Method development for the determination of cadmium,copper, lead,selenium and thallium in sediments by slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry and isotopic dilution calibration

A procedure for the determination of Cd, Cu, Pb, Se and Tl by slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) with calibration by isotopic dilution is proposed. The slurry is prepared by mixing the sample with diluted nitric and hydrofluoric acids in an ultrasonic bath and then in a water bath at 60 °C for 120 min. The slurries were let to stand at least for 12 h, manually shaken before poured into the autosampler cups and homogenized by passing through an argon flow, just before pipetting it into the furnace. The analytes were determined in two groups, according to their thermal behaviors. The furnace temperature program was optimized and the selected compromised pyrolysis temperatures were: 400 °C for Cd, Se and Tl and 700 °C for Cu and Pb. The vaporization temperature was 2300 °C. The analyses were carried out without modifier as no significant effect was observed for different tested modifiers. Different sample particle sizes did not affect the sensitivity significantly, then a particle size ≤50 μm was adopted. The accuracy was checked by analyzing five certified reference sediments, with analytes concentrations from sub-μg g⁻¹ to a few hundreds μg g⁻¹. The great majority of the obtained concentrations were in agreement with the certified values. The detection limits, determined for the MESS-2 certified sediment, were, in μg g⁻¹: 0.01 for Cd; 0.8 for Cu; 0.4 for Pb; 0.4 for Se and 0.06 for Tl. The precision was adequate with relative standard deviations lower than 12%. Isotopic dilution showed to be an efficient calibration technique for slurry, as the extraction of the analyte to the liquid phase of the slurry and the reactions in the vaporizer must help the equilibration between the added isotope and the isotope in the sample.     

Determination of cadmium, copper and lead in soils, sediments and sea water samples by ETAAS using a Sc + Pd + NH(4)NO(3) chemical modifier

Cadmium, copper and lead in soils, sediments and spiked sea water samples have been determined by electrothermal atomic absorption spectrometry (ETAAS) with Zeeman effect background corrector using NH₄NO₃, Sc, Pd, Sc + NH₄NO₃, Pd + NH₄NO₃, Sc + Pd and Sc + Pd + NH₄NO₃ as chemical modifiers. A comprehensive comparison was made among the modifiers and without modifier in terms of pyrolysis and atomization temperatures, atomization and background absorption profiles, characteristic masses, detection limits and accuracy of the determinations. Sc + Pd + NH₄NO₃ modifier mixture was found to be preferable for the determination of analytes in soil and sediment certified and standard reference materials, and sea water samples because it increased the pyrolysis temperature up to 900 °C for Cd, 1350 °C for Cu and 1300 °C for Pb. Optimum masses of mixed modifier components found are 20 μg Sc + 4 μg Pd + 8 μg NH₄NO₃. Characteristic masses of Cd, Cu and Pb obtained are 0.6, 5.3 and 15.8 pg, respectively. The detection limits of Cd, Cu and Pb were found to be 0.08, 0.57 and 0.83 μg l⁻¹, respectively. Depending on the solid sample type, the percent recoveries were increased up to 103% for Cd, Cu and Pb by using the proposed modifier mixture. The accuracy of the determination of analytes in the sea water samples was also increased.     

A direct solid sampling electrothermal atomic absorption spectrometry method for the determination of silicon in biological materials

A solid sampling electrothermal atomic absorption spectrometry method for direct determination of trace silicon in biological materials was developed and applied to analysis of pork liver, bovine liver SRM 1577b and pure cellulose. The organic matrix was destroyed and expelled from the furnace in the pyrolysis stage involving a step-wise increasing the temperature from 160 °C to 1200 °C. The mixed Pd/Mg(NO₃)₂ modifier has proved to be the optimum one with respect to the achievement of maximum sensitivity, elimination of the effect of the remaining inorganic substances and the possibility of using calibration curves measured with aqueous standard solutions for quantification. For the maximum applicable sample amount of 6 mg, the limit of detection was found to be 30 ng g^− 1. The results were compared with those obtained by different spectrometric methods involving sample digestion, by electrothermal atomic absorption spectrometry using slurry sampling, by wavelength dispersive X-ray fluorescence spectrometry and by radiochemical neutron activation analysis. The method seems to be a promising one for analysis of biological materials containing no significant fraction of silicon in form of not naturally occurring volatile organosilicon compounds. The still incessant serious limitations and uncertainties in the determination of trace silicon in solid biological materials are discussed.     

