Determination of cadmium in slurries of marine sediment samples by electrothermal atomic absorption spectrometry using palladium and phosphate as chemical modifiers

A method for the determination of cadmium in slurries of marine sediment using palladium and phosphate as chemical modifier has been optimized. To stabilize the marine sediment slurry, Triton X-100 at 0.1% was used. To obtain a complete pyrolysis of the slurry sample two mineralization steps were used, the first at 480 °C and the second at 600 °C and 700 °C for phosphate and palladium, respectively. The precision and accuracy of the method have been studied by analyzing the Reference Material PACS-1 (marine sediment) of National Research Council Canada. The detection limits (LOD) were 11.9 g kg^–1 for phosphate and 42.0 g kg^–1 when palladium was used. These methods have been applied to the determination of cadmium in marine sediment samples from the Galicia coast and the results of both methods were compared; no significant differences were found between the two procedures.     

Determination of tin in marine sediments by slurry sampling atomic absorption spectrometry with electrothermal atomization using a permanent modifier

A molecularly imprinted polymer (MIP) was synthesized by the precipitation polymerization method using triazophos (TAP) as the template. The MIP can selectively absorb TAP from sample solutions. The absorbed TAP strongly enhances the chemiluminescence (CL) of luminol-H₂O₂. This was applied to design a method for the on-line enrichment and detection of TAP. The change in CL intensity is linearly proportional to the concentration of TAP in the range from 1.0 μM to ~4.0 nM, and the detection limit is 2.5 nM (at an S/N of 3σ). This is about one order of magnitude lower than that of the conventional CL assay. The method was successfully applied to the determination of TAP in vegetable samples.     

Silicon determination in milk by electrothermal atomic absorption spectrometry using palladium as chemical modifier

A direct method for silicon determination in milk samples by Electrothermal Atomic Absorption Spectrometry was developed. Palladium was used as chemical modifier at a concentration of 610 mg L(-1); with this modifier, silicon was stable up to 1800 degrees C. The precision and accuracy of the method were investigated. The detection limit was 16.2, 2.7 and 7.2 micro g L(-1) for cows' milk, human milk and infant formula, respectively. The method was applied to silicon determination in 17 infant formula samples, 13 human milk samples and 12 cows' milk samples.     

Determination of tin and lead in sediment slurries by graphite furnace atomic absorption spectrometry

Methods were determined for lead and tin determinations in river, marine and lake sediments by slurry sampling and graphite furnace atomic absorption spectrometry. The optimizations were carried out using River Sediment BCR 320 and Marine Sediment PACS-2 for Pb and Sn, respectively. For Pb determination, the parameters studied included inorganic acid mixture, stabilizing agent, sample mass and sonication time. The influence of diluents and the extraction to the liquid phase for two different matrices was evaluated for Sn. The Pb content in the slurry liquid phase was ca. 56%, and ranged from 75% to 100% for Sn. Representative masses of 34 and 45 mg, and effective masses of 12 and 48 μg for Pb and Sn, respectively, were obtained under optimized conditions. Detection and quantification limits of 0.2 and 0.7 μg g⁻¹ for Pb, and 1.5–2.6 and 4.5–7.6 μg g⁻¹ for Sn were obtained.

     

Determination of vanadium in human hair slurries by electrothermal atomic absorption spectrometry

This work describes an analytical procedure for vanadium determination in human hair slurries by electrothermal AAS using longitudinal heating (LHGA) and transversal heating (THGA) graphite furnace atomizers. The samples were powdered using cryogenic grinding and the hair slurries containing 0.2% (m/v) were prepared in three different media for determination of vanadium: 0.14 mol L⁻¹ HNO₃, 0.1% (v/v) Triton X-100 and 0.1% (v/v) water soluble tertiary amines (CFA-C, pH 8). The limits of detection (LOD), limits of quantification (LOQ), and characteristic masses obtained were 0.28, 0.95 μg L⁻¹ and 35 pg (LHGA) and 0.34, 1.13 μg L⁻¹ and 78 pg (THGA), respectively. The accuracy of the analytical results obtained by the proposed procedure in both equipments was confirmed by a paired t-test at the 95% confidence level and compared with a conventional procedure based on acid digestion.     

