Determination of iron in seawater by electrothermal atomic absorption spectrometry and atomic fluorescence spectrometry: A comparative study

Two methods available for direct determination of total Fe in seawater at low concentration level have been examined: electrothermal atomization atomic absorption spectrometry (ETAAS) and electrothermal atomization laser excited atomic fluorescence spectrometry (ETA-LEAFS). In a first part, we have optimized experimental conditions of ETAAS (electrothermal program, matrix chemical modification) for the determination of Fe in seawater by minimizing the chemical interference effects and the magnitude of the simultaneous background absorption signal. By using the best experimental conditions, a detection limit of 80 ng L⁻¹ (20 μL, 3σ) for total Fe concentration was obtained by ETAAS. Using similar experimental conditions (electrothermal program, chemical modification), we have optimized experimental conditions for the determination of Fe by LEAFS. The selected experimental conditions for ETA-LEAFS: excitation wavelength (296.69 nm), noise attenuation and adequate background correction led to a detection limit (3σ) of 3 ng L⁻¹ (i.e. 54 pM) for total Fe concentration with the use a 20 μL seawater sample. For the two methods, concentration values obtained for the analysis of Fe in a NASS-5 (0.2 μg L⁻¹) seawater sample were in good agreement with the certified values.     

Direct determination of molybdenum in seawater by adsorption cathodic stripping square-wave voltammetry

A reliable and very sensitive procedure for the determination of trace levels of molybdenum in seawater is proposed. The complex of molybdenum with 8-hydroxyquinoline (Oxine) is analyzed by cathodic stripping square-wave voltammetry based on the adsorption collection onto a hanging mercury drop electrode (HMDE). This procedure of molybdenum determination was found to be more favorable than differential pulse cathodic stripping voltammetry because of inherently faster scan rate and much better linearity obtained through the one-peak (instead of one-of-two peaks) calibration. The variation of polarographic peak and peak current with a pH, adsorption time, adsorption potential, and some instrumental parameters such as scan rate and pulse height were optimized. The alteration of polarographic wave and its likely mechanism are also discussed. The relationship between peak current and molybdenum concentration is linear up to 150 mug l(-1). Under the optimal analytical conditions, the determination limit of 0.5 mug l(-1) Mo was reached after 60 s of the stirred collection. The estimated detection limit is better than 0.1 mug l(-1) of Mo. The applicability of this method to analysis of seawater was assessed by the determination of molybdenum in two certified reference seawater samples (CASS-2 and NASS-2) and the comparison of the analytical results for real seawater samples (study on a vertical distribution of Mo in the seawater column) with the results obtained by Zeeman-corrected electrothermal atomization atomic absorption spectrometry (Zeeman ETAAS). A good agreement between two used methods of molybdenum determination was obtained.     

Effects of various salts on the determination of arsenic by graphite furnace atomic absorption spectrometry. Direct determination in seawater

The effect of Na, Mg, Ca and Sr as their nitrate, chloride and sulfate salts and seasalt, with and without the use of palladium, on the determination of arsenic by electrothermal atomic absorption spectrometry was investigated. In the absence of any stabilizing agent, arsenic was partially lost as molecular species at low temperatures. The effect of salts on the shape of the atomization signal, the integrated absorbance and the stabilizing effect were highly dependent both on their nature and mass. By trapping arsenic, oxide species resulting from the decomposition of nitrate salts induced a high stabilization effect depending on their vaporization temperatures: MgO approximately CaO>SrO>Na2O. The stabilization effect of chlorides occurred about 200 degrees C lower and depended on mass, volatility and hydrolytic properties: SrCl2>CaCl2>MgCl2 approximately NaCl. The effect of sulfates was mainly dependent on their decomposition/vaporization mechanisms, and in the presence of Na2SO4 or CaSO4 a strong chemical interference effect was observed. Palladium stabilized arsenic in the presence of nitrates, chlorides or even sulfates, leading to a similar delaying effect, signal shape and integrated absorbance. Seasalt induced also important modifications to the atomization signal of As. Moreover, an interference effect was observed, which could probably be attributed to the simultaneous vaporization of sulfate in seasalt. In seawater, Pd suppressed this interference effect and permitted to use a high pyrolysis temperature up to 1400 C to remove the major part of the seawater matrix before atomization. Under optimized conditions, the detection limit for As obtained in unmodified seawater in the presence of Pd was 0.34 microg L(-1) for a 10 microl sample.     

