Autosampler Cups Research Articles

Speciation analysis of chromium in water samples using nanometer zirconium dioxide and direct ultrasonic slurry sampling with electrothermal atomic absorption spectrometry

ABSTRACTA new analytical procedure for the determination of chromium Cr(III) and Cr(VI) species in different water samples was developed. The method involves solid-phase extraction (SPE), direct ultrasonic slurry sampling (DUSSS), and subsequent electrothermal atomic absorption spectrometry (ETAAS). The nanometer-sized zirconium dioxide (ZrO2) was used as the sorbent material. The optimal conditions for the proposed solid phase extraction were: 50 mg ZrO2, 20 min extraction time, pH 2.5 for Cr(VI) and pH 8.0 for Cr(III) and for the ETAAS measurement: 1500°C pyrolysis and 2300°C atomisation temperatures, 1.5 g L−1 Mg(NO3)2 as matrix modifier. The samples were sonicated directly in the autosampler cup, using an ultrasonic probe at 20% power setting for 10 seconds prior to injection into the graphite tube with Ľvov platform. In this way, all drawbacks due to the elution procedure were eliminated. The limit of detection and limit of quantification for Cr(III) obtained under optimised conditions were 0.48 μg L−1, and 1.61 μg L−1, respectively, and for Cr(VI) 0.27 μg L−1 and 0.90 μg L−1. The pre-concentration factors attained for both the species were 25. The effects of alkaline, alkaline earth and some metal ions and some anions were also examined. The relative standard deviation estimated from six replicate measurements at a concentration of 0.4 μg L−1 for both Cr(III) and Cr(VI) with a pre-concentration factor of 25 was 2.96% and 4.06%, respectively. The accuracy of the method was confirmed by analysis of the standard reference material SRM 1643e “Trace Elements in Waterˮ. The proposed technique is simple, sensitive, environmentally friendly, and the risk of contamination is low. Hence, it was successfully applied to spiked synthetic and real water samples with recoveries ranging from 91.3% to 109.2%

Heat-assisted slurry sampling GFAAS method for determination of lead in food standard reference materials

A valid method based on heat-assisted slurry sampling graphic furnace atomic absorption spectrometry (HASS-GFAAS) was developed for the accurate determination of trace Pb in food standard reference materials (SRMs). The HASS technique significantly improved Pb recovery and precision compared to conventional slurry sampling techniques. The optimized HASS procedure was performed as follows: first, the sample (particle size≤150μm) was diluted with 0.05% (v/v) Triton X-100 containing 2% HNO3 and 1% H2O2 followed by heating for 20min at 120°C on a heating block. Next, the obtained slurry was sonicated in an autosampler cup, and finally, the slurry was introduced into a graphite tube and analyzed by the GFAAS with a Pb electrodeless discharge lamp (EDL). Calibration with aqueous standard solutions was used for Pb determination in food samples. The characteristic mass and limit of detection for Pb based on the integrated absorbance for a 2% (m/v) sample were 12±0.6pg and 0.003mgkg−1, respectively. The accuracy (95.1–102% recovery) and good precision (0.1–3.6%) of this procedure are illustrated by the results obtained for the 12 food reference materials. The proposed method is suitable for determination of trace Pb in solid food samples.

Green approaches to determine metals in lubricating oils by electrothermal atomic absorption spectrometry (ETAAS)

Two simple, fast and green procedures based on sample emulsification were developed to determine V, Ni, Cu, Cr, Pb, Mo and Ag by ETAAS in used lubricating oils; they will be termed “emulsion” and “three-component solution”. Reagent consumption and residues got reduced dramatically as solutions were prepared directly in 1mL autosampler cups. The emulsions were stable enough to perform the overall analysis without intermediate agitation between replicates. Quantitation was performed using aqueous standards and the standard additions method, except for Cu and Cr when the three-component solutions were employed. The preparation time for the two methods was 15min/emulsion and 30min/5 three-component solutions. Method validation was carried out with three reference materials: SRM 1084a “Wear-Metals in Lubricating Oil”, LO-010698 “Lubricating Oil” and “Used Oil” HU-1. The three-component solutions procedure was selected and applied to analyse several used lubricating oils.

