Nivaldo Baccan

Automated flow analysis system based on multicommutation for Cd, Ni and Pb on-line pre-concentration in a cationic exchange resin with determination by inductively coupled plasma atomic emission spectrometry

Abstract A flow system for on-line pre-concentration of Cd, Ni and Pb and determination by inductively coupled plasma atomic emission spectrometry is presented. The manifold comprised a set of three-way solenoid valves, which were controlled by a microcomputer running software written in Quick Basic 4.5 by means of an A/D board. Since the flow network was based on the multicommutation concept pre-concentration and elution steps could be simultaneously performed in several columns in parallel with significant analytical throughput improvement. Comparing obtained results with certified values, no significant difference at 95% confidence level was observed. Other valuable features such as an analytical throughput of 90 determinations per hour, relative standard deviation

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.

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.

Application of factorial design in optimization of preconcentration procedure for copper determination in soft drink by flame atomic absorption spectrometry

In the present paper, a procedure for preconcentration and determination of copper in soft drink using flame atomic absorption spectrometry (FAAS) is proposed, which is based on solid-phase extraction of copper(II) ions as its ion pair of 1,10-phenanthroline complexes with the anionic surfactant sodium dodecil sulphate (SDS), by Amberlite XAD-2 resin. The optimization process was carried out using 2(4-1) factorial and 2(2) factorial with a center point designs. Four variables (XAD-2 mass, copper mass, sample flow rate and elution flow rate) were regarded as factors in the optimization. Students t-test on the results of the 2(4-1) factorial design with eight runs for copper extraction, demonstrated that the factors XAD-2 mass and sample flow rate in the levels studied are statistically significant. The 2(2) factorial with a center point design was applied in order to determine the optimum conditions for extraction. The procedure proposed allowed the determination of copper with detection limits (3alpha/S) of 3.9mugl(-1). The precision, calculated as relative standard deviation (R.S.D.) was 1.8% for 20.0mugl(-1) of copper. The preconcentration factor was 100. The robustness of this procedure is demonstrated by the recovery achieved for determination of copper in the presence of several cations. This procedure was applied to the determination of copper in soft drink samples collected in Campinas, SP, Brazil.

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.

Flow-injection determination of low levels of ammonium ions in natural waters employing preconcentration with a cation-exchange resin

Abstract Ammonium ions in natural waters at the 50 gmg 1 −1 level were determined using Nessler reagent after preconcentration in a cation-exchange column coupled to a flow-injection analysis (FIA) system. The loading cycle, the elution cycle and the regeneration cycle were programmed for the resin used. The zone sampling approach using a computer-controlled commutator was employed in the FIA sytem design. Flow rates, resin loading, elution time, loop dimensions and resampling times for the zone sampling, column and coils dimensions, sensitivity and reproducibility were studied. The detection limit was improved tenfold over an earlier method that did not use a concentration step. A throughput of 45 sample analyses per hour was achieved for samples with concentration ranging from 50 to 500 μg 1 −1 . The result show agreement to better than 99% with those obtained by the manual procedure.

Dilute-and-shoot procedure for the determination of mineral constituents in vinegar samples by axially viewed inductively coupled plasma optical emission spectrometry (ICP OES)

Samples of commercial wine vinegar were introduced in an axially viewed inductively coupled plasma optical emission spectrometry instrument (AX-ICP OES) equipped with different sample introduction systems: a cross-flow nebulizer combined with a double-path spray chamber (CF-DP) and cone spray associated with a cyclone spray chamber (CS-CC). Samples of white and red wine vinegar were diluted with water before analysis. Higher magnesium Mg II/Mg I ratios (11 and 10 for CS-CC and CF-DP, respectively) were obtained using a nebulization gas flow rate of 0.6 l min−1 and an applied power of 1.3 kW. The background equivalent concentrations (BEC) and signal-to-background ratio (SBR) of analytes were improved using scandium (Sc) as the internal standard. The limits of detection (LOD) and limits of quantification (LOQ) for mineral constituents were similar for both introduction systems. Best recoveries values were obtained using a plasma under robust conditions, CS-CC system and Sc as the internal standard. The concentration determined in 13 commercial samples of wine vinegars varied between 0.2 and 3.0, between 0.02 and 0.4, between 8.5 and 100.0, between 0.01 and 0.05, between 27.0 and 540.0, between 4.0 and 79.0, between 0.4 and 10.0, and between 0.01 and 2.0 for aluminium (Al), barium (Ba), calcium (Ca), copper (Cu), potassium (K), magnesium (Mg), manganese (Mn), and zinc (Zn), respectively.

Continuous hydride generation system for the determination of trace amounts of bismuth in metallurgical materials by atomic absorption spectrometry using an on-line stripping-type generator/gas-liquid separator

A method for the determination of trace amounts of bismuth using flow injection and atomic absorption spectrometry with hydride generation was developed. The introduction of 50 µl of sample and tetrahydroborate solution into the HCl and aqueous carriers in a merging zones manifold allows the formation of bismuthine, which is separated from the liquid phase in an on-line stripping-type generator/gas–liquid separator. The calibration graph is linear from 0.1 to 100 ng ml -1 Bi with a detection limit (3 σ ) of 320 pg ml -1 Bi (corresponding to 16 pg Bi). The relative standard deviation for 20 replicates varies from 10% for 0.1 ng ml -1 Bi to 1.9% for 100 ng ml -1 Bi, with an injection frequency of up to 150 samples h -1 . Ni II , Co II , Ag I , Hg II , Se IV and Sb III interfere, but they can be masked with a thiourea–KI solution. The applicability of the proposed method to metallurgical samples was demonstrated by the analysis of certified reference materials.

Determination of bismuth in urine and prescription medicines using atomic absorption with an on-line hydride generation system

The bismuth contents of various digested urine samples and prescription medicines were determined by atomic absorption spectrometry combined with hydride generation. The procedure followed was a standard addition method for urine and direct calibration for the prescription medicines. The detection limit of the method was determined to be 320 pg ml-1 Bi with an analytical frequency of 150 h-1. A relative standard deviation of 4.7% was found for Bi in urine at the level of 4.3 ng ml-1 Bi. Interference caused by NiII, CoII, CuII, AgI, SeIV, SbIII and HgII could be controlled with a masking solution of thiourea (0.2%)-KI (10%).

Sulphate Preconcentration By Anion Exchange Resin In Flow Injection And Its Turbidimetric Determination In Water

A preconcentration procedure was established for sulphate determination in rain waters at the mg/l level, employing a small column packed with the AG1-X8 (200-400 mesh) anionic resin inserted into a flow injection system. Sulphate determination was performed by using the turbidimetric method based on reaction with barium. For concentrations within 0.10 and 2.0 MgSO(2-)(4)/l, a throughput of 50 determinations/hr was achieved, and the relative standard deviation of results was better than 2%.