Speciation of selenomethionine and selenourea using living bacterial cells†

Abstract

A novel and reliable method is proposed for speciation of selenomethionine (Se-Met) and selenourea (Se-U) combining a time-controlled solid phase extraction by using living bacterial cells and electrothermal atomic absorption spectrometry (ETAAS) for the determination of selenium. The extraction medium consists of a Pseudomonas putida strain cultivated in a culture medium based on glucose contaminated with an organoseleno compound. Firstly, equilibrium between the analyte in the solution and the retention medium is allowed to be established, and then the concentration of the organoseleno compound is determined directly in the biomass by slurry ETAAS. It is possible to discriminate between different chemical species of selenium by combining the optimization of both the growth conditions and the relative rates of their retention from the sample solution. A theoretical model of the retention process, based on a rate-determining step in reaching the adsorption equilibrium, is proposed to describe the experimental adsorption time profiles of the uptake process by the living bacterial cells. This relationship can also provide a feasible quantification of the extraction process before the adsorption equilibrium is reached, whenever the agitation conditions and the sampling time are under control. The experimental data agreed closely with the theoretical model. The study of the adsorption process was derived to develop an analytical procedure to determine Se-Met and Se-U in matrices containing other selenium species (Se-ethionine, Se-cystamine, Se-cystine and Se VI ). The best detection limits for the organoseleno compounds at their optimum extraction times are 1.5 ng ml 21 for Se-Met and 1.2 ng ml 21 for Se-U. The relative standard deviations of the retention/determination process are 2.2-5.6%.

Analytical Applications of Living Organisms for Preconcentration of Trace Metals and Their Speciation

“…These results could be explained on the basis of steric effect, because the two most effectively retained analytes Se-Met and Se-U are the two smallest molecules of those studied. 7 A promising application of erythrocyte ghosts for the specific accumulation of selenite was proposed by Neidhard et al 10 Natural erythrocytes are not able to accumulate different oxoanions except of chromate. 11 However, erythrocytes ghosts filled with the right intracellular reagents that only react with selenite can specifically accumulate selenite (but the uptake efficiency was less than 60%).…”

“…Living and lyophilized (dead) bacteria (Pseudomonas putida) were used for the preconcentration of selenocystamine (Se-Cystm) 9 or selenomethionine (Se-Met) and selenourea (Se-U) 7,8 prior to the determination of selenium in biomass pellet by slurry ETAAS. The highest SeCystm retention on biomass occurs in glucose solution, and the uptake increases with the seeding density of the bacterial cells.…”

“…9 Bacteria P. putida was also used for selective preconcentration of selenomethionine (Se-Met) and selenourea (Se-U). 7 The living bacterial cells were cultivated in glucose solution at pH = 5 with Se-Met (for 1.3 h) or with Se-U (for 12 h). The nine times higher glucose concentration, almost five times higher seeding density of cells, and nine times longer growth time were necessary for effective preconcentration of Se-U compare to Se-Met.…”

“…6 These properties can be used not only for removing heavy metals from environmental matrices but also for speciation analysis. [6][7][8][9][10][11][12][13][14][15][16][17][18] Recently, yeast are more widely used for this purpose owing to easy growth, nonhazard, great tolerance toward metals, and high binding capacity to the cell. 6,13,14,[17][18][19][20] An abundant source of potentially metal-sorbing biomass are marine algae.…”

Fourier-transform infrared spectroscopic study of the interactions of selenium species with living bacterial cells

“…In some applications, lyophilized bacterial cells were effectively adopted to preconcentrate metals (precious [9], alkaline-earth [10] and transition [11,12]) and metalloids [13] from aqueous solutions, with a particular emphasis on the ionic speciation. Nonetheless, speciation of organometals frequently required increased selectivity, paying special attention to the new possibilities of biological systems, and above all bacteria [14,15,16,17].…”