Determination of cadmium and lead in fresh meat by slurry sampling graphite furnace atomic absorption spectrometry

In this work a method for cadmium and lead determination in fresh meat based on slurry sampling graphite furnace atomic absorption spectrometry is proposed. The fresh meat samples were weighed directly into the autosampler cups of the spectrometer using a microbalance and the slurry was prepared using tetramethylammonium hydroxide (TMAH). The use of the response surface method for optimizing the slurry preparation has shown that it was possible to find the optimum zone in the experimental field of the variables under study. Calibration was performed against aqueous standards and a mixture of 0.05% v/v Pd + 0.03% v/v Mg + 0.05% v/v Triton X-100 was used as a modifier. The results obtained for cadmium and lead in two certified reference materials were statistically not different from the certified values on a 95% confidence level, indicating that calibration against aqueous standards is suitable for this application. A comparison of the results obtained by slurry sampling with the digestion method adopted by the Brazilian Ministry of Agriculture showed no significant differences between the results at the 95% confidence level. The positive results obtained in this work suggest that the application of this procedure in other element determinations is worthy of exploration.

A microdigestion procedure directly performed in the autosampler cups for the determination of trace elements in biological samples by GF AAS

A microdigestion procedure for the determination of Cd and Cu in biological samples by graphite furnace atomic absorption spectrometry (GF AAS) is described. Masses up to 5 mg are directly weighed in the autosampler cup and 100 µL of the digestion solution (1:1 v/v HNO3-H2SO4 or concentrated HNO3) are added. The cups are closed and the digestion is performed, at 60 oC overnight in a specially designed digestion block. After cooling, 900 µL of ultrapure water is added, the solution is homogenized and the cups are transferred to the autosampler tray. Since the digestion is performed in a sealed environment and the whole procedure uses only one flask, the risks of contamination and losses are minimized. Calibration was performed with external calibration curves, in the same medium as the reagents blank. The analysis of nine different standard reference materials permitted the assessment to the accuracy of the procedure. Considering a 5 mg sample mass, the limits of quantification in the original samples calculated from ten successive measurements of the blank solution (k=10) were 0.07 and 1.7 and 0.02 and 0.3 µg g-1 for Cd and Cu respectively, using the HNO3-H2SO4 mixture or concentrated HNO3 for the digestion. The procedure was used for the determination of Cu in human liver biopsy samples.

Flow injection on-line dilution for zinc determination in human saliva with electrothermal atomic absorption spectrometry detection

An automated method is described for the determination of zinc in human saliva by electrothermal atomic absorption spectrometry (ET AAS) after on-line dilution of samples with a significant reduction of sample consumption per analysis (<0.4 mL including the dead volume of the system). In order to fulfill this aim without changing the sample transport conduits during the experiments, a flow injection (FI) dilution system was constructed. Its principal parts are: one propulsion device (peristaltic pump, PP) for either samples, standards or washing solution all located in an autosampler tray and for the surfactant solution (Triton X-100) used as diluent, and a two-position time based solenoid injector (TBSI 1) which allowed the introduction of 10 μL of either solution in the diluent stream. To avoid unnecessary waste of samples, the TBSI 1 also permitted the recirculation of the solutions to their respective autosampler cups. The downstream diluted solution fills a home made sampling arm assembly. The sequential deposition of 20 μL aliquots of samples or standards on the graphite tube platform was carried out by air displacement with a similar time based solenoid injector (TBSI 2). The dilution procedure and the injection of solutions into the atomizer are computer controlled and synchronized with the operation of the temperature program. Samples or standards solutions were submitted to two drying steps (at 90 and 130 °C), followed by pyrolysis and atomization at 700 and 1700 °C, respectively. The aqueous calibration was linear up to 120.0 μg L −1 for diluted standard solutions/samples and its slope was similar ( p > 0.05) to the standard addition curve, indicating lack of matrix effect. The precision tested by repeated analysis of real saliva samples was less than 3% and the detection limit (3 σ) was of 0.35 μg L −1. To test the accuracy of the proposed procedure, recovery tests were performed, obtaining mean recovery of added zinc of 97.8 ± 1.3%. Furthermore, Zn values estimated by the procedure developed in this work were compared with those obtained by a standard addition flame-AAS method applied to 20 randomly selected saliva samples. No significant differences ( p > 0.05) were obtained between the two methods. Zinc levels in saliva samples from 44 healthy volunteers, 15 male and 29 female, with ages between 20 and 51 years (mean 30.50 ± 9.14 years) were in the range 22–98 μg L −1 (mean of 55 ± 17 μg L −1), similar to some and different from others reported in the literature. It was found that zinc values for male were statistically higher ( p = 0.006) than for female.

