Solange Cadore

Use of silica gel chemically modified with zirconium phosphate for preconcentration and determination of lead and copper by flame atomic absorption spectrometry.

An analytical method using silica gel chemically modified with zirconium (IV) phosphate for preconcentration of lead and copper, in a column system, and their sequential determination by flame atomic absorption spectrometry (FAAS), was developed. Sample solutions are passed through a glass column packed with 100 mg of the sorbent material, at pH 4.5, and lead and copper are eluted with 1.0 mol l(-1) HNO(3) at a flow rate of 2.0 ml min(-1). The extraction of copper is affected by Fe(II), Mn(II), Zn(II), Ni(II) and Co(II) while only Fe(II) interferes in the lead determination. These interferences may be overcome with an appropriate addition of a KI or NaF solution. An enrichment factor of 30 was obtained for both metals. While the limits of detection (3sigma) were 6.1 and 1.1 microg l(-1), for Pb and Cu, respectively, the limits of determination were 16.7 and 3.3 microg l(-1). The precision expressed as relative standard deviation (R.S.D.) obtained for 3.3 microg l(-1) of Cu and 16.7 microg l(-1) of Pb were 4.3 and 4.7%, respectively, calculated from ten measurements. The proposed method was evaluated with reference material and was applied for the determination of lead and copper in industrial and river waters.

Determination of manganese by flame atomic absorption spectrometry after its adsorption onto naphthalene modified with 1-(2-pyridylazo)-2-naphthol (PAN)

A system for determination of manganese, after preconcentration with 3% (w/w) 1-(2-pyridylazo)-2-naphthol (PAN), adsorbed on microcrystalline naphthalene is proposed. An amount of 200mg of this complexing mixture is placed in a glass column and conditioned with a NH(4)Cl/NH(4)OH buffer solution (pH 9.5). The aqueous sample, containing manganese, is treated with an ammonium tartrate solution, then with a hydroxylammonium chloride solution and, finally, with a buffer solution. The resulting solution is passed through the column containing microcrystalline naphthalene modified with 1-(2-pyridylazo)-2-naphthol (PAN) where Mn(II) is retained. The column is first washed with deionized water and then with 10.0ml of dimethylformamide to dissolve the Mn(II)-PAN/naphthalene complex. Manganese is determined by air-acetylene flame atomic absorption spectrometry. About 1mug of manganese can be concentrated from 200ml of aqueous sample, allowing a preconcentration factor of 20, a limit of quantification of 5ngml(-1) and R.S.D. of 3.8%. The accuracy was ascertained using certified reference materials, including samples of urine and glass. Water samples were also analysed and the results are in good agreement with those obtained by graphite furnace atomic absorption spectrometry.

Biomonitoring of metal contamination in a marine prosobranch snail (Nassarius reticulatus) by imaging laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS)

An imaging mass spectrometric method using laser ablation inductively coupled plasma spectrometry (LA-ICP-MS) was developed to determine Cu, Zn, Cd, Hg and Pb and metal distribution in longitudinal tissue sections of the marine snail Nassarius reticulatus (Gastropoda, Prosobranchia). Snails were sampled in northern Brittany (France) at three stations with different contamination levels. The quantification of metal distribution (imaging or mapping) in a thin slice of the snail tissue was carried out using different strategies: by one-point calibration and via matrix-matched laboratory standards using different biological materials (BCR 278, snail tissue, and rat brain). Together with the imaging of metals the distribution of two non-metals (carbon and sulfur) was analyzed. The imaging LA-ICP-MS analysis yielded an inhomogeneous distribution for all elements investigated. The detection limits for the distribution analysis of Cu, Zn, Cd, Hg and Pb measured by LA-ICP-MS were in the low microg g(-1) range.

Determination of total inorganic arsenic in water using on-line pre-concentration and hydride-generation atomic absorption spectrometry.

A rapid and sensitive method for the on-line separation and pre-concentration of inorganic arsenic in water samples is described. The analyte in the pentavalent oxidation state is reduced to its trivalent form with l-cysteine and the total inorganic arsenic is sorbed onto activated alumina in the acid form in a mini-column coupled to a FI-HG AAS system. Afterwards, it is eluted with 3moll(-1) HCl. An enrichment factor of 7 was obtained, allowing an analytical flow rate of about 28 determinations per hour. The limits of detection (3sigma) and of quantification (10sigma) were calculated as LOD=0.15mugl(-1) of As and LOQ=0.5mugl(-1) of As, respectively. Relative standard deviations (n=10) less than 8% were obtained for different arsenic concentrations and the accuracy was verified by analysing certified reference materials. Different kinds of samples, such as mineral water, drinking water, river water and natural spring water were analyzed and good agreement was obtained with the values from spiked experiments.