Determination of total tin and tributyltin in marine biological materials by electrothermal atomic absorption spectrometry

Total tin and tributyltin in marine biological tissue are determined at the sub-μg g^?1 level by graphite-furnace atomic absorption spectrometry. Total tin is extracted by digestion with nitric acid, and tributyltin is extracted by n-hexane after treatment with hydrochloric acid. A matrix modifier (ammonium dihydrogenphosphate), and a stabilized-temperature platform furnace are used to overcome matrix effects. Zeeman background correction is used. Results of analyses of oyster (Crassostrea gigas), salmon (Salmo salar) and a reference material (Bowen's kale) are presented. The detection limit for both methods is ca. 30 ng of tin with a relative standard deviation (n = 6) of 7.8% for a sample containing 200 ng of tin.     

Determination of beryllium by electrothermal atomic absorption spectrometry using tungsten surfaces and zirconium modifier

Electrothermal atomization of beryllium from graphite and tungsten surfaces was compared with and without the use of various chemical modifiers. Tungsten proved to be the best substrate, giving the more sensitive integrated atomic absorption signals of beryllium. Tungsten platform atomization with zirconium as a chemical modifier was used for the determination of beryllium in several NIST SRM certified reference samples, with good agreement obtained between the results found and the certified values. The precision of the measurements (at 10 μg L⁻¹), the limit of detection (3σ), and the characteristic mass of beryllium were 2.50%, 0.009 μg L⁻¹ and 0.42 pg, respectively.     

Determination of total tin in geological materials by electrothermal atomic absorption spectrometry

A graphite-furnace atomic-absorption spectrometric method is described for the determination of total tin in geological materials. Samples are decomposed by fusion with lithium metaborate and the melt is dissolved in diluted (1 + 9) nitric acid. Spectral and non-spectral interferences are minimized by a combination of platform volatilization, “normal” heating rate, addition of ammonia as chemical modifier, use of integrated absorbance values and Zeeman background correction. Results are reported for six reference materials showing good accuracy and a precision of 12% at the 3 μg g^?1 level. The detection limit for tin in the original materials in 0.7 μg g^?1.     

Comparison of palladium-magnesium nitrate and ammonium dihydrogenphosphate modifiers for cadmium determination in honey samples by electrothermal atomic absorption spectrometry

The occurrence of certain trace elements, such as cadmium, in honey bee can be considered as an indication of environmental pollution. In the present work, two methods for Cd determination in honey by electrothermal atomic absorption spectrometry, using palladium-magnesium nitrate and ammonium dihydrogenphosphate as chemical modifiers, have been developed. In none of these cases honey samples required pretreatment. Honey was diluted in water (20% w/v), and hydrogen peroxide, nitric acid, and Triton X-100 were added to minimize the matrix effect. For the first method, 21.6 μg of palladium and 4.5 μg of magnesium were added as chemical modifier; for the second method, 60 μg of ammonium dihydrogenphosphate were employed. The limits of detection obtained were 0.32 ng g⁻¹ for ammonium dihydrogenphosphate method and 0.54 ng g⁻¹ for palladium-magnesium nitrate method. The characteristic mass was 0.7 and 1.0 pg for ammonium dihydrogenphosphate and palladium-magnesium nitrate methods, respectively. The relative standard deviation (<10%) and the analytical recovery (98-105%) were comparable in both methods. The optimised methods were applied to the determination of the cadmium content in unpolluted Galician honey samples. Cd has been detected the analysed samples in the range (n.d.—4.3 ng g⁻¹).     