Minimization of sample pretreatment for Al, Cu and Fe determination in coconut water by electrothermal atomic absorption spectrometry

Fast and reliable methods for the direct determination of Al, Cu and Fe in unprocessed coconut water by electrothermal atomic absorption spectrometry are proposed. For Fe determination, 100 µL of sample were diluted with 1400 µL of 0.1% v/v HNO3. Aliquots of 10 µL of this solution were injected into the graphite tube without any chemical modifier. For Al and Cu determinations, samples were slightly diluted (1250 µL of sample + 250 µL of 0.6% v/v HNO3 + 0.6% m/v Triton X-100) directly into the auto sampler cups. In this case, aliquots of 10 µL of an oxidant mixture (15% v/v H2O2 + 1.0% v/v HNO3) were co-injected with 15 µL of samples or analytical solutions into the graphite tube. The oxidant mixture minimized the carbonaceous residues formation and increased graphite tube lifetime in 75%, allowing up to 200 heating cycles. The detection limits and characteristic masses were 1.0 mg L-1 and 30 pg for Al, 0.7 µg L-1 and 20 pg for Cu, and 2.0 µg L-1 and 10 pg for Fe, respectively. The reliability of the proposed methods was evaluated by addition and recovery tests (104 ± 1% for Al, 98 ± 3% for Cu, and 97 ± 1% for Fe).

Direct determination of lead in human urine and serum samples by electrothermal atomic absorption spectrometry and permanent modifiers

The object of the present study was the development of alternative methods for the direct determination of lead in undigested samples of human urine and serum by electrothermal atomic absorption spectrometry (ET AAS). Thus, some substances have been investigated to act as chemical modifiers. Volumes of 20 µL of diluted samples, 1 + 1, v/v for urine and 1 + 4, v/v for serum, with HNO3 1% v/v and 0.02% v/v of cetil trimethyl ammonium chloride (CTAC) were prepared directly in the autosampler cups and placed into the graphite furnace. For modifiers in solutions 10 µL were used. Pyrolysis and atomization temperature curves were used in all optimizations in the matrixes diluted as exposed. For urine with permanent iridium (500 µg), the best pyrolysis and atomization temperatures were 900 and 1600 oC, respectively, with a characteristic mass of 12 pg (recommended of 10 pg), with symmetrical absorption pulses and corrected background. Spiked urine samples presented recoveries between 86 and 112% for Ir permanent. The analysis results of certified urine samples are in agreement with certified values (95% of confidence) for two levels of the metal. For serum, good results were obtained with the mixture of Zr+Rh or Ir+Rh as permanent modifiers, with characteristic masses of 9.8 and 8.1 pg, respectively. Recoveries from spiked serum samples varied between 98.6 and 100.1% (Ir+Rh) and between 93.9 and 105.2% (Zr+Rh). In both recovery studies, the relative standard deviation (n=3) was lower than 7%. Calibration for both samples were made with aqueous calibration curves and presented r2 higher than 0.99. The limits of detection were 0.7 µg L-1 for serum samples, with Zr+Rh permanent, and 1.0 µg L-1 for urine with iridium permanent.