Determination of cadmium and lead in biological samples by Zeeman ETAAS using various chemical modifiers

The electrothermal atomic absorption spectrometric determination of cadmium and lead in biological certified reference materials (CRMs) has been carried out by using NH(4)H(2)PO(4), Ni, Pd, Ni+NH(4)H(2)PO(4), Pd+NH(4)H(2)PO(4) and Ni+Pd+NH(4)H(2)PO(4) as chemical modifiers. A comprehensive comparison was made among the modifiers in 1% Triton X-100 plus 0.2% nitric acid as diluent and without modifier. Zeeman background correction and graphite tubes inserted with platforms were used. Comparison was made in terms of pyrolysis and atomization temperatures, atomization and background absorption profiles. Ni+Pd+NH(4)H(2)PO(4) modifier mixture was found to be preferable for the determination of Cd and Pb. Pyrolysis temperatures of analytes were increased up to 900 degrees C for Cd and 1250 degrees C for Pb by using Ni+Pd+NH(4)H(2)PO(4) in 1% Triton X-100 plus 0.2% nitric acid diluent solution. Biological CRMs were analyzed to verify the accuracy and precision of this method. Depending on the biological sample type, the percent recoveries were increased from 62 to 102% for Cd and from 58 to 106% for Pb by using the proposed modifier mixture. The detection limits of Cd and Pb were found to be 0.04, 0.92 mug l(-1), respectively.     

Use of iridium plus rhodium as permanent modifier to determine As, Cd and Pb in acids and ethanol by electrothermal atomic absorption spectrometry

The most severe interferences in atomic absorption spectrometry are caused by the presence of anions when they are in different concentrations in the samples and in the calibration solutions. The analyte addition technique or matrix matching calibration can be employed to minimize or compensate the non-spectral interferences, but they are time consuming or difficult to be carried out. The use of chemical modifiers usually allows higher pyrolysis temperatures and consequently the removal of components of the sample matrix, equalizing the analyte signal in the sample and in the calibration solution. In this work, a mixture of Ir and Rh is proposed as permanent modifier to determine As, Cd and Pb in diluted hydrochloric, sulfuric and phosphoric acids and in ethanol and methanol by electrothermal atomic absorption spectrometry (ET AAS) with calibration against 1% v/v nitric acid aqueous solutions. The performance of the proposed permanent modifier was compared to that of Pd plus Mg nitrates in solution. Better recoveries, low background levels and faster analysis were obtained with the permanent modifier. The permanent modifier was also successfully employed for the determination of As, Cd and Pb in different concentrations of sulfuric and hydrochloric acids. For the phosphoric acid, the proposed modifier was only efficient for acid concentrations up to 2% v/v for As and up to 5% v/v for Cd and Pb. The precision, expressed as the relative standard deviation (n=3), was lower than 10%, for all samples, including ethanol and methanol.     

Cadmium,lead, copper and manganese determination in human deciduous teeth by electrothermal atomic absorption spectrometry using a lanthanum,palladium and citric acid mixture as chemical modifier

Cadmium, lead, copper and manganese were determined in human deciduous teeth and bone ash 1400 standard reference material by electrothermal atomic absorption spectrometry (ETAAS), using a lanthanum + palladium + citric acid (CA) modifier mixture. Optimum masses and mass ratios of La, La + Pd and La + Pd + CA modifiers for analytes in bone ash 1400 sample solution were investigated. Pyrolysis and atomization temperatures of analytes in a tooth sample solution were obtained with and without modifiers. The mixture of La + Pd + CA was found to be preferable for the determination of analytes in tooth samples and bone ash 1400, dissolved in a mixture of HNO₃ + H₂O₂. The detection limits and characteristic masses of analytes were obtained with or without modifiers based on integrated absorbance for tooth sample solution (2% m/v). The detection limits obtained with La + Pd + CA are 6,24,16 and 46 ng g^?1 for Cd, Cu, Mn and Pb, respectively. Recovery tests for analytes in bone ash 1400 and a tooth solution with La and La + Pd + CA modifier mixture were studied and compared with certified and non certified values. The La + Pd + CA mixture was also applied to the determination of Cd, Pb, Cu and Mn in tooth samples.     

