Determination of Ultratrace Amounts of Copper and Cadmium in Seawater by Graphite Furnace Atomic Absorption Spectrometry with Flow-Injection Semi On-line Preconcentration

Methods are described for the determination of ultratrace amounts of copper and cadmium in seawater by graphite furnace atomic absorption spectrometry with flow-injection, microcolumn preconcentration. A new type of C₁₈ column loaded with sodium diethyldithiocarbamate (sodium-DDC) was used to extract copper and cadmium from seawater as the DDC chelates. The analytical effects of the pH of the mixture of the sample and sodium-DDC solutions and the concentration of the chelating reagent were studied. Sodium-DDC-loaded columns and unloaded C₁₈ columns with different shapes and volumes were compared. To determine copper in seawater, a simple aqueous calibration was made with a mixture of palladium and magnesium nitrate as a matrix modifier, while for cadmium no matrix modifier was necessary. This method required only small seawater volumes, 600 and 400 μl for the determination of copper and cadmium respectively, with preconcentration factors of 15-fold for copper and 10-fold for cadmium. Detection limits for the preconcentration of aqueous solutions of copper and cadmium were 0.024 and 0.004 μg liter⁻¹ (3σ), respectively. Results for determinations of copper and cadmium in National Research Council of Canada, CASS-2, Nearshore Seawater Reference Material showed no significant differences between the certified values and the measured values, based on Student′s t test at the 95% confidence level. The relative standard deviations of the various measurements varied between 2 and 8%.     

Optimization of a chemical modifier in the determination of selenium by graphite furnace atomic absorption spectrometry and its application to wheat and wheat flour analysis.

A method for the determination of total selenium in wheat and wheat flour using graphite furnace atomic absorption spectrometry (GFAAS) with palladium/ascorbic acid as a chemical modifier was studied. The effects of nickel nitrate, palladium/ascorbic acid, and palladium/magnesium nitrate as chemical modifiers on the sensitivity in the determination of selenite, selenate and selenomethionine by GFAAS were compared. The palladium/ascorbic acid modifier was used for the determination of total selenium in wheat and wheat flour, because the oxidation states of the selenium ion are not important in the determination. The detection limit was estimated to be 1 microg L(-1) (calculated as 3sigma of the blank); the calibration curve was linear for the concentration range 5 - 50 microg L(-1) and the recovery range was 96.66 - 101.80%. The optimal ashing and atomizing temperatures were 1300 degrees C and 2250 degrees C, respectively. The proposed method was successfully applied to the determination of total selenium in wheat and wheat flour.     

Cadmium analysis in soil by microwave acid digestion and graphite furnace atomic absorption spectrometry

The need to determine micronutrients and toxic elements in soils has grown in recent years and cadmium is of special interest. A method has been developed for the determination of cadmium in soils based on a prior acid digestion of the samples with nitric acid in closed Teflon vessels, into a microwave over. The cadmium determination was carried out by graphite furnace atomic absorption spectrometry (GFAAS) with L'vov platform. Optimum operating conditions, analyte modifiers and matrix interferences have been investigated. The best matrix modifier was found to be ammonium dihydrogen phosphate. The interferences are greatly reduced under these operating conditions and calibration can be performed with simple aqueous solutions of the metal standard. The method is rapid and provides accurate and precise results that agree with certified values for two reference materials: BCR 141 (calcareous loam soil) and BCR 277 (estuarine sediment).     

石墨炉原子吸收法直接测定海水中铅的方法探索

目的探索石墨炉原子吸收法直接测定海水中铅的检测方法。方法用硝酸铵稀释海水样品,用硝酸钯和磷酸二氢铵作为基体改进剂,用石墨炉原子吸收法测定了海水中的铅含量。结果通过加标回收的验证,检测结果准确可靠。结论适合用于海水中铅含量的测定。     

Direct and simultaneous determination of copper and manganese in seawater with a multielement graphite furnace atomic absorption spectrometer

The direct and simultaneous determinations of Cu and Mn in seawater using a multielement graphite furnace atomic absorption spectrometer (Perkin-Elmer SIMAA6000) are described. Three kinds of chemical modifier (Mg(NO₃)₂, Pd(NO₃)₂ and a mixture of these) were tested. The matrix interferences were removed completely so that a simple calibration curve method could be used to determine Cu and Mn in seawater from the open ocean using Pd or a mixture of Pd and Mg as the chemical modifier. The relative standard deviations (RSDs) for the simultaneous determination of Cu and Mn in seawater from open ocean are 10% or less, and the detection limits were 0.07 μg 1⁻¹ for Cu and 0.10 μg 1⁻¹ for Mn, using Pd as the chemical modifier. The accuracy of the method is confirmed by analysis of four kinds of certified reference saline waters.     

