A. J. Aller

Determination of cadmium in biological and environmental samples by slurry electrothermal atomic absorption spectrometry

The retention of cadmium by the bacteria Escherichia coli and Pseudomonas putida was optimized in order to develop a rapid and selective preconcentration method for cadmium from biological and environmental samples prior to determination by electrothermal atomic absorption spectrometry. Living and lyophilized cells for both bacteria were used, but the method using dead cells shows better analytical capabilities. Cadmium from aqueous solutions is easily retained on the outer membrane of both bacteria in the pH range 4-10, although the selected working pHs for E. coli and P. putida were 5 and 9, respectively. Cadmium retained by the bacteria was dispersed in 3.5 M nitric acid and the slurry was introduced directly into the graphite tube. The best sensitivity and detection limit were obtained for E. coli (0.03 ng ml(-1) and 0.04 ng ml(-1) respectively, in the absence of any chemical modifier). A strong spectral interference from nickel chloride was found and methods to overcome it were developed. The proposed extraction procedure was tested by the determination of cadmium in different standard biological and environmental samples.

Flame atomic absorption spectrometric method for the determination of beryllium in natural waters after separation with N-benzoyl-N-phenylhydroxylamine

A procedure for the determination of beryllium in natural waters is proposed. A solvent extraction step was performed in order to overcome interferences and isolate beryllium before it was atomized by direct nebulization of the organic phase in a dinitrogen oxide-acetylene flame. N-Benzoyl-N-phenylhydroxylamine was used as the extractant whilst isobutyl methyl ketone was the organic solvent. The effects of pH, amine concentration in the organic phase, shaking time, stability of the complex and nature of the extracted species were studied. The detection limit and linear response range are 2 ng ml-1 and 0-1.0 microgram ml-1, respectively. The result obtained for a standard reference material compared well with the quoted value.

Retention of arsenate using genetically modified coryneform bacteria and determination of arsenic in solid samples by ICP-MS.

A novel method for the retention of arsenate [As(V)] combining time-controlled solid-phase extraction with living bacterial biomass is presented. As(V) retention was carried out by exposing the extractant, consisting of a living double-mutant of Corynebacterium glutamicum strain ArsC1-C2, to the sample for a retention time of 1-7min, before the arsenic distribution equilibrium between the sample solution and the extractant was established. The amount of As(V) retained in the biomass was measured by inductively coupled plasma-mass spectrometry (ICP-MS) after the sample had been treated with nitric acid. A theoretical model of the retention process was developed to describe the experimental retention-time profiles obtained with the bacterial cells. This relationship provided a feasible quantification of the retention process before steady-state was reached, providing that the agitation conditions and the retention time had been controlled. An analytical procedure for the retention/quantification of As(V) was then developed; the detection limit was 0.1 ng As(V)mL(-1) and the relative standard deviation 2.4-3.0%. The maximum effective retention capacity for As(V) was about 12.5mgAs(g biomass)(-1). The developed procedure was applied to the determination of total arsenic in coal fly ash, using a sample that had undergone oxidative pre-treatment.

Speciation of selenite and selenate using living bacteria

In this work, a reliable method is described for speciation of soluble inorganic selenium ions, Se(IV) and Se(VI), which combines an uptake process by using living bacterial cells and electrothermal atomic absorption spectrometry (ETAAS). A selective retention of either Se(IV) or Se(IV) plus Se(VI) can be carried out by using the uptake system made up of either Pseudomonas putida or Escherichia coli strains cultivated in a culture medium based on glucose (P. putida) and glucose plus dipotassium phosphate (E. coli) mixed together with the original sample solution containing the selenium species. Discrimination between inorganic selenium species is possible by combining the optimization of the bacterial cell, the growth conditions and the relative rates of their retention from the sample. In the general procedure, an equilibrium between the analyte in the solution and the uptake system is allowed to be established, and then the concentration of selenium is determined directly in the biomass by slurry sampling ETAAS. Nonetheless, a theoretical model is proposed to describe the retention process by the living bacterial cells, which also provides a feasible quantification of the extraction process before the adsorption equilibrium is reached and whenever the agitation conditions and the sampling time are under control. The detection limits for the inorganic selenium species at the best retention conditions are of 5.7 ng Se(IV) ml(-1) for P. putida and 6.1 ng Se(IV) ml(-1) and 6.3 ng Se(VI) ml(-1) for E. coli. The relative standard deviations of the adsorption/determination process are 2.9-6.3%.

Stability of bacterium-mercury complexes and speciation of soluble inorganic mercury species

Abstract Soluble inorganic mercury ions from aqueous solutions were retained on the external membrane of both lyophilized bacterial cells and living cells. Desorption studies were performed using both types of cells. Distribution coefficients of mercury between the aqueous and solid phases, as well as the conditional stability constants of mercury ions for the external membranes of bacteria were calculated. Loaded membranes and the amount of the unadsorbed ions were measured by electrothermal atomic absorption spectrometry (ETAAS) and/or gamma spectrometry. The 203Hg radiotracer ( t 1 2 = 46.6 days ) was used to monitor recoveries using gamma spectrometry in combination with an optimized extraction procedure. Depending on the pH of the solution mercury ions can be selectively retained by the bacterial external membrane and the speciation of the mercury(II) and mercury(I) ions is possible. Best retention pHs for both mercury ions and bacteria were the following: mercury(II): 1 (E. coli) and 3 (P. putida), and mercury(I): 4 (E. coli) and 8 (P. putida). Interelement effects from other ions in the retention process of mercury were also investigated. A technique involving a solid extraction stage of mercury from aqueous samples at ng ml−1 level was developed and applied to the determination of mercury by ETAAS. The mercury-biomass pellet is separated by centrifugation and treated with a nitric acid solution determining the content of mercury in the supernatant solution. The best detection limit (3 times stand. dev. of the blank) and the best sensitivity (Hg concentration for an absorbance peak of 0.0044s) of the method for the applied concentration procedure were, respectively, of 15.0 ng ml−1 and 3.0 ng ml−1 for mercury(I) and 22.0 ng ml−1 and 5.5 ng ml−1 for mercury(II).