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%.     

Use of aqueous slurry sampling for the determination of lead in human hair samples by electrothermal atomic absorption spectrometry

A method for the determination of lead in human hair slurries by electrothermal atomic absorption spectrometry was optimized. Particle size reduction was achieved with a vibrational mill ball equipped with zirconia cups, 20 min being sufficient grinding time to achieve an adequate particle diameter (<1 mum). The use of different thickening agents, namely glycerol, Triton X-100 and Viscalex HV30, was studied and glycerol was found to be the best. The use of Pd and Mg(NO(3))(2) at optimum concentrations of 20 and 25 mg l(-1) respectively was found to be satisfactory for stabilizing lead at 1100 degrees C. A limit of detection of 0.21 mg kg(-1) was obtained. The limit of detection can be reduced to 0.05 mg kg(-1) without loss of analytical performance by increasing four-fold the amount of hair sample. Accuracy was studied by analysis of a CRM 397 human hair reference material with a certified lead content of 33.0 +/- 1.2 mg Pb kg(-1). The standard addition method was used for the determination of lead in hair samples from healthy people, the levels being between 2.3 and 35.5 mg kg(-1).     

Determination of Ultratrace Amounts of Copper(Ⅱ) in Water Samples by Electrothermal Atomic Absorption Spectrometry After Cloud Point Extraction

A novel approach was developed for the determination of ultratrace amounts of copper in water samples by using electrothermal atomic absorption spectrometry (ETAAS) after cloud point extraction (CPE). 1-( 2-Pyridylazo)-2-naphthol was used as the chelating reagent and Triton X-114 as the micellar-forming surfactant. CPE was conducted in a pH 8.0 medium at 40 ℃ for 10 min. After the separation of the phases by centrifugation, the surfactant-rich phase was diluted with 1 mL of a methanol solution of 0. 1 mol/L HNO3. Then 20 μL of the diluted surfactant-rich phase was injected into the graphite furnace for atomization in the absence of any matrix modifier. Various experimental conditions that affect the extraction and atomization processes were optimized. A detection limit of 5 ng/L was obtained after preconcentration. The linear dynamic range of the copper mass concentration was found to be 0-2.0ng/mL, and the relative standard deviation was found to be less than 3.1% for a sample containing 1.0 ng/mL Cu(Ⅱ). This developed method was successfully applied to the determination of ultratrace amounts of Cu in drinking water, tap water, and seawater samples.     

Determination of Cd and Pb in seawater by graphite furnace atomic absorption spectrometry with the use of hydrofluoric acid as a chemical modifier

High concentration of added hydrogen fluoride converted the seawater chloride to the corresponding fluoride matrix, and the liberated hydrochloric acid could be removed during the drying step. The atomization of cadmium and lead could be performed at a relatively low temperature (∼1300 °C) at which the vaporization of the fluoride matrix was relatively slow, and the corresponding weak background signals could be separated from the analytical signals in time. Experimental conditions for the determination of Cd and Pb in seawater in the presence of HF were optimized with the use of the a priori calculation of the limit of detection. The experimental limit of detection obtained for Cd and Pb were, respectively, 0.007 and 0.25 μg l⁻¹ for a 15-μl seawater sample (3σ, 20 replicates). The concentrations of Cd determined in a SLEW-1 estuarine water and a CASS-2 seawater were 0.020±0.002 and 0.016±0.002 μg l⁻¹ Cd, respectively, in good agreement with the 0.018±0.003 and 0.019±0.004 μg l⁻¹ Cd certified values (At the 95% confident level, 10 replicates).     

