Flow injection hydride generation electrothermal atomic absorption spectrometric determination of toxicologically relevant arsenic in urine

Analytical procedure for the determination of toxicologically relevant arsenic (the sum of arsenite, arsenate, monomethylarsonate and dimethylarsinate) in urine by flow injection hydride generation and collection of generated inorganic and methylated hydrides on an integrated platform of a transverse-heated graphite atomizer for electrothermal atomic absorption spectrometric determination (ETAAS) is elaborated. Platforms are pre-treated with 2.7 μmol of zirconium and then with 0.10 μmol of iridium which serve both as an efficient hydride sequestration medium and permanent chemical modifier. Arsine, monomethylarsine and dimethylarsine are generated from diluted urine samples (10–25-fold) in the presence of 50 mmol L⁻¹ hydrochloric acid and 70 mmol L⁻¹ l-cysteine. Collection, pyrolysis and atomization temperatures are 450, 500, 2100 and 2150 °C, respectively. The characteristic mass, characteristic concentration and limit of detection (3σ) are 39 pg, 0.078 μg L⁻¹ and 0.038 μg L⁻¹ As, respectively. The limits of detection in urine are ca. 0.4 and 1 μg L⁻¹ with 10- and 25-fold dilutions. The sample throughput rate is 25 h⁻¹. Applications to several urine CRMs are given.     

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.     

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.     

Investigation of thallium hydride generation using in situ trapping in graphite tube by atomic absorption spectrometry

Thallium hydride was generated from aqueous solutions by merging sample and sodium tetrahydroborate reductant in a batch system. In situ preconcentration of volatile thallium hydride in a preheated graphite furnace coated with palladium, which was used as both the collection medium and atomizer, greatly improved the sensitivity for the determination of thallium by hydride generation atomic absorption spectrometry. The presence of tellurium can increase the generation efficiency of thallium hydride. The operating conditions were optimized. The calibration graph is linear up to 100 ng and the characteristic mass for thallium was 0.92 ng which is seventeen times lower than that obtained with the heated quartz tube atomizer.     

Comparison of modifiers for determination of arsenic, antimony and selenium by atomic absorption spectrometry with atomization in graphite tube or hydride generation and in-situ preconcentration in graphite tube

The study was performed to compare the effect of magnesium modifier (magnesium nitrate) with that of other modifiers (palladium nitrate and nickel nitrate) in determination of arsenic, antimony and selenium by atomic absorption spectroscopy with atomization in a graphite tube, with generation of hydrides and in situ preconcentration in a graphite tube. The assumed criterion of a modifier performance was the magnitude of the analytical signal. It was found that in determinations with atomization in a graphite furnace the effects of all these modifiers were comparable, while in those with hydride generation and in situ preconcentration in a graphite tube the magnesium modifier showed poorer performance (25% decrease of the analytical signal). In determinations of arsenic and selenium the analytical signal obtained with magnesium salt as a modifier was comparable with those obtained in the presence of all other modifiers.     

氢化物-原子吸收光谱法测定冶金企业废水中的砷

采用HNO3/HClO4(体积比10∶1)消解冶金废水样品,经6mol.L-1 HCl溶液酸化后,加入碘化钾(3%)、抗坏血酸(1%)及硫脲(1%)混合溶液进行还原,用氢化物-原子吸收光谱法(HG-AAS)测定了样品中的As含量.结果表明,该方法的检出限为0.297μg/L,相对标准偏差RSD为5.463%,样品加标回收率为93%～108%;其操作方便、选择性好、灵敏度高、干扰少,适合于复杂废水中微量和痕量As的测定.     

Microwave-assisted digestion of organoarsenic compounds for the determination of total arsenic in aqueous, biological, and sediment samples using flow injection hydride generation electrothermal atomic absorption spectrometry