Studies on transport phenomena in electrothermal vaporization sample introduction applied to inductively coupled plasma for optical emission and mass spectrometry

In the present work electrothermal vaporization (ETV) was used in both inductively coupled plasma mass spectrometry (ICP-MS) and optical emission spectrometry (OES) for sample introduction of solution samples. The effect of (Pd + Mg)-nitrate modifier and CaCl₂ matrix/modifier of variable amounts were studied on ETV-ICP-MS signals of Cr, Cu, Fe, Mn and Pb and on ETV-ICP-OES signals of Ag, Cd, Co, Cu, Fe, Ga, Mn and Zn. With the use of matrix-free standard solutions the analytical curves were bent to the signal axes (as expected from earlier studies), which was observed in the 20–800 pg mass range by ICP-MS and in the 1–50 ng mass range by ICP-OES detection. The degree of curvature was, however, different with the use of single element and multi-element standards. When applying the noted chemical modifiers (aerosol carriers) in microgram amounts, linear analytical curves were found in the nearly two orders of magnitude mass ranges. Changes of the CaCl₂ matrix concentration (loaded amount of 2–10 μg Ca) resulted in less than 5% changes in MS signals of 5 elements (each below 1 ng) and OES signals of 22 analytes (each below 15 ng). Exceptions were Pb (ICP-MS) and Cd (ICP-OES), where the sensitivity increase by Pd + Mg modifier was much larger compared to other elements studied. The general conclusions suggest that quantitative analysis with the use of ETV sample introduction requires matrix matching or matrix replacement by appropriate chemical modifier to the specific concentration ranges of analytes. This is a similar requirement to that claimed also by the most commonly used pneumatic nebulization of solutions, if samples with high matrix concentration are concerned.     

Evaluation of zirconium as a permanent chemical modifier using synchrotron radiation and imaging techniques for lithium determination in sediment slurry samples by ET AAS

In the present paper, lithium was determined in river sediment using slurry sampling and electrothermal atomic absorption spectrometry (ET AAS) after L’vov platform coating with zirconium (as a permanent chemical modifier). The performance of this modifier and its distribution on the L’vov platform after different heating cycles were evaluated using synchrotron radiation X-ray fluorescence (SRXRF) and imaging scanning electron microscopy (SEM) techniques. The analytical conditions for lithium determination in river sediment slurries were also investigated and the best conditions were obtained employing 1300 and 2300 °C for pyrolysis and atomization temperatures, respectively. In addition, 100 mg of sediment samples were prepared using 4.0 mol l⁻¹ HNO₃. The Zr-coating permitted lithium determination with good precision and accuracy after 480 heating cycles using the same platform for slurry samples. The sediment samples were collected from five different points of the Cachoeira river, São Paulo, Brazil. The detection and quantification limits were, respectively, 0.07 and 0.23 μg l⁻¹.     

Determination of volatile elements in biological materials by isotopic dilution ETV-ICP-MS after dissolution with tetramethylammonium hydroxide or acid digestion

Isotopic dilution for the determination of Ag, Cd, Hg, Pb and Tl in biological materials by ETV-ICP-MS is proposed. The sample was simply dissolved with tetramethylammonium hydroxide (TMAH) or acid digested in a microwave furnace, with an on line matrix separation. When the dissolution was employed, Ir was used as a chemical modifier for Hg and Pb and Pd was used for Cd and Tl. No modifier was used for Ag. The pyrolysis temperatures were taken from pyrolysis temperature curves. The on line preconcentration was performed in a flow injection system with solenoid valves and was based on the analyte complexation with ammonium diethyldithiophosphate and sorption of the complexes on C(18) bonded to silica gel in a minicolumn. For the digested sample submitted to the analyte preconcentration procedure, a modifier, Ir, was only used for Hg. For the other analytes, since a low pyrolysis temperature, 300 degrees C, was employed, no modifier was added. The isotopic dilution calibration was applied to two certified materials, bovine liver and dog fish muscle, dissolved with TMAH or acid digested, and to another two certified materials, corn bran and rice flour, acid digested and submitted to analyte preconcentration. The obtained concentration values agree with the certified ones, showing that this calibration procedure leads to accurate results in the determination of low concentrations of volatile elements. Due to simplicity, the dissolution with TMAH is very attractive.     