Determination of dysprosium and europium in sheep faeces by graphite furnace and tungsten coil electrothermal atomic absorption spectrometry

Tungsten coil atomizer atomic absorption spectrometry (TCAAS) was used to determine Dy and Eu in acid-digested faeces of sheep. These elements were used as markers in animal nutrition studies. Samples were dried, ground and decomposed using a nitric-perchloric acid mixture. The accuracy of the developed method was evaluated by graphite furnace atomic absorption spectrometry (GFAAS). The results obtained for Eu were validated at a 95% confidence level using a paired t-test. The results for Dy were not validated owing to memory effects caused by carbide formation into the graphite tube. This effect did not occur for Eu. The detection limits for Dy and Eu were 6.9 and 2.1 mug l(-1) by TCAAS, and 2.2 and 5.2 mug l(-1) by GFAAS, respectively. Relative standard deviations (R.S.D.; n=5) were 0.7-3.8 and 0.8-5.6% for Dy and Eu by TCAAS and 0.8-5.4 and 0.3-3.8% for Dy and Eu by GFAAS, respectively. The lifetime of the tungsten coil was around 200 heating cycles, which is three-fold higher than graphite tube lifetime. The proposed method can be used to determine the passage rate of feed through animal digestive tract.     

Cadmium analysis in soil by microwave acid digestion and graphite furnace atomic absorption spectrometry

The need to determine micronutrients and toxic elements in soils has grown in recent years and cadmium is of special interest. A method has been developed for the determination of cadmium in soils based on a prior acid digestion of the samples with nitric acid in closed Teflon vessels, into a microwave over. The cadmium determination was carried out by graphite furnace atomic absorption spectrometry (GFAAS) with Lvov platform. Optimum operating conditions, analyte modifiers and matrix interferences have been investigated. The best matrix modifier was found to be ammonium dihydrogen phosphate. The interferences are greatly reduced under these operating conditions and calibration can be performed with simple aqueous solutions of the metal standard. The method is rapid and provides accurate and precise results that agree with certified values for two reference materials: BCR 141 (calcareous loam soil) and BCR 277 (estuarine sediment).     

Determination of cadmium in paint samples by graphite furnace atomic absorption spectrometry with optical temperature control

A graphite furnace atomic absorption spectrometry (GFAAS) method with optical temperature control for the determination of trace cadmium in paint samples is described. Optical temperature control was superior in many respects to current temperature control. The sensibility increased by 60%, the linear range widened by 60%, and the life of graphite tube showed a 200–300% increase because atomization temperature was lowered distinctly and atomization time was shortened. Use of lanthanum chloride as a matrix modifier was investigated. The linear range of calibration curve was 0–24 ng mL⁻¹. The detection limit was 9.6 ng L⁻¹. The characteristic mass was 3.0 pg. The method also resulted in excellent reproducibility (≤2.5% R.S.D.) at such low levels, and the recovery of added cadmium in paint samples was from 94.6% to 102%. This method is readily applicable to the determination of cadmium in paint samples.     

Highly Oriented Pyrolytic Graphite as a Platform for Atomic Absorption Spectrometry

Compared to pyrolytic graphite (PG) and pyrolytically coated polycrystalline graphite (PCPG), which are commonly employed substrates for graphite furnace atomic absorption spectrometry (GFAAS), highly oriented pyrolytic graphite (HOPG) is characterized by a high degree ofc-axis alignment with relatively few active sites and imperfections present on the surface. The usefulness of HOPG and commercial PG platforms for the determination of lead, copper, and aluminum by GFAAS was compared. Qualitative comparison of the absorption profiles and temperature optimizations suggest that lead, copper with a chemical modifier (palladium), and aluminum interact similarly with the two graphite substrates, while copper without a modifier interacts less strongly with HOPG than with PG. These results are in agreement with previous studies that have demonstrated that copper interacts strongly with PG and PCPG. HOPG and PG were employed for the determination of a pine needles standard reference material (SRM) and Fraser fir (Abies fraseri) samples. The analyses of the SRM gave good agreement with the certified value using both substrates, and comparable values were obtained for the samples. These results suggest that HOPG may be useful as a model for PG or PCPG when techniques such as scanning tunneling microscopy that require a high degree ofc-axis alignment are employed.     