Determination of selenium by tungsten coil atomic absorption spectrometry using iridium as a permanent chemical modifier

Permanent chemical modifiers have been shown to prolong graphite tube lifetime while reducing the furnace cycle time, thus improving cost-effectiveness. In this work, iridium is used as a permanent chemical modifier for the first time in the determination of selenium by tungsten-coil atomic absorption spectrometry (W-Coil AAS). The iridium modifier is thermally coated onto the tungsten coil. After coating, the coil can be used for 300–400 firings without further application of the modifier. Thermal treatment with iridium permits operating with higher pyrolysis temperature and coil lifetime is extended up to 1600 firings. The sensitivity and linearity of the method is improved, and the analytical procedure allows the use of analyte solutions containing up to 8% nitric acid. The short-term stability of the absorbance measurements is demonstrated by the reproducibility in the measurements of a Se amount (6 ng) 30 times higher than the limit of detection (0.2 ng). A 7% relative standard deviation (R.S.D.) was observed for 10 consecutive measurements of 6 ng Se. The long-term stability is almost as good: less than 9% R.S.D. over a 3-week period and 1500 firings. The surface of the tungsten-coil treated with iridium is examined before and after intensive use by scanning electron microscopy. Finally, the thermal treatment of the tungsten-coil with iridium appears to delay the appearance of selenium atoms by approximately 0.2 s although the integrated absorbance measurements are unaffected. The magnitude of delay decreases with coil age.     

Determination of traces of silver in human scalp hair slurries by electrothermal atomic absorption spectrometry

A simple and rapid method for the determination of traces of silver in human hair by slurry sampling and electrothermal atomic absorption spectrometry was optimized. Hair pulverization and the particle size reduction were achieved using a vibrational zirconia mill ball for 20 min. Palladium nitrate, magnesium nitrate and palladium-magnesium nitrate were investigated as chemical modifiers to thermally stabilize silver. Glycerol was used as wetting agent to stabilize the hair slurries. A limit of detection of 21.6 g kg^–1 was obtained for the use of palladium nitrate as best chemical modifier. The repeatibility of the overall procedure (slurry preparation and atomic absorption spectrometric determination) corresponding to eleven measurements was 14.3%. Matrix effect was significant and so, the standard addition method was used to determine silver in hair samples from healthy people. The levels found varied between 0.10 and 1.62 mg kg^–1.     

Determination of cadmium, chromium and lead in marine sediment slurry samples by electrothermal atomic absorption spectrometry using permanent modifiers

A procedure for the determination of cadmium, chromium, and lead in marine sediment slurries by electrothermal atomic absorption spectrometry is proposed. Slurry was prepared by mixing 10 mg of ground sample with particle size smaller than 50 μm completed to the weight of 1.0 g with a 3% nitric acid and 10% hydrogen peroxide solution. The slurry was maintained homogeneous with an aquarium air pump. For cadmium, the best results were obtained using iridium permanent with optimum pyrolysis and atomization temperatures of 400 and 1300 °C, respectively, a characteristic mass, m_o (1% absorption), of 2.3 pg (recommended 1 pg). Without modifier use, zirconium, ruthenium, and rhodium m_o were 3.4, 4.1, 4.6, and 4.8 pg, respectively. For chromium, the most sensitive condition was obtained with zirconium permanent with optimum pyrolysis and atomization temperatures of 1500 and 2500 °C, m_o of 6.6 pg (recommended 5.5 pg); and without modifier use, rhodium, iridium, and ruthenium m_o were 5.3, 8.8, 8.8, and 8.9 pg, respectively. For lead, the best modifier was also zirconium, m_o of 8.3 pg for the optimum pyrolysis and atomization temperatures of 600 and 1400 °C, respectively, (recommended m_o of 9.0 pg). For iridium, ruthenium, without modifier, and rhodium, m_o were 14.7, 15.5, 16.5, and 16.5 pg, respectively. For all the modifiers selected in each case, the peaks were symmetrical with r² higher than 0.99. Being analyzed (n = 10), two marine sediment reference materials (PACS-2 and MESS-2 from NRCC), the determined values, μg l⁻¹, and certified values in brackets, were 2.17 ± 0.05 (2.11 ± 0.15) and 0.25 ± 0.03 (0.24 ± 0.01) for cadmium in PACS-2 and MESS-2, respectively. For chromium in PACS-2 and MESS-2 the values were 94.7 ± 5.6 (90.7 ± 4.6) and 102.3 ± 10.7 (106 ± 8), respectively. Finally, for lead in PACS-2 and MESS-2, the results obtained were 184 ± 7 (183 ± 8) and of 25.2 ± 0.40 (21.9 ± 1.2), respectively. For cadmium and lead in both samples and chromium in PACS-2, calibration was accomplished with aqueous calibration curves. For chromium in MESS-2, only with the standard addition technique results were in agreement with the certified ones. The limits of detection (k = 3, n = 10) obtained with the diluents were 0.1, 3.4, and 3.6 μg l⁻¹ for cadmium, chromium, and lead, respectively.     