A microwave assisted wet digestion method for organoarsenic compounds and subsequent determination of total arsenic in aqueous, biological and sediment samples by means of flow injection hydride generation electrothermal atomic absorption spectrometry (FI-HG-ETAAS) is described. Sodium persulfate, sodium fluoride and nitric acid serve as digestion reagents, which allow a quantitative transformation of organoarsenic compounds to hydride forming species in a commercial microwave sample preparation system. The maximum operating pressures of the applied tetrafluorometoxil (TFM) liners are 75 bar (high pressure vessels) and 30 bar (medium pressure vessels), corresponding to maximum solution temperatures of 300 and 260 °C. For the investigated samples, digestion temperatures of 210-230 °C (medium pressure vessels) and 240-280 °C (high pressure vessels) were obtained.In medium pressure vessels, arsenic recovery from aqueous testing solutions of dimethylarsinic acid (DMA), phenylarsonic acid (PAA) and tetraphenylarsonium chloride (TPA) at initial concentrations of 100 and 10 μg l⁻¹ is complete, even in the presence of an excess of organic carbon (potassium hydrogen phthalate, 2000 mg l⁻¹) or fatty acids (linolenic acid 70%; linoleic acid ≈20-25%; Oleic acid ≈3%, 900-4500 mg l⁻¹).Arsenic recovery from aqueous arsenobetaine (ASB) solutions with the same initial concentrations is also complete if high pressure vessels and a higher concentration of fluoride ions are used, whereas the addition of organic carbon (potassium hydrogen phthalate, 2000 mg l⁻¹, fatty acids, 900-4500 mg l⁻¹) leads to a decrease in arsenic recovery of about 2-5%. In all cases, residual carbon contents are close to the limit of detection for the applied analytical method (15 mg l⁻¹).Results of arsenic analysis in reference standard materials revealed a significant dependence on the material’s nature (sediment samples, plant materials and seafood samples). Sediment samples and plant materials show recoveries for arsenic around 100% after a single-step digestion in medium pressure TFM liners. Seafood (fish/lobster/mussel samples) usually require either the use of high pressure vessels or a second digestion step, if medium pressure vessels are used.     

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.     

Electrochemical hydride generation atomic absorption spectrometry for determination of cadmium

An electrolytic hydride generation system for determination of another hydride forming element, cadmium, by catholyte variation electrochemical hydride generation (EcHG) atomic absorption spectrometry is described. A laboratory-made electrolytic cell with lead-tin alloy as cathode material is designed as electrolytic generator of molecular hydride. The influences of several parameters on the analytical signal have been evaluated using a Plackett-Burman experimental design. The significant parameters such as cathode surface area, electrolytic current, carrier gas flow rate and catholyte concentration have been optimized using univariate method. The analytical figures of merit of procedure developed were determined. The calibration curve was linear up to 20 ng ml⁻¹of cadmium. The concentration detection limit (3σ, n = 8) of 0.2 ng ml⁻¹ and repeatability (relative standard deviation, n = 7) of 3.1% were achieved at 10.0 ng ml⁻¹. It was shown that interferences from major constituents at high concentrations were significant. The accuracy of method was verified using a real sample (spiked tap water) by standard addition calibration technique. Recovery of 104% was achieved for Cd in the spiked tap water sample.     

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.     

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.     

Mechanism of aluminium spike formation and dissipation in electrothermal atomic absorption spectrometry

The mechanism of aluminium spike formation and dissipation of aluminium atoms in electrothermal atomization absorption spectrometry has been investigated using two different approaches. The first approach employs a graphite electrothermal atomizer coupled to an inductively coupled plasma mass spectrometer (ICP-MS) in a configuration that allows simultaneous measurement of atomic, or molecular, absorption signals and mass spectrometric signals. Aluminium sub-oxide (AlO and Al₂O) and CO(g) spikes in ICP-MS are correlated with the appearance of both Al atom spikes and Al-containing molecule spikes in absorption spectrometry. The aluminium carbide (AlC₂) signal in ICP-MS is not coincident with the appearance of either Al atom spikes or Al-containing molecule spikes in absorption spectrometry. The second approach uses two different imaging systems, i.e. shadow spectral filming (SSF) and shadow spectral digital imaging (SSDI), to provide temporally and spatially resolved absorption profiles of Al atoms and Al-containing molecules during Al spike formation and dissipation. The transverse cross-sectional distribution of Al atoms and of Al-containing molecules in the graphite furnace are complementary to one another for both wall and platform atomization. The highest concentration of Al atoms is near the graphite surface, whereas the highest concentration of Al-containing molecular species is at the centre of the graphite tube. The Al-containing molecules observed in both wall and platform atomization consist of both gaseous Al-molecules and a non-uniformly distributed cloud of finely dispersed Al₂O₃(s,1) particles. A mechanism of formation that is consistent with the above experimental observations is presented. It is proposed that Al atom spikes are formed from gaseous Al₂O precursors and that this reaction is triggered by the formation of a molten, condensed-phase Al₄C₃ melt.     