Determination of cadmium and copper with ET-AAS after electrochemical deposition on a graphite electrode

The electrodeposition of cadmium and copper on a special graphite disk electrode has been performed at controlled potential. The electrode with the deposit has been inserted into the graphite atomizer HGA-400 by an adapted automatic sampler for the final determination by ET-ASS. The sensitivity of determination has been 0.371 (microg l(-1))(-1) for cadmium and 0.025 (microg l(-1))(-1) for copper for 2 min electrodeposition and increased linearly with the time of deposition. The limit of detection (3s(bl)) has been 7.9 ng l(-1) Cd(2+) and 0.11 microg l(-1) Cu(2+) for 2 min deposition and it has been improved with increased time of electrodeposition. The technique has been applied to the determination of both metals in seawater and to speciation in the presence of EDTA complexing agent.     

A back-extraction procedure for the dithiocarbamate solvent extraction method. Rapid determination of metals in seawater matrices

Summary A ligand exchange liquid/liquid extraction method using dithiocarbamate complexes is elaborated for the graphite furnace atomic absorption spectrometry (GF-AAS) of seawater and marine interstitial water. Palladium is used for the exchange. This metal ensures a rapid and quantitative back-extraction. It simultaneously works as matrix modifier in the GF-AAS analysis. The proposed method is evaluated in the analysis of lead, copper, nickel, and cadmium in CASS-II marine reference seawater and samples from the North Sea. A microanalytical variant of the method is applied in marine interstitial water analysis down to sample volumes of 500 l.     

Determination of cadmium,copper and lead in mineral coal using solid sampling graphite furnace atomic absorption spectrometry

Solid sampling graphite furnace atomic absorption spectrometry (SS-GF AAS) was investigated as a potential technique for the routine determination of trace elements in mineral coal and cadmium, copper and lead were chosen as the model elements. Cadmium and lead could be determined at their main resonance lines at 228.8 nm and 283.3 nm, respectively, but an alternate, less sensitive line had to be used for the determination of copper because of the high copper content in coal. No modifier was necessary for the determination of copper and calibration against aqueous standards provided sufficient accuracy of the results. For the determination of cadmium and lead two different modifiers were investigated, palladium and magnesium nitrates in solution, added on top of each sample aliquot before introduction into the atomizer tube, and ruthenium as a ‘permanent’ modifier. Both approaches gave comparable results, and it is believed that this is the first report about the successful use of a permanent chemical modifier in SS-GF AAS. Calibration against solid standards had to be used for the determination of cadmium and lead in order to obtain accurate values. The agreement between the values found by the proposed procedure and the certificate values for a number of coal reference materials was more than acceptable for routine purposes. The detection limits calculated for 1 mg of coal sample using the ‘zero mass response’ were 0.003 and 0.007 μg g⁻¹ for cadmium with the permanent modifier and the modifier solution, respectively, approximately 0.04 μg g⁻¹ for lead, and 0.014 μg g⁻¹ for copper.     

Determination of indium by graphite furnace atomic absorption spectrometry after coprecipitation with chitosan.

A sensitive and simple method for the determination of trace amounts of indium in water samples by graphite furnace atomic absorption spectrometry (GFAAS) after coprecipitation with chitosan was investigated. Indium was quantitatively preconcentrated from water samples by coprecipitation with chitosan at pH 7.0-9.0. The coprecipitant was easily dissolved with acetic acid, and indium in the resulting solution was determined by GFAAS. The addition of lanthanum as a chemical modifier was more effective for the atomic absorbance of indium. The detection limit (S/N > or = 3) for indium was 0.04 microg dm(-3), and the relative standard deviations (n = 5) were 3.5-4.5% at 1.0 microg/100 cm3. The results obtained in this study indicate that the proposed method can be successfully applied to the determination of trace indium in water samples.     

Development of 1-(2-pyridylazo)-2-naphthol-modified polymeric membranes for the effective batch pre-concentration and determination of zinc traces with flame atomic absorption spectrometry

The development of 1-(2-pyridylazo)-2-naphthol (PAN)-modified polymeric membranes for the effective batch pre-concentration and determination of zinc traces with flame atomic absorption spectrometry (FAAS) is described. The method is based on the chemical bonding of the metal species with a suitable ligand, which has been immobilized into a water-insoluble cellulose acetate (CA) membrane followed by simple rinsing of the chelating agent-metal complex with an acidified methanolic solution. The latter is directly aspirated to the nebulizer of a FAA spectrophotometer without any other treatment. As an analytical demonstration, trace concentrations of Zn(II) were successfully detected in real samples, such as seawater, river and lake water, wastewater as well as in a reference material, without any laborious and time-consuming treatment. Several working parameters were investigated. A pre-concentration factor of 100 was achieved by simple immersing of a circular piece of the CA-PAN membrane (0.6 cm diameter) in the tested samples for 30 min at room temperature. The analytical curve was rectilinear up to 30 mug l(-1) zinc with detection limit of 0.7 mug l(-1), a quantitation limit of 2.0 mug l(-1) and a relative standard deviation lower than 2%.     