Preconcentration and separation of cadmium by use of cobalt(III) hexamethylenedithiocarbamate as a collector prior to its determination by atomic absorption spectrometry

Co(III) hexamethylenedithiocarbamate has been applied as a collector in colloid flotation preconcentration of Cd from water prior to electrothermal atomic absorption spectrometry (ETAAS). All experimental parameters necessary for successful flotation have been studied and optimized. The ETAAS results were compared with those obtained by inductive coupled plasma-atomic emission spectrometry (ICP-AES). The ETAAS detection limit was found to be 0.003 microg L(-1) Cd.     

Effects of various salts on the determination of arsenic by graphite furnace atomic absorption spectrometry. Direct determination in seawater

The effect of Na, Mg, Ca and Sr as their nitrate, chloride and sulfate salts and seasalt, with and without the use of palladium, on the determination of arsenic by electrothermal atomic absorption spectrometry was investigated. In the absence of any stabilizing agent, arsenic was partially lost as molecular species at low temperatures. The effect of salts on the shape of the atomization signal, the integrated absorbance and the stabilizing effect were highly dependent both on their nature and mass. By trapping arsenic, oxide species resulting from the decomposition of nitrate salts induced a high stabilization effect depending on their vaporization temperatures: MgO～CaO>SrO>Na₂O. The stabilization effect of chlorides occurred about 200?°C lower and depended on mass, volatility and hydrolytic properties: SrCl₂>CaCl₂>MgCl₂～NaCl. The effect of sulfates was mainly dependent on their decomposition/vaporization mechanisms, and in the presence of Na₂SO₄ or CaSO₄ a strong chemical interference effect was observed. Palladium stabilized arsenic in the presence of nitrates, chlorides or even sulfates, leading to a similar delaying effect, signal shape and integrated absorbance. Seasalt induced also important modifications to the atomization signal of As. Moreover, an interference effect was observed, which could probably be attributed to the simultaneous vaporization of sulfate in seasalt. In seawater, Pd suppressed this interference effect and permitted to use a high pyrolysis temperature up to 1400?°C to remove the major part of the seawater matrix before atomization. Under optimized conditions, the detection limit for As obtained in unmodified seawater in the presence of Pd was 0.34 μg L^–1 for a 10 μl sample.     

Preconcentration and separation of cadmium by use of cobalt(III) hexamethylenedithiocarbamate as a collector prior to its determination by atomic absorption spectrometry

Co(III) hexamethylenedithiocarbamate has been applied as a collector in colloid flotation preconcentration of Cd from water prior to electrothermal atomic absorption spectrometry (ETAAS). All experimental parameters necessary for successful flotation have been studied and optimized. The ETAAS results were compared with those obtained by inductive coupled plasma-atomic emission spectrometry (ICP–AES). The ETAAS detection limit was found to be 0.003 μg L^–1 Cd.     

Determination of traces of sulphur by electrothermal evaporation and non-thermal excitation of S-containing species in a hollow cathode discharge (FANES/MONES) and in a microwave induced plasma (MIP)

Summary The determination of sulphur by emission of S-atoms, S⁺ ions, S₂ and CS molecules using sulphate and other ions was investigated in such non-thermal excitation sources as the normal atmospheric argon-MIP and glow discharge in FANES/MONES (Furnace Nonthermal Excitation Spectrometry/Molecular Nonthermal Excitation Spectrometry). In both cases electrothermal evaporation (ETE) of the sample is applied. In the MIP technique (ETE-MIP) electrothermal evaporation from a new tungsten coil system is used and in the FANES samples are brought in the furnace. The thermal, electrical, chemical and pressure conditions were optimized and the emission spectra recorded. Detection limits are 90 ng for the ETE-MIP technique using the S 469.413 nm atom line. With the tungsten tube-FANES/MONES detection limits of 17 ng are obtained with S₂ molecular band at 383.73 nm. With FANES/MONES in a carbon tube and measurements on CS molecular bands a detection limit of 2 ng is obtained.Dedicated to Prof. Dr. G. Tölg on the occasion of his 60th birthday     

