An in situ pre-concentration method for fluorine determination based on successive digestions by microwave-induced combustion.

A new strategy based on successive digestions by microwave-induced combustion (MIC) in the same reaction vessel with a single absorbing solution was proposed. As a proof of concept, F was determined by ion-selective electrode (ISE) in seafood digests. Samples were pressed as pellets (up to 0.7 g) and combusted in closed quartz vessels pressurized with oxygen. Sequential digestions were each performed (up to 4 combustion cycles) in the same vessel and using the same absorbing solution. In each cycle, a new filter paper, igniter and sample pellet (0.7 g of sample) were used. Ammonium hydroxide solutions (10-100 mmol L-1) were evaluated for F absorption. Accuracy of the proposed method was evaluated using certified reference material of oyster tissue (NIST 1566a) and also by comparison of results after pyrohydrolysis method. Up to 3 digestion cycles (total mass of 2.1 g) could be used with 50 mmol L-1 NH4OH as absorbing solution. Results were in agreement with those obtained using pyrohydrolysis and also with certified reference value; the coefficient of variation after 3 cycles was below 5%, which was considered as suitable for F determination even at low concentration. The residual carbon in digests was lower than 25 mg L-1, allowing F determination by ISE virtually free of interferences due to dissolved organic matter. The limit of quantification (LOQ) for F was 1.3 µg g-1 (using 2.1 g of seafood), which is almost 4 times lower than the LOQ obtained using the reference method (pyrohydrolysis). Contrary to the reference method, this relatively low LOQ allowed the determination of F in all the seafood samples analysed. Taking into account that only 6 mL of diluted NH4OH solution (50 mmol L-1) were used and the suitable LOQ, the proposed sequential digestion MIC method can be recommended for further F determination in trace levels in seafood, even using a low-cost technique such as ISE, instead of other, more powerful techniques, such as ion chromatography.

Feasibility of using solid sampling graphite furnace atomic absorption spectrometry for preparation of spiked filter papers with Cu and Zn as standards for direct solid analysis.

An approach was developed for the preparation of cryogenic ground spiked filter papers with Cu and Zn for use as synthetic calibrating standards for direct solid microanalysis. Solid sampling graphite furnace atomic absorption spectrometry was used to evaluate the microhomogeneity and to check the applicability of the synthetic calibrating standards for the direct determination of Cu and Zn in vegetable certified reference materials. The found concentrations presented no statistical differences at the 95% confidence level. The homogeneity factors ranged from 2.7 to 4.2 for Cu and from 6.4 to 11.5 for Zn.

Exploiting in situ hydride trapping in tungsten coil atomizer for Se and As determination in biological and water samples.

A flow injection hydride manifold was coupled to a 150W tungsten coil electrothermal atomizer for in situ hydride collection followed by selenium and arsenic determination by ET AAS. Rhodium (200mug), thermally reduced over the double layer tungsten atomizer, was very efficient at collecting selenium or arsenic hydrides. Prior to analysis, biological samples were digested in closed-vessels microwave digestion system. Prior to the hydride formation, both selenium and arsenic were reduced to valence state (IV) and (III), respectively. The detection limit was 35ngL(-1) for selenium and 110ngL(-1) for arsenic. Sample throughput was 70h(-1) using 30s of hydride trapping time. Method accuracy was evaluated by analyzing biological-certified reference materials from the National Institute of Standard and Technology (SRM-1577a and SRM-1577b "bovine liver" and RM-8414 "bovine muscle powder") and from the International Agency for Energy Atomic (A-13 "animal blood") and one water-certified reference material from the National Institute of Standard and Technology (SRM-1640 trace elements in natural water). By applying a t-test, there was no significant difference at the 95% probability level between the results obtained with the proposed method and those certified values.

Evaluation of the use of salivary lead levels as a surrogate of blood lead or plasma lead levels in lead exposed subjects.