Application of a fractional factorial design for the determination of cadmium by ETA-AAS in different atomization systems

A multivariate study was applied to the investigation of the variables affecting the cadmium sensitivity in a graphite furnace, with and without platform atomization or matrix modifier. The results indicated that, depending on the atomization system used, the factors studied (drying, ashing, atomization, calibration curve) exert an influence on the analysis. The interactions between the factors were also analyzed.     

Simultaneous spectrophotometric determination of nitrite and nitrate by flow-injection analysis

An automatic direct spectrophotometric method for the simultaneous determination of nitrite and nitrate by flow-injection analysis has been developed. Nitrite reacts with 3-nitroaniline in the presence of hydrochloric acid (0.96-1.8 M HCl or pH 0.5-0.7) to form a diazonium cation, which is subsequently coupled with N-(1-naphthyl)-ethylenediamine dihydrochloride to form a stable purple azo dye, the absorbance of which is measured at 535 nm. Nitrate is reduced on-line to nitrite in a copper-coated cadmium column which is then treated with azo dye reagent and the absorbance due to the sum of nitrite and nitrate is measured; nitrate is determined from the difference in absorbance values. A copper column incorporated into the reaction manifold before the copperised cadmium column not only improves the long-term accuracy, but also extends the life time of the copperised cadmium column. Various analytical parameters, such as effect of acidity (pH), flow rate, sample size, dispersion coefficient, time, temperature, reagent concentration and interfering species, were studied. The calibration graphs were rectilinear for 0.1-3.5 mug ml(-1) of NO(3) and 10 ng ml(-1)-2.2mug ml(-1) of NO(2). The method is successfully applied to some food samples (meat, flour and cheese), environmental waters (inland and surface), beer and soil samples. Up to 30 samples can be analysed per hour with a relative precision of approximately 0.1-2%.     

Spectrophotometric determination of copper(II) at low mug l(-1) levels using cation-exchange microcolumn in flow-injection

A simple spectrophotometric flow-injection method is reported for the highly sensitive and fast determination of copper(II). The method is based on the formation of coloured Cu(II)-(4-methylpiperidinedithiocarbamate)(2) complex when the copper solutions are introduced into a tertiary reagent stream containing 4-methylpiperidinedithiocarbamate. The coloured complex is then selectively monitored at 435 nm. To increase interactions between copper(II) and colour forming reagent and preconcentrate of copper(II), a microcolumn containing strong cation exchange resins was placed between injection manifold and spectrophotometer. The system required no mixing chamber and allowed a sample throughput >60 sample h(-1). The calibration graph was linear in the range 5-100 mug l(-1). The detection limit was <0.5 mug l(-1) for 20 mul injection volume of copper(II) ion solution. The developed method was applied to environmental, copper processing water, and ore samples.     

Direct sample introduction of wines in graphite furnace atomic absorption spectrometry for the simultaneous determination of arsenic, cadmium, copper and lead content