海水中甲基,丁基锡的形态分析

对海水中甲基、丁基锡的氢化反应与捕集、色谱分离及其原子化等进行了条件实验和最佳化。采用１５ｃｍＣｈｒｏｍｏｓｏｒｂＧＡＷ—ＤＭＣＳ载体和ＯＶ—３固定液，色谱分离锡的无机、一甲、二甲、三甲、一丁、二丁、三丁基化合物的保留时间分别为４０、１００、１２５、１３９、１６０、１９１、２２８ｓ；在０．２００ｄｍ３水样中直接测定海水中各形态锡的检出限分别为１．９、１．６、１．８、３．０、１．３、１．４、２２．４、ｎｇＳｎ·ｄｍ－３；其相应的测量精密度在１０％左右。     

浊点萃取电热原子吸收光谱法测定水中痕量铊

采用吡咯烷基二硫代氨基甲酸铵(APDC)为螯合剂,Triton X-114作为表面活性剂,建立了浊点萃取预富集电热原子吸收光谱法测定水中痕量铊的方法。在优化的实验条件下,方法的检出限可达0.07μg/L,相对标准偏差为3.6%(4μg/L,n=7),加标回收率为93%~106%,富集倍率为31。该方法成功应用于自来水和河水中痕量铊的测定。     

Determination of trace amounts of molybdenum in water samples by inductively coupled plasma atomic emission spectrometry after cobalt-dithiocarbamate coprecipitation

Summary A method for the determination of trace amounts of molybdenum in fresh water and seawater samples by sequential ICP-AES with microsampling technique after cobalt-dithiocarbamate coprecipitation was developed. The precipitate was dissolved in 100 l of diluted nitric acid (1:2), and the solution obtained was then introduced into an ICP via a concentric nebulizer. By use of 1.7 ml sample, a preconcentration factor of 17 was achieved. Different factors including integration time, sample volume, pumping rate as well as coprecipitation conditions such as pH of the solution, amounts of reagents, standing time for the precipitate and matrix effects were examined and optimized in detail. Under selected conditions the detection limit of the method for Mo is 0.52 g/l using 1.7 ml sample. The procedure was applied to the analysis of water samples (artificial water and open ocean seawater reference material) with quantitative recovery. The analytical results were in good agreement with the certified value. The method is sensitive, simple, accurate and effective, also in the presence of interfering salts and can be applied to small sample volumes.On leave from the Department of Chemistry, Wuhan University, Wuhan, 430072 China     

Slurry sampling techniques for the determination of lead in Bangladeshi fish samples by electrothermal atomic absorption spectrometry with a metal tube atomizer

Ultrasonic slurry sampling electrothermal atomic absorption spectrometry with a metal tube atomizer has been applied to the determination of lead in Bangladeshi fish samples. The slurry sampling conditions, such as slurry stabilizing agent, slurry concentration, pyrolysis temperature for the slurried fish samples, particle size and ultrasonic agitation time, were optimized for electrothermal atomic absorption spectrometry with the Mo tube atomizer. Thiourea was used as the chemical modifier for the interference of matrix elements. The detection limit was 53 fg (3S/N). The determined amount of lead in Bangladeshi fish samples was consistent with those measured in the dissolved acid-digested samples. The advantages of the proposed methods are easy calibration, simplicity, low cost and rapid analysis.     

固相萃取-液相色谱-串联质谱法测定海水中软骨藻酸

软骨藻酸(domoic acid,DA)是一种由海洋硅藻产生的生物毒素,具有强烈的神经毒性,近海水环境中的DA严重威胁海洋渔业生物和人类健康,因此对近海水环境中的DA进行有效监测至关重要.该文基于固相萃取-液相色谱-串联质谱联用技术(SPE-LC-MS/MS),建立了适用于海水中痕量、超痕量DA的检测方法.针对近海水生...     