Multivariate optimization for molybdenum determination in environmental solid samples by slurry extraction-ETAAS

A direct procedure to determine molybdenum in environmental solid samples (coal fly ash, sediment, soil and urban dust) by slurry extraction-electrothermal atomic absorption spectroscopy (SE-ETAAS) employing multivariate optimization is presented. Sample mass, ultrasonic power, HNO 3 concentration and HCl concentration were the most important variables affecting the extraction of Mo, as Plackett–Burman designs put forward. Time of agitation revealed not significant (within the 10–100 s range), thanks to the focused ultrasonic agitation program employed throughout (using a USS-100 probe). Two Simplex, a regular and a modified one, were carried out to simultaneously optimize the HNO 3 and HCl concentrations. Both Simplex converged to 14% (v/v) HCl and 10% (v/v) HNO 3. Sample mass was studied by means of a univariate procedure (optimum at 50 mg). Furnace programs were studied using wall atomization with and without BaF 2 as modifier, yielding similar results. Quantitative extraction was obtained, with good accuracy (ca. 90% recovery) and precision (R.S.D. < 9%), evaluated using five CRMs (coal fly ash SRM1633a, urban dust SRM1649a, marine sediments BCSS1 and PACS1, soil GBW07401). The limit of detection of the method was 0.1 μg g −1 (20 mg/1 mL slurry) and the characteristic mass was 9.5 ± 1.7 pg. Main advantages of the slurry extraction procedure are that it can be implemented directly on the autosampler cups, and that it is inexpensive and fast.

Determination of mercury in sewage sludge by direct slurry sampling graphite furnace atomic absorption spectrometry

Ultrasonic slurry sampling electrothermal atomic absorption spectrometry (ETAAS) method was elaborated to the determination of Hg in sewage sludge samples with the use of KMnO 4+Pd modifier. The minimum sample amount required for slurry preparation with respect to sample homogeneity was evaluated by weighting masses between 3 and 30 mg directly into the autosampler cups. Validation of the proposed method was performed with the use of Certified Reference Materials of sewage sludge, CRM 007-040 and CRM 144R. Two sewage sludge samples from Poznañ (Poland) city were analysed using the present direct method and a method with sample digestion, resulting in no difference within statistical error.

Determinação de cádmio em amostras de urina e soro humano por espectrometria de absorção atômica em forno de grafite usando irídio como modificador permanente

No presente estudo, foram investigadas diferentes substâncias para atuarem como modificadores químicos na determinação direta de cádmio em soro e urina humanos sem digestão prévia das amostras. A preparação da amostra foi feita diretamente nos copos do amostrador automático por diluição 1+4 de soro e 1+1 de urina com ácido nítrico 1% v/v contendo 0.02% v/v de cloreto de tricetil metil amônio (CTAC). Foram investigadas as melhores condições de determinação por meio de curvas de temperatura de pirólise e atomização na presença da matriz e do analito levando-se em conta a forma do pulso de absorção, baixas temperaturas na atomização, fundo corrigido e sensibilidade. Foram efetuados estudos na ausência de modificador e com a mistura universal em solução de Pd e Mg (10 e 15 µg, respectivamente) e com rutênio (500 µg) e irídio (500 µg) como modificadores permanentes. Para Ir permanente, as massas características foram 0.8 pg para soro e 0.7 pg para urina (recomendado de 2 pg). Na investigação do uso de Ir permanente, foi observado que o pico foi simétrico, retornando à linha de base em 3s e com fundo corrigido completamente com valores ótimos por pirólises e atomização de 300 e 1000°C para soro e 300 e 1100ºC para urina. A calibração foi feita por ajuste de matriz e apresentou coeficiente de correlação de regressão linear típico de 0.999. Análises de soro e urina fortificados mostraram recuperações que variaram entre 99.3 e 103.2 com um desvio padrão relativo (RSD, n=3) menor que 12% para soro e entre 93.1 e 102.2% com um RSD menor que 3% para urina. O limite de detecção (k=3, n=10) foi de 8 e 9 pg para soro e urina, respectivamente.