The development of a method for the determination of trace elements in fuel alcohol by electrothermal vaporization–inductively coupled plasma mass spectrometry using external calibration

A method for the determination of Ag, As, Cd, Cu, Co, Fe, Mn, Ni, Pb, Sn and Tl in fuel alcohol by electrothermal vaporization inductively coupled plasma mass spectrometry is proposed. The determinations were carried out by external calibration against ethanolic solutions, without a chemical modifier, employing the following pyrolysis and vaporization temperatures: 400 °C and 2300 °C for the more volatile analytes and 1000 °C and 2500 °C for the less volatile analytes. The determination of As, Cd, Pb, Sn and Tl was additionally carried out using Pd as modifier at 800 °C pyrolysis and 2400 °C vaporization temperatures. The temperatures were optimized through pyrolysis and vaporization curves. Seven common fuel ethanol, one fuel ethanol with additive and one anhydrous fuel ethanol sample have been analyzed. The measured concentrations were at the μg L⁻¹ level or lower. Since there is no certified reference material for fuel ethanol, the accuracy of the method was checked by the recovery test, with recoveries from 75% to 124%. The limits of detection (LODs), in μg L⁻¹, and the relative standard deviations for 5 replicates were, for the elements in the conditions without modifier: Ag: 0.015 and 9.1%, Co: 0.002 and 10%, Cu: 0.22 and 6.6%, Fe: 0.72 and 4.3%, Mn: 0.025 and 12%, Ni: 0.026 and 9.3%, and for the elements with Pd: As: 0.02 and 2.9%, Cd: 0.07 and 25%, Pb: 0.02 and 3.1%, Sn: 0.010 and 6.0%, Tl: 0.0008 and 2.5%. Electrothermal vaporization avoids the loading of the plasma with organics, allowing the analysis of fuel ethanol by ICP-MS with good accuracy and reasonable precision.     

Cloud point extraction for the determination of lead and cadmium in urine by graphite furnace atomic absorption spectrometry with multivariate optimization using Box–Behnken design

Cloud point extraction (CPE) is proposed as a pre-concentration procedure for the determination of Pb and Cd in undigested urine by graphite furnace atomic absorption spectrometry (GF AAS). Aliquots of 0.5 mL urine were acidified with HCl and the chelating agent ammonium O,O-diethyl dithiophosphate (DDTP) was added along with the non-ionic surfactant Triton X-114 at the optimized concentrations. Phase separation was achieved by heating the mixture to 50 °C for 15 min. The surfactant-rich phase was analyzed by GF AAS, employing the optimized pyrolysis temperatures of 900 °C for Pb and 800 °C for Cd, using a graphite tube with a platform treated with 500 μg Ru as permanent modifier. The reagent concentrations for CPE (HCl, DDTP and Triton X-114) were optimized using a Box–Behnken design. The response surfaces and the optimum values were very similar for aqueous solutions and for the urine samples, demonstrating that aqueous standards submitted to CPE could be used for calibration. Detection limits of 40 and 2 ng L^− 1 for Pb and Cd, respectively, were obtained along with an enhancement factor of 16 for both analytes. Three control urine samples were analyzed using this approach, and good agreement was obtained at a 95% statistical confidence level between the certified and determined values. Five real samples have also been analyzed before and after spiking with Pb and Cd, resulting in recoveries ranging from 97 to 118%.     