Application of micro‐solid‐phase extraction for the on‐site extraction of heterocyclic aromatic amines in seawater

An efficient on‐site extraction technique to determine carcinogenic heterocyclic aromatic amines in seawater has been reported. A micro‐solid‐phase extraction device placed inside a portable battery‐operated pump was used for the on‐site extraction of seawater samples. Before on‐site applications, parameters that influence the extraction efficiency (extraction time, type of sorbent materials, suitable desorption solvent, desorption time, and sample volume) were investigated and optimized in the laboratory. The developed method was then used for the on‐site sampling of heterocyclic aromatic amines determination in seawater samples close to distillation plant. Once the on‐site extraction completed, the small extraction device with the analytes was brought back to the laboratory for analysis using high‐performance liquid chromatography with fluorescence detection. Based on the optimized conditions, the calibration curves were linear over the concentration range of 0.05–20 μg/L with correlation coefficients up to 0.996. The limits of detection were 0.004–0.026 μg/L, and the reproducibility values were between 1.3 and 7.5%. To evaluate the extraction efficiency, a comparison was made with conventional solid‐phase extraction and it was applied to various fortified real seawater samples. The average relative recoveries obtained from the spiked seawater samples varied in the range 79.9–95.2%.     

Determination of tellurium in indium antimonide semiconductor material by electrothermal atomic absorption spectrometry

A method for the determination of the dopant concentration of tellurium in dissolved indium antimonide semiconductor material by electrothermal atomic absorption spectrometry (ETAAS) was developed. Efforts were made to investigate the optimal conditions of the furnace heating program and the effect of palladium modifier on the variation of tellurium and the background absorbance. According to the results obtained, the presence of palladium chemical modifier in the analysis of indium antimonide allowed the successful retention of tellurium in the graphite tube, and the optimum mass of palladium modifier was found to be dependent on the sample matrix concentration. The absorbance profile of tellurium and the background level were significantly improved when a pyrolysis temperature of 1100 degrees C and an atomization temperature of 2200 degrees C were employed in the optimized heating program. With the use of this method, a detection limit of 0.8 microg g(-1) tellurium in indium antimonide could be achieved. The applicability of the proposed method was evaluated by comparison with two independent methods, i.e. slurry sampling-ETAAS and ICP-MS. From the good agreement between the results, it was demonstrated that the proposed method is suitable for the determination of typical dopant concentrations of tellurium in indium antimonide.     

Cloud point extraction of mercury with PONPE 7.5 prior to its determination in biological samples by ETAAS

Cloud point extraction (CPE) has been used for the pre-concentration of mercury, after the formation of a complex with 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (5-Br-PADAP), and later analysis by electrothermal atomic absorption spectrometry (ETAAS) using polyethyleneglycolmono-p-nonyphenylether (PONPE 7.5) as surfactant. The chemical variables affecting the separation step were optimized. Under the optimum conditions, i.e, pH 8.5, cloud point temperature 80 degrees C, 5-Br-PADAP=4x10(-5) mol L(-1), PONPE 7.5=0.2%, sample volume=1.0 mL, an enhancement factor of 22-fold was reached. The lower limit of detection (LOD) obtained under the optimal conditions was 0.01 microg L(-1). The precision for 10 replicate determinations at 2.0 microg L(-1) Hg was 4.0% relative standard deviation (R.S.D.). The calibration graph using the pre-concentration system for mercury was linear with a correlation coefficient of 0.9994 at levels near the detection limits up to at least 16 microg L(-1). The method was successfully applied to the determination of mercury in biological samples and in certified reference material (QC METAL LL3).     

Triple-phase single-drop microextraction of silver and its determination using graphite-furnace atomic-absorption spectrometry.

A new method is described for the determination of silver based on triple-phase microextraction using diethyldithio-carbamate (DDTC) and thioaminophenol. Ag is separated and preconcentrated from the matrix of the sample solution, and finally determined by electrothermal atomic-absorption spectroscopy. The parameters that affect the efficiency were investigated. Under the optimized conditions, a 30-fold preconcentration factor with a detection limit of 0.05 microg L(-1) was achieved. The relative standard deviation was 10% (5 determinations). The developed method was applied to the determination of trace Ag in water samples.