Development of an automated sequential injection on-line solvent extraction-back extraction procedure as demonstrated for the determination of cadmium with detection by electrothermal atomic absorption spectrometry

An automated sequential injection (SI) on-line solvent extraction-back extraction separation/preconcentration procedure is described. Demonstrated for the assay of cadmium by electrothermal atomic absorption spectrometry (ETAAS), the analyte is initially complexed with ammonium pyrrolidinedithiocarbamate (APDC) in citrate buffer and the chelate is extracted into isobutyl methyl ketone (IBMK), which is separated from the aqueous phase by means of a newly designed dual-conical gravitational phase separator. A metered amount of the organic eluate is aspirated and stored in the PTFE holding coil (HC) of the SI-system. Afterwards, it is dispensed and mixed with an aqueous back extractant of dilute nitric acid containing Hg(II) ions as stripping agent, thereby facilitating a rapid metal-exchange reaction with the APDC ligand and transfer of the Cd into the aqueous phase. The aqueous phase is separated in a second dual-conical gravitational phase separator, and 30 μl of it is entrapped and metered in a sample loop (SL) and subsequently introduced via air segmentation into the graphite tube for analyte quantification. The ETAAS determination is performed in parallel with the separation/preconcentration process of the ensuing sample. An enrichment factor of 21.4, a detection limit of 2.7 ng l⁻¹, along with a sampling frequency of 13 h⁻¹ were obtained at a sample flow rate of 6.0 ml min⁻¹. The precision (R.S.D.) at the 0.4 μg l⁻¹ level was 1.8% as compared to 3.2% when quantifying the organic extractant directly. The applicability of the procedure is demonstrated for the determination of trace levels of cadmium in three certified reference materials.     

Underestimation of total arsenic concentration in groundwater samples determined by hydride generation quartz furnace atomic absorption spectrometry due to sample characteristics

Total arsenic concentrations in groundwater samples determined by hydride generation quartz furnace atomic absorption spectrometry may underestimated due to a loss of quartz cell surface “conditioning.” This loss of quartz cell surface “conditioning” is due to the analysis of many samples that do not contain measurable quantities of the analyte. This process is further accelerated by the use of high concentrations of sodium tetrahydroborate and hydrochloric acid. Analysis of the highest calibration standard in between the samples and the use of low concentrations of sodium tetrahydroborate and hydrochloric acid could minimize the error arising from this source.     

Flow injection determination of selenium by successive retention of Se(IV) and tetrahydroborate(III) on an anion-exchange resin and hydride generation electrothermal atomization atomic absorption spectrometry with in-atomizer trapping: Part 1. Method development and investigation of interferences

A sample solution was passed at 20 ml min⁻¹ through a column (150×4 mm²) of Amberlite IRA-410Stron anion-exchange resin for 60 s. After washing, a solution of 0.1% sodium borohydride was passed through the column for 60 s at 5.1 ml min⁻¹. Following a second wash, a solution of 8 mol l⁻¹ hydrochloric acid was passed at 5.1 ml min⁻¹ for 45 s. The hydrogen selenide was stripped from the eluent solution by the addition of an argon flow at 150 ml min⁻¹ and the bulk phases were separated by a glass gas–liquid separator containing glass beads. The gas stream was dried by passing through a Nafion® dryer and fed, via a quartz capillary tube, into the dosing hole of a transversely heated graphite cuvette containing an integrated L’vov platform which had been pretreated with 120 μg of iridium as trapping agent. The furnace was held at a temperature of 250°C during this trapping stage and then stepped to 2000°C for atomization. The calibration was performed with aqueous standards solution of selenium (selenite, SeO₃²⁻) with quantification by peak area. A number of experimental parameters, including reagent flow rates and composition., nature of the gas–liquid separator, nature of the anion-exchange resin, column dimensions, argon flow rate and sample pH, were optimized. The effects of a number of possible interferents, both anionic and cationic were studies for a solution of 500 ng 1⁻¹ of selenium. The most severe depressions were caused by iron (III) and mercury (II) for which concentrations of 20 and 10 mg  1⁻¹ caused a 5% depression on the selenium signal. For the other cations (cadmium, cobalt, copper, lead,. magnesium, and nickel) concentrations of 50–70 mg 1⁻¹ could be tolerated. Arsenate interfered at a concentration of 3 mg⁻¹, whereas concentrations of chloride, bromide, iodide, perchlorate, and sulfate of 500–900 mg l⁻¹ could be tolerated. A linear response was obtained between the detection limit of 4 ng 1⁻¹, with a characteristic mass of 130 pg. The RSDs for solutions containing 100 and 200 ng 1⁻¹ selenium were 2.3% and 1.5%, respectively.     