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.

Multielement determination of cadmium and lead in urine by simultaneous electrothermal atomic absorption spectrometry with an end-capped graphite tube.

A method for the multielement determination of cadmium and lead in urine is proposed by simultaneous electrothermal atomic absorption spectrometry (SIMAAS) with an end-capped transversely heated graphite atomizer (EC-THGA). The best conditions for cadmium and lead determination were obtained in the presence of NH4H2PO4 as a chemical modifier, using 500 degrees C and 1800 degrees C as the pyrolysis and atomization temperatures, respectively. Urine samples were diluted 1 + 4 directly in autosampler cups with a mixture of 0.125% (w/v) Triton X-100 + 2.5% (v/v) HNO3 + 0.31% (w/v) NH4H2PO4. The optimized heating program was carried out in 57 s, and the instrument calibration was done with aqueous reference solutions. The use of EC-THGA increased the sensitivity of cadmium and lead by 14% and 25%, respectively. The detection limits (n = 20, 3delta) were 0.03 microg L(-1) (0.36 pg) for cadmium and 0.57 microg L(-1) (6.8 pg) for lead. The performance of EC-THGA was acceptable up to 500 heating cycles. The reliability of the entire procedure was checked with the analysis of a lyophilized urine certified reference material. The found concentrations were in agreement with the recommended values (95% confidence level).

Systematic Errors in the Determination of Trace Metals by GFAAS Technique, Part I

The behaviour of solutions containing 7 metals in trace range (pH=2) prepared in borosilicate glass and polyethylene containers and transferred into commercial polyethylene–polypropylene and home-made quartz autosampler cups for measurements were studied using graphite furnace atomic absorption spectrometry. The different interactions between metal solution and vessel material were observed for the metals studied. The most significant losses of chromium and nickel occurred on a polyethylene surface, while the highest absorbance signals were registered from quartz containers. Higher absorbance signals from quartz containers were also obtained for cadmium and copper solutions. Contrary to these results, the absorbance signals for lead solutions were lowest when measured from quartz vessels. The container material had no influence on the analytical signals of cobalt and manganese.

Determination of cadmium in sediments and in sewage sludge by slurry sampling electrothermal atomic absorption spectrometry using iridium as permanent modifier

A procedure for the determination of Cd in sediment and sewage sludge as slurries by electrothermal atomic absorption spectrometry is proposed. The slurry, 1 mg mL-1, was prepared by mixing sample ground to a particle size £ 50 mm with 5% v/v nitric acid in an ultrasonic bath. The homogeneity of the slurries was assured by passing a constant flow of argon into the autosampler cup, just before transferring an aliquot to the graphite furnace. Two permanent modifiers deposited on the platform were tested: Ru and Ir. Modifiers in solution were also tested: Pd plus Mg and phosphate alone or plus Mg. The Ir-treated tube was adopted due to its good performance as modifier and also for practical reasons. About 80% of Cd is extracted to the water phase of the slurry. To test the accuracy of the method, three certified materials were analyzed: a marine sediment, a river sediment and a domestic sewage sludge. The concentrations obtained, using calibration against aqueous standards prepared in the same medium as the slurries, are in agreement with the certified values, at a confidence level of 95%, according to the Student-t test. The limit of detection (3s) was 43 ng g-1 in the solid sample and the relative standard deviation for the sediment MESS-2 was 2.3% (n = 10).

