Photoacoustic Determination of Cobalt after Solid-Phase Concentration on an Empore Silica-gel Thin-Layer Plate

Abstract

A method used to determine trace amounts of samples in aqueous solutions is proposed. Cobalt ion was extracted as a 1-(2-pyridylazo)-2-naphthol (PAN) complex into chloroform. The extract was filtered through an Empore silica-gel TLC plate (2.5cm square) having no backing material. Excessive PAN and other metal-PAN complexes were washed out through the TLC plate by filtering twice 5ml of chloroform. Using these procedures only the cobalt-PAN complex was concentrated on the surface of the TLC plate. The photoacoustic signal of the TLC plate was detected by using a He-Ne laser as a light source. A linear relationship was obtained between the concentration of cobalt and the photoacoustic intensities in the 0.1-20ppb range. A five-hundred-times concentration of Ni, Cu and Fe did not significantly interfere with the photoacoustic signal. The determination limit of cobalt when the sample volume was 100ml was about 0.15ppb.