, was observed at temperatures above 2000 °C. The temperature program was optimized accordingly for these volatile analytes in atomization and cleaning steps in order to prevent this interference and to prolong significantly the analytical lifetime of the boat to more than one thousand runs. For all elements, calibration by aqueous standard addition method, by wet-chemically analyzed samples with different content of analytes and/or by dosing one sample in different amounts, were proved as adequate quantification procedures. Linear dynamic calibration working ranges can be considerably expanded up to two orders of magnitude within one measurement run by applying three-field dynamic mode of the Zeeman background correction system. The results obtained by true direct solid sampling technique are compared with those of other independent, mostly wet-chemical methods. Very low limits of detection (3σ criterion) of true solid sampling technique of 21, 0.27, 24, 3.9, 6.3 and 0.9 ng g^− 1 were achieved for As, Cd, Hg, Pb, Sb and Zn, respectively.     

流动注射在线分离富集-电热原子吸收法测定地球化学样品中的痕量金、铂、钯

建立了流动注射在线同时分离富集，无火焰原子吸收法测定地球化学样品中金、铂、钯的分析方法。研究了联用技术并进行了吸附条件和解脱条件的优化实验。当采样频率为20样/h时，Au、Pt、Pd的富集倍数分别为43、37、41。Au、Pt、Pd的检出限(3σ)分别为5、16、9ng／L。将Au、Pt、Pd质量浓度分别为50、200、100ng／L的混合标准溶液平行测定7次，求得Au、Pt、Pd的相对标准偏差分别为3．6％、5．1％、4．7％。并对国家级标准样品进行了测定，其结果及精密度符合要求。     

Separation and preconcentration by flow injection coupled to tungsten coil electrothermal atomic absorption spectrometry

A flow injection system coupled to a tungsten coil electrothermal atomizer has been developed for on-line separation and preconcentration, using lead as a model element. The system utilizes three-way solenoid valves for sampling, buffering, washing and reconditioning solution management, and the resin column is inserted in the tip of the autosampler arm of a Varian GTA-96. The solenoid valves and tungsten coil power supply were controlled by a computer program written in Visual Basic, interfaced with the built-in Varian software. The system performance was tested by loading the resin column with the sample flowing at 3 ml min⁻¹ for 60 s. Elution was performed automatically by sampling 20 μl of the eluent from a sample cup of the autosampler, and this aliquot was delivered into a 150 W tungsten coil. With Chelex-100 resin, the separation of concomitants was tested with lead in the presence of as much as 1000 mg l⁻¹ of Ca, Mg, Na or K. The model system presented an enrichment factor of 64 at a sampling rate of 30 samples per hour.     

石墨炉原子吸收光谱法测定蚕蛹中Cr、Se量

建立了石墨炉原子吸收光谱法测定蚕蛹中Cr、Se的方法,为蚕蛹新资源食品的开发及明确其营养价值提供科学数据。利用石墨炉原子吸收光谱法,偏振塞曼效应扣除背景,石墨炉程序升温方式进行Cr、Se的原子化,检测峰值吸收。加入硝酸镍、吐温X-100为基体改进剂,在体积分数0.5%HNO3介质中对桑蚕蛹中Cr、Se进行测定。方法的精密度:4.0%(Cr),3.1%(Se)。加标回收率:96.8%~105.3%(Cr),92.1%~108.8%(Se)。Cr、Se的线性范围和检出限分别为:0~10μg/L(Cr),0~40μg/L(Se);LOD=1.22μg/L(Cr),1.86μg/L(Se)。建立的分析方法适用于蚕蛹中Cr、Se的测定。     

Arsenic in marine tissues — The challenging problems to electrothermal and hydride generation atomic absorption spectrometry