用ETV-ICP-MS研究Cr、Ni、Zr、Nb、Yb在石墨炉中的蒸发/原子化机理

本文以电热蒸发电感耦合等离子体质谱（ETV-ICP-MS）为手段,探讨了Cr、Ni、Zr、Nb和Yb在石墨炉中的蒸发/原子化机理;比较了不同化学改进剂存在条件下,Cr、Ni、Zr、Nb和Yb的蒸发行为和在石墨炉原子吸收（GFAAS）中的原子化行为;考察了石墨炉温度和ICP功率等实验参数对上述元素发射强度及轮廓的影响.结果表明,Pd和Mg化合物的存在对Cr、Ni、Zr、Nb和Yb的蒸发/原子化行为没有明显的化学改进作用;然而,以聚四氟乙烯（PTFE）为化学改进剂时,可显著改善Cr、Ni、Zr、Nb和Yb的蒸发行为,避免难熔碳化物的形成,降低待测物的蒸发温度;对Cr和Ni的GFAAS信号强度略有增强;但是,由于Yb、Nb和Zr氟化物的离解键能很高,难以离解/原子化,PTFE的存在反而降低了Yb、Nb和Zr在GFAAS中的信号强度.     

Ionic liquids based single drop microextraction combined with electrothermal vaporization inductively coupled plasma mass spectrometry for determination of Co,Hg and Pb in biological and environmental samples

A new method of ionic liquids based cycle flow single drop microextraction combined with electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) was proposed for the determination of trace Co, Hg and Pb with 1-(2-pyridylazo)-2-naphthol (PAN) as both extractant and chemical modifier and 1-butyl-3-methylimidazolium hexafluorophosphate as the extraction solvent. Several factors that influence the microextraction efficiency, such as sample pH, sample flow rate, microdrop volume and extraction time, were investigated and the optimized microextraction conditions were established. Co, Hg and Pb in the post-extraction ionic liquids phase were directly determined by ETV-ICP-MS with the use of PAN as chemical modifier. The chemical modification of PAN in ETV-ICP-MS was studied and the factors affecting the vaporization behaviors of target analytes were investigated. Under the optimized conditions, the detection limits of the method were 1.5, 9.8 and 6.7 pg/mL for Co, Hg and Pb, with the relative standard deviations for 0.5 ng/mL (n = 7) of Co, Hg and Pb were 7.7%, 5.2% and 12.0%, respectively. After 10 min of extraction, the enrichment factors were 350 (Co), 50 (Hg) and 60 (Pb). The proposed method was successfully applied to the determination of trace Co, Hg and Pb in human serum and environmental water samples. In order to validate the developed method, a certified reference material of human hair (GBW07601) was analyzed and the determined values were in good agreement with the certified values.     

Use of cetyltrimethylammonium bromide as surfactant for the determination of copper and chromium in gasoline emulsions by electrothermal atomic absorption spectrometry

In this work, the use of cetyltrimethylammonium bromide as surfactant for the preparation of oil-in-water emulsions for the determination of Cu and Cr in gasoline by electrothermal atomic absorption spectrometry (ET AAS) was evaluated. The surfactant amount was tested in the range of 25 to 300 mg, added to 2 ml of gasoline, and completed to 10 mL with 0.1% (v/v) nitric acid solution. 150 mg of surfactant was found optimum, and a sonication time of 10 min sufficient to form an oil-in-water emulsion that was stable for several hours. The ET AAS temperature program was established based on pyrolysis and atomization curves. The pyrolysis temperatures were set at 700 and 1300 °C for Cu and Cr, respectively and the selected atomization temperatures were 2400 and 2500 °C. The time and temperature of the drying stage and the atomization time were experimentally tested to provide optimum conditions. The limits of detection were found to be 5 μg L^− 1 and 1.5 μg L^− 1 for Cu and Cr, respectively in the original gasoline samples. The relative standard deviation (RSD) ranged from 4 to 9% in oil-in-water emulsions spiked with 5 μg L^− 1 and 15 μg L^− 1 of each metal, respectively. Recoveries varied from 90 to 98%. The accuracy of the proposed method was tested by an alternate procedure using complete evaporation of the gasoline sample. The method was adequate for the determination of Cu and Cr in gasoline samples collected from different gas stations in Salvador, BA, Brazil.     