We conducted a study to evaluate the use of parotid salivary lead (Pb-saliva) levels as a surrogate of the blood lead (Pb-B) or plasma lead levels (Pb-P) to diagnose lead exposure. The relationship between these biomarkers was assessed in a lead exposed population. Pb-saliva and Pb-P were determined by inductively coupled plasma mass spectrometry, while in whole blood lead was determined by graphite furnace atomic absorption spectrometry. We studied 88 adults (31 men and 57 women) from 18 to 60 years old. Pb-saliva levels varied from 0.05 to 4.4 microg/l, with a mean of 0.85 microg/l. Blood lead levels varied from 32.0 to 428.0 microg/l in men (mean 112.3 microg/l) and from 25.0 to 263.0 microg/l (mean 63.5 microg/l) in women. Corresponding Pb-Ps were 0.02-2.50 microg/l (mean 0.77 microg/l) and 0.03-1.6 microg/l (mean 0.42 microg/l) in men and women, respectively. A weak correlation was found between Log Pb-saliva and Log Pb-B (r=0.277, P<0.008), and between Log Pb-saliva and Log Pb-P (r=0.280, P=0.006). The Pb-saliva/Pb-P ratio ranged from 0.20 to 18.0. Age or gender does not affect Pb-saliva levels or Pb-saliva/Pb-P ratio. Taken together, these results suggest that salivary lead may not be used as a biomarker to diagnose lead exposure nor as a surrogate of plasma lead levels at least for low to moderately lead exposed population.

Biomonitoring of Pb and Cd in two impacted watersheds in Southeast Brazil, using the freshwater mussel Anodontites trapesialis (Lamarck, 1819) (Bivalvia: Mycetopodidae) as a biological monitor

Studies were carried out to investigate the contamination of Piracicaba and Mogi-Guaçu River basins (Säo Paulo State, Southeastern, Brazil) for heavy metals (Cd and Pb), using the limnic bivalve Anodontites trapesialis as a biological monitor. The results showed that the concentrations of Pb were higher than the control group in both basins, showing the bioavailability of this non-essential element in the basins. The concentrations were higher in the Mogi-Guaçu than in the Piracicaba basin, and in the slightly contaminated sites in both basins. There was no correlation between the degree of human impact and Cd and Pb concentrations, it was not possible to infer about concentrations of these heavy metals in the bivalves based only in a broad evaluation of human impact

Effect of lead on dental enamel formation.

In this work the effects of lead toxicity on dental enamel formation were studied. Epidemiological data and animal studies show an association between lead exposure and higher caries prevalence, but the mechanism underlying this association is still unknown. Here we present data on enamel formation in rats exposed to lead for 70 days in the drinking water. Enamel matrix was used for protein analysis and dry weight determination, while mature enamel was used for microhardness testing. Enamel matrix was scraped from the teeth and analyzed by electrophoresis in bulk or according to developing stage. Increased amounts of protein were observed in animals exposed to lead when the same weight of matrix was electrophoresed by protein electrophoresis. When extracts were prepared according to developing stages, no differences in the amount of protein or band pattern were observed. Upper incisors were cut longitudinally for Knoop enamel microhardness determination in four regions of the teeth. Microhardness analysis revealed statistically significant (P<0.05) decrease in the microhardness values of enamel from rats exposed to lead in regions of maturation but not of fully mature enamel. These results indicate a delay in enamel mineralization in incisor teeth from animals exposed to lead, highlighting a potentially important effect of lead toxicity not yet explored.

Copper determination in biological materials by ETAAS using W-Rh permanent modifier.

A tungsten-rhodium treatment on the integrated platform of a transversely heated graphite atomiser was used as a permanent chemical modifier for the determination of copper in biological materials by using digested samples as well as slurry sampling in electrothermal atomic absorption spectrometry. The W-Rh permanent modifier was as efficient as Pd+Mg(NO(3))(2) conventional modifier for obtaining good Cu thermal stabilisation in the digested and slurry samples. The permanent W-Rh modifier remained stable by approximately 300 and 250 firings when 20 mul of digested sample and 20 mul of slurry were delivered into the atomiser, respectively. In addition, the permanent modifier increased the tube lifetime up to 1370 and 744 analytical measurements in the digested and slurry samples, respectively. Also, when the W-Rh permanent modifier was employed, there was less variation of the slope of the analytical curves during the total atomiser lifetime, resulting in a decreased need of re-calibration during routine analysis, increasing the sample throughput, and consequently diminishing the variable analytical costs. Detection limits obtained with W-Rh permanent modifier were 0.64 and 0.33 mug g(-1) Cu for digested (dilution factor 100 ml g(-1)) and 1.0% m/v slurries of biological materials, respectively. Results for the determination of copper in the samples were in agreement with those obtained with decomposed sample solutions by using Pd+Mg(NO(3)), since no statistical differences were found after applying the paired t-test at the 95% level.