PhD: Determination of total content and chemical species of antimony, arsenic, selenium and tin in environmental samples with atomic absorption spectrometry

Jozhica Majda Boris Serafimovska
Institute of Chemistry, Faculty of Natural Sciences and Mathematics, Ss. Cyril and Methodius University, Skopje, Macedonia
March, 2012
 

Abstract

The methods for determination of total contents and speciation of arsenic, antimony, selenium and tin in environmental samples using atomic absorption spectrometry were investigated.

The influences of EDTA, carboxylic acids, amino- and hydroxocarboxylic acids, mono-saccharide and humic acids on the generation of arsines and stibines in HG-AAS were investigated. EDTA (0.02 mol/l), ascorbic acid (0.02 mol/l) and glucose or fructose (0.2 mol/l) are useful additives for leveling sensitivities for As(III), monomethylarsеnite (MMA) and dimethylarsеnite (DMA). The presence of glycine, malonic, tartaric acid, BICIN and soil humin extracts leads to differences in analytical signal response between these As species. An analytical application to the determination of the sum of As(III), MMA and DMA as well as the sum of toxicologically relevant hydride forming As fraction As(III) + As(V) + MMA + DMA in EDTA soil/sediment extracts using HG-AAS was demonstrated. The limit of detection was 0.2 mg/kg. EDTA, tartaric, citric and malonic acid, fructose and N,N-bis(2-hydroxyethyl)glycine (BICIN) were found as appropriate reaction media for selective and sensitive determination of Sb(III). The prereduction of Sb(V) to Sb(III) in the presence of organic ligands is quantitative with L-cysteine (1% m/v) as reductant. An analytical application to the determination of Sb(III) and Sb(V) in waters, tea infusions, EDTA soil and sediment extracts using continuous flow HG-AAS was demonstrated. The limit of detection was 0.08 μg/l. Within-day precision was 5–20% in the range 0.2–1 μg/l Sb and 4–12% in the range 1–5 μg/l Sb with recoveries between 94 and 102%.

A modified liquid phase semimicroextraction (LSME) method was developed for preconcentration and determination of ultra trace levels of inorganic Sb species in waters using ETAAS. Sb(III) species were selectively extracted as dithiocarbamate complexes from 100 ml aqueous phase into 250 μl xylene at pH 5–8. Total Sb was determined by the same extraction with a pH of 0–1.2 without the prereduction of Sb(V) to Sb(III). The concentration of Sb(V) was obtained as the difference between that of total Sb and Sb(III). The enrichment factor of the method is 400 fold. The limit of detection was 2 ng/l Sb. Recoveries of spiked Sb(III) and Sb(V) in river, tap, and sea water samples ranged from 93 to 107%. The results for total Sb concentration in the river water reference material SLRS-5 were in good agreement with the certified reference. The method was applied for determination of dissolved inorganic species of Sb, Sn and Se in river Vardar and its main tributaries. The higher oxidation states of Sb and Se were found as the predominant form in the studied surface waters.

Fractionation analysis was performed to determine the distribution of Sb in soils. The applied procedures included: four step sequential extraction BCR procedure for determination of acid soluble, reducible, oxidizible and residual soil antimony; single extraction with EDTA and NaOH; determination of inorganic Sb(III,V) species in acetic acid- and EDTA- extractable fraction; selective precipitation of higher molecular humic acids fraction from the soil-derived humic substances. The predominant forms were found to be Sb(V) in acetic acid/ EDTA extracts and Sb-bound to humic acids in alkaline extract.