Determination of As, Cd, Pb and Se in DORM-1 dogfish muscle reference material using alkaline solubilization and electrothermal atomic absorption spectrometry with Ir+Rh as permanent modifiers or Pd+Mg in solution

In this work, tetramethylammonium hydroxide (TMAH) was used to solubilize the DORM-1 dogfish muscle certified reference material as a model substance for the determination of As, Cd, Pb and Se by electrothermal atomic absorption spectrometry (ET AAS). The sample was mixed with a small amount of TMAH and heated to 60 °C for 10 min in a water bath. After dissolution, As and Se were determined using palladium and magnesium nitrates as a chemical modifier added in solution. For Cd and Pb, best results were obtained with a mixture of 250 μg of each of iridium and rhodium as permanent modifiers. In both cases, the calibration was performed with aqueous solutions in 0.2% v/v HNO₃. The temperature program for each analyte was optimized using pyrolysis and atomization curves established with the fish reference material. The detection limits in dry samples and the characteristic mass values were: Cd 0.005 μg g⁻¹ and 0.9 pg; Pb 0.04 μg g⁻¹ and 7.6 pg; As 0.4 μg g⁻¹ and 13 pg and Se 0.6 μg g⁻¹ and 20 pg, respectively. Results from the determination of these elements in the DORM-1 certified fish reference material were within the 95% confidence interval of the certified values.     

Feasibility of employing permanent chemical modifiers for the determination of cadmium in coal using slurry sampling electrothermal atomic absorption spectrometry

Iridium and ruthenium, alone and in combination with tungsten, thermally deposited on the platform of a transversely heated graphite tube, were investigated for their suitability as permanent chemical modifiers for the determination of cadmium in coal slurries by electrothermal atomic absorption spectrometry (ET AAS). The conventional mixed palladium and magnesium nitrates (Pd–Mg) modifiers, added in solution, were also investigated for comparison. The latter one showed the best performance for aqueous solutions, and the mixed W–Ir and W–Ru permanent modifiers had the lowest stabilizing power. All of the investigated modifiers lost some of their stabilizing power when coal slurries were investigated. The Pd–Mg modifier, pure Ir and Ru, and a mixture of 300 μg W + 200 μg Ir could stabilize Cd at least to a pyrolysis temperature of 600 °C, whereas all the other combinations already failed at temperatures above 500–550 °C. Additional investigations of the supernatant liquid of the slurries supported the assumption that the high acid concentration of the slurries and/or a concomitant leaching out of the coal might be responsible for the reduced stabilizing power of the modifiers. The maximum applicable pyrolysis temperature of 600 °C was not sufficient to reduce the background absorption to a manageable level in the majority of the coal samples. High-resolution continuum source ET AAS revealed that the continuous background absorption was exceeding values of A = 2, and was overlapping with the analyte signal. Although the latter technique could correct for this background absorption, some analyte was apparently lost with the rapidly vaporizing matrix so that the method could not be considered to be rugged. A characteristic mass of 1.0 pg and a detection limit of 0.6 ng g^− 1 could be obtained under these conditions.     

Simultaneous determination of lead, nickel, tin and copper in aluminium-base alloys using slurry sampling by electrical discharge and multielement ETAAS

The simultaneous multielement determination of Pb, Sn, Ni and Cu in aluminium alloys by electrothermal atomic absorption spectrometry (ETAAS) was performed by a quick method using slurry sampling. The metallic colloidal slurries were obtained by an electrical discharge operated in liquid medium. In this work, the effects of aluminium were evaluated and the results show that it causes a strong retention of Pb, Ni and Cu at low pyrolysis temperatures which is overcome by employing high pyrolysis temperatures. Aluminium also significantly improves the thermal stabilisation of Pb and Sn, it being possible to reach pyrolysis temperatures of 1100 and 1300 °C, respectively. Such stabilisation indicates that the performance of aluminium as a matrix modifier for Pb is better than that obtained using phosphate and magnesium nitrate without substantial changes of the figures of merit. The effects of aluminium on the atomisation characteristics of the elements and those coming from the simultaneous multielement determination on the figures of merit of the elements are also discussed. In this work, a calibration procedure involving a matrix matching method with aqueous aluminium standards is proposed as a simple and efficient way to solve the inconveniences originated by the aluminium matrix. The proposed method was applied to the simultaneous multielement determination of several aluminium-base alloy standards giving results well within the recommended values.     

