High-Performance Liquid Chromatographic Determination of Micro Amounts of Some Metal Ions Following Ion-Pair Extraction with 2-(5-Nitro-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)phenol

Abstract

Several metal chelates with 2-(5-nitro-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)phenol (Nitro-PAPS) have been extracted into 1, 2-dichloroethane forming ion-pairs with the tetraphenylphosphonium ion (TPP⁺) as a counter cation. The extracted chelates were back-extracted into the aqueous phase containing dodecylbenzenesulfonate as a counter anion for TPP⁺. The metal chelates in the aqueous phase were separated and detected by reversed-phase high- performance liquid chromatography using tetrahydrofuran-acetonitrile-water (15:10:75) containing a 0.01M phosphate buffer (pH 6.0) and a 2×10^-6M Nitro-PAPS as a mobile phase. The detection limits (10σ) were 0.1ppb for copper and nickel, 0.05ppb for cobalt, and 0.4ppb for iron. The proposed method was applied to the determination of those metal ions in actual samples, such as river and rain water.