Determination of cadmium by flame-atomic absorption spectrometry after preconcentration on silica gel modified with cupferron

A method for the determination of cadmium by flame atomic absorption spectrometry (FAAS) after its preconcentration onto a column containing silica gel modified with cupferron was developed. The pH, amount of adsorbent material, concentration of eluent, volume of sample and amount of Cd were optimized. The effect of several foreign ions was also investigated and showed that the retention of cadmium depended on the amounts of Zn(II) and Cu(II) present and that these interferences could be overcome by using a 0.05 mmol KI. An enrichment factor of up to 30 was obtained , the LOD was 0.5 µg L-1 (3s) and the LOQ was 2.0 µg L-1 (10s) with rsd of 1.1% (n = 10). The accuracy of the proposed method was ascertained by using certified reference material and the obtained result (3.93 ± 0.01 µg g-1) agrees with the certified value (4.15 ± 0.38 µg g-1). The determination of Cd in nail polish showed quantitative recoveries for the spiked samples. The proposed method is characterized by simplicity, efficiency and low cost.

Determination of toxic elements in plastics from waste electrical and electronic equipment by slurry sampling electrothermal atomic absorption spectrometry

Cadmium, chromium, lead and antimony were determined in slurries prepared using pulverized samples of personal computers and mobile phones dispersed in dimethylformamide medium. Determinations were carried out by electrothermal atomic absorption spectrometry (ETAAS) using a graphite furnace atomic absorption spectrometer. The optimization of the experimental conditions (chemical modifier, pyrolysis time, pyrolysis temperature and atomization temperatures) was accomplished by evaluating pyrolysis and atomization curves. Optimization was also used to determine the temperatures corresponding to the best sensitivities and the lowest background signals. The pyrolysis temperatures were fixed at 600 degrees C (for Cd), 700 degrees C (for Pb), 1100 degrees C (for Sb), and 1200 degrees C (for Cr); atomization temperatures were established as 1400 degrees C (for Cd), 1300 degrees C (for Pb), 1900 degrees C (for Sb), and 2300 degrees C (for Cr), and the chemical modifier (50microg NH(4)H(2)PO(4)+3microg Mg(NO(3))(2) was used for Cd and Pb while 5microg Pd+3microg Mg(NO(3))(2) was used for Sb). The use of a chemical modifier for Cr determination was not necessary. The characteristic masses were 1.9pg for Cd, 32.3pg for Pb, 54.1pg for Sb, and 9.1pg for Cr. Calibration was performed using standard additions in a range of 5-20microgL(-1) for Cd, 5-30microgL(-1) for Cr, 12.5-50microgL(-1) for Pb, and 25-100microgL(-1) for Sb with linear correlation coefficients higher than 0.99. Limits of detection were 0.9, 1.4, 6.8, and 2.9microgL(-1) for Cd, Pb, Sb, and Cr, respectively. The results indicate that recoveries for all metals agreed at a 95% confidence level when a paired t-test was applied and presented good precision. The accuracy of the proposed method was evaluated by addition-recovery experiments, showing results in the 96-112% range, and also by comparison of the results using Students t-test with another method developed using ETAAS for digested samples. Analyte concentrations in the samples investigated varied from 5 to 525, 51 to 611, and 30 to 458mgkg(-1) for Cd, Cr, and Pb, respectively, while the content of Sb was in the 0.2-1.65% range.

River Sediment Analysis by Slurry Sampling FAAS: Determination of Copper, Zinc and Lead

