Thesis (M.Sc.)--Chulalongkorn University, 2011

Hollow fiber supported liquid membrane (HF-SLM) was developed for speciation and preconcentration of inorganic arsenic in drinking water. The three-phase extraction mode was applied, where the sample solution was a donor phase; the Aliquat 336 in kerosene impregnated in the pores of the membrane was an extracting phase; and NaOH was an acceptor phase. The sample solution was adjusted to pH 6, so As(V) was in anion form (H2AsO4-) while As(III) was in neutral form (H3AsO3). The As(V) in the donor phase was extracted into the acceptor phase via anion-exchange mechanism. After extraction, As(V) was determined by the flow-based molybdenum blue method. For the determination of As(III), As(III) was oxidized to As(V) by KMnO4 and determined as total As. Then the amount of As(III) was obtained by subtracting of As(V) from the total amount of As. The method was applied for speciation of inorganic arsenic in drinking water from local market. The enrichment factor more than 250 was obtained. The linear range was 30-110 μg L-1, which provided the correlation coefficients (R2) of more than 0.99. The detection limit was about 5 µg L-1. The recoveries for determination of As(III) and As(V) were 86 to 102% and 92 to 112%, respectively and relative standard deviations of As(III) and As(V) were less than 5%. The method was compared with the ICP-AES method for the determination of total As. The concentration of total As from both methods were not significantly different (P > 0.05, Paired t-Test). This method is simple, low cost, uses less solvent and can be used for determination of inorganic arsenic at trace level.