Determination of Hg and Tl in environmental reference materials using slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry with permanganate as modifier and calibration against aqueous standards

A method for the determination of Hg and Tl in environmental samples by slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry is proposed. The slurry is prepared by mixing the sample, ground to a particle size of ≤50 µm, with 5% v/v nitric and 1% v/v hydrofluoric acids in an ultrasonic bath, and leaving it to stand for 40 h before analysis. The slurry was homogenized in the autosampler cup with a constant flow of argon, just before transferring an aliquot to the graphite furnace. Potassium permanganate in solution, in an untreated and a Ru-treated tube, as well as potassium and manganese in solution were studied as modifiers and carriers. Best thermal stabilization and sensitivity were obtained with KMnO4 in an untreated tube, especially for Tl. These conditions were adopted, together with the optimized pyrolysis temperatures of 300 °C for Hg and 500 °C for Tl, and a vaporization temperature of 1000 °C for both analytes. The accuracy of the method was assured by the analysis of eight certified reference materials, using external calibration with aqueous standards prepared in the same medium as the slurries. The limits of detection in the samples were 0.18 µg g−1 for Hg and 0.07 µg g−1 for Tl. The precision found for the different samples, expressed as relative standard deviation, was 0.8–11% for Hg and 1–9% for Tl (n = 3).

Determination of Cd, Hg, Pb and Tl in coal and coal fly ash slurries using electrothermal vaporization inductively coupled plasma mass spectrometry and isotopic dilution

A method has been investigated for the determination of Cd, Hg, Pb and Tl in coal and in coal fly ash, using slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry and isotope dilution. The slurry, 25 mg ml−1, was prepared by mixing the powdered sample (≤36–45 µm) with acid solutions (nitric acid for coal and nitric and hydrofluoric acids for coal fly ash) and submitting the mixture to an ultrasonic agitation, letting it stand afterwards in a water bath at 60 °C for 2 h. An ultrasonic probe was used to homogenize the slurry in the autosampler cup just before its introduction into the graphite tube. The best conditions were determined regarding analyte sensitivity, furnace temperature program, amount of modifier, acid concentration, gas flow rate and particle size. For Hg, the pyrolysis stage was omitted and a low vaporization temperature was used (450–1000 °C); the residual matrix was eliminated in the first step of the following cycle. The modifiers used were: Pd for Cd and Tl; Au, Ir or Pd for Hg; Ir or Pd for Pb. The accuracy of the method was checked by analyzing six certified coal reference materials (SARM 20, SARM 19, BCR No. 40, BCR No. 180, BCR No. 181 and NIST 1630a) and one certified coal fly ash (NIST 1633b). With one exception (Hg in BCR No. 180), the found concentrations were typically within 95% confidence interval of the certified values, or close enough to the recommended values, as long as the samples were ground to a small enough particle size. The limits of detection were typically around 0.08 µg g−1, 0.03 µg g−1, 1 µg g−1 and 0.02 µg g−1 for Cd, Hg, Pb and Tl, respectively. The precision was also adequate with relative standard deviations of usually <5%.

Cryogenic sample grinding for copper, lead and manganese determination in human teeth by slurry sampling GFAAS

A simple method is proposed for copper, lead and manganese determination in deciduous teeth by graphite furnace atomic absorption spectrometry (GFAAS) using slurry sampling introduction and cryogenic sample preparation. Teeth samples were ground in a cryogenic mill in two steps: pre-cooling (5 min) and cryogenic grinding (2 min) in liquid nitrogen. After grinding, 90% of the sample particles were lower than 150 µm. The minimum mass necessary for slurry preparation as an indicator of sub-sample homogeneity was evaluated by weighting masses between 5 and 20 mg directly in autosampler cups, followed by addition of 1 mL of a solution containing 0.04% Triton® X-100 and 0.2% v/v HNO3. Samples (20 µL) were sonicated during 20 s, before delivering into a W–Rh coated platform. Detection limits based on integrated absorbance were 34.0 ng g−1 Pb, 7.4 ng g−1 Mn and 18.0 ng g−1 Cu for 2% m/v slurries. W–Rh permanent modifier permitted calibration against aqueous standards. The Certified Reference Material (H-5 animal bone) from the International Agency of Atomic Energy (IAEA) was analyzed to determine lead for method validation. For copper, lead and manganese, 12 human teeth samples were analyzed using the proposed method with calibration against aqueous solution and using a comparative Pd/Mg method with the same digested samples, and standard addition calibration, with no statistical difference at 95% level on applying the t-test.