A multi-element graphite furnace atomic absorption spectrometry (GFAAS) method was elaborated for the simultaneous determination of As, Cd, Cu, and Pb in wine samples of various sugar contents using the transversally heated graphite atomizer (THGA) with end-capped tubes and integrated graphite platforms (IGPs). For comparative GFAAS analyses, direct injection (i.e., dispensing the sample onto the IGP) and digestion-based (i.e., adding oxidizing agents, such as HNO(3) and/or H(2)O(2) to the sample solutions) methods were optimized with the application of chemical modifiers. The mixture of 5 microg Pd (applied as nitrate) plus 3 microg Mg(NO(3))(2) chemical modifier was proven to be optimal for the present set of analytes and matrix, it allowing the optimal 600 degrees C pyrolysis and 2200 degrees C atomization temperatures, respectively. The IGP of the THGA was pre-heated at 70 degrees C to prevent the sputtering and/or foaming of sample solutions with a high organic content, dispensed together with the modifier solution, which method also improved the reproducibility of the determinations. With the digestion-based method, the recovery ranged between 87 and 122%, while with the direct injection method it was between 96 and 102% for Cd, Cu, and Pb, whereas a lower, compromise recovery of 45-85% was realized for As. The detection limits (LODs) were found to be 5.0, 0.03, 1.2, and 0.8 microg l(-1) for As, Cd, Cu, and Pb, respectively. The characteristic mass (m(0)) data were 24 pg As, 1.3 pg Cd, 13 pg Cu, and 35 pg Pb. The upper limits of the linear calibration range were 100, 2, 100, and 200 microg l(-1) for As, Cd, Cu, and Pb, respectively. The precisions were not worse than 4.8, 3.1, 3.7, and 2.3% for As, Cd, Cu, and Pb, respectively. For arsenic, a higher amount of the modifier (e.g., 20 microg Pd plus 12 microg Mg(NO(3))(2)) could be recommended to overcome the interference from the presence of sulphate and phosphate in wines. Although this method increased the sensitivity for As (m(0)=20 pg), it also enhanced the background noise, thus only a slight improvement in the LOD of As (3.9 microg l(-1)) was realized. For the 35 red and white wine samples studied, the highest metal contents were observed for Cu ranging from 20 to 640 microg l(-1) (average: 148 microg l(-1)), followed by Pb from 6 to 90 microg l(-1) (average: 32.3 microg l(-1)), and Cd from 0.05 to 16.5 microg l(-1) (average: 1.06 microg l(-1)), whereas the As content was below the LOD. This wide fluctuation in the trace metal content could be associated with the origin of wines from various regions (i.e., different trace metal level and/or quality of soil, and/or anthropogenic impact), and with diverse materials (e.g., additives and containers) involved in the wine production processes. The Cu content of wine samples was significantly correlated with Pb, whereas its weak anti-correlation was found with Cd. Interestingly, the level of Pb was anti-correlated with the year of production of the wines. This is likely due to the gradual decrease in the Pb content of soils of vineyards by time, which certainly causes less Pb-uptake of the grape plant, thus a decrease in the Pb content of wines as well.     

Determination of arsenic, cadmium, lead and selenium in highly mineralized waters by graphite-furnace atomic-absorption spectrometry

A graphite-furnace AAS method using the stabilized-temperature platform furnace (STPF) concept, mixed palladium and magnesium nitrates as chemical modifier and Zeeman background correction has been applied to the direct determination of As, Cd, Pb and Se in highly mineralized waters used for medicinal purposes. These contain 20-40 g/l. concentrations of salts, mainly sodium and magnesium chlorides, bicarbonates and sulphates. The use of a pre-atomization cool-down step to 20 degrees in the graphite-furnace programme reduced the background absorption. Increasing the mass of magnesium nitrate modifier to 5 times that originally proposed improved the analyte peak shape. Under these conditions, no interference was found in analysis of the chloride/bicarbonate type of water, but the sodium and magnesium sulphate type of water had to be diluted, and even then an interference remained. Calibration with matrix-free standard solutions was used, but use of spike recovery is strongly recommended for testing the accuracy. The limits of determination (4.65sigma) of the proposed method for undiluted samples are 2.0 mug/l. for As, 0.05 mug/l. for Cd, 1.0 mug/l. for Pb and 1.5 mug/l. for Se.     

Preconcentration and separation of copper(II), cadmium(II) and chromium(III) in a syringe filled with 3-aminopropyltriethoxysilane supported on silica gel

In this study, a syringe was filled with silica gel loaded with 3-aminopropyltriethoxysilane, for the separation and preconcentration of copper, cadmium and chromium prior to their determination by graphite furnace atomic absorption spectrometry (GFAAS) in seawater. For this purpose, a syringe was filled with 0.5 g of modified silica gel and the sample solution was drawn into the syringe and ejected back again. The analyte elements were quantitatively retained at pH 5. Then, the elements sorbed by the silica gel were eluted with 2.0 M of HCl and determined by GFAAS. At optimum conditions, the recovery of Cu, Cd and Cr were 96-98%. Detection limits (3delta) were 6.6, 7.5 and 6.0 micro g L(-1) for Cu, Cd and Cr, respectively. The elements could be concentrated by drawing and discharging several portions of sample successively but eluting only once. Cu, Cd and Cr added to a seawater sample were quantitatively recovered (>95%) in the range of the 95% confidence level. The method proposed in this paper was compared with a column technique. Optimum experimental conditions, reproducibility, precision and recoveries of both techniques are the same, but the syringe technique is much faster, easier and more practical than the column technique. It is a portable system and allows one to make the sorption process in the source of sample. In addition, the risk of contamination is less than in the column technique.