Cloud point extraction for the determination of cadmium and lead in biological samples by graphite furnace atomic absorption spectrometry

The phase-separation phenomenon of non-ionic surfactants occurring in aqueous solution was used for the extraction of Cd and Pb from digested biological samples. After complexation with O,O-diethyldithiophosphate (DDTP) in hydrochloric acid medium, the analytes are quantitatively extracted to the phase rich in the non-ionic surfactant octylphenoxypolyethoxyethanol (Triton X-114) after centrifugation. Methanol acidified with 0.1 mol L⁻¹ HNO₃ was added to the surfactant-rich phase prior to its analysis by electrothermal atomic absorption spectrometry (ET AAS). The adopted concentrations for DDTP, Triton X-114 and hydrochloric acid were all optimized. Pyrolysis and atomization temperatures were optimized using the extracts and pyrolysis temperatures of 700 °C for both elements and atomization temperatures of 1400 and 1600 °C for cadmium and lead, respectively, were used without adding any modifier, which shows that considerable analyte stabilization is provided by the medium itself. A more detailed investigation was carried out to determine which components of the extract were responsible for the high thermal stability achieved and it revealed that the amount of DDTP added and the phosphorus content of the digested samples contributed significantly to this phenomenon. Detection limits (3σ_B) of 6 and 40 ng g⁻¹, along with enrichment factors of 129 and 18 for Cd and Pb, respectively, were achieved. The proposed procedure was applied to the analysis of five certified biological reference materials after microwave-assisted acid digestion in a mixture of H₂O₂ and HNO₃. Comparison with certified values was performed for accuracy evaluation, resulting in good agreement according to the t-test for a 95% confidence level. The high efficiency of cloud point extraction to carry out the determination of the studied analytes in complex matrices was, therefore, demonstrated.     

Direct determination of Cr and Cu in urine samples by electrothermal atomic absorption spectrometry using ruthenium as permanent modifier (R1)

In this study Ru, deposited thermally on an integrated platform pyrolytic graphite tube, is proposed as a permanent modifier for the determination of Cu and Cr in urine samples by electrothermal atomic absorption spectrometry. The samples were diluted 1:1 with nitric acid (1% v/v). Pyrolysis and atomization temperatures for spiked urine samples were 1,100 degrees C and 1,900 degrees C respectively for Cu, and 1,400 degrees C and 2,500 degrees C respectively for Cr. For comparison purposes, the conventional modification with Pd+Mg was also studied. The sensitivity for Ru as permanent modifier was higher for the two analytes. The characteristic masses were 7.3 and 17.7 for Cr and Cu. The detection limits (3sigma) were 0.22 and 0.32 microg/L, for Cr and Cu, respectively. Good agreement was obtained with certified urine samples for the two elements.     

Determination of bismuth, indium and lead in geological samples by electrothermal AAS Part 2. Comparative study of palladium and molybdenum containing chemical modifiers*

A comparative and systematic study has been carried out of the effects of palladium and molybdenum containing chemical modifiers, such as Pd + Rh, Pd + Pt, Pd + Ru, Pd + Rh + Pt, Pd + Rh + Ru, Mo + Pd, Mo + Rh, Mo + Ru and Mo + Pt and additionally tartaric acid (TA) as a reducing agent together with mixed modifiers for the thermal stabilization of Bi, In and Pb in a Zeeman electrothermal atomic absorption spectrometer (ETAAS). The effect of the mass ratios of the mixed modifier components on the maximum pretreatment temperature for the analytes has been determined. The modifier mixtures of Pd + Rh + Pt, Mo + Pd + TA and Mo + Pt + TA were found to be especially powerful for the determination of Bi, In and Pb. These mixed modifiers could increase the ashing temperatures of the analytes up to 1250–1400° C. They were applied to the determination of Bi and Pb in dissolved geological reference samples and accuracy and precision of the method were thereby enhanced. The percent relative error was decreased from 20.0 to 0.4 for Bi and from 10.5 to 0.3 for Pb, depending on the sample type. Received: 9 May 1997 / Revised: 19 August 1997 / Accepted: 20 August 1997