Preconcentration of lead complexed with O,O-diethyl-dithiophosphate by column solid-phase extraction using different sorbents in a flow injection system coupled to a flame atomic absorption spectrometer.

A comparative study of C(18) immobilized on silica, activated carbon and a polyurethane foam, as sorbents for Pb complexed with O,O-diethyl-dithiophosphate in a flow injection preconcentration system is reported. The complex was formed in 1.0 M HCl medium and processed in a simple system using a peristaltic pump, a manual injector-commutator and a mini-column filled with the sorbent. Using ethanol as eluent, the richest 150-mul fraction was collected and measured (after discarding 150, 200 and 0 mul for the activated carbon, foam and C(18), respectively) by flame atomic absorption spectrometry. The optimum concentration of the complexing agent was 0.05% m/v for C(18) and 0.2% m/v for the activated carbon and the polyurethane foam. The best sample loading flow rate was 4.0 ml min(-1) for the activated carbon and 2.0 ml min(-1) for C(18) and the polyurethane foam, while the best elution flow rate was 1.0 ml min(-1) (activated carbon) and 0.6 ml min(-1) (C(18) and foam). It was found that beyond a certain loading sample volume, for a constant analyte mass, the signal decreased. The maximum loading sample volume, for a constant analyte mass, before the signal started to decrease, was 50 ml for the activated carbon and 150 ml for the other materials. By processing 25 ml, the enrichment factors were 23, 55 and 166 for the activated carbon, foam and C(18), respectively. The best limit of detection (3sigma) was 0.3 mug l(-1) for the C(18) (1.2 mug l(-1) for the foam and 3 mug l(-1) for the activated carbon). As shown, the C(18) has a much superior retention performance in comparison to the other two materials.

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.

Determination of arsenic(III) and arsenic(V) by electrothermal atomic absorption spectrometry after complexation and sorption on a C-18 bonded silica column.

A flow injection procedure for the separation and pre-concentration of inorganic arsenic based on the complexation with ammonium diethyl dithiophosphate (DDTP) and sorption on a C-18 bonded silica gel minicolumn is proposed. During the sample injection by a time-based fashion, the As(3+)-DDTP complex is stripped from the solution and retained in the column. Arsenic(V) and other ions that do not form complexes are discarded. After reduction to the trivalent state by using potassium iodide plus ascorbic acid, total arsenic is determined by electrothermal atomic absorption spectrometry (ETAAS). Arsenic(V) concentration can be calculated by difference. After processing 6 ml sample volume, the As(3+)-DDTP complexes were eluted directly into the autosampler cup (120 mul). Ethanol was used for column rinsing. Influence of pH, reagent concentration, pre-concentration and elution time and column size were investigated. When 30 mul of eluate plus 10 mul of 0.1% (w/v) Pd(NO(3))(2) were dispensed into the graphite tube, analytical curve in the 0.3-3 mug As l(-1) range was obtained (r=0.9991). The accuracy was checked for arsenic determination in a certified water, spiked tap water and synthetic mixtures of arsenite and arsenate. Good recoveries (97-108%) of spiked samples were found. Results are precise (RSD 7.5 and 6% for 0.5 and 2.5 mug l(-1), n=10) and in agreement with the certified value of reference material at 95% confidence level.

Determination of Mo, U and B in waters by electrothermal vaporization inductively coupled plasma mass spectrometry.

A method for the determination of Mo, U and B in waters by inductively coupled plasma mass spectrometry, using an electrothermal vaporizer for sample introduction, is described. For Mo and U, NH(4)F was chosen as modifier and for B, synthetic sea water plus mannitol were used. The modifier effect was verified and the optimized pyrolysis and vaporization temperatures were obtained from pyrolysis and vaporization curves, together with the transient signals of the analytes. The masses of the modifiers added to the tube were also optimized. The detection limits were 0.018 or 0.30 ng ml(-1) for Mo, 0.03 ng ml(-1) for U and 0.68 ng ml(-1) for B. The analytes were determined in certified waters and the obtained results agree with the certified or recommended values or, in the case of B in sea waters, with the values obtained by other methods. Uranium could not be measured in the sea water samples due to strong memory effect.