Analytical problems in determination of arsenic in marine tissues are addressed. Procedures for the determination of total As in solubilized or extracted tissues with tetramethylammonium hydroxide and methanol have been elaborated. Several typical lyophilized tissues were used: NIST SRM 1566a ‘Oyster Tissue’, BCR-60 CRM ‘Trace Elements in an Aquatic Plant (Lagarosiphon major)’, BCR-627 ‘Forms of As in Tuna Fish Tissue’, IAEA-140/TM ‘Sea Plant Homogenate’, NRCC DOLT-1 ‘Dogfish Liver’ and two representatives of the Black Sea biota, Mediterranean mussel (Mytilus galloprovincialis) and Brown algae (Cystoseira barbata). Tissues (nominal 0.3 g) were extracted in tetramethylammonium hydroxide (TMAH) 1 ml of 25% m/v TMAH and 2 ml of water) or 5 ml of aqueous 80% v/v methanol (MeOH) in closed vessels in a microwave oven at 50 °C for 30 min. Arsenic in solubilized or extracted tissues was determined by electrothermal atomic absorption spectrometry (ETAAS) after appropriate dilution (nominally to 25 ml, with further dilution as required) under optimal instrumental parameters (pyrolysis temperature 900 °C and atomization temperature 2100 °C) with 1.5 μg Pd as modifier on Zr–Ir treated platform. Platforms have been pre-treated with 2.7 μmol of zirconium and then with 0.10 μmol of iridium which served as a permanent chemical modifier in direct ETAAS measurements and as an efficient hydride sequestration medium in flow injection hydride generation (FI-HG)–ETAAS. TMAH and methanol extract 96–108% and 51–100% of As from CRMs. Various calibration approaches have been considered and critically evaluated. The effect of species-dependent slope of calibration graph or standard additions plot for total As determination in a sample comprising of several individual As species with different ETAAS behavior has been considered as a kind of ‘intrinsic element speciation interference’ that cannot be completely overcome by standard additions technique. Calibration by means of CRMs has given only semi-quantitative results. The limits of detection (3σ) were in the range 0.5–1.2 mg kg^− 1 As dry weight (wt.) for direct ETAAS analysis of extracts in both TMAH and MeOH. Within-run precision (RSD%) was 5–15% and 7–20% for TMAH and MeOH extracts at As levels 4–50 mg kg^− 1 dry wt., respectively.     

Overcoming interference from the alumina matrix on the determination of arsenic at 189 nanometers using electrothermal atomic absorption spectrometry

A method is described enabling to eliminate the spectral interference from alumina matrix onto As determination at the wavelength 189 nm by electrothermal atomic absorption spectrometry with deuterium background correction. Matrix modification was performed by the addition of ammonium fluoride to protect the formation of aluminium oxide implicated in causing spectral interference and to increase volatility of alumina matrix via the formation of AlF₃. Pre-treating of the pyrolytic graphite platform with a solution of rhodium and citric acid has enabled to stabilize the analyte up to temperature of 1300 °C at which most of AlF₃ could be removed from the graphite furnace. The application of 2 μg of Rh + 20 μg of citric acid + 200 μg of NH₄F has enabled an accurate and interference-free determination of As up to 40 μg of Al in the form of AlCl₃ as verified by analytical recoveries study and resulted in characteristic mass and LOD value in the original sample 15 pg and 50 ng g⁻¹, respectively (10-μL aliquots of sample).     

On-line flow injection solvent extraction for electrothermal atomic absorption spectrometry: Determination of nickel in biological samples

A flow injection (FI) on-line solvent extraction system for electrothermal atomic absorption spectrometry (ETAAS) was developed with nickel as a model trace element. The nickel pyrrolidine-dithiocarbamate chelate was extracted on line into isobutyl methyl ketone, which was delivered into the FI system by a peristaltic pump equipped with poly(tetrafluoroethylene) tubing. The organic phase was separated from the aqueous phase by a novel gravity phase separator with a small conical cavity, and stored in a collector tube, from which 50 μl organic concentrate was introduced into the graphite tube by an air flow. ETAAS determination of the analyte was performed in parallel with the extraction process. An enrichment factor of 25 was obtained in comparison with 50 μl direct introduction while achieving a detection limit of 4 ng l⁻¹ (3σ), and a precision of 1.5% relative standard deviation for 1.0 μg l⁻¹ nickel (n = 11). The proposed method was successfully applied to the determination of nickel in body fluids and other biological samples.     

Determination of total thallium in fresh water by electrothermal atomic absorption spectrometry after colloid precipitate flotation

Tl(I) and Tl(III) are preconcentrated simultaneously from aqueous solutions by colloid precipitate flotation using two collectors: hydrated iron(III) oxide (Fe₂O₃·xH₂O) and iron(III) tetramethylenedithiocarbamate (Fe(TMDTC)₃). After the coprecipitation step and the addition of foaming agents, Tl(I) and Tl(III) were separated from the water by a stream of air bubbles. Various factors affecting Tl(I) and Tl(III) recoveries during the separation from water, including the collector mass, the nature of the supporting electrolyte, pH, ζ potential of the collector particle surfaces, type of tenside, etc., were investigated. Within the optimal pH range (6–6.5), establishing by a recommended procedure, Tl(I) and Tl(III) were separated quantitatively (94.9–100.0%) with 30 mg Fe(III). Both Tl ions were simultaneously separated without any previous conversion of one type of Tl ion to the other. Total Tl determination was performed by electrothermal atomic absorption spectrometry by previous matrix modification of the concentrated samples. The determination limit of Tl by this method is 0.108 μg l⁻¹.