Determination of submicrogram amounts of tin by atomic absorption spectrometry with electrothermal atomization

The determination of tin is described with particular reference to the addition of organic compounds to the graphite tube for the suppression of interferences of other ions. Most were suppressed by adding 20 μl of 10% ascorbic acid to 20 μl of sample in the furnace. The method was used for the determination of tin in waste-waters and sediments.     

Determination of vanadium in mussels by electrothermal atomic absorption spectrometry without chemical modifiers

A method was developed for the quantitative determination of total vanadium concentration in mussels via electrothermal atomic absorption spectrometry (ETAAS). After the microwave digestion of the samples, a program using temperatures of 1600 °C and 2600 °C for ashing and atomization respectively, without any matrix modifiers, allowed us to obtain results that were satisfactory since they agreed closely with certified reference material values. The detection limit was 0.03 mg kg^–1 (dry weight), indicating that the method is suitable for the analysis of mussel samples. This determination was compared with matrix modifiers that have been reported previously. The method was applied to various cultivated and wild mussels from the Galician coast, yielding levels below 1 mg kg^–1 (wet weight).     

Determination of indium in high purity antimony by electrothermal atomic absorption spectrometry (ETAAS) using boric acid as a modifier

The use of boric acid as a modifier for the determination of trace amount of indium in high purity antimony by electrothermal atomic absorption is described. It was found that the negative influence of the hydrofluoric acid, used for the digestion could not be eliminated by using stabilized temperature platform furnace (STPF) alone. Due to the high dissociation energy (D₀ = 506 kJ mol⁻¹) of indium fluoride, it is difficult to dissociate in the gas phase and hence is lost. In presence of HF (used for the dissolution of antimony), the universal Pd-Mg modifier does not work satisfactorily. Additionally, rising corrosion and reduced tube lifetime were observed when the acid digested (HF-HNO₃) antimony solution was injected in to the platform. Improvement in platform life and elimination of interferences were achieved by the addition of boric acid as a chemical modifier together with ruthenium coating of the platform. Corrosive changes of the transversely heated graphite atomizer (THGA) platform surface were examined by scanning electron microscopy. The standard addition method was applied. A characteristic mass of 36 pg was obtained. The detection limit of the proposed method is around 0.04 μg g⁻¹. The developed method was applied to the determination of indium in real samples. The data obtained by this method were in good agreement with those obtained by ICP-MS.     

Determination of cadmium in biological samples solubilized with tetramethylammonium hydroxide by electrothermal atomic absorption spectrometry, using ruthenium as permanent modifier

The feasibility of Ru as a permanent modifier for the determination of Cd in biological samples treated with tetramethylammonium hydroxide (TMAH) by ET AAS was investigated. The tube treatment with Ru was carried out only once and lasted for about 300 atomization cycles. The pyrolysis and atomization temperatures, 750 °C and 1300 °C, respectively, were chosen from the temperature curves. The sample dissolution procedure was very simple: a sample aliquot was mixed with a small volume of a 25% m/v TMAH solution, the volume was made up to 50 ml and the mixture was kept at 60 °C for 1 h. Six certified biological reference materials were analyzed and the obtained Cd concentrations are within the 95% confidence interval of the certified values, proving the accuracy of the proposed procedure for a variety of biological samples. The calibration curve, with correlation coefficient higher than 0.99, was established for a working range up to10 μg l⁻¹. The precision was good as demonstrated by relative standard deviations below 3%, except for one sample. The limit of detection (3σ) was 0.05 μg l⁻¹ and the characteristic mass was 1.30 pg, obtained in the presence of the Ru modifier.     