Direct determination of bismuth in urine samples by electrothermal atomic absorption spectrometry: study of chemical modifiers

In this work the performance of some chemical modifiers (no modifier, Pd + Mg, Ir in solution, Ru, Ir or Zr independently as permanent modifier and Ir + Rh permanent) was investigated for the direct determination of Bi in human urine by electrothermal atomic absorption spectrometry (ETAAS). The urine samples were diluted directly in the autosampler cups with one-fold dilution with nitric acid 1% v/v. The obtaining of the permanent modifiers (500 µg of iridium, ruthenium and zirconium independently and 250 µg of Ir plus 250 µg of rhodium) was described elsewhere. Without modifier at all temperatures the signal was negative with a high background. Using Pd + Mg the best temperatures were of 1000 and 2500 °C, respectively, for pyrolysis and atomization, but the sensitivity was half that when using Ir + Rh. Using ruthenium, iridium or zirconium independently no peak was obtained but a plateau that did not return to baseline even in 15 s of atomization. With iridium applied in solution together with the sample the best pyrolysis and atomization temperatures were of 900 and 2500 °C, respectively, but the sensitivity was analogous with that obtained using Pd + Mg. Using Ir + Rh, the optimum pyrolysis and atomization temperatures were lower (900 and 1400 °C), but in this case the best sensitivity was obtained with a characteristic mass of 29.2 pg (recommended of 30 pg for the manufacturer for the metal in aqueous solutions). With this modifier, the obtained peak was very symmetrical, returning to the baseline in 3 s with very low background. The use of low temperatures and a low time of atomization coupled to the use of permanent modifer will certainly extend the lifetime of the graphite tube. Aqueous calibration curves and standard addition were parallel with slopes of 0.042 and 0.044 for aqueous and standard addition, respectively. For this reason, the calibration was carried out with aqueous solutions. The r values of calibration curves were higher than 0.99. Spiked urine samples with 5.0, 10.0, 15.0, 20.0, 25.0 and 30.0 µg l−1, analysed on different days, presented a recovery between 80.0 and 100.0%. The limit of detection was 50 pg. The lifetime of the tube was more than 500 cycles of atomization.

Determination of arsenic, lead, selenium and tin in sediments by slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry using Ru as permanent modifier and NaCl as a carrier

A procedure for the determination of As, Pb, Se and Sn in sediment slurries by electrothermal vaporization inductively coupled plasma mass spectrometry is proposed. The slurry, 1 mg ml −1, is prepared by mixing the sample ground to a particle size ⩽50 μm with 5% v/v nitric and 1% v/v hydrofluoric acids in an ultrasonic bath. The slurry was homogenized with a constant flow of argon in the autosampler cup, just before transferring an aliquot to the graphite furnace. The tube was treated with Ru as a permanent modifier, and an optimized mass of 1 μg of NaCl was added as a physical carrier. The pyrolysis temperature was optimized through pyrolysis curves, and a compromised temperature of 800 °C was used; the vaporization temperature was 2300 °C. The effect of different acid concentrations in the slurry on the analyte signal intensities was also evaluated. The accuracy of the method was assured by the analysis of certified reference sediments MESS-2, PACS-2 and HISS-1 from the National Research Council Canada, SRM 2704 and SRM 1646a from the National Institute of Standards and Technology and RS-4 from a round robin test, using external calibration with aqueous standards prepared in the same medium as the slurries. The obtained concentrations were in agreement with the certified values according to the Student's t-test for a confidence level of 95%. The detection limits in the samples were: 0.17 μg g −1 for As; 0.3 μg g −1 for Pb; 0.05 μg g −1 for Se and 0.28 μg g −1 for Sn. The precision found for the different sediment samples, expressed as R.S.D. was 1–8% for As, 2–9% for Pb, 6–12% for Se and 3–8% for Sn ( n=5).