Determination of gold in ores by flame and graphite furnace atomic absorption spectrometry using a vanadium chemical modifier

Abstract The determination of gold in ores by both flame and graphite furnace atomic absorption spectrometry at different analytical wavelengths are compared. Vanadyl chloride was shown to be effective as a chemical modifier for determining gold in the presence of heavy metals. A sensitivity of 1 μg l−1 and a detection limit of 1 μg l−1 (or 0.1 μg g−1 in the original sample) were obtained. The best linear range was between 1 and 120 μg l−1 and a characteristic mass of 1 pg was obtained.

Determination of selenium in coal fly ashes by graphite furnace atomic absorption spectrometry using a cadmium-palladium chemical modifier

Abstract A simple and reliable method is described for the determination of selenium in coal fly ashes. Wall atomization and Smith-Hieftje background correction were used. A chemical modifier containing CdCl 2 -PdCl 2 was used. Concentrations of selenium in coal fly ashes were calculated directly by a standard additions method. A detection limit of 7 μg 1 −1 , a sensitivity of 1.37 μg 1 −1 and an optimum concentration range up to 100 μg 1 −1 were obtained. The characteristic integrated mass was 13.7 pg of selenium for an absorbance peak of 0.0044 s.

Total and extractable contents of trace metals in agricultural soils of the valderas area, Spain

The surface horizons of four agricultural field soils (Mollic ustifluvents, Alfic Xerochrepts, Typic Palexeralfs, Typic Haploxeralfs) were sampled to determine the total copper, cobalt, molybdenum, zinc, chromium, nickel, selenium, cadmium, lead, mercury, lithium and strontium, and were also fractionated by an extraction procedure to estimate the quantities of these trace metals in soluble form. The extractants used were the following: 1.0 N NH4 OAc for lithium and strontium, 0.05 M Na2-EDTA for cadmium, copper, nickel and zinc, 2.5% (w/v) acetic acid for lead, 2.5% (w/v) acetic acid and 2% (w/v) dithizone for cobalt, 2% (w/v) diethyldithiocarbamate solution for selenium, 0.1 NHCl for chromium, and 0.5 NHCl for mercury. The total content of these twelve elements in the four field soils sampled were lower than the levels quoted in the literature, although for different geochemical systems. The percentage of the total element content in soluble form was (except for selenium) generally very low, averaging between 5.5 and 8% for copper, 1.6 and 2.5% for cobalt, 8 and 10% for molybdenum, 1.8 and 2.2% for zinc, 14.2 and 17.7% for chromium, 5.5 and 6.4% for nickel, 30 and 55% for selenium, 8 and 14% for cadmium, 3 and 3.6% for lead, 8.3 and 11% for mercury, 5 and 7% for lithium, and 4.4 and 5.7% for strontium, regardless of the soil type.

Behavior of thorium, zirconium, and vanadium as chemical modifiers in the determination of arsenic by electrothermal atomization atomic absorption spectrometry

Abstract The comparative effect of thorium, zirconium and vanadium used as chemical modifiers in wall and platform atomization of arsenic using two sample introduction modes (aerosol vs. liquid drop) was studied. The effect of proton concentration (as hydrochloric acid and nitric acid) on the behavior of these modifiers was also tested. A beneficial effect on the stabilization of arsenic from all the chemical modifiers was essentially derived in the presence of nitric acid mainly for the aerosol introduction mode. Nonetheless, the highest sensitivity and the best stabilization of arsenic were obtained using zirconium and thorium as a chemical modifier, because pyrolysis temperatures as high as ∼1500°C can be used. The mechanistic action of the chemical modifiers used is also studied, resulting in the formation of a mixture of oxides stabilized at high temperatures.

Preconcentration of beryllium on the outer membrane of Escherichia coli and Pseudomonas putida prior to determination by electrothermal atomic absorption spectrometry

A rapid, simple and selective preconcentration method involving retention of the analyte on the outer wall of Escherichia coli and Pseudomonas putida has been developed. Several factors affecting the retention of beryllium by the outer membrane of bacterial cells were optimized. This procedure was used to preconcentrate trace amounts of beryllium prior to determination by electrothermal atomic absorption spectrometry. Both batch and immobilization techniques for the two bacteria were compared, but the former methods showed better analytical capabilities. Beryllium ions are easily retained on the outer membrane at pH 6–9 for E. coli and pH 3–10 for P. putida. The bacterial mass that retained the beryllium was centrifuged and dispersed in 3.5 mol –1 nitric acid. The resulting slurry was introduced directly into the graphite tube. The best analytical figures of merit were obtained for E. coli using a slurry sampling technique with a sensitivity and detection limit of 0.015 and 0.05 ng ml–1, respectively, for the platform atomization of beryllium in the absence of a chemical modifier. No interferences from the main major and minor ions of environmental interest were found. The proposed method was applied to the determination of beryllium in an environmental reference material.