Direct determination of aluminium in serum and urine by electrothermal atomic absorption spectrometry using ruthenium as permanent modifier

Ruthenium (Ru), thermally deposited on a integrated platform graphite furnace, was investigated as a permanent modifier for the determination of Aluminum (Al) in blood serum and urine by electrothermal atomic absorption spectrometry (ETAAS). The platform was treated with 500 μg of Ru as previously described. The pyrolysis and atomization temperatures for each material were of 1300 and 2300 °C, for serum sample and of 1000 and 2400 °C, for urine. The characteristic mass were of 31 and 33 pg for Al in serum sample and urine, respectively (recommended of 31 pg for Al in nitric acid 0.2% (v/v)). For this reason, the calibration was made with aqueous solutions for both the samples. Calibration curves presented r of 0.99145 and 0.99991 for serum and urine, respectively. With the optimized temperatures, being analyzed eight spiked blood serum samples, the recovery was between 95.90 and 113.50%. Two certified urines samples were analyzed with good agreement between experimental and reference values. In both the samples the R.S.D. were <5% (n=3). The detection limit (k=3, n=10) was of 0.40 μg of Al per liter for both the samples. The absorption pulses obtained were symmetrical, with very low background and without interferences. The life time of the tube-platform was higher than 600 cycles of atomizations for both the urine and serum samples.     

Determination of selenium in human milk by electrothermal atomic absorption spectrometry and chemical modification

A method was developed for the determination of selenium in human milk using electrothermal atomic absorption spectrometry. The use of chemical modifiers as well as their implications during the pyrolysis step was examined. The chemical modifiers that were studied were Zr, Ir as well as the mixed modifier Zr-Ir. The Ir modifier stabilized selenium at 1000 °C, Zr at 800 °C, while the mixed modifier at 1200 °C. The effect of modifier mass was studied and was found that better results are achieved with addition of 2 μg Zr and 2 μg Ir. The characteristic masses of selenium in the presence of Zr, Ir and the mixed modifier were found to be 73.3, 18.0 and 14.7 pg, respectively, while the corresponding limits of detection were found 2.0, 0.50 and 0.41 μg l⁻¹. Consequently better results were obtained with the mixed modifier. The developed method was applied for the determination of selenium in human milk, which was digested with a HNO₃ + H₂O₂ mixture in a microwave oven. The limit of detection of the method was 1.37 μg l⁻¹, the characteristic mass, m₀, was 48.8 pg and the repeatability was less than 5% as R.S.D.(%). Matrix matched calibration was used. Recoveries were estimated to be 93-105%. The method was applied to breast milk of Greek women (n = 9) and the Se content was found to be in the range 16.7-42.6 μg l⁻¹ with mean value 27.4 ± 5.5 μg l⁻¹.     

Determination of tin by resin-suspension electrothermal atomic absorption spectrometry after enrichment as the complex with ammonium pyrrolidinedithiocarbamate.

A resin-phase extraction method has been optimized for the trace determination of tin(II) by ETAAS. Tin(II) was extracted on a finely divided anion exchange resin as the complex with ammonium pyrrolidinedithiocarbamate (APDC). The resin was collected on a membrane filter and then dispersed in 1.00 ml of 1 mol l(-1) nitric acid containing 100 microg of Pd(II) and 60 microg of Ni(II). The resulting resin suspension was subjected to GFAAS. The proposed method was applied to the determination of tin(II) in hydrochloric acid.     

Determination of selenium in water by electrothermal atomic absorption spectrometry

Summary The electrothermal atomization of selenium has been investigated for the accurate determination of selenium in water samples. Hydrogen seriously affects the atomization temperature of selenium in a molybdenum micro-tube atomizer. The atomization of selenium also suffers from serious interferences caused by salts and other elements. The extraction of selenium diethyldithiocarbamate complex serves to eliminate the interferences from the matrix. The addition of copper allows the suppression of interferences from elements extracted with selenium. The method permits the determination of selenium(IV) and selenium(VI) separately.This research was in part funded by the Ministry of Education, Science and Culture, Japan, under Grant-in-Aid for Scientific Research, for which we express our appreciation.