Foi desenvolvido um procedimento experimental para a analise direta de sedimento. Com o emprego deste procedimento, foram determinados cobre, zinco e chumbo, e foram conseguidas recuperacoes quantitativas para esses metais com baixo custo e manipulacao minima das amostras. Foram investigadas a influencia da concentracao do acido nitrico no preparo da suspensao, bem como o tamanho de particula do sedimento. As suspensoes do sedimento foram tratadas com acido nitrico 6,0 mol L -1 e cloreto de amonio 2% (m/v), e sonicadas por 15 minutos em um banho de ultrasom antes da quantificacao por espectrometria de absorcao atomica com chama. Empregando essas condicoes, a porcentagem de recuperacao para cobre, zinco e chumbo foram 96,4 ± 4,9; 97,0 ± 4,0 e 99,7 ± 4,0, respectivamente, empregando-se um material certificado de referencia. An experimental procedure for direct sediment analysis was developed. Using this procedure, copper, zinc and lead were determined and quantitative recoveries for these metals were accomplished at a low cost and with minimal sample manipulation. The influence of the nitric acid concentration on the slurry preparation, as well as the sediment particle size was investigated. Sediment slurries were treated with 6.0 mol L -1 nitric acid and 2% (m/v) ammonium chloride, and sonicated for 15 minutes in an ultrasonic bath before quantification by flame atomic absorption spectrometry. Using these conditions for a certified reference material, the percentage of recovery for copper, zinc and lead were 96.4 ± 4.9, 97.0 ± 4.0 and 99.7 ± 4.0, respectively.

Cadmium and Lead in Chocolates Commercialized in Brazil

Cadmium (Cd) and lead (Pb) concentrations and their relationship to the cocoa content of chocolates commercialized in Brazil were evaluated by graphite furnace atomic absorption spectrometry (GF AAS) after microwave-assisted acid digestion. Several chemical modifiers were tested during method development, and analytical parameters, including the limits of detection and quantification as well as the accuracy and precision of the overall procedure, were assessed. The study examined 30 chocolate samples, and the concentrations of Cd and Pb were in the range of <1.7-107.6 and <21-138.4 ng/g, respectively. The results indicated that dark chocolates have higher concentrations of Cd and Pb than milk and white chocolates. Furthermore, samples with five different cocoa contents (ranging from 34 to 85%) from the same brand were analyzed, and linear correlations between the cocoa content and the concentrations of Cd (R(2) = 0.907) and Pb (R(2) = 0.955) were observed. The results showed that chocolate might be a significant source of Cd and Pb ingestion, particularly for children.

Determination of Cd, Cr, Hg and Pb in plastics from waste electrical and electronic equipment by inductively coupled plasma mass spectrometry with collision–reaction interface technology

A procedure based on the use of a quadrupole inductively coupled plasma-mass spectrometer equipped with a collision-reaction interface (CRI) for control of spectral overlap interferences was developed for simultaneous determination of Cd, Cr, Hg, and Pb in plastics from waste electrical and electronic equipment (WEEE). The injection of H(2) and He (80 and 60 mL min(-1), respectively) into the sampled plasma, colliding and reacting with potentially interfering polyatomic ions, allows interference-free determination of chromium via its isotopes (52)Cr and (53)Cr that are freed from overlap due to the occurrence of (40)Ar(12)C(+), (40)Ar(12)C(1)H(+), (36)S(16)O(+) or (1)H(36)S(16)O(+). Cadmium, Hg and Pb were directly determined via their isotopes (110)Cd, (111)Cd, (112)Cd, (199)Hg, (200)Hg, (201)Hg, (202)Hg, (206)Pb, (207)Pb, and (208)Pb, without using CRI. The CRI can be quickly activated or deactivated before each analyte measurement. Limits of detection for (52)Cr were 0.04 or 0.14 μg L(-1) with He or H(2) injected in CRI. Cadmium and Pb have LODs between 0.02 and 0.08 μg L(-1) and Hg had 0.93-0.98 μg L(-1), without using CRI. Analyte concentrations for samples varied from 16 to 43, 1 to 11, 4 to 12, and 5 to 13 mg kg(-1) for Cr, Cd, Hg and Pb, respectively.

Flame atomic absorption determination of cobalt in water after extraction of its morpholinedithiocarbamate complex

A preconcentration system for the determination of cobalt in water was developed. The studied system uses a glass column packed with Amberlyst A-26 resin modified with ammonium morpholinedithiocarbamate. The metal was quantitatively retained in the column containing 1.30 g of resin modified with 6% (m/m) of chelating reagent, at pH 5.5, resulting in a coloured complex which was eluted with 10.0 mL of ethanol. The final solution was analysed by flame atomic absorption spectrometry at 240.7 nm. Using these conditions a preconcentration factor of 25 was obtained and depending on the concentration of cobalt present in the solution it was possible to re-utilise the packed column several times. The limit of quantification was 2.0 µg L-1 with RSD of 2.9%. The foreign ions effect was studied and only Cd(II) and Ni(II) showed interference. The proposed method showed to be simple, of low cost, easy to handle and has been applied for the determination of cobalt in natural water samples.