Selenium speciation in soils using flow injection hydride generation atomic absorption spectrometry with on-line removal of organic matter interferences.

A method based on flow injection hydride generation atomic absorption spectrometry (FI-HGAAS) with an on-line pre-reduction of Se(VI) to Se(IV) was developed and optimized to determine phosphate-extractable Se (0.1 M phosphate buffer KH2PO4/K2HPO4 at pH 7). The extracted fraction involves water-soluble Se (i.e. the most mobile Se fraction) and exchangeable Se (i.e. sorbed onto soil component surface). Kinetic discrimination mechanisms allowed the complete removal of interferences caused by organic matter due to the formation of humic substances (HS)-Se(IV) complexes observed when batch pre-reduction processes were used. Se(IV) and Se(VI) recoveries ranged 95-105% at a fortification level of 150 µg kg-1. The pre-reduction was efficiently carried out in 20 s in a 6 M HCl medium at 100 °C. Results from phosphate-extractable fractions were comparable to those obtained by ICP-MS. Se bound to organic matter was released digesting the remaining material from the phosphate buffer extraction with 0.1 M K2S2O8. Detection and quantification limits were 15 µg kg-1 Se and 50 µg kg-1 Se, respectively, in each fraction. The methodology was applied to 10 agricultural soils from Argentina with total Se concentration levels between 130 µg kg-1 and 419 µg kg-1.

Total arsenic in selected food samples from Argentina: Estimation of their contribution to inorganic arsenic dietary intake.

An optimized flow injection hydride generation atomic absorption spectroscopy (FI-HGAAS) method was used to determine total arsenic in selected food samples (beef, chicken, fish, milk, cheese, egg, rice, rice-based products, wheat flour, corn flour, oats, breakfast cereals, legumes and potatoes) and to estimate their contributions to inorganic arsenic dietary intake. The limit of detection (LOD) and limit of quantification (LOQ) values obtained were 6µgkg(-)(1) and 18µgkg(-)(1), respectively. The mean recovery range obtained for all food at a fortification level of 200µgkg(-)(1) was 85-110%. Accuracy was evaluated using dogfish liver certified reference material (DOLT-3 NRC) for trace metals. The highest total arsenic concentrations (in µgkg(-)(1)) were found in fish (152-439), rice (87-316) and rice-based products (52-201). The contribution to inorganic arsenic (i-As) intake was calculated from the mean i-As content of each food (calculated by applying conversion factors to total arsenic data) and the mean consumption per day. The primary contributors to inorganic arsenic intake were wheat flour, including its proportion in wheat flour-based products (breads, pasta and cookies), followed by rice; both foods account for close to 53% and 17% of the intake, respectively. The i-As dietary intake, estimated as 10.7µgday(-)(1), was significantly lower than that from drinking water in vast regions of Argentina.

Determination of selenium in selected food samples from Argentina and estimation of their contribution to the Se dietary intake.

An optimised FI-HGAAS method was applied to determine the total selenium concentrations in selected high consumption food (fish, beef, chicken, milk, rice, wheat flour, egg) and to estimate their contribution to the Argentinean dietary intake, whose information is scarce nowadays. Through several optimisation steps a suitable method was achieved showing satisfactory figures of merit for all matrices. Average recovery was 96%, RSD<5%, LODs ranged 2.0-7.0 µg kg(-1) and the accuracy was assessed using DOLT-3 NRC certified reference material. Meat and eggs showed the highest values (in µg kg(-1), beef: 42-153; chicken: 62-205; fish: 94-314; canned tuna: 272-282; eggs: 134-217), minor values were found for wheat flour (22-42), rice: (<22), pasta (47-64) and milk (<7-9). An estimated intake of 32 and 24 µg day(-1) for adult men and women, respectively, suggested a deficient Se intake, leading to further comprehensive surveys of Se occurrence in Argentina.