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.     

Organic,inorganic and total mercury determination in fish by chemical vapor generation with collection on a gold gauze and electrothermal atomic absorption spectrometry

A method for organic, inorganic and total mercury determination in fish tissue has been developed using chemical vapor generation and collection of mercury vapor on a gold gauze inside a graphite tube and further atomization by electrothermal atomic absorption spectrometry. After drying and cryogenic grinding, potassium bromide and hydrochloric acid solution (1 mol L^− 1 KBr in 6 mol L^− 1 HCl) was added to the samples. After centrifugation, total mercury was determined in the supernatant. Organomercury compounds were selectively extracted from KBr solution using chloroform and the resultant solution was back extracted with 1% m/v L-cysteine. This solution was used for organic Hg determination. Inorganic Hg remaining in KBr solution was directly determined by chemical vapor generation electrothermal atomic absorption spectrometry. Mercury vapor generation from extracts was performed using 1 mol L^− 1 HCl and 2.5% m/v NaBH₄ solutions and a batch chemical vapor generation system. Mercury vapor was collected on the gold gauze heated resistively at 80 °C and the atomization temperature was set at 650 °C. The selectivity of extraction was evaluated using liquid chromatography coupled to chemical vapor generation and determination by inductively coupled plasma mass spectrometry. The proposed method was applied for mercury analysis in shark, croaker and tuna fish tissues. Certified reference materials were used to check accuracy and the agreement was better than 95%. The characteristic mass was 60 pg and method limits of detection were 5, 1 and 1 ng g^− 1 for organic, inorganic and total mercury, respectively. With the proposed method it was possible to analyze up to 2, 2 and 6 samples per hour for organic, inorganic and total Hg determination, respectively.     

Flow injection-hydride generation atomic absorption spectrometric determination of selenium, arsenic and bismuth

A simple and robust flow injection system which permits low sample and reagent consumption is described for rapid and reliable hydride generation atomic absorption spectrometric determination of selenium, arsenic and bismuth. The system, which composed of one peristaltic pump and one four channel solenoid valve, used water as the carrier streams for both sample and NaBH₄ solution. Rapid off-line pre-reduction of the analytes was achieved by using hydroxylamine hydrochloride for selenium and a mixture of potassium iodide and ascorbic acid for arsenic and bismuth. Transition metal interference was eliminated with the addition of thiourea and EDTA into the NaBH₄ solution and significant sensitivity enhancement was observed for selenium in the presence of thiourea in the reductant solution. Under optimised conditions, the method achieved detection limits of 0.2 ng mL⁻¹ for Se, 0.5 ng mL⁻¹ for As and 0.3 ng mL⁻¹ for Bi. The method was very reproducible, achieving relative standard deviations of 6.3% for Se, 3.6% for As and 4.7% for Bi, and has a sample throughput of 360 h⁻¹. Successful application of the method to the quantification of selenium, arsenic and bismuth in a certified reference river sediment sample is reported.     

Speciation of inorganic arsenic by electrochemical hydride generation atomic absorption spectrometry

A simple procedure was developed for the speciation of inorganic arsenic by electrochemical hydride generation atomic absorption spectrometry (EcHG–AAS), without pre-reduction of As(V). Glassy carbon was selected as cathode material in the flow cell. An optimum catholyte concentration for simultaneous generation of arsine from As(III) and As(V) was 0.06 mol l⁻¹ H₂SO₄. Under the optimized conditions, adequate sensitivity and difference in ratio of slopes of the calibration curves for As(III) and As(V) can be achieved at the electrolytic currents of 0.6 and 1 A. The speciation of inorganic arsenic can be performed by controlling the electrolytic currents, and the concentration of As(III) and As(V) in the sample can be calculated according to the equations of absorbance additivity obtained at two selected electrolytic currents. The calibration curves were linear up to 50 ng ml⁻¹ for both As(III) and As(V) at 0.6 and 1 A. The detection limits of the method were 0.2 and 0.5 ng ml⁻¹ for As(III) and As(V) at 0.6 A, respectively. The relative standard deviations were of 2.1% for 20 ng ml⁻¹ As(III) and 2.5% for 20 ng ml⁻¹ As(V). The method was validated by the analysis of human hair certified reference material and successfully applied to speciation of soluble inorganic arsenic in Chinese medicine.