Determination of Mo and Bi in steels by electrothermal atomic absorption spectrometry after complexation and sorption on activated carbon.

A simple method for the preconcentration of Mo and Bi in steels is proposed. The analytes are complexed with the ammonium salt of dithiophosphoric acid O,O-diethyl ester and sorbed onto activated carbon. After desorption into a small volume of nitric acid at low pH, Mo and Bi are determined by electrothermal atomic absorption spectrometry. Iron(III) is reduced to Fe(II), which is not complexed and not significantly retained on the carbon. Enrichment factor of 23 and 26 were obtained for Mo and Bi, respectively. The method was applied to the analysis of four certified reference steels, after acid dissolution in a microwave system and good agreement was obtained with the certified or recommended values.

Automated determination of tin and nickel in brass by on-line anodic electrodissolution and electrothermal atomic absorption spectrometry.

The application of an on-line metallic alloy dissolution system using anodic electrodissolution in a flow injection system for the determination of tin and nickel in copper alloys is described. After the electrolyzed material was collected in the autosampler cup, determination was carried out using electrothermal atomic absorption spectrometry (ETAAS). Using specific software developed in Turbo Pascal 7.0, it is possible to control electrolysis time, intensity of the applied current, and triggering of the three-way solenoid valves that push the fluids. Through manipulation of these variables, it is possible to adjust the analytical signal to within the working range of the spectrometer. Calibration of the spectrometer was accomplished by processing reference material. For tin, relative standard deviations for a series of measurements (n=5) performed on the same point and on different points of the sample was smaller than 2 and 4%, respectively; for nickel, 2 and 5%, respectively. The results for tin and nickel were in good agreement with those obtained through application of the classical methodology, as well as with data obtained by optical emission spectrometry. The detection limit for tin was 0.001% (w/w), whereas for nickel it was 0.003% (w/w). The analytical throughput is 30 samples h(-1).

Determination of cadmium in whole blood and urine electrothermal atomic absorption spectrometry using palladium-based modifiers and in situ decontamination.

The determination of Cd in whole blood and urine by electrothermal atomic absorption spectrometry using Pd-based modifiers and in situ decontamination was studied. The performance of Pd, Pd + NH4NO3, and Pd + Mg(NO3)2 as modifiers were compared with respect to maximum pyrolysis and atomization temperatures, background attenuation, linear calibration range and matrix interference. Samples were diluted (1 + 4) with 0.1% Triton X-100 (blood) or 0.2% HNO3 (urine), and introduced onto the graphite tube platform already containing the in situ dried and decontaminated modifier. The influence of modifier volume and concentration, as well as that of the dilution ratio was investigated. The proposed procedure involves the use of Pd(NO3)2 + (Mg(NO3)2 as modifier, a pyrolysis temperature of 700 degree C and an in situ decontamination step of 1200 degrees C. The atomization temperature was 1700 degrees C. The detection limit (n = 10, k = 3) was 0.22 micrograms l-1 for both samples. Typical relative standard deviation values (n = 3) were below 3%. Using matrix-matched standards, good agreement was observed between experimental and reference values in the analysis of certified reference materials. Interlaboratory comparison data have confirmed the validity of the proposed analytical procedure.

Determination of Sb, Ni and V in slurry from airborne particulate material collected on filter by graphite furnace atomic absorption spectrometry.

A microdigestion procedure performed directly in the autosampler cup is proposed. Small quartz filter pieces loaded with the particulate material are transferred to the cup. The sample is digested by a mixture of nitric, sulfuric and hydrofluoric acid (1:1:1) under sonication. After the addition of a boric acid solution the elements are determined by graphite furnace atomic absorption spectrometry using the autosampler to deliver the slurry into the furnace. A mixture of palladium and magnesium nitrates was used as a modifier for Sb. Spiking studies showed recoveries close to 100% using aqueous analytical curves for Ni and Sb. For V, an analytical curve in the blank slurry, obtained by submitting an unloaded filter to the same procedure, was used. The method was applied to two standard reference materials, Coal Fly Ash (NIST 1633a) and Urban Particulate (NIST 1648) and the concentrations showed good agreement with the certified or recommended values using aqueous analytical solutions.